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MAHMOUD A. ABDALLA | Assistant Professor, Electronic Engineering Department, MTC College, Cairo, Egypt,
E-mail: maaabdalla@ieee.org
ASHRAF Y. HASSAN | Ph. D. Student, Electronics and Communications Department, MSA University, Giza, Egypt,
E-mail: ashrafyoussef92@hotmail.com
AHMED A. IBRAHIM | Assistant Professor, Communications and Electronics Department, Faculty of Engineering,
Minia University, Minia, Egypt and University Oierre and Marie Curie, Sorbonne University, Paris VI, France;
E-mail: ahmedabdel_monem@mu.edu.eg
Building a
Zero-Order BPF
with CRLH
Transmission Lines
Miniaturization of RF/microwave filters
helps pave the way to developing small-
er wireless devices for internet access.
Using metamaterials and circuit struc-
tures such as composite-right-left-handed (CRLH) resonators
has proven effective in shrinking RF/microwave filter circuits
and was demonstrated in the design of a compact bandpass
filter (BPF) well-suited for WiMAX wireless applications.
Leveraging third-order coupled CRLH resonators, the filter
achieves a center frequency of 5.9 GHz with transmission zero
at 6.4 GHz. Measuring just 16 × 24 mm2, or about 40% the
size of BPFs based on conventional resonators, the filter has a
passband insertion loss of just 1.5 dB.
Metamaterials have shown great promise for the fabrication
of compact, high-frequency RF/microwave circuits.1-4 First
proposed in 2002, CRLH transmission lines (CRLH-TLs) are
forms of high-frequency transmission lines that exhibit back-
ward-wave transmission behavior capable of unusual electro-
magnetic (EM) wave propagation. Metamaterial approaches
to microwave circuit design are typically based on CRLH or
negative-refractive-index transmission lines in planar struc-
tures by loading a host transmission line with series capacitor
and shunt inductive load.
Use of metamaterials and CRLH-TLs enables the design
of RF/microwave BPFs with small size, low passband loss,
and even low cost. The small sizes supported by metamate-
rials make possible multiple-band filters that are a fraction
of the size of BPFs formed with conventional transmission
lines.5-10 Coupled metamaterial resonators have formed com-
pact BPFs.8,10 In addition, compact microwave CRLH gap
resonators with high quality factors (Qs) show great promise
for forming miniature BPFs.11,12
To demonstrate, by combining high-Q CRLH gap resona-
tors with third-order zeroth-order-resonator (ZOR) cou-
pled resonators, a microwave BPF with extremely compact
dimensions was designed and fabricated for WiMAX appli-
cations with standard, low-cost circuit materials. The filter
was constructed on RT/duroid 6010 circuit material from
Rogers Corp. (www.rogerscorp.com). The 1.27-mm-thick
circuit material has dielectric constant of 10.8 at 10 GHz in
the z-axis (thickness). Commercial electromagnetic (EM)
simulation software helped optimize the design, which was
Design Feature
characterized using a 50-Ω microstrip feed line and com-
mercial test equipment, notably an RF/microwave vector
network analyzer (VNA).
Figure 1 shows an equivalent-circuit model of the CRLH-TL
that consists of right-handed inductance (LR), right-handed
capacitance (CR), left-handed inductance (LL), and left-hand-
ed capacitance (CL). In a practical circuit design, CL is fabri-
cated as a four-finger interdigital capacitor, LL is a viahole in
the printed-circuit-board (PCB) material, and capacitance CR
and inductance LR are parasitic circuit elements essentially
invisible in size.
Mathematical analysis of the CRLH structure can be per-
formed by applying transmission-line theory to the equiva-
lent circuit of a CRLH cell. In this case, the CRLH cell is
coupled to a short 50-Ω (Z0) feed line for impedance match-
ing to 50-Ω environments and measurements with an RF/
microwave VNA.
The frequency of a ZOR is independent of the order of the
unit cell. This property can be parlayed into the design of
a novel filter in which the center frequency is independent
of the physical length of the transmission lines. In turn, the
filter’s size can be dramatically reduced, since the resonator
frequency does not rely on the half-wavelength size of the
transmission lines.5-8
The phase of the transmission lines can be found by apply-
ing Eq. 1, as a super-position of right- and left-banded phases
from the CRLH transmission lines. By controlling the cir-
cuit loading elements (CL and LL), a zero-phase condition
(φCRLH = 0) is achievable:
φCRLH = -βl = [1/ω(CL LL)0.5 – ω(CR LR)0.5] (1)
Figure 2 provides a layout of the CRLH unit cell used in
the design of the compact BPF. Figure 3 shows the computer-
simulated full-wave scattering (S) parameters of the CRLH
cell. The curves indicate a sharp resonance at 5.9 GHz, where
the value of S21 (insertion loss) is almost −1 dB and the value
of S11 (return loss) is less than −20 dB. Figure 4 shows the
computer-simulated phase of the CRLH resonator cell, where
Metamaterials and unconventional CRLH transmission lines combine to create RF/
microwave bandpass filters with miniature dimensions for wireless applications such
as WiMAX.
MW/DF/AUGUST/abdalla/31KCALLS.doc
Figure callouts for Abdalla (31K)
Figure 1
2LL
Figure 2
2.1 mm
3.4 mm
0.25 mm
0.3 mm
1.2 mm
0.3 mm
0.4 mm
0.1 mm
0.7 mm
0.2 mm
Figure 3
S11
S21
Frequency—GHz
4
5
6
7
Magnitude—dB
0
-10
-20
-30
S21 5.8 -0.4
S11 5.8 -19.0
Figure 4
S11 5.8
Angle—deg.
200
100
0
-100
-200
Frequency—GHz
4
5
6
7
S11
Figure 5
LR
CL
Cgap
2LL
CR/2
CR/2
2LL
2LL2
CR2/2
CR2/2
2LL2
LR2
CL2
Figure 6
(a)
(b)
17 mm
17 mm
Figure 7
Magnitude—dB
0
-10
-20
-30
-40
Frequency—GHz
5.0
5.5
6.0
6.5
7.0
S21, simulated
S11, simulated
S21, measured
S11, measured
Figure 8
16 mm
24 mm
(a)
(b)
Figure 9
Magnitude—dB
0
-10
-20
-30
-40
-50
-60
-70
Frequency—GHz
5.0
5.5
6.0
6.5
7.0
S21, simulated
S11, simulated
S21, measured
S11, measured
CRLH Transmission Lines
Form Zero-Order BPF
Metamaterials and unconventional CRLH transmission lines combine to create RF/microwave bandpass filters with miniature dimensions for a wide range of wireless applications, such as WiMAX.
Mahmoud A. Abdalla
Assistant Professor
Electronic Engineering Department, MTC College, Cairo, Egypt, E-mail: maaabdalla@ieee.org.
Ashraf Y. Hassan
Ph. D. Student
Electronics and Communications Department, MSA University, Giza, Egypt, E-mail: ashrafyoussef92@hotmail.com
Ahmed A. Ibrahim
Assistant Professor
Communications and Electronics Department
Faculty of Engineering, Minia University, Minia, Egypt and University Oierre and Marie Curie, Sorbonne University, Paris VI, France; E-mail: ahmedabdel_monem@mu.edu.eg
Miniaturization of RF/microwave filters will enable the development of smaller wireless devices for internet access. The use of metamaterials and circuit structures such as composite-right-left-handed (CRLH) resonators has been
effective in shrinking RF/microwave filter circuits and has been demonstrated in the design of a compact bandpass filter (BPF) well suited for WiMAX wireless applications. With third-order coupled CRLH resonators, the filter
achieves a center frequency of 5.9 GHz with transmission zero at 6.4 GHz. Measuring just 16 × 24 mm2 or about 40% the size of BPFs based on conventional resonators, the filter achieves passband insertion loss of just 1.5 dB.
Metamaterials have shown great promise for the fabrication of compact, high-frequency RF/microwave circuits.1-4 First proposed in 2002, CRLH transmission lines (CRLH-TLs) are forms of high-frequency transmission lines that
exhibit backward-wave transmission behavior capable of unusual electromagnetic (EM) wave propagation. Metamaterial approaches to microwave circuit design have been based on CRLH or negative-refractive-index transmission
lines in planar structures by loading a host transmission line with series capacitor and shunt inductive load.
The use of metamaterials and CRLH-TLs enables the design of RF/microwave BPFs with small size, low passband loss, and even low cost. The small sizes supported by metamaterials make possible multiple-band filters a fraction of
the size of BPFs formed with conventional transmission lines.5-10 Coupled metamaterial resonators have formed compact BPFs.8,10 In addition, compact microwave CRLH gap resonators with high quality factors (Qs) show great
promise for forming miniature BPFs.11,12 To demonstrate, by combining high-Q CRLH gap resonators with third-order zeroth-order-resonator (ZOR) coupled resonators, a microwave BPF with extremely compact dimensions was
designed and fabricated for WiMAX applications with standard, low-cost circuit materials. The filter was constructed on RT/duroid 6010 circuit material from Rogers Corp. (www.rogerscorp.com). The 1.27-mm-thick circuit material
has dielectric constant of 10.8 at 10 GHz in the z-axis (thickness). The filter design was optimized with the aid of commercial electromagnetic (EM) simulation software and characterized using a 50-Ω microstrip feed line and
commercial test equipment, notably an RF/microwave vector network analyzer (VNA).
Figure 1 shows an equivalent-circuit model of the CRLH-TL, which consists of right-handed inductance (LR), right-handed capacitance (CR), left-handed inductance (LL), and left-handed capacitance (CL). In a practical circuit design,
CL is fabricated as a four-finger interdigital capacitor, LL is a viahole in the printed-circuit board (PCB) material, and capacitance CR and inductance LR are parasitic circuit elements essentially invisible in size. Mathematical analysis
of the CRLH structure can be performed by applying transmission-line theory to the equivalent circuit of a CRLH cell. In this case, the CRLH cell is coupled to a short 50-Ω (Z0) feed line for impedance matching to 50-Ω environments
and measurements with an RF/microwave VNA.
The frequency of a ZOR is independent of the order of the unit cell. This property can be parlayed into the design of a novel filter in which the center frequency is independent of the physical length of the transmission lines, allowing
a dramatic size reduction in the filter since the resonator frequency does not rely on the half-wavelength size of the transmission lines.5-8
The phase of the transmission lines can be found by applying Eq. 1, as a super-position of right- and left-banded phases from the CRLH transmission lines. By controlling the circuit loading elements (CL and LL), a zero-phase
condition (φCRLH = 0) can be achieved:
φCRLH = -βl = [1/ω(CL LL)0.5 – ω(CR LR)0.5] (1)
Figure 2 provides a layout of the CRLH unit cell used in the design of the compact BPF. Figure 3 shows the computer-simulated full-wave scattering (S) parameters of the CRLH cell. The curves indicate a sharp resonance at 5.9 GHz,
where the value of S21 (insertion loss) is almost -1 dB and the value of S11 (return loss) is less than -20 dB. Figure 4 shows the computer-simulated phase of the CRLH resonator cell, where the phase at 5.9 GHz is almost equal to 0.
This is the justification for claiming that a zeroth-order coupled resonator has been created.
CRLH Construction
A microstrip configuration was used to fabricate a two-pole filter using equivalent circuits of the CRLH unit cell resonators (Fig. 5) as building blocks along with a capacitive gap, with the design aided by full-wave EM simulations in
the Ansoft HFSS software to find computer-simulated S-parameters. The filter was constructed on commercial PCB material (including low-loss viaholes). The circuit material was RT/duroid 6010.2 from Rogers Corp., with dielectric
constant of 10.8 and dissipation factor of 0.0023, both at 10 GHz. The substrate thickness was 1.27 mm, with 0.35-µm-thick copper cladding for forming the circuit traces. These parameters were duplicated in the HFSS EM
simulation software from Ansys (www.ansys.com). The lumped-element circuit parameters for the equivalent-circuit model of a two-pole filter, which were also developed with the aid of the Advanced Design System (ADS) simulation
software from Keysight Technologies, include CR of 0.2 pF, LR of 0.21 nH, CL of 5.0 pF, LL of 5.2 nH, center frequency, f0 , of 5.9 GHz, and feed-line impedance, Z0 , of 50 Ω.
Figure 6(a) shows the layout of the two-pole symmetrical BPF using coupled CRLH transmission-line resonators, where the overall size of the filter is 17 × 17 mm2. Figure 6(b) shows s prototype of the fabricated CRLH filter. Figure 7
contains the simulated S-parameter magnitudes, where it should be clear that the passband surrounds a center frequency of 5.9 GHz with magnitude values of S21 = -2 dB and S11 = -25 dB. By comparing full-wave HFSS EM
simulations with S-parameters measured with a VNA on the fabricated prototype, values of S21 = -2.5 dB and S11 approaching -10 dB were found for the experimental CRLH BPF design.
Third-Order Results
Figure 8(a) shows the layout of the BPF designed with third-order coupled CRLH-TL resonators, where the overall size of the BPF formed of these resonators is 16 × 24 mm2. The simulated (HFSS) scattering parameters for the filter
(Fig. 9) indicate that it provides excellent performance through the passband surrounding its center frequency at 5.9 GHz, with passband insertion loss, S21, of just 1.5 dB, and passband return loss, S11, close to 30 dB. The filter
has a transmission zero at 6.3 GHz, which equips it with an advantage in smaller dimensions compared to a conventional two-pole filter design. The single transmission zero also yields much improvement in skirt selectivity, with the
order number of the transmission zero equal to N – 2, with N the number of resonators in the design. Figure 9 shows good agreement between design theory and the EM simulation results, indicating that a lower transmission zero
can be added to the design by increasing the filter order.
In fact, the compact filter has a frequency and passband characteristics that make it well suited for WiMAX applications. It takes full advantage of the zeroth-order resonance of third-order coupled CRLH resonators to achieve good
passband loss characteristics in a small size. The zeroth-order resonance at 6.3 GHz improves the passband skirt selectivity in a filter size of only 16 × 24 mm2. By following a design procedure in which good agreement was
achieved among theory, computer simulations, and measurements, a 5.9-GHz BPF was created with CRLH resonators with about 40% reduction in size compared to BPFs designed with conventional microstrip transmission-line
resonators.
References
1. C. Caloz, “Metamaterial Dispersion Engineering Concepts and Applications,” Proceedings of the IEEE, Vol. 99, No. 10, 2011, pp. 1711-1719.
2. Yuandan Dong and T. Itoh, “Promising Future of Metamaterials,” IEEE Microwave Magazine, Vol. 13, No. 2, 2012, pp. 39-56.
3. G. V. Eleftheriades, “Enabling RF/microwave devices using negative refractive-index transmission-line (NRI-TL) metamaterials,” IEEE Antennas and Propagation Magazine, Vol. 49, No. 2, 2007, pp. 34-51
4. M. A. Abdalla and Z. Hu, “Design and analysis of tunable left handed zeroth-order resonator on ferrite substrate,” IEEE Transaction on Magnetics, Vol. 11, 2008, pp. 3095-3098.
5. C. L. Holloway, Edward F. Kuester, J. A. Gordon, J. O'Hara, J. Booth, and D. R. Smith, “An Overview of the Theory and Applications of Metasurfaces: The 2-Dimensional Equivalents of Metamaterials,” IEEE Antennas and
Propagation Magazine, Vol. 54, No. 2, 2012, pp. 10-35.
6. Qingshan Yang and Yunhua Zhang, “Negative-order ridge substrate integrated waveguide coupled-resonator filter,” Electronics Letters, Vol. 50, No. 4, 2014, pp. 290-291.
7. M. A. Abdalla, M. A. Fouad, and A. A. Mitkees, “Wideband Negative Permittivity Metamaterial for Size Reduction of Stopband Filter in Antenna Applications,” Progress in Electromagnetics Research C, Vol. 25, 2012, pp.
55-66.
8. J. Sorocki, I. Piekarz, K. Wincza, and S. Gruszczynski, “Right/Left-Handed Transmission Lines Based on Coupled Transmission-Line Sections and Their Application Towards Bandpass Filters,” IEEE Transactions on Microwave
Theory and Techniques, Vol. 63, No. 2, Part: 1, 2015, pp. 384-396.
9. Mohammed. A. Fouad, and Mahmoud A Abdalla, “A New π-T Generalized Metamaterial NRI Transmission Line for a Compact CPW Triple BPF Applications,” IET Microwave, Antenna, and Propagation, Vol. 8, No. 9, 2014,
pp. 1097-1104.
10. Ahmed A. Ibrahim, Mahmoud A. Abdalla, and Diuradi Budimir, “Coupled CRLH Transmission Lines for Compact and High Selectivity Bandpass Filters,” Microwave and Optical Technlogy Letters, Vol. 59, No. 6, 2017.
11. Ahmed Ibrahim, Adel Abdel-Rahman, and Mahmoud Abdalla, “Design of Third-Order Band Pass Filter Using Coupled Meta-Material Resonators,” 2014 IEEE AP-S 2014, Memphis, USA, pp. 1702-1703.
12. Ahmed F. Daw, Mahmoud A. Abdalla, and Hadya M. Elhennawy, “Dual Band High Selective Compact Transmission Line Gap Resonator,” 2014 Loughborough Antennas & Propagation Conference, 2014, Loughborough, UK,
pp. 91-94.
13. Ahmed Fawzy Daw, Mahmoud Abd El Rahman Abdalla, Hadia Mohamed El Hennawy, “Multiband Sharp-Skirt Compact Gap Resonator Based D-CRLH,” 32th National Radio Science Conference (NRSC2015), March 24-26,
2015, MSA University Egypt, pp. 43-50.
14. S. Karimian, M. Abdalla, and Z. Hu, “Left-Handed Stepped Impedance Resonator for WLAN Applications,” 3rd International Congress on Advanced Electromagnetic Materials in Microwaves and Optics, August 30-September
4, 2009, London, UK, pp. 105-107.
15. M. A. Abdalla, A. Y. Hassan, and A. M. Galal Eldin, “A Compact High Selective Gap Bandpass Filter Based CRLH TL,” 2015 9th International Congress on Advanced Electromagnetic Materials in Microwaves and Optics –
Metamaterials, 2015, Oxford, UK.
Figure captions
1. This is an equivalent-circuit representation of a composite-right-left-handed (CRLH) unit cell resonator.
2. This layout was used in the fabrication of a CRLH unit cell on commercial PCB material.
3. These simulated scattering parameters depict the insertion loss (S21) and return loss (S11) of the CRLH unit cell.
4. This plot shows the simulated S21 phase angle (in deg.) of the CRLH unit cell.
5. This CRLH resonator equivalent-circuit diagram was used to construct a two-pole CRLH filter.
6. The layout of a two-pole CRLH-based bandpass filter (a) is shown next to a fabricated prototype of the filter.
7. Two-Pole Filter scattering parameters and fabrication measurement
8. The layout of the ZOR BPF formed with third-order CRLH resonators (a) is shown next to the fabricated prototype (b).
9. These measured results show the performance of the BPF fabricated with third-order CRLH resonators.
NOTE FOR THE AUTHORS
Renumbering of the figures
OLD IS NOW
Figure 1 Figure 1
Figure 2 Figure 2
Figure 3 Figure 3
Figure 4 Figure 4
NO FIGURE 5
Figure 6 Figure 5
Figure 7 Figure 6
Figure 8 Figure 7
Figure 9 Figure 8
Figure 10 Figure 9
2LL
LRCL
2LL
CR/2 CR/2
1. Shown is an equivalent-circuit representation of a composite-
right-left-handed (CRLH) unit cell resonator.
MW/DF/AUGUST/abdalla/31KCALLS.doc
Figure callouts for Abdalla (31K)
Figure 1
2LL
Figure 2
Figure 3
S11
S21
Frequency—GHz
4
5
6
7
Magnitude—dB
0
-10
-20
-30
S21 5.8 -0.4
S11 5.8 -19.0
Figure 4
S11 5.8
Angle—deg.
200
100
0
-100
-200
Frequency—GHz
4
5
6
7
S11
Figure 5
LR
CL
Cgap
2LL
CR/2
CR/2
2LL
2LL2
CR2/2
CR2/2
2LL2
LR2
CL2
Figure 6
(a)
(b)
17 mm
17 mm
Figure 7
Magnitude—dB
0
-10
-20
-30
-40
Frequency—GHz
5.0
5.5
6.0
6.5
7.0
S21, simulated
S11, simulated
S21, measured
S11, measured
Figure 8
16 mm
24 mm
(a)
(b)
Figure 9
Magnitude—dB
0
-10
-20
-30
-40
-50
-60
-70
Frequency—GHz
5.0
5.5
6.0
6.5
7.0
S21, simulated
S11, simulated
S21, measured
S11, measured
CRLH Transmission Lines
Form Zero-Order BPF
Metamaterials and unconventional CRLH transmission lines combine to create RF/microwave bandpass filters with miniature dimensions for a wide range of wireless applications, such as WiMAX.
Mahmoud A. Abdalla
Assistant Professor
Electronic Engineering Department, MTC College, Cairo, Egypt, E-mail: maaabdalla@ieee.org.
Ashraf Y. Hassan
Ph. D. Student
Electronics and Communications Department, MSA University, Giza, Egypt, E-mail: ashrafyoussef92@hotmail.com
Ahmed A. Ibrahim
Assistant Professor
Communications and Electronics Department
Faculty of Engineering, Minia University, Minia, Egypt and University Oierre and Marie Curie, Sorbonne University, Paris VI, France; E-mail: ahmedabdel_monem@mu.edu.eg
Miniaturization of RF/microwave filters will enable the development of smaller wireless devices for internet access. The use of metamaterials and circuit structures such as composite-right-left-handed (CRLH) resonators has been
effective in shrinking RF/microwave filter circuits and has been demonstrated in the design of a compact bandpass filter (BPF) well suited for WiMAX wireless applications. With third-order coupled CRLH resonators, the filter
achieves a center frequency of 5.9 GHz with transmission zero at 6.4 GHz. Measuring just 16 × 24 mm2 or about 40% the size of BPFs based on conventional resonators, the filter achieves passband insertion loss of just 1.5 dB.
Metamaterials have shown great promise for the fabrication of compact, high-frequency RF/microwave circuits.1-4 First proposed in 2002, CRLH transmission lines (CRLH-TLs) are forms of high-frequency transmission lines that
exhibit backward-wave transmission behavior capable of unusual electromagnetic (EM) wave propagation. Metamaterial approaches to microwave circuit design have been based on CRLH or negative-refractive-index transmission
lines in planar structures by loading a host transmission line with series capacitor and shunt inductive load.
The use of metamaterials and CRLH-TLs enables the design of RF/microwave BPFs with small size, low passband loss, and even low cost. The small sizes supported by metamaterials make possible multiple-band filters a fraction of
the size of BPFs formed with conventional transmission lines.5-10 Coupled metamaterial resonators have formed compact BPFs.8,10 In addition, compact microwave CRLH gap resonators with high quality factors (Qs) show great
promise for forming miniature BPFs.11,12 To demonstrate, by combining high-Q CRLH gap resonators with third-order zeroth-order-resonator (ZOR) coupled resonators, a microwave BPF with extremely compact dimensions was
designed and fabricated for WiMAX applications with standard, low-cost circuit materials. The filter was constructed on RT/duroid 6010 circuit material from Rogers Corp. (www.rogerscorp.com). The 1.27-mm-thick circuit material
has dielectric constant of 10.8 at 10 GHz in the z-axis (thickness). The filter design was optimized with the aid of commercial electromagnetic (EM) simulation software and characterized using a 50-Ω microstrip feed line and
commercial test equipment, notably an RF/microwave vector network analyzer (VNA).
Figure 1 shows an equivalent-circuit model of the CRLH-TL, which consists of right-handed inductance (LR), right-handed capacitance (CR), left-handed inductance (LL), and left-handed capacitance (CL). In a practical circuit design,
CL is fabricated as a four-finger interdigital capacitor, LL is a viahole in the printed-circuit board (PCB) material, and capacitance CR and inductance LR are parasitic circuit elements essentially invisible in size. Mathematical analysis
of the CRLH structure can be performed by applying transmission-line theory to the equivalent circuit of a CRLH cell. In this case, the CRLH cell is coupled to a short 50-Ω (Z0) feed line for impedance matching to 50-Ω environments
and measurements with an RF/microwave VNA.
The frequency of a ZOR is independent of the order of the unit cell. This property can be parlayed into the design of a novel filter in which the center frequency is independent of the physical length of the transmission lines, allowing
a dramatic size reduction in the filter since the resonator frequency does not rely on the half-wavelength size of the transmission lines.5-8
The phase of the transmission lines can be found by applying Eq. 1, as a super-position of right- and left-banded phases from the CRLH transmission lines. By controlling the circuit loading elements (CL and LL), a zero-phase
condition (φCRLH = 0) can be achieved:
φCRLH = -βl = [1/ω(CL LL)0.5 – ω(CR LR)0.5] (1)
Figure 2 provides a layout of the CRLH unit cell used in the design of the compact BPF. Figure 3 shows the computer-simulated full-wave scattering (S) parameters of the CRLH cell. The curves indicate a sharp resonance at 5.9 GHz,
where the value of S21 (insertion loss) is almost -1 dB and the value of S11 (return loss) is less than -20 dB. Figure 4 shows the computer-simulated phase of the CRLH resonator cell, where the phase at 5.9 GHz is almost equal to 0.
This is the justification for claiming that a zeroth-order coupled resonator has been created.
CRLH Construction
A microstrip configuration was used to fabricate a two-pole filter using equivalent circuits of the CRLH unit cell resonators (Fig. 5) as building blocks along with a capacitive gap, with the design aided by full-wave EM simulations in
the Ansoft HFSS software to find computer-simulated S-parameters. The filter was constructed on commercial PCB material (including low-loss viaholes). The circuit material was RT/duroid 6010.2 from Rogers Corp., with dielectric
constant of 10.8 and dissipation factor of 0.0023, both at 10 GHz. The substrate thickness was 1.27 mm, with 0.35-µm-thick copper cladding for forming the circuit traces. These parameters were duplicated in the HFSS EM
simulation software from Ansys (www.ansys.com). The lumped-element circuit parameters for the equivalent-circuit model of a two-pole filter, which were also developed with the aid of the Advanced Design System (ADS) simulation
software from Keysight Technologies, include CR of 0.2 pF, LR of 0.21 nH, CL of 5.0 pF, LL of 5.2 nH, center frequency, f0 , of 5.9 GHz, and feed-line impedance, Z0 , of 50 Ω.
Figure 6(a) shows the layout of the two-pole symmetrical BPF using coupled CRLH transmission-line resonators, where the overall size of the filter is 17 × 17 mm2. Figure 6(b) shows s prototype of the fabricated CRLH filter. Figure 7
contains the simulated S-parameter magnitudes, where it should be clear that the passband surrounds a center frequency of 5.9 GHz with magnitude values of S21 = -2 dB and S11 = -25 dB. By comparing full-wave HFSS EM
simulations with S-parameters measured with a VNA on the fabricated prototype, values of S21 = -2.5 dB and S11 approaching -10 dB were found for the experimental CRLH BPF design.
Third-Order Results
Figure 8(a) shows the layout of the BPF designed with third-order coupled CRLH-TL resonators, where the overall size of the BPF formed of these resonators is 16 × 24 mm2. The simulated (HFSS) scattering parameters for the filter
(Fig. 9) indicate that it provides excellent performance through the passband surrounding its center frequency at 5.9 GHz, with passband insertion loss, S21, of just 1.5 dB, and passband return loss, S11, close to 30 dB. The filter
has a transmission zero at 6.3 GHz, which equips it with an advantage in smaller dimensions compared to a conventional two-pole filter design. The single transmission zero also yields much improvement in skirt selectivity, with the
order number of the transmission zero equal to N – 2, with N the number of resonators in the design. Figure 9 shows good agreement between design theory and the EM simulation results, indicating that a lower transmission zero
can be added to the design by increasing the filter order.
In fact, the compact filter has a frequency and passband characteristics that make it well suited for WiMAX applications. It takes full advantage of the zeroth-order resonance of third-order coupled CRLH resonators to achieve good
passband loss characteristics in a small size. The zeroth-order resonance at 6.3 GHz improves the passband skirt selectivity in a filter size of only 16 × 24 mm2. By following a design procedure in which good agreement was
achieved among theory, computer simulations, and measurements, a 5.9-GHz BPF was created with CRLH resonators with about 40% reduction in size compared to BPFs designed with conventional microstrip transmission-line
resonators.
References
1. C. Caloz, “Metamaterial Dispersion Engineering Concepts and Applications,” Proceedings of the IEEE, Vol. 99, No. 10, 2011, pp. 1711-1719.
2. Yuandan Dong and T. Itoh, “Promising Future of Metamaterials,” IEEE Microwave Magazine, Vol. 13, No. 2, 2012, pp. 39-56.
3. G. V. Eleftheriades, “Enabling RF/microwave devices using negative refractive-index transmission-line (NRI-TL) metamaterials,” IEEE Antennas and Propagation Magazine, Vol. 49, No. 2, 2007, pp. 34-51
4. M. A. Abdalla and Z. Hu, “Design and analysis of tunable left handed zeroth-order resonator on ferrite substrate,” IEEE Transaction on Magnetics, Vol. 11, 2008, pp. 3095-3098.
5. C. L. Holloway, Edward F. Kuester, J. A. Gordon, J. O'Hara, J. Booth, and D. R. Smith, “An Overview of the Theory and Applications of Metasurfaces: The 2-Dimensional Equivalents of Metamaterials,” IEEE Antennas and
Propagation Magazine, Vol. 54, No. 2, 2012, pp. 10-35.
6. Qingshan Yang and Yunhua Zhang, “Negative-order ridge substrate integrated waveguide coupled-resonator filter,” Electronics Letters, Vol. 50, No. 4, 2014, pp. 290-291.
7. M. A. Abdalla, M. A. Fouad, and A. A. Mitkees, “Wideband Negative Permittivity Metamaterial for Size Reduction of Stopband Filter in Antenna Applications,” Progress in Electromagnetics Research C, Vol. 25, 2012, pp.
55-66.
8. J. Sorocki, I. Piekarz, K. Wincza, and S. Gruszczynski, “Right/Left-Handed Transmission Lines Based on Coupled Transmission-Line Sections and Their Application Towards Bandpass Filters,” IEEE Transactions on Microwave
Theory and Techniques, Vol. 63, No. 2, Part: 1, 2015, pp. 384-396.
9. Mohammed. A. Fouad, and Mahmoud A Abdalla, “A New π-T Generalized Metamaterial NRI Transmission Line for a Compact CPW Triple BPF Applications,” IET Microwave, Antenna, and Propagation, Vol. 8, No. 9, 2014,
pp. 1097-1104.
10. Ahmed A. Ibrahim, Mahmoud A. Abdalla, and Diuradi Budimir, “Coupled CRLH Transmission Lines for Compact and High Selectivity Bandpass Filters,” Microwave and Optical Technlogy Letters, Vol. 59, No. 6, 2017.
11. Ahmed Ibrahim, Adel Abdel-Rahman, and Mahmoud Abdalla, “Design of Third-Order Band Pass Filter Using Coupled Meta-Material Resonators,” 2014 IEEE AP-S 2014, Memphis, USA, pp. 1702-1703.
12. Ahmed F. Daw, Mahmoud A. Abdalla, and Hadya M. Elhennawy, “Dual Band High Selective Compact Transmission Line Gap Resonator,” 2014 Loughborough Antennas & Propagation Conference, 2014, Loughborough, UK,
pp. 91-94.
13. Ahmed Fawzy Daw, Mahmoud Abd El Rahman Abdalla, Hadia Mohamed El Hennawy, “Multiband Sharp-Skirt Compact Gap Resonator Based D-CRLH,” 32th National Radio Science Conference (NRSC2015), March 24-26,
2015, MSA University Egypt, pp. 43-50.
14. S. Karimian, M. Abdalla, and Z. Hu, “Left-Handed Stepped Impedance Resonator for WLAN Applications,” 3rd International Congress on Advanced Electromagnetic Materials in Microwaves and Optics, August 30-September
4, 2009, London, UK, pp. 105-107.
15. M. A. Abdalla, A. Y. Hassan, and A. M. Galal Eldin, “A Compact High Selective Gap Bandpass Filter Based CRLH TL,” 2015 9th International Congress on Advanced Electromagnetic Materials in Microwaves and Optics –
Metamaterials, 2015, Oxford, UK.
Figure captions
1. This is an equivalent-circuit representation of a composite-right-left-handed (CRLH) unit cell resonator.
2. This layout was used in the fabrication of a CRLH unit cell on commercial PCB material.
3. These simulated scattering parameters depict the insertion loss (S21) and return loss (S11) of the CRLH unit cell.
4. This plot shows the simulated S21 phase angle (in deg.) of the CRLH unit cell.
5. This CRLH resonator equivalent-circuit diagram was used to construct a two-pole CRLH filter.
6. The layout of a two-pole CRLH-based bandpass filter (a) is shown next to a fabricated prototype of the filter.
7. Two-Pole Filter scattering parameters and fabrication measurement
8. The layout of the ZOR BPF formed with third-order CRLH resonators (a) is shown next to the fabricated prototype (b).
9. These measured results show the performance of the BPF fabricated with third-order CRLH resonators.
NOTE FOR THE AUTHORS
Renumbering of the figures
OLD IS NOW
Figure 1 Figure 1
Figure 2 Figure 2
Figure 3 Figure 3
Figure 4 Figure 4
NO FIGURE 5
Figure 6 Figure 5
Figure 7 Figure 6
Figure 8 Figure 7
Figure 9 Figure 8
Figure 10 Figure 9
2.1 mm
3.4 mm
0.25 mm
0.3 mm
1.2 mm
0.3 mm
0.4 mm
0.1 mm
0.7 mm
0.2 mm
2. This layout was used in the fabrication of a CRLH unit cell on com-
mercial PCB material.
S11
S21
Frequency (GHz)
4 5 6 7
0
–10
–20
–30
Magnitude (dB)
S21 5.8 –0.4
S11 5.8 –19.0
3. These simulated scattering parameters depict the insertion loss
(S21) and return loss (S11) of the CRLH unit cell.
Figure 5
LR
CL
Cgap
2LL
CR/2
CR/2
2LL
2LL2
CR2/2
CR2/2
2LL2
LR2
CL2
Figure 6
(a)
(b)
17 mm
17 mm
Figure 7
Magnitude—dB
0
-10
-20
-30
-40
Frequency—GHz
5.0
5.5
6.0
6.5
7.0
S21, simulated
S11, simulated
S21, measured
S11, measured
Figure 8
16 mm
24 mm
(a)
(b)
Figure 9
Magnitude—dB
0
-10
-20
-30
-40
-50
-60
-70
Frequency—GHz
5.0
5.5
6.0
6.5
7.0
S21, simulated
S11, simulated
S21, measured
S11, measured
CRLH Transmission Lines
Form Zero-Order BPF
Metamaterials and unconventional CRLH transmission lines combine to create RF/microwave bandpass filters with miniature dimensions for a wide range of wireless applications, such as WiMAX.
Mahmoud A. Abdalla
Assistant Professor
Electronic Engineering Department, MTC College, Cairo, Egypt, E-mail: maaabdalla@ieee.org.
Ashraf Y. Hassan
Ph. D. Student
Electronics and Communications Department, MSA University, Giza, Egypt, E-mail: ashrafyoussef92@hotmail.com
Ahmed A. Ibrahim
Assistant Professor
Communications and Electronics Department
Faculty of Engineering, Minia University, Minia, Egypt and University Oierre and Marie Curie, Sorbonne University, Paris VI, France; E-mail: ahmedabdel_monem@mu.edu.eg
Miniaturization of RF/microwave filters will enable the development of smaller wireless devices for internet access. The use of metamaterials and circuit structures such as composite-right-left-handed (CRLH) resonators has been
effective in shrinking RF/microwave filter circuits and has been demonstrated in the design of a compact bandpass filter (BPF) well suited for WiMAX wireless applications. With third-order coupled CRLH resonators, the filter
achieves a center frequency of 5.9 GHz with transmission zero at 6.4 GHz. Measuring just 16 × 24 mm2 or about 40% the size of BPFs based on conventional resonators, the filter achieves passband insertion loss of just 1.5 dB.
Metamaterials have shown great promise for the fabrication of compact, high-frequency RF/microwave circuits.1-4 First proposed in 2002, CRLH transmission lines (CRLH-TLs) are forms of high-frequency transmission lines that
exhibit backward-wave transmission behavior capable of unusual electromagnetic (EM) wave propagation. Metamaterial approaches to microwave circuit design have been based on CRLH or negative-refractive-index transmission
lines in planar structures by loading a host transmission line with series capacitor and shunt inductive load.
The use of metamaterials and CRLH-TLs enables the design of RF/microwave BPFs with small size, low passband loss, and even low cost. The small sizes supported by metamaterials make possible multiple-band filters a fraction of
the size of BPFs formed with conventional transmission lines.5-10 Coupled metamaterial resonators have formed compact BPFs.8,10 In addition, compact microwave CRLH gap resonators with high quality factors (Qs) show great
promise for forming miniature BPFs.11,12 To demonstrate, by combining high-Q CRLH gap resonators with third-order zeroth-order-resonator (ZOR) coupled resonators, a microwave BPF with extremely compact dimensions was
designed and fabricated for WiMAX applications with standard, low-cost circuit materials. The filter was constructed on RT/duroid 6010 circuit material from Rogers Corp. (www.rogerscorp.com). The 1.27-mm-thick circuit material
has dielectric constant of 10.8 at 10 GHz in the z-axis (thickness). The filter design was optimized with the aid of commercial electromagnetic (EM) simulation software and characterized using a 50-Ω microstrip feed line and
commercial test equipment, notably an RF/microwave vector network analyzer (VNA).
Figure 1 shows an equivalent-circuit model of the CRLH-TL, which consists of right-handed inductance (LR), right-handed capacitance (CR), left-handed inductance (LL), and left-handed capacitance (CL). In a practical circuit design,
CL is fabricated as a four-finger interdigital capacitor, LL is a viahole in the printed-circuit board (PCB) material, and capacitance CR and inductance LR are parasitic circuit elements essentially invisible in size. Mathematical analysis
of the CRLH structure can be performed by applying transmission-line theory to the equivalent circuit of a CRLH cell. In this case, the CRLH cell is coupled to a short 50-Ω (Z0) feed line for impedance matching to 50-Ω environments
and measurements with an RF/microwave VNA.
The frequency of a ZOR is independent of the order of the unit cell. This property can be parlayed into the design of a novel filter in which the center frequency is independent of the physical length of the transmission lines, allowing
a dramatic size reduction in the filter since the resonator frequency does not rely on the half-wavelength size of the transmission lines.5-8
The phase of the transmission lines can be found by applying Eq. 1, as a super-position of right- and left-banded phases from the CRLH transmission lines. By controlling the circuit loading elements (CL and LL), a zero-phase
condition (φCRLH = 0) can be achieved:
φCRLH = -βl = [1/ω(CL LL)0.5 – ω(CR LR)0.5] (1)
Figure 2 provides a layout of the CRLH unit cell used in the design of the compact BPF. Figure 3 shows the computer-simulated full-wave scattering (S) parameters of the CRLH cell. The curves indicate a sharp resonance at 5.9 GHz,
where the value of S21 (insertion loss) is almost -1 dB and the value of S11 (return loss) is less than -20 dB. Figure 4 shows the computer-simulated phase of the CRLH resonator cell, where the phase at 5.9 GHz is almost equal to 0.
This is the justification for claiming that a zeroth-order coupled resonator has been created.
CRLH Construction
A microstrip configuration was used to fabricate a two-pole filter using equivalent circuits of the CRLH unit cell resonators (Fig. 5) as building blocks along with a capacitive gap, with the design aided by full-wave EM simulations in
the Ansoft HFSS software to find computer-simulated S-parameters. The filter was constructed on commercial PCB material (including low-loss viaholes). The circuit material was RT/duroid 6010.2 from Rogers Corp., with dielectric
constant of 10.8 and dissipation factor of 0.0023, both at 10 GHz. The substrate thickness was 1.27 mm, with 0.35-µm-thick copper cladding for forming the circuit traces. These parameters were duplicated in the HFSS EM
simulation software from Ansys (www.ansys.com). The lumped-element circuit parameters for the equivalent-circuit model of a two-pole filter, which were also developed with the aid of the Advanced Design System (ADS) simulation
software from Keysight Technologies, include CR of 0.2 pF, LR of 0.21 nH, CL of 5.0 pF, LL of 5.2 nH, center frequency, f0 , of 5.9 GHz, and feed-line impedance, Z0 , of 50 Ω.
Figure 6(a) shows the layout of the two-pole symmetrical BPF using coupled CRLH transmission-line resonators, where the overall size of the filter is 17 × 17 mm2. Figure 6(b) shows s prototype of the fabricated CRLH filter. Figure 7
contains the simulated S-parameter magnitudes, where it should be clear that the passband surrounds a center frequency of 5.9 GHz with magnitude values of S21 = -2 dB and S11 = -25 dB. By comparing full-wave HFSS EM
simulations with S-parameters measured with a VNA on the fabricated prototype, values of S21 = -2.5 dB and S11 approaching -10 dB were found for the experimental CRLH BPF design.
Third-Order Results
Figure 8(a) shows the layout of the BPF designed with third-order coupled CRLH-TL resonators, where the overall size of the BPF formed of these resonators is 16 × 24 mm2. The simulated (HFSS) scattering parameters for the filter
(Fig. 9) indicate that it provides excellent performance through the passband surrounding its center frequency at 5.9 GHz, with passband insertion loss, S21, of just 1.5 dB, and passband return loss, S11, close to 30 dB. The filter
has a transmission zero at 6.3 GHz, which equips it with an advantage in smaller dimensions compared to a conventional two-pole filter design. The single transmission zero also yields much improvement in skirt selectivity, with the
order number of the transmission zero equal to N – 2, with N the number of resonators in the design. Figure 9 shows good agreement between design theory and the EM simulation results, indicating that a lower transmission zero
can be added to the design by increasing the filter order.
In fact, the compact filter has a frequency and passband characteristics that make it well suited for WiMAX applications. It takes full advantage of the zeroth-order resonance of third-order coupled CRLH resonators to achieve good
passband loss characteristics in a small size. The zeroth-order resonance at 6.3 GHz improves the passband skirt selectivity in a filter size of only 16 × 24 mm2. By following a design procedure in which good agreement was
achieved among theory, computer simulations, and measurements, a 5.9-GHz BPF was created with CRLH resonators with about 40% reduction in size compared to BPFs designed with conventional microstrip transmission-line
resonators.
References
1. C. Caloz, “Metamaterial Dispersion Engineering Concepts and Applications,” Proceedings of the IEEE, Vol. 99, No. 10, 2011, pp. 1711-1719.
2. Yuandan Dong and T. Itoh, “Promising Future of Metamaterials,” IEEE Microwave Magazine, Vol. 13, No. 2, 2012, pp. 39-56.
3. G. V. Eleftheriades, “Enabling RF/microwave devices using negative refractive-index transmission-line (NRI-TL) metamaterials,” IEEE Antennas and Propagation Magazine, Vol. 49, No. 2, 2007, pp. 34-51
4. M. A. Abdalla and Z. Hu, “Design and analysis of tunable left handed zeroth-order resonator on ferrite substrate,” IEEE Transaction on Magnetics, Vol. 11, 2008, pp. 3095-3098.
5. C. L. Holloway, Edward F. Kuester, J. A. Gordon, J. O'Hara, J. Booth, and D. R. Smith, “An Overview of the Theory and Applications of Metasurfaces: The 2-Dimensional Equivalents of Metamaterials,” IEEE Antennas and
Propagation Magazine, Vol. 54, No. 2, 2012, pp. 10-35.
6. Qingshan Yang and Yunhua Zhang, “Negative-order ridge substrate integrated waveguide coupled-resonator filter,” Electronics Letters, Vol. 50, No. 4, 2014, pp. 290-291.
7. M. A. Abdalla, M. A. Fouad, and A. A. Mitkees, “Wideband Negative Permittivity Metamaterial for Size Reduction of Stopband Filter in Antenna Applications,” Progress in Electromagnetics Research C, Vol. 25, 2012, pp.
55-66.
8. J. Sorocki, I. Piekarz, K. Wincza, and S. Gruszczynski, “Right/Left-Handed Transmission Lines Based on Coupled Transmission-Line Sections and Their Application Towards Bandpass Filters,” IEEE Transactions on Microwave
Theory and Techniques, Vol. 63, No. 2, Part: 1, 2015, pp. 384-396.
9. Mohammed. A. Fouad, and Mahmoud A Abdalla, “A New π-T Generalized Metamaterial NRI Transmission Line for a Compact CPW Triple BPF Applications,” IET Microwave, Antenna, and Propagation, Vol. 8, No. 9, 2014,
pp. 1097-1104.
10. Ahmed A. Ibrahim, Mahmoud A. Abdalla, and Diuradi Budimir, “Coupled CRLH Transmission Lines for Compact and High Selectivity Bandpass Filters,” Microwave and Optical Technlogy Letters, Vol. 59, No. 6, 2017.
11. Ahmed Ibrahim, Adel Abdel-Rahman, and Mahmoud Abdalla, “Design of Third-Order Band Pass Filter Using Coupled Meta-Material Resonators,” 2014 IEEE AP-S 2014, Memphis, USA, pp. 1702-1703.
12. Ahmed F. Daw, Mahmoud A. Abdalla, and Hadya M. Elhennawy, “Dual Band High Selective Compact Transmission Line Gap Resonator,” 2014 Loughborough Antennas & Propagation Conference, 2014, Loughborough, UK,
pp. 91-94.
13. Ahmed Fawzy Daw, Mahmoud Abd El Rahman Abdalla, Hadia Mohamed El Hennawy, “Multiband Sharp-Skirt Compact Gap Resonator Based D-CRLH,” 32th National Radio Science Conference (NRSC2015), March 24-26,
2015, MSA University Egypt, pp. 43-50.
14. S. Karimian, M. Abdalla, and Z. Hu, “Left-Handed Stepped Impedance Resonator for WLAN Applications,” 3rd International Congress on Advanced Electromagnetic Materials in Microwaves and Optics, August 30-September
4, 2009, London, UK, pp. 105-107.
15. M. A. Abdalla, A. Y. Hassan, and A. M. Galal Eldin, “A Compact High Selective Gap Bandpass Filter Based CRLH TL,” 2015 9th International Congress on Advanced Electromagnetic Materials in Microwaves and Optics –
Metamaterials, 2015, Oxford, UK.
Figure captions
1. This is an equivalent-circuit representation of a composite-right-left-handed (CRLH) unit cell resonator.
2. This layout was used in the fabrication of a CRLH unit cell on commercial PCB material.
3. These simulated scattering parameters depict the insertion loss (S21) and return loss (S11) of the CRLH unit cell.
4. This plot shows the simulated S21 phase angle (in deg.) of the CRLH unit cell.
5. This CRLH resonator equivalent-circuit diagram was used to construct a two-pole CRLH filter.
6. The layout of a two-pole CRLH-based bandpass filter (a) is shown next to a fabricated prototype of the filter.
7. Two-Pole Filter scattering parameters and fabrication measurement
8. The layout of the ZOR BPF formed with third-order CRLH resonators (a) is shown next to the fabricated prototype (b).
9. These measured results show the performance of the BPF fabricated with third-order CRLH resonators.
NOTE FOR THE AUTHORS
Renumbering of the figures
OLD IS NOW
Figure 1 Figure 1
Figure 2 Figure 2
Figure 3 Figure 3
Figure 4 Figure 4
NO FIGURE 5
Figure 6 Figure 5
Figure 7 Figure 6
Figure 8 Figure 7
Figure 9 Figure 8
Figure 10 Figure 9
Frequency (GHz)
4 5 6 7
S11 5.8
S11
200
100
0
-100
-200
Angle (deg)
4. The plot shows the simulated S21 phase angle (in deg.) of the
CRLH unit cell.
45
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CRLH Transmission Lines
the phase at 5.9 GHz is almost equal to 0. This is the justifica-
tion for claiming that a zeroth-order coupled resonator has
been created.
CRLH CONSTRUCTION
A microstrip configuration was used to fabricate a two-pole
filter using equivalent circuits of the CRLH unit cell resonators
(Fig. 5) as building blocks along with a capacitive gap, with
the design aided by full-wave EM simulations in the ANSYS
HFSS software to find computer-simulated S-parameters. The
filter was constructed on commercial PCB material (including
low-loss viaholes). The circuit material was Rogers Corp.’s RT/
duroid 6010.2, with dielectric constant of 10.8 and dissipation
factor of 0.0023, both at 10 GHz. Substrate thickness was 1.27
mm, with 0.35-µm-thick copper cladding for forming the
circuit traces.
These parameters were duplicated in the HFSS EM simula-
tion software from ANSYS (www.ansys.com). The lumped-
element circuit parameters for the equivalent-circuit model
of a two-pole filter, which were also developed with the aid of
the Advanced Design System (ADS) simulation software from
Keysight Technologies, include CR of 0.2 pF, LR of 0.21 nH, CL
of 5.0 pF, LL of 5.2 nH, center frequency (f0) of 5.9 GHz, and
feed-line impedance (Z0) of 50 Ω.
Figure 6a shows the layout of the two-pole symmetrical BPF
using coupled CRLH transmission-line resonators, where the
overall size of the filter is 17 × 17 mm2. And Figure 6b shows a
prototype of the fabricated CRLH filter. Figure 7 contains the
simulated S-parameter magnitudes, where it should be clear
that the passband surrounds a center frequency of 5.9 GHz
with magnitude values of S21 = −2 dB and S11 = −25 dB. By
comparing full-wave HFSS EM simulations with S-parameters
measured with a VNA on the fabricated prototype, values of
S21 = −2.5 dB and S11 approaching −10 dB were found for the
experimental CRLH BPF design.
5. This CRLH resona-
tor equivalent-circuit
diagram was used to
construct a two-pole
CRLH filter.
(a) (b)
17 mm
17 mm
6. The layout of a two-pole CRLH-based bandpass filter (a) is shown
next to a fabricated prototype of the filter (b).
46 AUGUST 2018 MICROWAVES & RF
Figure 5
CL
2LL
CR/2
CR/2
2LL
2LL2
CR2/2
CR2/2
2LL2
LR2
CL2
Figure 6
(a)
(b)
17 mm
17 mm
Figure 7
Magnitude—dB
0
-10
-20
-30
-40
Frequency—GHz
5.0
5.5
6.0
6.5
7.0
S21, simulated
S11, simulated
S21, measured
S11, measured
Figure 8
16 mm
24 mm
(a)
(b)
Figure 9
Magnitude—dB
0
-10
-20
-30
-40
-50
-60
-70
Frequency—GHz
5.0
5.5
6.0
6.5
7.0
S21, simulated
S11, simulated
S21, measured
S11, measured
CRLH Transmission Lines
Form Zero-Order BPF
Metamaterials and unconventional CRLH transmission lines combine to create RF/microwave bandpass filters with miniature dimensions for a wide range of wireless applications, such as WiMAX.
Mahmoud A. Abdalla
Assistant Professor
Electronic Engineering Department, MTC College, Cairo, Egypt, E-mail: maaabdalla@ieee.org.
Ashraf Y. Hassan
Ph. D. Student
Electronics and Communications Department, MSA University, Giza, Egypt, E-mail: ashrafyoussef92@hotmail.com
Ahmed A. Ibrahim
Assistant Professor
Communications and Electronics Department
Faculty of Engineering, Minia University, Minia, Egypt and University Oierre and Marie Curie, Sorbonne University, Paris VI, France; E-mail: ahmedabdel_monem@mu.edu.eg
Miniaturization of RF/microwave filters will enable the development of smaller wireless devices for internet access. The use of metamaterials and circuit structures such as composite-right-left-handed (CRLH) resonators has been
effective in shrinking RF/microwave filter circuits and has been demonstrated in the design of a compact bandpass filter (BPF) well suited for WiMAX wireless applications. With third-order coupled CRLH resonators, the filter
achieves a center frequency of 5.9 GHz with transmission zero at 6.4 GHz. Measuring just 16 × 24 mm2 or about 40% the size of BPFs based on conventional resonators, the filter achieves passband insertion loss of just 1.5 dB.
Metamaterials have shown great promise for the fabrication of compact, high-frequency RF/microwave circuits.1-4 First proposed in 2002, CRLH transmission lines (CRLH-TLs) are forms of high-frequency transmission lines that
exhibit backward-wave transmission behavior capable of unusual electromagnetic (EM) wave propagation. Metamaterial approaches to microwave circuit design have been based on CRLH or negative-refractive-index transmission
lines in planar structures by loading a host transmission line with series capacitor and shunt inductive load.
The use of metamaterials and CRLH-TLs enables the design of RF/microwave BPFs with small size, low passband loss, and even low cost. The small sizes supported by metamaterials make possible multiple-band filters a fraction of
the size of BPFs formed with conventional transmission lines.5-10 Coupled metamaterial resonators have formed compact BPFs.8,10 In addition, compact microwave CRLH gap resonators with high quality factors (Qs) show great
promise for forming miniature BPFs.11,12 To demonstrate, by combining high-Q CRLH gap resonators with third-order zeroth-order-resonator (ZOR) coupled resonators, a microwave BPF with extremely compact dimensions was
designed and fabricated for WiMAX applications with standard, low-cost circuit materials. The filter was constructed on RT/duroid 6010 circuit material from Rogers Corp. (www.rogerscorp.com). The 1.27-mm-thick circuit material
has dielectric constant of 10.8 at 10 GHz in the z-axis (thickness). The filter design was optimized with the aid of commercial electromagnetic (EM) simulation software and characterized using a 50-Ω microstrip feed line and
commercial test equipment, notably an RF/microwave vector network analyzer (VNA).
Figure 1 shows an equivalent-circuit model of the CRLH-TL, which consists of right-handed inductance (LR), right-handed capacitance (CR), left-handed inductance (LL), and left-handed capacitance (CL). In a practical circuit design,
CL is fabricated as a four-finger interdigital capacitor, LL is a viahole in the printed-circuit board (PCB) material, and capacitance CR and inductance LR are parasitic circuit elements essentially invisible in size. Mathematical analysis
of the CRLH structure can be performed by applying transmission-line theory to the equivalent circuit of a CRLH cell. In this case, the CRLH cell is coupled to a short 50-Ω (Z0) feed line for impedance matching to 50-Ω environments
and measurements with an RF/microwave VNA.
The frequency of a ZOR is independent of the order of the unit cell. This property can be parlayed into the design of a novel filter in which the center frequency is independent of the physical length of the transmission lines, allowing
a dramatic size reduction in the filter since the resonator frequency does not rely on the half-wavelength size of the transmission lines.5-8
The phase of the transmission lines can be found by applying Eq. 1, as a super-position of right- and left-banded phases from the CRLH transmission lines. By controlling the circuit loading elements (CL and LL), a zero-phase
condition (φCRLH = 0) can be achieved:
φCRLH = -βl = [1/ω(CL LL)0.5 – ω(CR LR)0.5] (1)
Figure 2 provides a layout of the CRLH unit cell used in the design of the compact BPF. Figure 3 shows the computer-simulated full-wave scattering (S) parameters of the CRLH cell. The curves indicate a sharp resonance at 5.9 GHz,
where the value of S21 (insertion loss) is almost -1 dB and the value of S11 (return loss) is less than -20 dB. Figure 4 shows the computer-simulated phase of the CRLH resonator cell, where the phase at 5.9 GHz is almost equal to 0.
This is the justification for claiming that a zeroth-order coupled resonator has been created.
CRLH Construction
A microstrip configuration was used to fabricate a two-pole filter using equivalent circuits of the CRLH unit cell resonators (Fig. 5) as building blocks along with a capacitive gap, with the design aided by full-wave EM simulations in
the Ansoft HFSS software to find computer-simulated S-parameters. The filter was constructed on commercial PCB material (including low-loss viaholes). The circuit material was RT/duroid 6010.2 from Rogers Corp., with dielectric
constant of 10.8 and dissipation factor of 0.0023, both at 10 GHz. The substrate thickness was 1.27 mm, with 0.35-µm-thick copper cladding for forming the circuit traces. These parameters were duplicated in the HFSS EM
simulation software from Ansys (www.ansys.com). The lumped-element circuit parameters for the equivalent-circuit model of a two-pole filter, which were also developed with the aid of the Advanced Design System (ADS) simulation
software from Keysight Technologies, include CR of 0.2 pF, LR of 0.21 nH, CL of 5.0 pF, LL of 5.2 nH, center frequency, f0 , of 5.9 GHz, and feed-line impedance, Z0 , of 50 Ω.
Figure 6(a) shows the layout of the two-pole symmetrical BPF using coupled CRLH transmission-line resonators, where the overall size of the filter is 17 × 17 mm2. Figure 6(b) shows s prototype of the fabricated CRLH filter. Figure 7
contains the simulated S-parameter magnitudes, where it should be clear that the passband surrounds a center frequency of 5.9 GHz with magnitude values of S21 = -2 dB and S11 = -25 dB. By comparing full-wave HFSS EM
simulations with S-parameters measured with a VNA on the fabricated prototype, values of S21 = -2.5 dB and S11 approaching -10 dB were found for the experimental CRLH BPF design.
Third-Order Results
Figure 8(a) shows the layout of the BPF designed with third-order coupled CRLH-TL resonators, where the overall size of the BPF formed of these resonators is 16 × 24 mm2. The simulated (HFSS) scattering parameters for the filter
(Fig. 9) indicate that it provides excellent performance through the passband surrounding its center frequency at 5.9 GHz, with passband insertion loss, S21, of just 1.5 dB, and passband return loss, S11, close to 30 dB. The filter
has a transmission zero at 6.3 GHz, which equips it with an advantage in smaller dimensions compared to a conventional two-pole filter design. The single transmission zero also yields much improvement in skirt selectivity, with the
order number of the transmission zero equal to N – 2, with N the number of resonators in the design. Figure 9 shows good agreement between design theory and the EM simulation results, indicating that a lower transmission zero
can be added to the design by increasing the filter order.
In fact, the compact filter has a frequency and passband characteristics that make it well suited for WiMAX applications. It takes full advantage of the zeroth-order resonance of third-order coupled CRLH resonators to achieve good
passband loss characteristics in a small size. The zeroth-order resonance at 6.3 GHz improves the passband skirt selectivity in a filter size of only 16 × 24 mm2. By following a design procedure in which good agreement was
achieved among theory, computer simulations, and measurements, a 5.9-GHz BPF was created with CRLH resonators with about 40% reduction in size compared to BPFs designed with conventional microstrip transmission-line
resonators.
References
1. C. Caloz, “Metamaterial Dispersion Engineering Concepts and Applications,” Proceedings of the IEEE, Vol. 99, No. 10, 2011, pp. 1711-1719.
2. Yuandan Dong and T. Itoh, “Promising Future of Metamaterials,” IEEE Microwave Magazine, Vol. 13, No. 2, 2012, pp. 39-56.
3. G. V. Eleftheriades, “Enabling RF/microwave devices using negative refractive-index transmission-line (NRI-TL) metamaterials,” IEEE Antennas and Propagation Magazine, Vol. 49, No. 2, 2007, pp. 34-51
4. M. A. Abdalla and Z. Hu, “Design and analysis of tunable left handed zeroth-order resonator on ferrite substrate,” IEEE Transaction on Magnetics, Vol. 11, 2008, pp. 3095-3098.
5. C. L. Holloway, Edward F. Kuester, J. A. Gordon, J. O'Hara, J. Booth, and D. R. Smith, “An Overview of the Theory and Applications of Metasurfaces: The 2-Dimensional Equivalents of Metamaterials,” IEEE Antennas and
Propagation Magazine, Vol. 54, No. 2, 2012, pp. 10-35.
6. Qingshan Yang and Yunhua Zhang, “Negative-order ridge substrate integrated waveguide coupled-resonator filter,” Electronics Letters, Vol. 50, No. 4, 2014, pp. 290-291.
7. M. A. Abdalla, M. A. Fouad, and A. A. Mitkees, “Wideband Negative Permittivity Metamaterial for Size Reduction of Stopband Filter in Antenna Applications,” Progress in Electromagnetics Research C, Vol. 25, 2012, pp.
55-66.
8. J. Sorocki, I. Piekarz, K. Wincza, and S. Gruszczynski, “Right/Left-Handed Transmission Lines Based on Coupled Transmission-Line Sections and Their Application Towards Bandpass Filters,” IEEE Transactions on Microwave
Theory and Techniques, Vol. 63, No. 2, Part: 1, 2015, pp. 384-396.
9. Mohammed. A. Fouad, and Mahmoud A Abdalla, “A New π-T Generalized Metamaterial NRI Transmission Line for a Compact CPW Triple BPF Applications,” IET Microwave, Antenna, and Propagation, Vol. 8, No. 9, 2014,
pp. 1097-1104.
10. Ahmed A. Ibrahim, Mahmoud A. Abdalla, and Diuradi Budimir, “Coupled CRLH Transmission Lines for Compact and High Selectivity Bandpass Filters,” Microwave and Optical Technlogy Letters, Vol. 59, No. 6, 2017.
11. Ahmed Ibrahim, Adel Abdel-Rahman, and Mahmoud Abdalla, “Design of Third-Order Band Pass Filter Using Coupled Meta-Material Resonators,” 2014 IEEE AP-S 2014, Memphis, USA, pp. 1702-1703.
12. Ahmed F. Daw, Mahmoud A. Abdalla, and Hadya M. Elhennawy, “Dual Band High Selective Compact Transmission Line Gap Resonator,” 2014 Loughborough Antennas & Propagation Conference, 2014, Loughborough, UK,
pp. 91-94.
13. Ahmed Fawzy Daw, Mahmoud Abd El Rahman Abdalla, Hadia Mohamed El Hennawy, “Multiband Sharp-Skirt Compact Gap Resonator Based D-CRLH,” 32th National Radio Science Conference (NRSC2015), March 24-26,
2015, MSA University Egypt, pp. 43-50.
14. S. Karimian, M. Abdalla, and Z. Hu, “Left-Handed Stepped Impedance Resonator for WLAN Applications,” 3rd International Congress on Advanced Electromagnetic Materials in Microwaves and Optics, August 30-September
4, 2009, London, UK, pp. 105-107.
15. M. A. Abdalla, A. Y. Hassan, and A. M. Galal Eldin, “A Compact High Selective Gap Bandpass Filter Based CRLH TL,” 2015 9th International Congress on Advanced Electromagnetic Materials in Microwaves and Optics –
Metamaterials, 2015, Oxford, UK.
Figure captions
1. This is an equivalent-circuit representation of a composite-right-left-handed (CRLH) unit cell resonator.
2. This layout was used in the fabrication of a CRLH unit cell on commercial PCB material.
3. These simulated scattering parameters depict the insertion loss (S21) and return loss (S11) of the CRLH unit cell.
4. This plot shows the simulated S21 phase angle (in deg.) of the CRLH unit cell.
5. This CRLH resonator equivalent-circuit diagram was used to construct a two-pole CRLH filter.
6. The layout of a two-pole CRLH-based bandpass filter (a) is shown next to a fabricated prototype of the filter.
7. Two-Pole Filter scattering parameters and fabrication measurement
8. The layout of the ZOR BPF formed with third-order CRLH resonators (a) is shown next to the fabricated prototype (b).
9. These measured results show the performance of the BPF fabricated with third-order CRLH resonators.
NOTE FOR THE AUTHORS
Renumbering of the figures
OLD IS NOW
Figure 1 Figure 1
Figure 2 Figure 2
Figure 3 Figure 3
Figure 4 Figure 4
NO FIGURE 5
Figure 6 Figure 5
Figure 7 Figure 6
Figure 8 Figure 7
Figure 9 Figure 8
Figure 10 Figure 9
C
L
2L
L2
2L
L
C
R
/2 2L
L
C
R2
/2
L
R2
C
L2
2L
L
C
R
/2 C
R2
/2
L
R
C
gap
P.O. Box 718, West Caldwell, NJ 07006
(973) 226-9100 Fax: 973-226-1565
E-mail: wavelineinc.com
CRLH Transmission Lines
THIRD-ORDER RESULTS
Figure 8a shows the layout of the BPF designed with third-
order coupled CRLH-TL resonators, where the overall size
of the BPF formed with these resonators is 16 × 24 mm2. The
simulated (HFSS) scattering parameters for the filter (Fig. 9)
indicate that it provides excellent performance through the
passband surrounding its center frequency at 5.9 GHz, with
passband insertion loss, S21, of just 1.5 dB, and passband
return loss, S11, close to 30 dB. The filter has a transmis-
sion zero at 6.3 GHz, which equips it with an advantage in
smaller dimensions compared to a conventional two-pole
filter design.
The single transmission zero also yields much improve-
ment in skirt selectivity; the order number of the transmission
zero is equal to N – 2, with N the number of resonators in the
design. Fig. 9 shows good agreement between design theory
and the EM simulation results, indicating that a lower trans-
mission zero can be added to the design
by increasing the filter order.
In fact, the compact filter has a fre-
quency and passband characteristics
that make it well-suited for WiMAX
applications. It takes full advantage of the
zeroth-order resonance of third-order
coupled CRLH resonators to achieve
good passband loss characteristics in a
small size. The zeroth-order resonance
at 6.3 GHz improves the passband skirt
selectivity in a filter size of only 16 × 24
mm2. By following a design procedure
that achieved good agreement among
theory, computer simulations, and mea-
surements, a 5.9-GHz BPF was created
with CRLH resonators that’s about 40%
smaller than BPFs designed with con-
ventional microstrip transmission-line
resonators.
0
–10
–20
–30
–405.0 5.5 6.0 6.5 7.0
Frequency (GHz)
Magnitude (dB)
S21, simulated
S11, simulated S21, measured
S11, measured
7. Two-pole filter scattering parameters and fabrication measure-
ments are provided in this plot.
(b)
(a)
16 mm
24 mm
8. The layout of the ZOR BPF formed with third-order CRLH resonators (a) is shown next
to the fabricated prototype (b).
5.0 5.5 6.0 6.5 7.0
Frequency (GHz)
Magnitude (dB)
0
–10
–20
–30
–40
–50
–60
–70
S21, simulated
S11, simulated
S21, measured
S11, measured
9. These measured results reveal the performance of the BPF fabricated with third-order
CRLH resonators.
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REFERENCES
1. C. Caloz, “Metamaterial Dispersion Engineering
Concepts and Applications,” Proceedings of the IEEE,
Vol. 99, No. 10, 2011, pp. 1711-1719.
2. Yuandan Dong and T. Itoh, “Promising Future of
Metamaterials,” IEEE Microwave Magazine, Vol. 13,
No. 2, 2012, pp. 39-56.
3. G. V. Eleftheriades, “Enabling RF/microwave devic-
es using negative refractive-index transmission-line
(NRI-TL) metamaterials,” IEEE Antennas and Propa-
gation Magazine, Vol. 49, No. 2, 2007, pp. 34-51
4. M. A. Abdalla and Z. Hu, “Design and analysis of
tunable left handed zeroth-order resonator on ferrite
substrate,” IEEE Transactions on Magnetics, Vol. 11,
2008, pp. 3095-3098.
5. C. L. Holloway, Edward F. Kuester, J. A. Gordon,
J. O’Hara, J. Booth, and D. R. Smith, “An Overview
of the Theory and Applications of Metasurfaces: The
2-Dimensional Equivalents of Metamaterials,” IEEE
Antennas and Propagation Magazine, Vol. 54, No. 2,
2012, pp. 10-35.
6. Qingshan Yang and Yunhua Zhang, “Negative-
order ridge substrate integrated waveguide coupled-
resonator filter,” Electronics Letters, Vol. 50, No. 4,
2014, pp. 290-291.
7. M. A. Abdalla, M. A. Fouad, and A. A. Mitkees,
“Wideband Negative Permittivity Metamaterial for
Size Reduction of Stopband Filter in Antenna Applica-
tions,” Progress in Electromagnetics Research C, Vol.
25, 2012, pp. 55-66.
8. J. Sorocki, I. Piekarz, K. Wincza, and S. Gruszczyn-
ski, “Right/Left-Handed Transmission Lines Based on
Coupled Transmission-Line Sections and Their Appli-
cation Towards Bandpass Filters,” IEEE Transactions
on Microwave Theory and Techniques, Vol. 63, No. 2,
Part: 1, 2015, pp. 384-396.
9. Mohammed. A. Fouad, and Mahmoud A. Abdalla,
“A New π-T Generalized Metamaterial NRI Transmis-
sion Line for a Compact CPW Triple BPF Applica-
tions,” IET Microwave, Antenna, and Propagation, Vol.
8, No. 9, 2014, pp. 1097-1104.
10. Ahmed A. Ibrahim, Mahmoud A. Abdalla, and
Diuradi Budimir, “Coupled CRLH Transmission Lines
for Compact and High Selectivity Bandpass Filters,”
Microwave and Optical Technlogy Letters, Vol. 59,
No. 6, 2017.
11. Ahmed Ibrahim, Adel Abdel-Rahman, and Mah-
moud Abdalla, “Design of Third-Order Band Pass Fil-
ter Using Coupled Meta-Material Resonators,” 2014
IEEE AP-S, Memphis, USA, pp. 1702-1703.
12. Ahmed F. Daw, Mahmoud A. Abdalla, and Hadya
M. Elhennawy, “Dual Band High Selective Compact
Transmission Line Gap Resonator,” 2014 Loughbor-
ough Antennas & Propagation Conference, 2014,
Loughborough, UK, pp. 91-94.
13. Ahmed Fawzy Daw, Mahmoud Abd El Rah-
man Abdalla, Hadia Mohamed El Hennawy, “Multi-
band Sharp-Skirt Compact Gap Resonator Based
D-CRLH,” 32nd National Radio Science Conference
(NRSC2015), March 24-26, 2015, MSA University
Egypt, pp. 43-50.
14. S. Karimian, M. Abdalla, and Z. Hu, “Left-Handed
Stepped Impedance Resonator for WLAN Appli-
cations,” 3rd International Congress on Advanced
Electromagnetic Materials in Microwaves and Optics,
August 30-September 4, 2009, London, UK, pp. 105-
107.
15. M. A. Abdalla, A. Y. Hassan, and A. M. Galal Eldin,
“A Compact High Selective Gap Bandpass Filter
Based CRLH TL,” 2015 9th International Congress on
Advanced Electromagnetic Materials in Microwaves
and Optics – Metamaterials, 2015, Oxford, UK.
By following a
design pro-
cedure that achieved
good agreement
among theory, com-
puter simulations, and
measurements, a 5.9-
GHz BPF was created
with CRLH resonators
that’s about 40% small-
er than BPFs designed
with conventional
microstrip transmis-
sion-line resonators.
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