Design of hairpin band pass filters for K-Band application

Conference Paper (PDF Available) · January 2009with486 Reads
DOI: 10.1109/RFM.2008.4897401 · Source: IEEE Xplore
Conference: RF and Microwave Conference, 2008. RFM 2008. IEEE International
Abstract
This paper presents Chebyshev three and four poles microstrip hairpin filter for radar applications. The filters are operated at K-band frequency segment of 20-20.3 GHz. The filters were designed using Genesys software and implemented on Roger 5870 substrate. The results from simulation and measurement show that both filters were operating at the desired specification. Based on the experimental analysis, it was observed that the filter with four elements better than the three which was quite agree to other researchers.
2008 IEEE INTERNATIONAL RF AND MICROWAVE CONFERENCE PROCEEDINGS
2008 IEEE INTERNATIONAL RF AND MICROWAVE CONFERENCE PROCEEDINGS 2008 IEEE INTERNATIONAL RF AND MICROWAVE CONFERENCE PROCEEDINGS
2008 IEEE INTERNATIONAL RF AND MICROWAVE CONFERENCE PROCEEDINGS December 2
December 2December 2
December 2-
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-4, 2008, Kuala Lump
4, 2008, Kuala Lump4, 2008, Kuala Lump
4, 2008, Kuala Lumpur, MALAYSIA
ur, MALAYSIAur, MALAYSIA
ur, MALAYSIA
978-1-4244-2867-0/08/$25.00 ©2008 IEEE
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Design of Hairpin Band Pass Filters for K-Band Application
A. A. Sulaiman
1
, M. F. Ain
1
, S. I. S. Hassan
1
, A. Othman
1
, M. A. Othman
1
, R. A. Majid
1
, M. Z.
Saidin
1
, M. H. A. Hamid
1
, M. H. Jusoh
2
, Z. I. Khan
2
, N. H. Baba
2
, R. A. Awang
2
, Z. Awang
2
, N.
A. Z. Zakaria
2
, M. K. A. Mahmood
2
1
School of Electrical & Electronic Engineering, Universiti Sains Malaysia, Engineering Campus, 14300 Nibong Tebal, Pulau Pinang, Malaysia.
2
Faculty of Electrical Engineering, Universiti Teknologi Mara Malaysia, 40450 Shah Alam, Selangor, Malaysia
A
bstract - This paper presents Chebyshev three and
four poles microstrip hairpin filter for radar
applications. The filters are operated at K-Band
frequency segment of 20 20.3 GHz. The filters were
designed using Genesys software and implemented on
Roger 5870 substrate. The results from simulation and
measurement show that both filters were operating at
the desired specification. Based on the experimental
analysis, it was observed that the filter with four
elements better than the three which was quite agree to
other researchers.
Keywords Bandpass, Filter, K-Band, Design, Hairpin, RF,
Simulation.
1. Introduction
Microstrip filters play an important role in many
RF applications. As technologies advances, more
stringent requirements of filters are required. One of
the requirements is the compactness of filters.
Bandpass filters are essential building blocks for
communication systems. They can reduce the harmonic
and spurious emissions for transmitters, and may
improve the rejection of interferences for receivers. To
ensure an easy integration between band pass filters
and other active devices, many previous works on
designing planar filter were reported [1-2]. Among
various types of planar filters, the parallel-coupled
band pass filter based on half-wavelength, λ/2
resonators exhibits the merits of simple synthesis
procedure, good repetition, and a wider range of
realizable fraction in bandwidth.
However, the conventional microstrip parallel-
coupled band pass filter suffers from the spurious
response at twice the center frequency, 2f
0
, making the
r
ejection of the upper stop band worse than the lower
stop band. This was due to unequal even and odd mode
propagation constants for microstrip coupled-line
sections.
Many works have been reported to tackle this issue
by equalizing the effective dielectric constants or
electrical lengths of the even and odd modes. However,
these techniques either rely on complex
design/optimization procedures or limit the filter to
specific circuit configurations [3-6]. Some works on
improving the selectivity of the conventional parallel-
coupled band pass filters were also reported in [1], the
shunt-connected together with quarter-wavelength,
(λ/4) open stubs were introduced to create transmission
zeros at stop band. In [2], the capacitive coupled gap
and the λ/4 open stubs were adopted in the circuit to
create two transmission zeros, such that the selectivity
of parallel-coupled band pass filter can be improved.
On the other hand, microstrip band pass filters based on
λ/4 resonators may feature more compact circuit size as
well as better stopband rejection with no spurious
response at 2f
0
.
T
his paper will focus on the design of hairpin band
pass filter for K-band application. Two hairpin filters
with different number of elements were designed and
compared the performance of the devices in the
extreme high frequency.
2. Methodology
Order of the filters can be determined as explained
by [7]. Based on the design specification, 3
rd
and 4
th
orders filter were chosen using the proposed hairpin
structure. The element values for both
orders were
taken from normalized values of 0.1 dB equal ripple
low-pass prototype and the method of calculation were
such as in [8]. The value of components can be
calculated using equation (1) and (2). Where g
n
was
indicated the number of elements, while n was an
integer numbers 1, 2, 3…, n+1. High number of n
contributes small transition band and sharp cut-off.
=
n
g
2
sin
2
1
π
γ
(1)
(
)
(
)
( )
+
=
+
n
i
n
i
n
i
g
g
i
i
π
γ
ππ
1
sin
2
32
sin
2
12
sin4
1
22
1
(2)
The element values that have been obtained for the
3
rd
and 4
th
orders of the filters were shown in Table 1.
Authorized licensed use limited to: UNIVERSITI SAINS MALAYSIA. Downloaded on September 30, 2009 at 22:29 from IEEE Xplore. Restrictions apply.
Table 1: Low-Pass Prototype Elements Values
Order g
0
g
1
g
2
g
3
g
4
3
rd
1 1.0315 1.1474 1.0315
4
th
1 1.1088 1.3061 1.7703 0.8180
The values from the table then were converted to
band pass filter prototype at the specific cut off
frequency. The characteristic impedance and dimension
of the coupled lines can be obtained from the values. In
this paper, a three pole and four pole microstrip hairpin
filters will be presented. The proposed filters were
operated in the K-Band and covered from 20 GHz to
20.3 GHz. The design specifications of the filters
including the pass band ripple of 0.1 dB and the
minimum attenuation of -30 dB at 20.15 GHz. The
specifications of the filters were shown in Table 2.
Table 2: Bandpass Filter Design Specifications
Centre frequency 2
0.15 GHz
Upper cut-off frequency 20.3 GHz
Lower cut-off frequency 20 GHz
Bandwidth 0.3 GHz
Passband ripple 0.1 dB
One of the most popular microstrip filter
configurations is the hairpin resonator. In term of
manufacturing, it can be considered an ease structure to
be manufactured because of open-circuited ends with a
ground plane. The filter was derived from an edge-
coupled resonator by folding back the ends of the
resonators into a “U” shape. This approach reduces the
length and improves the ratio of the microstrip size
significantly.
(a) 3 elements
a
) Four pole hairpin filter
(b) 4 elements
Fig. 1: The layout of Hairpin filters with different
element
Fig. 1 shows two layouts of the hairpin filter
bended by half wavelength resonator in a U-shape. By
bending structure on the resonators, the overall
dimensions of the filter were greatly reduced as
compared to conventional parallel-coupled and edge-
coupled filters.
Table 3: Substrate Properties
Dielectric Constant 2
.33
Loss Tangent 0.0012
Resistivity 1
Metal Thickness 0.035 mm
Metal Roughness 2.4e
-3
mm
Substrate Height 0.508 mm
The circuit was constructed on Roger 5870
substrate with dielectric constant of 2.33, loss tangent
of 0.0012 and substrate height of 0.508 mm. Table 3
indicates the detail properties of the substrate.
3. Results
T
he circuit then was simulated using Genesys and
optimized using Electronic Design Automation (EDA).
This software using an iteration algorithm which
adjusts space of short couple section cascades with two
adjacent lines to match the characteristics of the
original quarter-wave [9].
Fig. 2: Responses of filter with three elements
Fig. 3: Responses of filter with four elements
-35
-30
-25
-20
-15
-10
-5
0
19775 19975 20175 20375
Frequency (MHz)
Magnitude(dB)
Return Loss
Insertion Loss
-70
-60
-50
-40
-30
-20
-10
0
19775 19975 20175 20375
Frequency (MHz)
Magnitude (dB)
Return
Loss
Insertion
Loss
Authorized licensed use limited to: UNIVERSITI SAINS MALAYSIA. Downloaded on September 30, 2009 at 22:29 from IEEE Xplore. Restrictions apply.
Fig. 2 and Fig. 3 show responses of each filter with
different number of elements. The responses from four
elements were better compared to the three. In term of
return loss and insertion loss, both results were almost
the same. However the four elements return loss able to
swing to up to a value that more than -60 dB. These
two parameters were crucial to analyze to obtain a good
performance of filters. A good filter will be high return
loss and small insertion loss ripple in passband.
4. Discussion
T
he simulated circuits then were fabricated on
Roger’s microstrip as shown in Fig. 4. The filters then
measured using a Vector Network Analyzer (VNA).
The results obtained from the measurement then were
used to analyze the performance of the designs. There
were slightly different between the measured and the
simulated values.
-
(a) 3 elements
(b) 4 elements
Fig. 4: Fabricated hardware with difference
e
lements
Fig.5: Comparison of return loss for circuit with th
ree
elements
Fig. 5 and Fig. 6 indicate comparisons between
r
eturn and insertion losses from the design between
simulated and measured results. Both graphs show the
measured values compose of higher losses compared to
the simulated. The measured return loss bandwidth was
smaller compared to the simulated. High return loss at
stop band indicates that the filter was not operate well
at the design frequency since the filter could not
differentiate between the pass and stop bands.
The different between measured and simulated
was about 30 dB for insertion loss in Fig. 6. This may
due to the limitation of the substrate. The substrate may
b
e unstable to operate well at frequency above 10 GHz.
The dielectric loss of the substrate was high at that
extreme frequency. The other factors may due to
interference that affect the circuit in an open air
environment since the circuits were not measure in an
anechoic chamber.
Fig. 6: Comparison of insertion loss for three eleme
nts
5. Conclusion
Two designs of hairpin filter at K-band frequency
were presented in this paper. Both filters have been
successfully designed at the desired specifications. A
data analysis has been done. The filter with four
elements gives better responses compared to the three.
Even both filters have been successfully fabricated; the
high substrate loss cause the insertion loss drops in the
pass band.
Acknowledgement
Authors would like to thank Universiti Teknologi Mara
Malaysia, Universiti Sains Malaysia, The Ministry of
Science Technology and Inovation (MOSTI) and the
Malaysian Communications and Multimedia Commission
(MCMC) for supporting and funding the project.
-45
-40
-35
-30
-25
-20
-15
-10
-5
0
19775 19875 19975 20075 20175 20275 20375 20475
Frequency (MHz)
Insertion Loss (dB)
Simulation
Measurement
-35
-30
-25
-20
-15
-10
-5
0
19775 19975 20175 20375
Frequency (MHz)
Return Loss (dB)
Simulation
Measurement
Authorized licensed use limited to: UNIVERSITI SAINS MALAYSIA. Downloaded on September 30, 2009 at 22:29 from IEEE Xplore. Restrictions apply.
References
[1] J. R. Lee, J. H. Cho, and S. W. Yun, “New
compact bandpass filter using microstrip λ/4
resonators with open stub inverter,” IEEE
Microwave Guided Wave Lett., vol. 10, pp. 526-
527, Dec. 2000.
[2] Y. M. Yan, Y. T. Chang, H. Wang, R. B. Wu, and
C. H. Chen, "Highly selective microstrip bandpass
filters in Ka-band," in 32th Eur. Microwave Conf.
Proc., 2002, pp. 1137-1140.
[3] Kuo, Hsu and Huang, “Parallel Coupled micro
strip filters with suppression of harmonic
response”, IEEE Microwave and Wireless letters,
Oct 2002
[4] W. Chang et al, “Miniaturized Spurious Pass band
Suppression micro strip filter using Meandered
Parallel Coupled lines”, IEEE Trans. MTT, Feb
2005,pp 747-753
[5] Lopetegi et al,” New microstrip Wiggly-Line
Filters with spurious Pass band suppression”, IEEE
Trans. MTT, Sept.2001,pp 1593-1597
[6] J. S. Wong, “Microstrip Tapped-Line Filter
Design”, IEEE Trans. MTT-27, 1979, pp. 44 - 50.
[7] M. G. Young, L. Jones, Microwave Filters,
Impedance-Matching Network and coupling
Structures, Artech House, 1980
[8] T. Laverghetta, Microwave Materials and
Fabrication Techniques, 3
rd
ed., Norwood, MA:
A
rtech House, 2000.
[9] R. Rhea, HF Filter Design and Computer
Simulation. Atlanta, GA: Noble Publishing, 1994.
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