A New Design of a Miniature Microstrip Bandpass Filter for DCS Applications

Abstract

This paper presents a new miniature Microstrip Bandpass Filter optimized and validated for DCS (Digital Cellular System) Band. The proposed filter is based on a Microstrip resonator. Each port has a step impedance feed line that can be used to adapt the filter's input impedance to the characteristic impedance Z0. The suggested filter is installed on a low-cost FR-4 substrate with a dielectric constant of 4.4, a thickness of 1.6 mm, a loss tangent tan (δ) = 0.025, and a metal thickness of t = 0.035 mm. It has a bandwidth of 1.68GHz to 2.05GHz. Two electromagnetic solvers are used to optimize and validate this filter. The whole dimensions of the final circuit are 33.6x40 mm ² .
This filter is suitable for mobile communication .

Full text

* Corresponding author: a.kadiri@uhp.ac.ma
A New Design of a Miniature Microstrip Bandpass Filter for DCS
Applications
Amal Kadiri 1, Abdelali Tajmouati1, Jamal Zbitou2, Issam Zahraoui3, Ahmed Errkik1, Mohamed Latrach4
1MIET laboratory FSTS, Hassan First University of Settat, Morocco.
2LABTIC, ENSA of Tangier, University of Abdelmalek Essaadi.
3LIMIE laboratory ISGA Casablanca, Morocco.
4Microwave group, ESEO, Angers France
Abstract. This paper presents a new miniature Microstrip Bandpass Filter optimized and validated for DCS (Digital
Cellular System) Band. The proposed filter is based on a Microstrip resonator. Each port has a step impedance feed
line that can be used to adapt the filter's input impedance to the characteristic impedance Z0. The suggested filter is
installed on a low-cost FR-4 substrate with a dielectric constant of 4.4, a thickness of 1.6 mm, a loss tangent tan (δ) =
0.025, and a metal thickness of t = 0.035 mm. It has a bandwidth of 1.68GHz to 2.05GHz. Two electromagnetic solvers
are used to optimize and validate this filter. The whole dimensions of the final circuit are 33.6x40 mm2.
This filter is suitable for mobile communication.
Keywords: Microstrip Bandpass Filter, Microstrip resonator, DCS.
1 Introduction
A filter is a component or function that selects and
eliminates one or more frequency bands from the
electromagnetic spectrum.
They are devices that filter, eliminate, or separate signals
in distinct frequency ranges. They can be passive or
active. Planar filters are made up of metallized lines that
act as resonators and have a length proportional to the
wavelength of the operating frequency [1-3].
In recent years, resonators have been widely used in the
design of filters. To improve performance or reduce size,
filters based on resonators, quarter-wave and quasi-
quarter-wave have been proposed. [4-6].
One of the most significant components in microwave
circuits is the bandpass filter. Planar BPF have recently
sparked increased interest due to their ease of
fabrication. [7-9].
To achieve miniature planar filters, we can use Dual-
mode resonators. As shown in Figure 1, Microstrip dual-
mode resonator has a two-dimensional (2-D) symmetry:
Fig. 1. Microstrip dual-mode resonators.
The number of resonators required for an n-degree filter
is cut in half by using a dual-mode resonator as a double
tuned resonant circuit [10-11].
This filter operates as the shunt-resonator with the design
is described by the following equations [10-14]:



=

󰇡

󰇢
(1)
,+1

0
=
2

+1
j=1 to n-1 (2)
,
=
󰇡
󰇢
(3)
E3S Web of Conferences 351, 01083 (2022) https://doi.org/10.1051/e3sconf/202235101083
ICIES’22
© The Authors, published by EDP Sciences. This is an open access article distributed under the terms of the Creative Commons Attribution
License 4.0 (http://creativecommons.org/licenses/by/4.0/).
,*

Where go, g1 . . . gn are the element of a ladder-type
Lowpass Prototype with a normalized cutoff Ωc = 1, The
Jj,j+1 are the characteristic admittances of J-inverters and
Y0 is the characteristic admittance of the Microstrip line
and FBW is the fractional bandwidth [2].
2 Design procedure
The proposed BPF's configuration is illustrated in Figure
2. The design strategy begins with the construction of a
double resonator Microstrip Bandpass Filter connected
with two resonators that contain slots, as shown in
Figure 2. A passband of 1.68 GHz to 2.05 GHz is shown
in the proposed BPF. The suggested BPF has a
dimension of 33.6 x 40 mm2, which is miniature in
contrast to typical Microstrip filters. Two
electromagnetic solvers, one based on the Moments
approach and the other on the Finite Integration
methodology, were used to model the suggested filter. A
low-cost FR-4 substrate is used to print the suggested
filter.
Fig. 2. The proposed structure of the Microstrip Bandpass filter
The influence of the slot width on the proposed Filter in
terms of electrical characteristics has been retrieved from
a parametric analysis on the effect of critical side length
'c'. After this parametric study we have conducted many
series of optimization based on random method in order
to obtain the fixed goal.
Table 1. The different values of the parameter ‘c’
Parameter
Value (mm)
c
1
5
c
2
4
c
3
3
Figure 3 shows the varied transmission coefficient S21
filter responses as a function of different 'c' values. We
can see that lowering the 'c' value allows us to alter the
bandwidth at the DCS Band, which corresponds to c = 3
mm.
Fig. 3. Simulated result S21 of proposed BPF versus the value
of ‘c.
To have more precision we carried out another
parametric study by decreasing the parameter ‘c’.
Table 2. The different values of the parameter c.
Parameter
Value (mm)
c
1
3
c
2
2
c
3
1
Fig. 4. Simulated result S21 of proposed BPF as a function of
(c) versus the value of ‘c’
At c = 1 mm, the optimal value of 'c' for generating a
good frequency response may be seen. The optimum size
of the parameters of the proposed Bandpass filter are
shown in Table 3.
Table 3. The dimensions of the proposed Bandpass Filter
Parameter
Value (mm)
a
2
b
3
c
1
d
33.6
e
33.6
f
25.6
3 Results and discussion
2
E3S Web of Conferences 351, 01083 (2022) https://doi.org/10.1051/e3sconf/202235101083
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Figure 5 displays the proposed filter's final response in
terms of (S11) and (S21), with a bandwidth of roughly
370 Mhz.
Fig. 5. S-parameters of the Bandpass Filter versus frequency.
In order to verify the simulation findings obtained using
the Moments technique, we conducted the same inquiry
using another electromagnetic solution utilizing Finite
Integration Technique.
Fig. 6. Three-dimensional view of the proposed filter
Figure 7 shows that the two electromagnetic solvers have
a good agreement, with just a minor difference due to the
different numerical methods used in both
electromagnetic solvers.
Fig.7. S parameters of the proposed Bandpass Filter obtained
using Finite Integration Method.
Previous works in the literature are compared to the
suggested Bandpass Filter. Table 4 demonstrates that the
proposed circuit has a fractional bandwidth of 20.55%
and outstanding electrical performance bandwidth.
Compared to other works included in the table below,
the proposed Bandpass Filter is miniature and compact.
Table 4. Performance comparison with published studies
Parameters
/Ref
Pass
Band
(GHz)
FBW
Size
mm2
[13]
[1.8-2.1]
15%
1000
[14]
[1.8-2.2]
20%
1400
This Work
[1.68-
2.05]
20.55%
1344
The surface current distributions at frequencies of 1 GHz
and 1.8 GHz are presented in Fig.8 to further explain the
behavior of the proposed BPF. It's evident that the
surface current distributions at these two frequencies
aren't the same. When the first resonance frequency is 1
GHz, the majority of the surface current is focused in the
supply line's left half Fig.8-(a). At 1.8 GHz, the surface
current distribution becomes more concentrated along
the filter, as shown in Fig.8-(b).
(a) (b)
Fig. 8. Current distributions of the BPF (a) at 1 GHz and (b) at
1.8 GHz
Conclusion
A new Microstrip Bandpass Filter based on resonators
with compact size and good electrical performance is
proposed for DCS applications. The originality of this
circuit is there dimensions which are miniature in
comparison with standard Bandpass Filter configurations
and in the same time the final proposed circuit presents
good performances in terms of insertion loss and return
loss. The proposed circuit's frequency response was
investigated using two separate electromagnetic
simulators. This final circuit is suitable for DCS
applications and can be reconfigurable in term of
frequency by association with varactors diodes.
3
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