Effect of Wideband Microstrip BPF Design for Bandwidth
Enhancement and Its Equivalent Circuit
Shita Fitria Nurjihan
1
and Yenniwarti Rafsyam
1
1
Department of Electrical Engineering, Politeknik Negeri Jakarta, Indonesia
Keywords: Bandpass Filter, Equivalent Circuit, Microstrip, Wideband
Abstract: Characteristic of microstrip filter can be analyzed with equivalent circuit. In this paper, wideband microstrip
bandpass filter was analyzed by means of its equivalent circuit with lumped element of capacitor and inductor.
Meanwhile, bandwidth enhancement is done by adding strip and DGS slot. Simulation results show that
design changes can enhance the bandwidth up to 0.95 GHz for microstrip simulation and 1.25 GHz for
equivalent circuit.
1 INTRODUCTION
Filter is one of the important devices in
communication system used to pass the desired signal
and reject undesired signals (Misra, 2004). Many
researches have been done in filter development to
get a good performance [2-6]. One of the filter
implementations is by using a microstrip with
multiple design like Defected Ground Structure
(DGS), multi-layered microstrip, L and T shaped
resonator, and Substrate Integrated waveguide (SIW).
On a research, L and T shaped resonator produces two
transmission zeros in the stopband as well as three
reflection zeros in the passband, other than that
between simulation and measurement produces good
performance (Esmaeili and Bornemann, 2015).
Meanwhile in another research, the measurement
result with simulation are satisfactory with the
fractional bandwidth of 13.5 % (Chen et all, 2015).
Characteristic of microstrip filter can be analyzed
with equivalent circuit of lumped element capasitor
and inductor. There has been a lot of research on
equivalent circuit. On a research, equivalent circuit of
square-loop-resonator bandpass filter has been
analyzed and compared with 3D simulation result.
The reflection coefficient of equivalent circuit has a
better response than the 3D simulation, but it has a
bandwidth of 50 MHz narrower than the 3D
simulation (Edwar and Munir, 2017). And in another
research, microstrip bandpass filter with DGS have
been analyzed using equivalent circuit of capasitor
and inductor. The scattering parameter has almost the
same result as the simulation microstrip with a
bandwidth of about 1 GHz (Zheng and Wang, 2019).
In this paper, wideband microstrip bandpass filter
was analyzed by means of its equivalent circuit with
lumped element of capacitor and inductor. Bandwidth
enhancement is done by changing the filter design
that is by adding more strip and DGS slot. To show
the feasibility of equivalent circuit analysis, the
simulation of equivalent circuit is compared with
microstrip simulation.
2 OVERVIEW OF EQUIVALENT
CIRCUIT
Generally, microstrip filters are designed with
microstrip elements. To get the perfect frequency
response, microstrip filter can be analyzed with
equivalent circuit. To analyze this equivalent circuit
can use lumped element of capacitor and inductor.
For instance, the distance between strip in microstrip
elements can be illustrated as a divider between strips.
The equivalent circuit of the distance between strip in
microstrip is represented by capacitor with phi shape
and strip in microstrip elements can be represented by
inductor with shunt capacitor. Its equivalent circuit is
shown in Figure 1. From that explanation, an analysis
of wideband microstrip bandpass filter with defected
ground structure using equivalent circuit for the
proposed design shown in Figure 2.
Nurjihan, S. and Rafsyam, Y.
Effect of Wideband Microstrip BPF Design for Bandwidth Enhancement and Its Equivalent Circuit.
DOI: 10.5220/0010509400270030
In Proceedings of the 9th Annual Southeast Asian International Seminar (ASAIS 2020), pages 27-30
ISBN: 978-989-758-518-0
Copyright
c
2021 by SCITEPRESS Science and Technology Publications, Lda. All rights reserved
27
Figure 1: Equivalent circuit of microstrip element (Gupta,
1996).
Figure 2: Proposed wideband microstrip BPF applying
DGS (unit in mm).
The proposed design of wideband microstrip BPF
applying DGS is 27.4 x 22 mm consist of two strips
on the top side and two slots mixed with a ring slot on
the bottom.
The equivalent circuit of microstrip BPF shown in
Figure 3 and Figure 4. On the top side, two strips and
feedline configured with lumped element inductor
and gap between strips represented by capacitor. The
dielectric substrate between top and bottom side is
represented by capacitors mounted in parallel on each
inductor.
Figure 3: Equivalent circuit of two strips on top side.
Figure 4: Equivalent circuit of two slots combined with a
ring slot on the bottom.
And representation of ground plane is done by adding
a capacitor at each element connected to ground. On
the bottom side, DGS slots is represented by inductor
and capacitor. For ring slots, capacitors mounted in
series on inductor of DGS slots and capacitors in
parallel with inductor mounted in series on capacitor
of DGS slots. So, the whole of equivalent circuit of
wideband microstrip BPF applying DGS shown in
Figure 5.
ASAIS 2020 - Annual Southeast Asian International Seminar
28
Figure 5: Equivalent circuit of wideband microstrip BPF.
3 SIMULATION RESULT
The simulation result of proposed wideband
microstrip BPF and its equivalent circuit shown in
Figure 6. between the two has a small difference in
bandwidth of 0.05 GHz. The proposed wideband
microstrip BPF applying DGS can pass frequencies in
the range of 1.5 GHz to 4.6 GHz with bandwidth of
3.1 GHz. And the equivalent circuit can pass
frequencies in the range of 1.55 GHz to 4.6 GHz with
bandwidth of 3.05 GHz. At a certain frequency, the
value of equivalent circuit return loss is greater than
the microstrip simulation, this is because the structure
of DGS ring slot has an effect on patch, especially for
lumped element capacitors that have dominant effect
for return loss.
Based on characterization result above, change in
the number of strips and DGS slot is carried out to see
the effect of bandwidth. Change of slots and strip by
adding to be 3 strips and DGS slots. The simulation
result shown in Figure 7.
From the simulation result, change in the number
of strips and DGS slot can affect the bandwidth.
Additional of strip and DGS slot can enhances the
bandwidth up to 0.95 GHz for microstrip simulation
and 1.25 GHz for equivalent circuit, it shown in Tabel
1. The proposed wideband microstrip BPF applying
DGS that changed of strip and slot can pass
frequencies in the range of 1.4 GHz to 5.45 GHz with
bandwidth of 4.05 GHz. And the equivalent circuit
can pass frequencies in the range of 1.3 GHz to 5.6
GHz with bandwidth of 4.3 GHz. From figure 7,
equivalent circuit has better insertion loss than
microstrip simulation because of the equivalent
circuit is considered ideal and there is no attenuation.
The comparison of equivalent circuit shown in
Figure 8. When the number of strip and DGS slot is
added, the frequency response shifts to low frequency
region for low frequency and shifts to high frequency
region for high frequency with good response in
return loss and insertion loss. Meanwhile, change in
the number of strips and DGS slots results in a better
return loss value.
Figure 6: Simulation result of proposed microstrip BPF and
its equivalent.
Figure 7: Simulation result of 3 strips and DGS slots.
Effect of Wideband Microstrip BPF Design for Bandwidth Enhancement and Its Equivalent Circuit
29
Figure 8: Results comparison of equivalent cirrcuit.
Table 1: Simulation Result
Desi
g
n Bandwidth
2 strips and DGS slots 3.05 GHz
3 strips and DGS slots 4.3 GHz
4 CONCLUSIONS
Study of wideband microstrip BPF design and its
equivalent circuit using lumped element of capacitor
and inductor have been done. Bandwidth
enhancement is done by adding strips and DGS slots.
Additional of strips and DGS slots can enhances the
bandwidth up to 0.95 GHz for microstrip simulation
and 1.25 GHz for equivalent circuit. Lumped element
of capacitor and inductor in equivalent circuit for
DGS slot has an effect on return loss. The bandwidth
response value of the equivalent circuit is 3.05 GHz
for 2 strips and DGS slots. While for 3 strips and DGS
slots, the bandwidth response value of the equivalent
circuit is 4.3 GHz.
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