Effect of Wideband Microstrip BPF Design for Bandwidth

Enhancement and Its Equivalent Circuit

Shita Fitria Nurjihan

and Yenniwarti Rafsyam

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: 10.5220/0010509400003153

In Proceedings of the 9th Annual Southeast Asian International Seminar (ASAIS 2020), pages 27-30

ISBN: 978-989-758-518-0

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

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

Figure 8: Results comparison of equivalent cirrcuit.

Table 1: Simulation Result

Desi

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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ASAIS 2020 - Annual Southeast Asian International Seminar