DESIGN OF MICROSTRIP BANDPASS FILTER FOR 20% FRACTIONAL BANDWIDTH AROUND 3 GHz

Submitted By(A2 slot):

Kaushik kumar (11BEC0441)

Tauseef khan (11BEC0511)

ABSTRACTBandpass filters are widely used in wireless transmitters and receivers. The main function of such a filter in a transmitter is to limit the bandwidth of the output signal to the band allocated for the transmission. This prevents the transmitter from interfering with other stations. In a receiver, a bandpass filter allows signals within a selected range of frequencies to be heard or decoded, while preventing signals at unwanted frequencies from getting through. A bandpass filter also optimizes the signal-to-noise ratio and sensitivity of a receiver.

In both transmitting and receiving applications, well-designed bandpass filters, having the optimum bandwidth for the mode and speed of communication being used, maximize the number of signal transmitters that can exist in a system, while minimizing the interference or competition among signals.

This Project deals with the design of microstrip band pass filter using quarter wave shorted stub resonators and the design is simulated using Microwave Office AWR DE simulation software

INTRODUCTION :

A microwave filter is a two-port network used to control the frequency response at a certain point in a microwave system by providing transmission at frequencies within the passband of the filter and attenuation in the stopband of the filter. Typical frequency responses include low-pass, high-pass, bandpass, and band-reject characteristics. Applications can be found in virtually any type of microwave communication, radar, or test and measurement system.

We know that quarter-wave open-circuited or short-circuited transmission line stubs look like series or parallel resonant circuits, respectively. Thus we can use such stubs in shunt along a transmission line to implement bandpass or bandstop filters.

Quarter-wavelength sections of line between the stubs act as admittance inverters to effectively convert alternate shunt resonators to series resonators. The stubs and the transmission line

sections are λ/4 long at the center frequency 0

For narrow bandwidths the response of such a filter using N stubs is essentially the same as that of a coupled line filter using N + 1 sections. The internal impedance of the stub filter is Z0, while in the case of the coupled line filter end sections are required to transform the impedance level. This makes the stub filter more compact and easier to design. A disadvantage, however, is that a filter using stub resonators often requires characteristicimpedances that are difficult to realize in practice

The design specifications for this filter is as as follows:

Filter order=3

Center frequency f0=3 GHz

Bandwidth ∆=20%

100 Ω Impedence

Insertion Loss < 4 dB within the given band

Band Pass filter lumped

Element model

The Band Pass filter can designed using three quarter wave short circuited stub resonators. Bandpass filter consist of λ/4 stubs connected by λ/4 transmission lines

Band Pass Filter

For a bandpass filter using short-circuited stub resonators the following characteristic Impedence is obtained:

n gn Z0n (Ω)

1 1.5963 9.84

2 1.0967 14.32

3 1.5963 9.84

Block Diagram :

Fig. 1: Block diagram of the BPF design based on AWR DE

Fig. 2: Front panel of the simulation system

Implementation :

According to the equations provided, the model for simulating the Microstrip BandPass Filter on AWR DE software is provided in Fig1. Implementation of this filter in Microwave AWR DE is done on FR4 Substrate having following specifications:

4.2

H 0.79mm

T 0.5mm

0.02

Conductor Copper

Fig. 2 shows the front panel of the system.

Result and Graph :

The plots of scattering parameters s(1,1)dB and s(2,1)dB are shown in Fig. 3

Microstrip Band Pass Filter is designed and simulated successfully on AWR DE Microwave office software Results obtained are as follows:

Center frequency f0=3 GHz

Pass Band :fh =3.268 GHz , fl =2.712 GHz

Bandwidth ∆=20%

Insertion Loss < 4 dB within the given band

Fig -3: Scattering parameters vs frequency

Conclusion :

In this project, design and simulation of an Microstrip Band Pass Filter with 20% fractional Bandwidth around 3 GHz is considered.

The design is simulated on Microwave Office AWR DE software.

The Ideal Electrical model is based on quarter wave short circuit stub resonators.

Quarter-wavelength sections of line between the stubs act as admittance Inverters to effectively convert alternate shunt resonators to series resonators. The stubs and the transmission line sections are λ/4 long at the center frequency.

In this project, design and simulation of an Microstrip Band Pass Filter with 20% fractional Bandwidth around 3 GHz is considered.

The Ideal Electrical model is based on quarter wave short circuit stub resonators.

Quarter-wavelength sections of line between the stubs act as admittance Inverters to effectively convert alternate shunt resonators to series resonators. The stubs and the transmission line

sections are λ/4 long at the center frequency 0

The stub filter are more compact and easier to design

A disadvantage, however, is that a filter using stub resonators often requires characteristic impedence that are difficult to realize in practice.

References :

[1]. Cansever, Cem, "Design of a Microstrip Bandpass Filter for 3.1-10.6 GHz Uwb Systems" (2013). Electrical Engineering and Computer Science – Thesis. Paper

[2]. Microwave engineering ,Third edition David.M.Porzar,University of Massachusetts at Amherst

[3]. www.wikipedia.com