Method to Improve the Roll-Off and Stopband Response in Low Pass Filter Using Patch Resonators for Modern Wireless Communication

Abstract

In this paper, several types of patch resonators design procedure are proposed and analysed to improve the roll-off and stopband response in low pass filter. The proposed patch resonators consist of T-shaped patch resonator (TS-PR) that provides instant sharp roll-off and also dual folded T-shaped resonator (DFTS-PR) that improves the roll-off of the previous TS-PR. The transmission zeros of the resonators can be adjusted by varying length and width of high and low impedance microstrip lines. It has been shown that the final design of the patch resonators provides sharp roll-off and acceptable stopband bandwidth by adopting both TS-PR and DFTS-PR. The proposed low pass filter with 3-dB cut-off frequency (fc ) of 5.26 GHz exhibits excellent roll-off rate of 82.2 dB/GHz from 5.5 GHz to 11.7 GHz. Moreover, the transition of the proposed filter is 0.45 GHz which contributes to a sharper transition band from passband to stopband.