Design of Compact Microstrip Low Pass Filter using Transfer Function analysis

A novel compact and improved microstrip lowpass filter (LPF) is designed to achieve sharpness of transition band and ultra-widestop-band. To achieve this goal, In this filter structure, the T and L shape resonators are used. The proposed filter with ۳ dB cut-offfrequency at ( ۲.۴GHz )has been designed. The calculated roll-off, in filter is equal to (۱۳۰).The size of the designed filter is (۰.۱۹*۰.۱۱۵ ). LC equivalent circuit is obtained , using the LC circuit , the transfer function of the filter is calculated .Exact equationfor the most important transmission zero which placed after transition band, is computed based on LC equivalent circuit andtransformation function. The filter has an ultra-wide stopband from ( ۲.۶) GHz up to(۱۵) GHz with suppression level more than(۲۰.۲) dB.

Keywords:

Microstrip , Lowpass filter , Sharp roll off , Transfer function , Ultra Wide stop band