A novel compact and improved microstrip lowpass filter (LPF) is designed to achieve sharpness of transition band and ultra-wide stop-band. To achieve this goal, In this filter structure, the T and L shape resonators are used. The proposed filter with 3 dB cut-off frequency at ( 2.4GHz )has been designed. The calculated roll-off, in filter is equal to (130).The size of the designed filter is ( 0.19*0.115 ). LC equivalent circuit is obtained , using the LC circuit , the transfer function of the filter is calculated .Exact equation for the most important transmission zero which placed after transition band, is computed based on LC equivalent circuit and transformation function. The filter has an ultra-wide stopband from ( 2.6) GHz up to(15) GHz with suppression level more than (20.2) dB.
