Synthesizing and Optimizing of Wide Stopband Low-Pass Filter with Improved Infinite Attenuation Unit Based on Stubs

Abstract Currently, most microwave filters are designed using sophisticated computer-aided design (CAD) tools, which primarily based on the insertion loss method. The image parameter method (IPM), which can provide an effective control for the passband and stopband of microwave filters without any use of lumped prototypes, is paid little attention to microwave filter design. In this paper, the detailed design procedures for synthesizing microwave low-pass filter (LPF) and optimizing the performance of Butterworth filter with IPM are proposed. Based on the IPM, the improved infinite attenuation unit (IAU) cell can be designed firstly, which can attain higher selectivity and better stopband rejection of LPF while maintain good performance in passband. Then a 2 GHz ten-order high-performance LPF and an optimized Butterworth LPF are designed using improved IAU cell. Experiment results of the fabricated LPF agree well with the full-wave EM simulation, which shows the proposed approach can provide improved characteristics for both passband and stopband of LPFs.