A Mixed Cross-coupling Microstrip Filter with Multiple Transmission Zeros

Abstract

A novel three-pole microstrip filter with four transmission zeros is proposed. The coupling between input and output hairpin-comb resonators of the trisection filters, regarded as the cross-coupling, provides a close-to-band transmission zero. This cross-coupling component is also a mixed EM coupling component, which introduces another adjustable transmission zero beyond the passband. Due to the combination of the cross-coupling technique and the mixed electric and magnetic (EM) coupling approach, multiple transmission zeros can be achieved, which means a high rejection level. Therefore, fewer resonators are needed to obtain the same number of transmission zeros than inline filters. The measured result is in good agreement with the simulated S-parameters.