Triple mode resonator bandpass filters with source-load coupling

This paper presents an analytical technique for the study of transmission zeros, which appeared close to the passband edges of a microstrip bandpass filter. The bandpass filter uses a published triple mode resonator, which exhibits two transmission zeros close to the passband and odd resonance suppression in its wideband response. Source-load coupling is introduced to produce an additional transmission zero located to the right of the passband. The stopband response is further improved by this transmission zero. These filters demonstrate good selectivity, compact size, and predictable transmission zeros