Microstrip filters with selectivity improvement using the new concept of signal-interference source/load coupling

An original and simple method to design high-performance microwave planar bandpass filters (BPFs) is reported. It makes use of traditional low-order coupled-resonator BPF networks properly modified in base of signal-interference techniques. Thus, through these mixed coupled-resonator/signal-interference BPF schemes, high-selectivity bandpass filtering functions also exhibiting low in-band group-delay variation can be synthesized. A detailed explanation of the proposed BPF concept is provided. Furthermore, as experimental validation, several prototypes are developed in microstrip technology and characterized.