Microstrip Band-Pass Filters using Nonuniform Coupled Lines

Dummy channels are introduced into the coupled region to achieve physical realizability and significantly increase rejection in nonuniform type coupled-line filters. Theory is verified by a filter circuit designed on alumina substrate to demonstrate 4 different band-pass filters using two cascaded coupler-filters with 50% bandwidth at X-band. Rejection in excess of 40 dB with sharp passband skirts have been achieved.