Compact lowpass filter with wide stopband using modified semi-elliptic and semi-circular microstrip patch resonator

A compact microstrip lowpass filter based on a novel patch resonator is reported. The novel semi-circle and semi-ellipse patch resonators are loaded by rhomboid and delta-stub structures, respectively. The filter consists of three cascaded microstrip patch resonators with different dimensions. The stopband with an attenuation level better than -20 dB is obtained from 3.68 up to 19 GHz. The proposed filter has low insertion loss in the passband, sharp, high and wide rejection in the stopband, and compact size. The filter is optimally designed, fabricated and measured. Simulation and measurement results are presented and compared and good agreement with the response of simulation and measurement is demonstrated.