Characteristics of a microstrip semi-circular patch resonator filter

This paper presents the characteristics of a microwave band pass filter using microstrip semi-circular patch resonators. Design method is based on coupling coefficients of inter-coupled resonator and the external quality factors of the input and output resonators. To improve the filter characteristics by using coupling structure, the microstrip semi-circular patch resonators are used instead of the microstrip circular patch resonators. The conventional microstrip circular patch resonators are difficult to design by using coupling structure method due to weakly coupling coefficient between resonators, and it is required the advanced technologies for fabrication. The simulated bandwidth of 3-pole microstrip semi-circular patch band pass filter at the center frequency of 2 GHz was about 60 MHz (-3 dB of S₂₁ magnitude). The return loss is better than 15 dB along the pass band. The measured result shows 45 MHz bandwidth and 50 dB insertion loss at stop band. The center frequency is shift to 2.03 GHz and 2.8 dB insertion loss in passband.