A method of synthesizing microwave bandpass filters constructed with symmetrical or asymmetrical compact microstrip resonators

This paper presents a method of synthesizing microwave filters consisting of compact microstrip resonators (CMRs). The synthesizing method is based on the conventional insertion-loss design method and can be applied to the design of filters consisting of symmetrical and asymmetrical CMRs. The synthesizing method can help the designer to determine the appropriate layout according to the specified passband and stopband characteristics of the filter. A new type of CMR layout is proposed to suppress the spurious passband response and is applied to the implementation of a K u-band filter. The measurement of the prototype shows approximately 1.5-dB insertion loss in the passband and a rejection greater than 40 dB at the specified frequencies. Besides, an asymmetrical CMRs filter operated at K u-band was also designed and fabricated. The measurement result is also close to the computer simulation result. This demonstrates the effectiveness of the proposed design concept.