Microstrip cross-coupled trisection bandpass filters with asymmetric frequency characteristics

A pair of microstrip trisection bandpass filters, consisting of cross-coupled open-loop resonators and exhibiting asymmetric frequency characteristics, are introduced. The utilisation of the microstrip open-loop resonators not only makes the filters compact, but also allows either positive or negative cross coupling to be realised. This results in an attenuation pole of finite frequency on either the high side or the low side of the pass band, so that the frequency response is asymmetric. Two filter designs of this type are described. Theoretical and experimental results are presented.