Compact Broadband Bandpass Filter on Quarter-Mode Substrate Integrated Waveguide Loaded with CRLH Interdigital Slots

A compact broadband bandpass filter (BPF) on Composite right/left-handed (CRLH) Quarter-Mode Substrate Integrated Waveguide (QMSIW) is presented and analyzed in this paper. A size reduction is implemented by etching the CRLH interdigital slots (CRLH-IS) in the compact QMSIW cavity to introduce a lower resonant frequency less than that of the QMSIW. The influence of the rotation angle of the CRLH-IS on the frequency response of the CRLH QMSIW BPF is analyzed, and the optimal rotation angle is used to implement a BPF with good out-band rejection. The proposed CRLH QMSIW shows the characteristics of low quality factor and high coupling coefficient that make it a good solution to design a broadband bandpass filter. The measured insertion loss is less than 1.8 dB at 4.43 GHz with a fractional bandwidth (FBW) of around 22%. The measured results agree well with the simulated ones.