Compact triple-band bandpass filter using multi-mode HMSIW cavity and half-mode DGS

In this paper, a triple-band bandpass filter using a multi-mode half-mode substrate integrated waveguide (HMSIW) cavity is presented. In this design, back-to-back connected half-mode defected ground structure (DGS) is loaded into the HMSIW cavity, which generates the first passband. The first four modes of HMSIW cavity are TM110, TM120, TM310, and TM320. They have been used to generate second and third passbands. The slot line perturbation is used to shift the modes close to each other. Here, TM110 and TM120 constitute second passband, and TM310 and TM320 give third passband. Moreover, the notch band is designed using embedded open-circuited stub to improve the attenuation between the second and third passbands. The proposed filter is designed and fabricated on RT/Duroid 5880 substrate with a thickness of 0.508 mm. The measured results are in line with simulated ones for each of the passbands, and the center frequencies are 6.28, 13, and 19.12 GHz.