A compact triple-band bandpass filter based on half-mode substrate integrated waveguides

A triple-band, bandpass filter, that is six times smaller than a similar substrate integrated waveguide filter, is designed and implemented in half-mode substrate integrated waveguide technology for the first time. The highly compact structure makes the design very challenging, so an iterative optimization technique based on full-wave simulation is proposed. Using this technique, a triple-band filter is designed with center frequencies of 1.105 GHz, 1.295 GHz, and 1.505 GHz. Simulations show a return loss better than 15 dB, and an insertion loss better than 2 dB over all three bands, in addition to bandstop regions with rejection levels better than 40 dB separating the three bands. A prototype is then designed, fabricated, and measured to validate the design procedure. Reasonably good agreement between measurement and simulation is observed.