Quasi quarter SIW-mode resonator and its application to sierpinski fractal filter design

In this letter, a new kind of quasi quarter SIW resonator (QQSIWR) using Sierpinski fractal defected structure is presented first. Comparing with SIW resonator, this novel resonator has lower resonant frequency (f0) and acceptable unloaded quality (Qu) value, while maintaining almost unchanged electromagnetic fields distributions. The frequency characteristics and Qu of this resonator is investigated under different fractal sizes. To validate the properties of QQSIWR, a miniature cross-coupled bandpass filter (BPF) with a size reduction over 88% is proposed and optimized using Sierpinski fractal structure and cross coupling technology. It can produce asymmetrical frequency response by generating a transmission zero (TZ) on the high side of passband. A prototype of the filter is fabricated and measured, and the measured results are in good agreement well with the simulated ones. © 2016 Wiley Periodicals, Inc. Microwave Opt Technol Lett 58:1176–1179, 2016