Novel hybrid coupling structure for HMSIW resonators and its application to bandpass filter

In this paper, a novel hybrid coupling structure including a magnetic coupling iris and an electric coupling etched bowtie-shape structure was studied in detail and used to improve the coupling of the two adjacent resonant cavities. The coupling effect provided by the hybrid structure can be accurately modified and optimized by tuning the dimensions of the coupling structure. It was also shown that the electric scatter of the proposed structure allows the implementation of a forward-wave passband propagating below the characteristic cutoff frequency of the waveguide. To demonstrate the validity of the design strategies, a compact 2.4 GHz bandpass HMSIW filter using bowtie-shape coupling structure with sharp selectivity is simulated, fabricated and measured. The dimension of this filter is as small as 0.4λg×0.16λg, where λg is the guide wavelength at the center frequency. The measured results are in good agreement with the simulation.