Compact hybrid spoof surface plasmon polaritons and via-free half-mode substrate integrated waveguide bandpass filter with wide stopband

In this paper, a novel hybrid spoof surface plasmon polaritons (SSPPs) and via-free half-mode substrate integrated waveguide (HMSIW) is proposed to constitute a compact bandpass filter (BPF). Different from the conventional HMSIW with ground holes, the grounding operation of the presented via-free HMSIW is conducted by edge grounding to bottom layer. Thus, more space can be provided for SSPPs structure. Besides, the new proposed SSPPs unit contains two shorted-end slots and one open-end slot, which not only provides abundant freedom on adjustment of desirable fundamental mode, but also the controllable of high-order modes for wide stopband. The upper cutoff frequency can be controlled by the heights of the slots of SSPPs unit and the lower cutoff frequency can be adjusted by the height of via-free HMSIW unit. Finally, a compact BPF with measured operating band of 3.01-3.81 GHz and wide stopband reaches 15.2 GHz is designed. Multiple transmission zeros generated at two sides of the passband enable the filter has high selectivity. The measured results agree well with the simulations, validating the proposed structure and design method.