Substrate integrated waveguide bandstop filter using partial-height via-hole resonators in thick substrate

A substrate integrated waveguide (SIW) bandstop filter on thick substrate is introduced. The increased substrate height permits partial-height via holes to act as resonators whose interaction provides a wide range of possible coupling coefficients that result in wideband bandstop filters. In contrast to ridged all-metal waveguide filters, SIW filters with partial-height via holes maintain a small profile, low manufacturing cost and they can be integrated with other planar circuitry such as microstrip or coplanar waveguide. The design method of the bandstop filter relies on the well-known extracted-pole technique which allows designers to independently control the locations of reflection zeros. The parameters of the lowpass equivalent circuit of the filter are extracted and used for the initial design of the physical dimensions of the filter. The software packages μWave Wizard and CST are used for filter simulation and optimisation. A prototype bandstop filter is designed for a centre frequency of 10.74 GHz and a bandwidth of 1.58 GHz. Tolerance analyses demonstrate the influence of manufacturing inaccuracies on the filter performance. Good agreement between simulated and measured results confirms the reliability and robustness of the design method and its applicability to SIW technology on thick substrate.