Implementation Methods for Transmission Zeros in Groove Gap Waveguide Filters at W-Band

Abstract In this paper, three groove gap waveguide (GGW) filters are presented, which utilize different techniques to create transmission zeros (TZs) in the W-band. First, a fourth-order filter with cross-coupling of non-adjacent cavities realizes five TZs. The filter is implemented using a stacked cavity approach, which simplifies the realization of cross-couplings with positive and negative signs. The source to load cross-coupling realizes one TZ more than predicted from theory. In the second filter, two off-centered posts with partial height are used to realize two TZs. These posts act as strongly frequency-dependent coupling elements and enable the realization of TZs in an inline filter topology. An interdigital-pin implementation has been used since otherwise, the distance between the posts and the sidewalls is too small to allow manufacturing using the Computerized Numerical Control (CNC) milling approach. The third filter is of fourth order and implements two TZs by using a stub-loaded cavity approach. All filters are designed as a proof of concept in the W-band (75–110 GHz) to verify the manufacturability at high-frequency bands. The manufactured components are realized by high-precision CNC milling and measurement results show good agreement with the simulation for all proposed filters.