Fabrication-Tolerant AFSIW Filters Based on Quadruplet Through-Hole Mounted Inductive Posts

In this paper, air-filled substrate integrated waveguide (AFSIW) bandpass filters based on quadruplet through-hole mounted inductive posts are proposed and demonstrated. First, a comparison between the conventional inductive iris coupling and the inductive post coupling is introduced. Both geometries are compared in terms of performances and fabrication tolerance. A Monte Carlo analysis shows that printed circuit board (PCB) drilling process is more accurate than machining process. Then, a study on the internal coupling based on single inductive post is compared with its counterpart based on quadruplet inductive posts. For demonstration purposes, a fourth-order bandpass filter centered at 21 GHz with 1.4 % relative bandwidth is synthesized and fabricated. It achieves a -19 dB return loss with a -0.73 dB insertion loss. The calculated unloaded quality factor of the prototyped bandpass filter is 1594. This fabrication-tolerant topology is of high interest for future systems on substrate. The proposed low-cost and manufacturing tolerant filter structure is believed by the authors to contribute to the democratization of the millimetre-wave spectrum earth resource.