Compact G-CPW Fed Air-Filled SIW (AFSIW) Filters For Systems on Substrate

Abstract

This paper presents the investigation and demonstration of novel compact grounded coplanar waveguide (G-CPW) fed air-filled substrate integrated waveguide (AFSIW) filters. The proposed topology implements input and output feedings from the top layer of the multilayer printed circuit board (PCB) that is used in microwave and millimeter-wave circuits and systems to host surface mount devices such as MMICs, which are interconnected using G-CPW or microstrip lines. In this purpose, the top substrate is typically a thin substrate implementing on its top G-CPW lines to minimize radiation and couplings compared to microstrip lines. In the proposed topology, coupling windows are etched on the top substrate ground to create the input and output couplings of the AFSIW filter. The design of the proposed AFSIW filter, which is of high interest for systems on substrate (SoS), is presented in detail. For demonstration purposes, a fourth order AFSIW filter operating at 21 GHz with a 325 MHz (1.55 %) bandwidth is designed, fabricated and measured. The results obtained in measurements are in good agreement with the simulations. The fabricated filter exhibits an insertion loss of 0.99 dB and an unloaded Q-factor of 1157.