Air-Filled SIW Filters for K- to E-Band Substrate Integrated Systems

In this paper, air-filled substrate integrated waveguide (AFSIW) bandpass filters based on inductive iris coupling are proposed for K- to E-band applications in substrate integrated circuits and systems. Three filters, operating in the K-band, Q-band and E-band are designed and experimentally demonstrated. First, the theory of this type of bandpass filters is detailed. Then, for demonstration purposes, three fourth-order AFSIW bandpass filters centered at 21 GHz, 38 GHz and 78 GHz with 1.4 %, 2.63 % and 5.23 % bandwidth respectively are synthesized and fabricated. The filters operating in the K-band, Q-band and E-band achieves a 20 dB, 17 dB and 10 dB return loss and a 0.7 dB, 0.55 dB and 0.91 dB insertion loss, respectively, without time-consuming post process tuning. The calculated unloaded quality factors are 1607 and 1065 respectively for the K-band and Q-band. This technology is of particular interest for the design of low cost extremely high frequency integrated systems on substrate.