Co‐design of a low noise amplifier with compact substrate integrated waveguide bandpass filtering matching network

Abstract

This article presents a co-design of a low noise amplifier (LNA) and bandpass filter (BPF) input matching network (IMN) based on quarter-mode and one-eight-mode substrate integrated waveguide (SIW) cavities. The transmission zeros (TZs) of the proposed BPF IMN occur in the stopband and demonstrate improved frequency selectivity compared to conventional methods. Our design can reduce the complexity and circuit sizes of receiving BPFs and LNAs in communication systems, and improve the receiving performance of radio frequency (RF) front-end circuitry. Three different LNAs were fabricated and tested. The proposed LNA features a three-stage compact-size SIW BPF IMN at a center frequency (f0) of 8 GHz. The proposed LNA with a compact SIW BPF IMN exhibits better electrical performance than a conventional LNA (CLNA) with a full-mode (FM) SIW BPF. We found that the small signal gains at f0 of the standalone CLNA, FM SIW BPF cascaded with CLNA, and the proposed LNA were 15.69, 14.72, and 15.18 dB, respectively. The measured noise figure (NF) at f0 of CLNA was 0.86 dB, while the NF of the FM SIW BPF cascaded with CLNA was 2.23 dB, and the NF of the proposed LNA at f0 was 1.71 dB. In addition, the circuit size of the proposed LNA is 48% smaller than that of an FM SIW BPF cascaded with CLNA.