A compact lowpass filter with ultra-high figure-of-merit for integrating with Class-F/F−1 power amplifiers

Abstract

This Paper presents a microstrip lowpass filter (LPF) with compact size, and ultra-wide stopband. The structure consists of a semi-circular shaped resonator (SCSR) and circular patches as the suppressing cell. The proposed LPF has a − 3 dB cutoff frequency at 1.53 GHz. It also has suitable performances such as an extended stopband width from 1.62 to 19.1 GHz (with the attenuation level of more than − 20 dB), ultra-sharp transition-band of 0.09 GHz (from − 3 to − 20 dB). Low insertion loss, high return loss and flat group delay in the region of the passband are very significant properties of this LPF. A proper agreement between the simulation and measurement results has been achieved after the fabrication and testing. Proposed LPF has an ultra-high figure-of-merit (FOM) of 126168, showing its strong efficiency. Forasmuch as harmonic control circuits (HCCs) play a key role in designing Class-F/F−1 power amplifiers (PAs); the asymmetric high performance LPFs can be used at the input and output of these PAs in the HCC section. Therefore, the proposed LPF can be suggested for this application.