One‐Octave Bandwidth‐Tunable Filter Power Amplifier Based on Radial Stub Matching Network

ABSTRACT In this paper, a one‐octave broadband filtering power amplifier (FPA) with bandpass filtering response is presented by utilizing a bandwidth‐tunable bandpass filter (BPF) as the matching network (MN). Existing FPAs cannot achieve flexible bandwidth adjustments by changing only the circuit parameters. The MN structure incorporates the bandwidth ( θ c ) as a variable in the closed‐form equations of the bandpass filter prototype, enabling the flexible design of MNs with bandpass filtering response. The MN employed is of fixed order, and the bandwidth can be extended from narrowband to more than one octave by simplymodifying the impedance characteristics of the microstrip lines. Furthermore, this paper innovatively adopts quarter‐wavelength radial stubs instead of conventional short‐circuited branch lines in the bandpass filter prototype, which enhances both the bandwidth and efficiency of the power amplifier. To verify the theory, a bandpass FPA was fabricated capable of supporting over one‐octave bandwidth (1.8–3.6 GHz), with measured drain efficiency ranging from 54% to 71% and output power varying from 39.3 to 41.7 dBm.