A compact bandpass filter based on co-design of highly efficient power amplifier

Abstract

This paper presents a compact two-order bandpass filter based on the Co-design with power amplifier (PA). Compared with a classical filter, the input impedance of the filter in this design is no longer 50 Ω, but a complex impedance. So that it can match the output impedance of the PA directly. And then high efficient power amplifier can be obtained. Besides, a conventional output matching network (OMN) of the PA is eliminated entirely, which leads to a small size and low insertion loss. The bandpass filter is made up of microstrip quarter-wavelength stepped-impedance resonators (SIRs) and with controllable mixed electric and magnetic coupling. Two transmission zeros are generated at the both edges of the passband of the filter, resulting in high selectivity. Both theoretical analysis and measured results are presented for validation.