A 5–19GHz amplitude-shaped power amplifier using microstrip SIRs loaded with film resistors

An ultra-wideband power amplifier (PA) module with pre-specified curve of output power over 5-19GHz is presented in this paper. The whole PA circuit is composed of three stages of amplifier MMICs followed by four microstrip stub resonant cells loaded with film resistors as low Q-fator resonators. Traditionally, the resonator cells used for a microwave amplitude equalizer are straight short or open stubs. In order to fulfill the shaping of amplitude curve over a nearly quadruple frequency band, we propose a circuit scheme where microstrip step-impedance resonators (SIR) loaded with thin-film resistors are utilized to increase the degree of freedom in the design of the amplitude-shaping circuit. The return loss and insertion loss of the amplitude-shaping circuit is optimized by Ansoft HFSS to fit the pre-specified curve in frequency domain. A prototype of the amplitude-shaped PA is designed and fabricated. The measured results of frequency response of the output power are in agreement with the specified one with a difference less than ±1.0dB within 5-19GHz. Experimental results indicate that the proposed low Q-factor resonant cells consisting of the SIRs and thin-film resistors are well suited for the design of ultra-wideband amplitude equalizing and shaping circuits.