X-band balanced power amplifier using novel coupler with 50% power-added efficiency

In this paper, we demonstrate an X-band balanced power amplifier using a novel microstrip line dc blocking impedance-transforming branch-line coupler (DCITBC). This novel coupler has the function of dc blocking, which can easily cascade two stages of an active circuit together. Therefore, we can reduce the cost and the circuit size. The measured power-added efficiency of this balanced power amplifier is 50% over the 9.8–10.2 GHz band, with an associated gain of 9 dB and 25 dBm output power. Additional important results are the superior performance of the harmonic suppression; the measured result shows a second harmonic below −40 dBc without an extra harmonic rejector. ©1999 John Wiley & Sons, Inc. Microwave Opt Technol Lett 20: 192–195, 1999.