A Tradeoff Design of Broadband Power Amplifier in Doherty Configuration Utilizing a Novel Coupled-Line Coupler

A broadband power amplifier designed and implemented in Doherty configuration is illustrated in this paper. Both input and output networks adopt the broadband matching topology. Additionally a compensation network, consisting of a series transmission line shunted with a capacitance, is set behind the peak amplifier to avoid in-band power leakage in the low-power section while at the cost of peak output power in partial band. A novel coupler is designed as an uneven power-divided splitter and experimentally validated for a broadband power amplifier module. A tradeoff of bandwidth, efficiency and output power is fulfilled through parameters select and postproduction tuning. According to the measured results, the proposed broadband Doherty power amplifier achieves an average saturated output power of 42 dBm, an average gain of 10.6 dB, an average peak and 6 dB back-off efficiency of 48.4% and 32.8%, respectively, and a fractional bandwidth of 51.4%, from 1.3 GHz to 2.2 GHz. The adjacent channel power ratio is better than −40 dBc when the amplifier is driven with 10-MHz QPSK signal, thus exhibiting a high linearity performance.