A practical design method of microwave Doherty amplifiers is proposed. A general circuit condition to sum up exactly output-powers of two amplifiers connected directly to a common output load at a given input power level for each amplifier is presented. The condition is applied to design microwave Doherty amplifiers. First, two amplifiers, which will consist of carrier and peak amplifiers in a Doherty amplifier, are tuned typically for a 50-ohm load, respectively. Next, an output power ratio of the carrier amplifier and the peak amplifier at a selected same input power level for each amplifier is introduced as a design parameter. From the parameter, the common load combining the two amplifiers and a quarter-wave transformer in carrier amplifier output are calculated. Microwave Doherty amplifiers consisting of power Si MOSFETs is designed at 1 GHz and their superior performance over a wide range of output power is confirmed by a circuit simulator.
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