A Compact Output Power Combiner for Broadband Doherty Power Amplifiers

Abstract

A novel compact output power combiner for broadband Doherty Power Amplifiers is proposed in this paper. The proposed output power combiner avoids the use of quarter-wave impedance transformers as they are sizable and work over narrow bandwidths. Instead, the proposed combiner utilizes a distributed Brune Section to implement a compact broadband impedance inverter. The final area of the proposed output combiner is λ2/48. When compared to the conventional broadband Doherty structure, which has an approximate area of λ2/16, this structure offers an approximate size reduction of 67%. The proposed combiner is verified by using it in the design of a broadband Doherty power amplifier with an operating bandwidth of 1.7 GHz to 3.4 GHz. The saturated output power varies from 39.2 to 40.4 dBm with a peak power drain efficiency ranging from 58% to 66%. The drain efficiency at 6 dB Output Power Back-Off (OPBO) varies from 37.4% to 45% over an octave.