A Compact Output Power Combiner for Broadband Doherty Power Amplifiers

Ken Mcknight,Ali Darwish,Mona Zaghloul

doi:10.3390/electronics8030275

Ken Mcknight, Ali Darwish + Show 1 more

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https://doi.org/10.3390/electronics8030275

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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.

Highlights

The Doherty Power Amplifier (DPA) is an efficiency enhancement scheme which addresses efficiency at Output Power Back-Off (OPBO) and saturation simultaneously
The dimensions of the final output power combiner are λ/12 by λ/4
A compact output combiner for broadband Doherty Amplifiers was presented in this paper

Summary

Introduction

The Doherty Power Amplifier (DPA) is an efficiency enhancement scheme which addresses efficiency at Output Power Back-Off (OPBO) and saturation simultaneously. The standard DPA consists of two amplifiers and an Impedance Inverting Network (IIN). This implementation is narrowband by nature due to the fact that the IIN is usually implemented with a quarter-wave transmission line. Some of the broadband methods include the use of a lumped element equivalent of the quarter-wave IIN to absorb the output device capacitance of the amplifiers [5]. A Transformer-Less Load Modulated scheme was proposed [6]. This method uses a combination of Tee and Pi three-element networks to construct the output power combining network.

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