Experimental Validation of a Four-Way Outphasing Combiner for Microwave Power Amplification

Abstract

Abstract-This paper presents a 2.14-GHz, four-way power combining and outphasing system for high-power amplifiers such as those in radio basestations (RBS). The combiner is ideally lossless, and enables power control through load modulation of the power amplifiers (PAs). A discrete-component power combiner is designed and characterized, and combined with inverse Class-F PAs using GaN HEMT devices to develop a complete PA system. We demonstrate the effectiveness of the system over a range of outphasing control angles. This first-ever microwave implementation of the outphasing system has a peak CW drain efficiency of 68.9%, with efficiency greater than 55% over a 5.5-dB power range. It provides an average modulated efficiency of 57% for a W-CDMA signal with 3.47-dB peak to average power ratio (PAPR) at 42-dBm output power.Index Terms-base stations, outphasing, power amplifier (PA)

Multi-Way Lossless Outphasing System Based on an All-Transmission-Line Combiner

“…Combining (8) and (9), the combiner's load current I L can be written as per (10). Note that (10) allows one to calculate the combiner's load current (for base = λ/2 in Fig.…”

“…A comparison of the theoretical effective loading conditions for Chireix combining, lumpedelement four-way [10], and transmission-line-based four-way combining is shown in Fig. 7 for example combiner designs of similar dynamic ranges.…”

“…In particular, the branch PAs are mounted on carriers that require spacing of at least 81.3 mm between input ports. In order to experimentally validate the approach (using the same power amplifiers as for previous outphasing systems [10]- [12] for comparison purposes), therefore, a second prototype combiner was designed using the "T" structure layout shown in Fig. 14.…”

“…As described in [10], multi-way combiners may be characterized through reverse drive (operating the combiner as a splitter and measuring the response). When the system was measured by driving the output port (with the four input ports terminated with 50 ohms), the port magnitude match was found to be within ±5% in voltage amplitude of an ideal (even) split, and the phase within 3…”

“…Four-way implementations of this approach have been demonstrated using all lumped elements in a tree structure [9], [10], and by incorporating microstrip lines with ground-referenced shunt reactive elements [11], [12]. In [12] it was shown that these various realizations of the multi-way combining approach could be related through network transformations and shown to have identical theoretical port relationships.…”