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

• Published in: IEEE transactions on microwave theory and techniques 2016-04, Vol.64 (4), p.1313-1326
• Main Authors: Barton, Taylor W., Jurkov, Alexander S., Pednekar, Prathamesh H., Perreault, David J.
• Format: Article
• Language: English
• Subjects: Admittance; Base stations; Chireix; Impedance; LINC; load modulation; Loading; Microwave theory and techniques; Modulation; outphasing; Ports (Computers); power amplifier (PA); Power generation; Receivers & amplifiers; wideband code division multiple access (W-CDMA)
• ISSN: 0018-9480; 1557-9670
• DOI: 10.1109/TMTT.2016.2531691

A lossless power-combining network comprising cascaded transmission-line segments in a tree structure is introduced for a multi-way outphasing architecture. This architecture addresses the suboptimal loading conditions in Chireix outphasing transmitters while offering a compact and microwave-friendly implementation compared to previous techniques. In the proposed system, four saturated power amplifiers (PAs) interact through an all-TL power-combining network to produce nearly ideal resistive load modulation of the branch PAs over a 10:1 range of output powers. This work focuses on the operation of the combining network, deriving analytical expressions for input-port admittance characteristics and an outphasing control strategy to modulate output power while minimizing reactive loading of the saturated branch amplifiers. A methodology for combiner design is given, along with a combiner design example for compact layout. An experimental four-way outphasing amplifier system operating at 2.14 GHz demonstrates the technique with greater than 60% drain efficiency for an output power range of 6.2 dB. The system demonstrates a W-CDMA modulated signal with a 9.15-dB peak-to-average power ratio with 54.5% average modulated efficiency at 41.1-dBm average output power.