A Multioutput and Highly Efficient GaN Distributed Power Amplifier for Compact Subarrays in Wideband Phased Array Antennas

This article presents the design, implementation, and measurement results of a multioutput distributed power amplifier (MODPA) in 100-nm AlN-GaN-AlGaN high-electron-mobility transistor (HEMT) on a silicon substrate. The proposed MODPA improves power-added efficiency (PAE) in distributed amplifiers (DAs) by not wasting reverse traveling waves and delivering all forward and reverse waves to the output ports. Utilizing MODPA in implementing a subarray-based phased-array transceiver reduces the number of power splitters and PAs, significantly reducing the subarray's chip area and power loss. A design methodology for broadband, efficient amplifier implementation by optimizing load/source impedances at the fundamental and harmonic frequencies is presented based on comprehensive source/load-pull simulations and class-J dynamic load lines. The presented broadband design methodology addresses an ambiguity for picking optimum load/source impedance at a single frequency caused by higher order harmonics of operating frequencies dropping in the band. The fabricated MODPA occupies a 1 x 3 mm(2) chip area. In 0.01-25-GHz frequency, MODPA delivered 37-41-dBm power to the four outputs, with a 17-21-dB total power gain and 22%-73% total PAE. The power gain and phase variation between the four matched-output ports are less than 1.5 dB and 3 degrees, respectively, making MODPA an attractive design for implementing subarrays.