A 28-GHz Passive Outphasing Load Modulator in 40-nm GaN

This paper presents a passive tunable matching network for load-modulation of a power amplifier (PA). With a set of discrete RF switches, different real impedance transformations can be realized to optimize the loadline match of the PA for output power and/or efficiency. To handle high-power, a 40-nmGaN MMIC process was used to realize three RF switches that switch across a ring impedance network. The tunable matching network realizes 15, 40, or 80Ω depending on the switch state with insertion loss (IL) between 1.7 and 3.3 dB at a center frequency of 28 GHz. The GaN devices have a high breakdown point and therefore the network P1dB exceeds 33 dBm. The bandwidth of the network exceeds 2.5 GHz.