GaN solid state power amplifiers (SSPA) for wireless power transfer and microwave heating have been reviewed. For wireless power transfer, 9 W output power with 79% power added efficiency at 5.8 GHz has been achieved. For microwave heating, 450 W output power with 70% drain efficiency at 2.45 GHz has been achieved. Microwave power concentration and uniform microwave heating by phase control of multiple SSPAs are demonstrated.

This invited paper is dedicated to introduce recent activities of Japanese microwave industries. 7 topics are introduced from major microwave companies in Japan. All topics are from invited talks in 2014 Asia-Pacific microwave conference (APMC2014) held in Sendai, November, 2014.

The large signal performance and model for GaN FET devices was evaluated with DC, S-parameters, and large signal measurements. The large signal model was extended with bias and temperature dependence of access resistances, modified capacitance and charge equations, as well as breakdown models. The model was implemented in a commercial CAD tool and exhibits good overall accuracy.

A large-signal simulation program for multi-stage power amplifier modules by using a novel interpolation is presented. This simulation program has the function to make the Load-Pull and Source-Pull (LP/SP) data required for the simulation. By using the interpolation, a lot of LP/SP data can be made from a small number of measured LP/SP data. The interpolation is based on the calculation method using a two-dimensional function. By using the simulation program, we can calculate the large-signal characteristics depended on frequency and temperature of the multi-stage amplifier module. We apply the simulation program to the design of the amplifier. The calculated and measured results agree well. The accuracy of the presented interpolation is confirmed. It is considered that the presented program is useful to calculate large-signal characteristics of the amplifier module.

Satellite broadcasting of 4K/8K ultra-high definition television (UHDTV) was launched in Japan in December 2018. Because this system uses the amplitude and phase shift keying (APSK) modulation scheme, there is a need to improve the non-linear characteristics of the satellite transponders. To meet this requirement, we have been developing a 120-W-class Ku-band solid state power amplifier (SSPA) as a replacement for the currently used traveling wave tube amplifier (TWTA). In this study, we developed a gallium-nitride (GaN) SSPA and linearizer (LNZ). The SSPA achieved an output power of 120W while maintaining a power added efficiency (PAE) of 31%. We evaluated the transmission performance of 16APSK in this SSPA channel in comparison with that in the TWTA channel.

High power amplifier technologies for base transceiver stations (BTSs) for the 5th generation (5G) mobile communication systems and so-called beyond 5G (B5G) systems are reviewed. For sub-6, which is categorized into frequency range 1 (FR1) in 5G, wideband Doherty amplifiers are introduced, and a multi-band load modulation amplifier, an envelope tracking amplifier, and a digital power amplifier for B5G are explained. For millimeter wave 5G, which is categorized into frequency range 2 (FR2), GaAs and GaN MMICs operating at around 28GHz are introduced. Finally, future prospect for THz GaN devices is described.