In this paper, we present a Ku-band 50 W internally-matched power amplifier that asymmetrically combines the power transistor cells of the GaN high electron mobility transistor (HEMT) (CGHV1J070D) from Wolfspeed. The amplifier is designed using a large-signal transistor cell model in the foundry process, and asymmetric power combining, which consists of a slit pattern, oblique wire bonding and an asymmetric T-junction, is applied to obtain the amplitude/phase balance of the combined signals at the transistor cell combining position. Input and output matching circuits are implemented using a thin film process on a titanate substrate and an alumina substrate with the relative dielectric constants of 40 and 9.8, respectively. The pulsed measurement of a 330 μs pulse period and 6% duty cycle shows the maximum saturated output power of 57 to 66 W, drain efficiency of 40.3 to 46.7%, and power gain of 5.3 to 6.0 dB at power saturation from 16.2 to 16.8 GHz.
Keywords: GaN high electron mobility transistor (HEMT); Ku-band; amplitude balance; asymmetric power combining; phase balance; power amplifier.