Multi-octave GaN high power amplifier using planar transmission line transformer

In this work, design, implementation and experimental results of an efficient, high power and multi-octave GaN-HEMT power amplifier (PA) are presented. To overcome the low optimum source and load impedances of a large transistor, various topologies of a broadside coupled impedance transformer are simulated, implemented and measured. The used transformer achieves a flat measured insertion loss (IL) of 0.5 dB and a return loss (RL) higher than 10 dB over a decade bandwidth [0.4–4] GHz. The transformer is integrated at the drain and gate side of the transistor using pre-matching networks to transform the complex optimum source/ load impedances to the appropriate impedances of the transformer plane. The measurement results illustrate a saturated output power ranged between 49.6 ± 1 dBm with an average drain efficiency of 57 % and gain of 10.5 dB across 0.6–2.6 GHz.