A 63-73 GHz GaN Power Amplifier with a Compact Power Combiner

A 63-73 GHz GaN power amplifier (PA) with four cascaded stages is presented. At the final stage, the outputs of two transistors are combined to produce a maximum output power of 29.6 dBm at 70 GHz, along with a good power added efficiency (PAE) of 17%. A compact 2-way power combiner based on a quadrature coupler is utilized, which comprises two coupled transmission lines (TL), with one TL having an open termination. Furthermore, this combiner is used for not only power combination but also impedance matching between its input and output ports by selecting a suitable coupling coefficient. The size of the 2-way power combiner used here is 84× 300$\mu \mathrm{m}^{2}$, and the size of the entire PA is 2.5 m$\mathrm{m}^{2}$. The power density per chip area is 364 mW/m$\mathrm{m}^{2}$, which is the second largest value reported in the literature. In addition, this PA achieves a large signal gain of 20 dB at the maximum output power, the highest reported value in the literature.