Investigation of high-efficiency hybrid power combining for ka-band frequencies

In this paper, planar hybrid assembly is investigated as a cost-effective alternative to waveguide and radial power combining of high-power GaN MMICs. To that end, a low loss three-section branch-line coupler is developed and used as a power divider/combiner. It achieves an insertion loss of less than 0.3 dB between 25 and 35 GHz, which is a relative bandwidth of more than 30 %. Together with two Ka-band power amplifier MMICs, it is assembled onto a baseplate. Small-signal characterization show very little deterioration in gain. Thus, the achievable output power nearly doubles over the whole frequency range.