A high-power solid-state RF source driven by a doubly-differential signal

This letter presents a new solid-state RF source generating kW-level output power at HF band. Four power transistors are driven in a doubly-differential way, operated in a switching mode, and combined together to produce high output power. A multilayered input feed network is carefully designed, such that an accurate doubly-differential signal is provided to the transistors. The output matching and combining circuitry is optimized toward a high efficiency. The implemented RF source produces a CW signal of 1.5 kW at 29 MHz with a drain efficiency of 85%. The measured high efficiency is attributed to the well-balanced and symmetric switching-mode operation of each transistor, which is verified experimentally by a thermal image.