Compact 3.5 kW semiconductor RF modules based on SiC-VJFETs for accelerator applications

We present first prototypes of compact low cost high power semiconductor RF amplifier modules based on silicon carbide (SiC) normally-on vertical JFETs that can operate at VHF frequencies. The RF amplifiers have a modified parallel push pull topology (floating bridge or circlotron) with two parallelized transistors per side. They were tested in pulsed mode at drain voltage levels up to 500 V and at an operation frequency of 150 MHz. The RF amplifier modules delivered an effective output power of 3500 W into a 12.5 Ω resistive load at a duty cycle of 1:1000. The achieved power gain was 9.5 dB at the 1 dB compression point. The corresponding efficiency was 45%. Simulations and first measurements indicate that a new optimized transistor generation will provide a factor of four higher output power in a similar RF module circuit.