High Power 2.85 GHz GaN RF Source for Direct Detection of Multipactor Research

A pulsed 2.85 GHz RF source design with high average power is presented for use as the principle exciter in an experiment to directly detect multipactor. With a rated output power of 700 W each in long pulse mode (∼ 100 □s), four Cree GaN HEMTs are used to achieve a maximum of 2.8 kW rated output. A fifth HEMT is used to drive the four output devices with approximately 40 W each. A free running VCO with low tuning sensitivity is used which ensures a stable frequency output despite a noisy environment. Buffering and initial amplification is provided by an LNA with a TTL RF switch used to generate the pulses. With a rise time of 35 ns, this switch is fast enough to create reasonably square pulse edges. A microwave amplifier with 45 dB of gain provides the majority of the gain in the system and the power necessary for the final GaN stages, approximately 9 W. An in-line micrometer adjusted, continuously variable attenuator between LNA and TTL switch provides level control.

A pulsed 2.85 GHz RF source design with high average power is presented for use as the principle exciter in an experiment to directly detect multipactor. With a rated output power of 700 W each in long pulse mode (∼ 100 □s), four Cree GaN HEMTs are used to achieve a maximum of 2.8 kW rated output. A fifth HEMT is used to drive the four output devices with approximately 40 W each. A free running VCO with low tuning sensitivity is used which ensures a stable frequency output despite a noisy environment. Buffering and initial amplification is provided by an LNA with a TTL RF switch used to generate the pulses. With a rise time of 35 ns, this switch is fast enough to create reasonably square pulse edges. A microwave amplifier with 45 dB of gain provides the majority of the gain in the system and the power necessary for the final GaN stages, approximately 9 W. An in-line micrometer adjusted, continuously variable attenuator between LNA and TTL switch provides level control.