Measured impact of different back‐off points and cooling methods on pulse‐to‐pulse stability and sidelobe level of a high‐power solid‐state amplifier

Using solid-state power amplifiers for next generation of weather radars becomes feasible by pulse compression techniques. In this study a 1.5 kW solid-state power amplifier (transmitter) for C-band weather radars is designed and fabricated by GaN high electron mobility transistor (HEMT) technology. An experimental setup based on heterodyne receiver with 16-bit digitiser is developed to investigate the behavior of the power amplifier under different cooling methods and back-off points. Several measurements with shaped LFM pulse show an approximately identical pulse to pulse (P2P) stability for 3 dB compression, P1dB and 2 dB back-off points while the best sidelobe level (SLL) is achieved for 2 dB back-off point. To study the effect of different cooling techniques on P2P stability and time SLL, two power amplifiers with the same transistors but different cooling methods are examined. Measurement results for 100 µs pulse duration indicate that the power amplifier with liquid cooling method shows 56 dBm output power with 0.1 dB droop while the forced-air cooling one shows 55.5dBm output power with 0.3 dB droop. While the liquid cooling technique shows 3 dB improvement in the overall P2P stability, its time SLL is deteriorated. To the authors' knowledge, this is the first experimental study on the time SLL under different back-off points and cooling techniques.