183 Adaptive junction temperature cooling to enable the next-generation of single-assembly solid-state high-power RF amplifiers

Thursday, 29 September 2011
Grand Ballroom (William Penn Hotel)
K. Namjou, University of Oklahoma, Norman, OK; and P. McCann, M. Yeary, and R. Kelley

Semiconductor radio frequency (RF) power amplifiers (PA) with large emission powers are the key components in a wide variety of applications including wireless communication, radar, and especially the next-generation of phased array weather radars. Developing an approach to adaptively regulate the junction temperature by cooling is a key to enable the next-generation of single-stage, solid-state, high-power RF amplifiers. It is well-known that removing the heat buildup from the semiconductor RF-power amplifiers is a crucial thermal management task for effective functioning and long-term device reliability; however, to make a paradigm shift in which single-stage, high-powered solid-state amplifiers become viable replacements for the traditional filament-based Klystron, magnetron, or traveling-wave-tube (TWT) amplifier, then new cooling approaches are needed at the wire bonding stages of the solid-state amplifier manufacturing process.

To support these claims, the team has made several initial laboratory investigations. The measurement system was comprised of two types of RF-amplifiers with operating frequency at S-band, were selected for this experiment, an InGaP-based HBT and a GaAs-based FET. It was shown experimentally that amplifier performance in terms of output power and efficiency improved at lower temperatures. This is consistent with a higher transistor gain associated with a larger electron mobility at a lower active region lattice temperature. A synthesized RF-generator (HP, model 8671B) provided a 2.0 to 18.0 GHz RF signal with adjustable power to the input of the amplifiers via a flexible UTiFLEX microwave cable assembly (Micro-Coax) and a variety of measurements were recorded. For example, HEMTs are more sensitive to temperature level, the selected HEMT device showed a 26% improvement in linear and 10% in saturated output power region when its base plate was cooled from +65 degrees C to +5 degrees C. Future work will develop a new efficient packaging technique to integrate Peltier-cooler modules with RF-power transistors using existing low cost devices.

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