Thermal Challenges Due to Improved RF Performance

Transmit/Receive (T/R) modules are the heart of many Active Electroncially Scanned Antennas (AESA). AESA’s enable a great deal of modern radar technology used on many military platforms. In the case study presented, a radar design necessitated the modification of an existing T/R module to increase the output power by 3dB. The RF design of the module demonstrated that a 3× increase of input power would be needed to achieve the desired performance. Increasing the input power creates extra power dissipated on the chips within the module, in the form of heat, resulting in significant thermal challenges. Chip junction temperatures directly affect the performance and reliability of the T/R Module. That is why thermal management of the module became the driving engineering concern. In this project, significant redesign of the T/R module was not possible due to the cost and schedule implications for this program. Therefore multiple engineering techniques were used to adequately cool all portions of the T/R module. These included refined RF modeling of the module to determine operating duty cycles, a re-designed coldplate to better remove heat, a modification of the power supply to lower the T/R module overhead voltage, and a re-designed Power Amplifier/Low Noise Attenuator (PA/LNA) on the module. The end result was a T/R module, with only one of five chips redesigned, which met desired output power, and demonstrated a positive temperature margin on all module components. All of this was accomplished within an acceptable cost and schedule budget.