On Removing Circulator and Isolators from Active Electronic Scanned Array Front Ends

Active, electronically scanned arrays (AESAs) present an impedance mismatch that varies with frequency, scan angle and polarization to their RF front end electronics. AESAs that transmit high power RF often use ferrite circulators or isolators to dissipate the reflected RF power, protect the RF electronics from being damaged, and provide a constant impedance match to the power amplifier and low noise amplifier, allowing them to operate optimally as the AESA scans its beam over frequency. Circulators and isolators add front-end loss and increase AESA size, weight, power consumption, cooling and cost compared to systems not having circulators or isolators. As a result, engineers developing AESA systems today often choose not to use circulators or isolators. Since the receive electronics are easily protected with a solid-state limiter, the high power amplifier (HPA) is our focus. We recommend analysis that should be considered as part of the AESA concept design process prior to making the decision to remove or include circulator and isolators.