Importance and measurement of phase-stiffness in RF switching amplifiers

Phase-stiffness is a measure of the ability of an RF power amplifier to tolerate disturbance injected into its output. Phase-stiffness of conventional (linear) RF power amplifiers used in phased-array radar results from inserting circulators and isolators on their output as they can not tolerate typical disturbances arising from antenna mismatch and signals arriving from mutual coupling of array elements. We show that the output stage of a RF switching amplifier employing a single AlGaN/GaN HEMT loaded with an inductor exhibits high tolerance to external signal disturbance at the carrier frequency. This RF amplifier architecture shows promise for use in phase-array radar and active antenna array transmit/receive modules as this may operate without isolators.