Monolithic Attenuator/Limiter Using Nonlinear Resistors

Abstract

A novel attenuator/limiter circuit that uses nonlinear GaN epitaxial resistors is presented. The circuit is small, broadband as it does not use any reactive elements, does not use DC bias, and can be integrated on GaN or GaAs with other microwave elements and/or circuits. GaN epitaxial resistors have a saturation current limit which provides a limiting function. Resistive T-and Pi-network attenuators are implemented using GaN epitaxial resistors to limit the total power through the attenuator. A first-order equation of the trade-off between attenuation and flat leakage power is derived. Fabricated circuits show flat leakage powers 0.4 - 10 W with input powers $> \mathbf{30\ W}$, No noticeable spike-leakage is observed. The limiting attenuator is implemented at the input of an S-band 32 W PA for radar applications, and is shown to protect the input from overdrive while delivering consistent output power after limiter saturation.