Highly Linear Microwave Signal Detection for Cognitive Radio

This paper presents a highly linear sensing approach to detect arbitrarily modulated input signals with respect to identifying the spectrum holes available for cognitive radio applications. The sensing technique is based on a completely passive six-port circuit, to process the sensed signal without requiring active, hence non-linear components (e.g., mixers) in the front-end of the receiver circuit. Such a technique provides a fast, low-power sensing strategy along with minimal non-linear distortion of the resultant receiver signal. It offers, therefore, an extremely interesting alternative to rapid wide-band sensing which is a key pre-requisite for any cognitive radio system.