Feature article: Potential transmit beamforming schemes for active LPI radars

Active radar using phased array has the ability to steer a high-gain beam toward any desired direction, while nulling in undesired directions to cancel jammers or interferences. However, the highpower transmission signals are often highly visible to intercept receivers; consequently, the radar may be detected and destroyed [1]. It is, thus, necessary to develop low probability of intercept (LPI) techniques to increase the system surveillance [2]. Note that although LPI technology has been defined for nearly half a century and used operationally for more than 20 years [3], which provides the user a significant advantage over his adversary by making it more difficult for a foe to detect an opponent, current LPI technologies concentrate on low observability against radars by reducing the radar cross section (RCS). Different from these existing RCS reduction methods against radar detection, this article discusses potential transmit beamforming techniques for active LPI radars to increase their survivability against undesired interceptors. However, active radar is not LPI by its nature, because the radar cannot avoid illustrating the interceptor. The interceptor is passive, and its location is probably unknown. The interceptor can have a good antenna with significant receiving aperture and a low-noise amplifier. All of these factors can be more or less equal for the radar and the interceptor. What is not equal is the large reduction of the radar signal on the return path from the target [4].