LPI radar is a system that consists of a radar and ES system. Its performance depends on both components. An LPI performance factor is derived and applied to several examples. Operational LPI radars are described. A digital LPI radar detector is described and test results presented. A recent book on LPI radar received a number of somewhat critical reviews that were published in Systems magazine. Although these reviews made a number of excellent points, several questioned the existence of LPI radar. The objectives of this article are to provide a sound technical basis for determining LPI properties of radar, examine several radars that have LPI qualities, and then to describe digital LPI radar detector designed and tested against the PILOT Mk2 radar. LPI radar is a system that represents a confluence between radar and electronic support (ES) technology. The objective of LPI radar is clear; that is, to escape detection by the ES receiver. However, the capability of the LPI radar system depends upon the characteristics of both the radar and ES receiver. To understand LPI radar one must first understand the nature of ES receivers. The functions performed by tactical ES receivers are immediate interception, identification, and location of both friendly and hostile emitters. Location requires interception in the emitter's sidelobes. Identification is performed by comparing the intercepted signature against the signatures contained within its threat library (Schelher, 1999). The metric that establishes the quality of interception is called the probability of intercept (POI) and is generally included in its specifications (Schleher, 1999). From the above discussion it is evident that radar might have LPI properties with respect to one type, but not to another type of ES system. This situation can be clarified if the claim of radar being LPI radar is accompanied by a description of the various types of ES systems for which this claim applies. However the LPI radar can never completely escape detection since there is always a minimum range (R/sub ES/) between the ES system and radar where the interception receiver detection threshold is exceeded.

LPI radar: fact or fiction

Simulated annealing is a statistical computational technique for obtaining approximate solutions to combinatorial optimization problems. An efficient simulated annealing algorithm is used to design binary sequence sets which have good autocorrelation and crosscorrelation properties. Some of the synthesized results are presented, and their properties are better than any other known in the literature. The synthesized binary sequence sets promise to be practically applicable.

Synthesis of binary sequences with good autocorrelation and crosscorrelation properties by simulated annealing

Besides some general requirements, modern military radars should possess excellent LPI (low probability of intercept) properties. And civilian radars should satisfy the rigorous requirement of EMC (electro-magnetic compatibility) performance. The special features of random signal radar are analyzed here based on the different requirements for military and civilian use. Results show that random signal radar has excellent LPI property and EMC performance simultaneously, which can satisfy both military and civilian requirements.

Random signal radar - a winner in both the military and civilian operating environments

In the modern battlefield, radar faces more and more serious threats from ECM and ARM, etc. Only the Low Probability of Intercept (LPI) radar can survive. In this paper, the principle of LPI radar is introduced first. Then the effects of radar parameters on LPI performance are discussed in detail. Finally, some advice is proposed for the design of the ideal LPI radar system.

The analysis and design of modern Low Probability of Intercept radar

Passive receivers can be used to detect radar emissions over considerable distances. If range resolution requirements are fixed, it is of interest to compare the detectability of equal-bandwidth/equal-energy waveforms regardless of their time duration. Relative detection ranges are predicted, via computer simulation, for two types of transmitted waveforms: a benchmark rectangular pulse and a Welti binary coded waveform. The waveforms will be detected by square-law, delay and multiply, wideband, and channelized passive receivers possessing typical bandwidth, noise-floor, and loss parameters. A comparison is given showing the relative low probability of intercept and low probability of detection (LPI/LPD) attributes of each waveform and the relative detection attributes of each receiver.

D. C. Schleher

Papers

Low probability of intercept radar