OVERVIEW

In recent years, microwave passive direction finding (DF) has emerged as a distinct technology apart from HF/VHF and radar associated DF methods. This has occurred as the result of many factors, the most important being recognition of electronic warfare as an art. In the post-World War II period, radar-controlled weapon systems have undergone extensive development aided, in no small part, by the enormous worldwide investments and subsequent achievements in avionics, semiconductor, and radar technologies. In the initial stages of this expansion, the use of direction finding, both active and passive, was part of the more general task of gathering electronic battlefield intelligence (ELINT). At first, the recognition of the number and types of hostile emitters, in a field of many signals, was accomplished by low probability-of-intercept systems, typically using rotating antennas, narrow bandwidth scanning receivers, and real-time pulse processing and display techniques. This methodology was consistent with speed of the available data-handling processes of that time and the human operator's ability to make use of the information.

More recently, with the advent of sophisticated high-performance antiaircraft and antiship missile systems, electronic warfare has been tasked with the problem of recognizing not just the threat but rather the state it is in: acquisition, launch, and control or terminal guidance. The need for early warning and protection for ships, high-speed aircraft, and ground forces has led to the development of complex electronic warfare protection suites and a class of equipment known as radar warning receivers (RWR), both of which make extensive...