Since World War II, radar techniques have continued to improve with advances in antenna materials, solid-state electronics, digital signal processing, and software.
The purpose of radar is to provide some form of warning, whether as part of a military surveillance system, a weather-tracking system, or our efforts to better know the universe. Short for radio detection and ranging, radar was initially developed for military use (to detect ships and aircraft during World War II), but now has many applications. Radar systems have matured with the development of different technologies, such as RF/microwave amplification and digital signal processing (DSP). They are now used on earth, at sea, on the road, and even in outer space.
Radar can operate with continuous-wave (CW) signals. More commonly, though, it transmits and receives pulses, measuring the range or distance to a target based on the delay time of the pulses and the velocity of the target based on the Doppler frequency shift of the received signals. A great deal can be learned about the target by analyzing the radar return signals, including the size of the target (based on the magnitude of the returned signals) and any moving parts on a target (based on modulation of the radar returns). Radar systems can be configured in a number of different ways and across many different frequency bands (see table).
In a bistatic radar system, the radar’s transmit and receive antennas are at different locations relative to the target, such as a ground-based transmitter and an airborne receiver. In a monostatic radar system, the transmitter and receiver are in the same location. In a quasi-monostatic radar system, the transmit and receive antennas are slightly separated but still appear to be in the same location as viewed by the target. As with many systems and technologies, the cost increases with the number of functions provided.
1. Large ground-based radar systems, which must scan a large amount of airspace, can appear physically imposing. (Photo courtesy of Raytheon Co.)
For many, radar technology signifies a physically imposing system (Fig. 1), either looming from the edge of a desert or humming within the nose of a fighter aircraft. Domestic companies providing such technology also tend to be large, including such names as BAE Systems, ITT Exelis, Lockheed Martin, Northrop Grumman, Raytheon Co., and Telephonics. Raytheon, for example, supplies radar systems for the ground, at sea, and in the air, employing a variety of technologies and approaches. The firm’s active electronically scanned array (AESA) radar systems have been used throughout the world, by different fighting forces, to provide early warning for fighter jet pilots
2. The AESA radar is a multimode radar system that has been installed in a large number of F-15 fighter jets throughout the world. (Photo courtesy of Raytheon Co.)
The APG-63(V)3 AESA radar (Fig. 2) is an adaptable, all-weather system that has been installed in a large number of F-15 fighter jets throughout the world, evolving into a multimode electronic system capable of numerous radar-based functions. AESA radar systems employ electronic (rather than mechanic) beam steering, with the capability of detecting targets in multiple directions and tracking both air and surface targets at the same time. Raytheon’s engineers have enhanced their AESA radar systems over the years by means of a modular design approach, using replaceable function boards to simplify service and repair (Fig. 3).
More recent radar systems, such as the AN/TPS-78 S-band long-range radar developed by Northrop Grumman, leverage solid-state device technology for high-power signal generation. The firm’s AN/TPS-78 system as well as the TPS-703 radar system used a stacked-beam approach to illuminate and detect targets, and can simultaneously detect low- and high-altitude targets even with a great deal of clutter. Both systems are used in numerous applications, including for air traffic control (ATC) and air-defense systems. Both feature a “wartime” mode in which they can operate their beams with frequency agility to prevent interference from jammers.
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