Continuous-wave radar system is a radar system where a continuous wave is transmitted by one antenna and a second receives the radio energy reflected from an object. This long range radar antenna (approximately 40m (130ft) in diameter) rotates on a track to observe activities near the horizon. ... A continuous wave (CW) is an electromagnetic wave of constant amplitude and frequency. ... In biology, antenna (plural: antennae) refers to the sensing organs of several arthropods. ...

A very pure signal of a known frequency is transmitted by one antenna. Return signals received by the second atenna from targets are shifted away from this base frequency via the Doppler effect. Sound waves emanating from an ambulance moving to the right. ...

The main advantage of the CW radars is that they have no pulsing, and thus no minimum or maximum ranges (although the broadcast strength imposes a practical limit on the latter) as well as maximizing power on the target. However they also have the disadvantage of only being able to detect moving targets, as motionless ones (along the line of sight) will not cause a Doppler shift and the signal from such a target will be filtered out. Military aircraft often attempt to avoid detection by CW radar by 'orbiting' around the transmitter. CW radar systems thus find themselves being used at either end of the range spectrum, as radio-altimeters at the close-range end (where the range may be a few feet) and long distance early-warning radars at the other. See also: line of sight in gaming, referring to visibility of units. ... A foot (plural: feet) is a non-SI unit of distance or length, measuring around a third of a metre. ...

CW radars have the disadvantage that they cannot measure distance, because there are no pulses to time. In order to correct for this problem, frequency shifting methods can be used. When a reflection is received the frequencies can be examined, and by knowing when in the past that particular frequency was sent out, you can do a range calculation similar to using a pulse. It is generally not easy to make a broadcaster that can send out random frequencies cleanly, so instead these frequency-modulated continuous wave radars (FMCW), use a smoothly varying "ramp" of frequencies up and down. For this reason they are also known as a chirped radar.

The military uses continuous-wave radar to guide semi-active radar homing (SARH) air-to-air missiles, such as the US AIM-7 Sparrow. The launch aircraft illuminates the target with a CW radar signal, and the missile homes in on the reflected radar waves. Most modern air combat radars, even pulse Doppler sets, have a CW function for missile guidance purposes. The disadvantage of CW radar and SARH weapons is that the launch aircraft must continue to point its radar (and thus its nose) at the target for the entire duration of the missile's flight, leaving the attacker vulnerable to a counterattack. In addition, most mechanically steered radar sets can attack only one target at a time, and cannot search for other targets (or imminent attacks) while guiding a SARH missile. Semi-active radar homing, or SARH, is a common type of missile guidance system, perhaps the most common type for longer range air-to-air and ground-to-air missile systems. ... A US Navy VF-103 Jolly Rogers F-14 Tomcat fighter launchers an AIM-54 Phoenix long-range air-to-air missile. ... Wikiquote has a collection of quotations by or about: United States Wikinews has news related to this article: United States United States government CIA World Factbook Entry for United States House. ... A RIM-7 Sea Sparrow being launched from the USS Essex (LHD-2) The AIM-7 Sparrow is a medium-range semi-active radar homing air-to-air missile operated by the USAF, US Navy, and USMC as well as various allied air forces. ... Pulse-doppler is a radar system that functions by sending short pulses of radio energy and simultanously listens for the echo from objects using the same attenna. ...