Radar is a detection system that uses radio waves to determine the distance (ranging), angle, and radial velocity of objects relative to the site. It can be used to detect aircraft, ships, spacecraft, guided missiles, motor vehicles, weather formations, and terrain. A radar system consists of a transmitter producing electromagnetic waves in the radio or microwaves domain, a transmitting antenna, a receiving antenna and a receiver and processor to determine properties of the objects. Radio waves from the transmitter reflect off the objects and return to the receiver, giving information about the objects' locations and speeds.
In antenna theory, a phased array usually means an electronically scanned array, a computer-controlled array of antennas which creates a beam of radio waves that can be electronically steered to point in different directions without moving the antennas.
An active electronically scanned array (AESA) is a type of phased array antenna, which is a computer-controlled array antenna in which the beam of radio waves can be electronically steered to point in different directions without moving the antenna. In the AESA, each antenna element is connected to a small solid-state transmit/receive module (TRM) under the control of a computer, which performs the functions of a transmitter and/or receiver for the antenna. This contrasts with a passive electronically scanned array (PESA), in which all the antenna elements are connected to a single transmitter and/or receiver through phase shifters under the control of the computer. AESA's main use is in radar, and these are known as active phased array radar (APAR).
In a radio antenna, the feed line (feedline), or feeder, is the cable or other transmission line that connects the antenna with the radio transmitter or receiver. In a transmitting antenna, it feeds the radio frequency (RF) current from the transmitter to the antenna, where it is radiated as radio waves. In a receiving antenna it transfers the tiny RF voltage induced in the antenna by the radio wave to the receiver. In order to carry RF current efficiently, feed lines are made of specialized types of cable called transmission line. The most widely used types of feed line are coaxial cable, twin-lead, ladder line, and at microwave frequencies, waveguide.
A slot antenna consists of a metal surface, usually a flat plate, with one or more holes or slots cut out. When the plate is driven as an antenna by an applied radio frequency current, the slot radiates electromagnetic waves in a way similar to a dipole antenna. The shape and size of the slot, as well as the driving frequency, determine the radiation pattern. Slot antennas are usually used at UHF and microwave frequencies at which wavelengths are small enough that the plate and slot are conveniently small. At these frequencies, the radio waves are often conducted by a waveguide, and the antenna consists of slots in the waveguide; this is called a slotted waveguide antenna. Multiple slots act as a directive array antenna and can emit a narrow fan-shaped beam of microwaves. They are used in standard laboratory microwave sources used for research, UHF television transmitting antennas, antennas on missiles and aircraft, sector antennas for cellular base stations, and particularly marine radar antennas. A slot antenna's main advantages are its size, design simplicity, and convenient adaptation to mass production using either waveguide or PC board technology.
A radio transmitter or receiver is connected to an antenna which emits or receives the radio waves. The antenna feed system or antenna feed is the cable or conductor, and other associated equipment, which connects the transmitter or receiver with the antenna and makes the two devices compatible. In a radio transmitter, the transmitter generates an alternating current of radio frequency, and the feed system feeds the current to the antenna, which converts the power in the current to radio waves. In a radio receiver, the incoming radio waves excite tiny alternating currents in the antenna, and the feed system delivers this current to the receiver, which processes the signal.
The AN/SPS-48 is a US naval electronically scanned array air search three-dimensional radar system manufactured by ITT Exelis and deployed in the 1960s as the primary air search sensor for anti-aircraft warships. The deployment of the AN/SPY-1 and the end of the Cold War led to the decommissioning of many such ships, and many of these vessels AN/SPS-48 sets were reused on aircraft carriers and amphibious ships, where it is used to direct targets for air defense systems such as the Sea Sparrow and RIM-116 SAM missiles. Existing sets are being modernized under the ROAR program to AN/SPS-48G standard for better reliability and usability.
The AN/SPS-49 is a United States Navy two-dimensional, long range air search radar built by Raytheon that can provide contact bearing and range. It is a primary air-search radar for numerous ships in the U.S. fleet and in Spain, Poland, Taiwan aboard Oliver Hazard Perry-class frigates, Canada on its Halifax-class frigate and New Zealand on its Anzac-class frigates. It formerly served in a complementary role aboard Aegis cruisers with the AN/SPY-1 but the systems are currently being removed during routine upgrade with no replacement.
AN/SPQ-9A,, is a United States Navy multi-purpose surface search and fire control radar used with the Mk-86 gun fire-control system. It is a two dimensional surface-search radar, meaning it provides only range and bearing but not elevation. It is intended primarily to detect and track targets at sea level, on the surface of the water for either gun fire engagement or navigation. It can however, also detect and track low altitude air targets.
The AN/SPS-67 is a short-range, two-dimensional, surface-search/navigation radar system that provides highly accurate surface and limited low-flyer detection and tracking capabilities.
Radar engineering details are technical details pertaining to the components of a radar and their ability to detect the return energy from moving scatterers — determining an object's position or obstruction in the environment. This includes field of view in terms of solid angle and maximum unambiguous range and velocity, as well as angular, range and velocity resolution. Radar sensors are classified by application, architecture, radar mode, platform, and propagation window.
The AN/SPS-40 is a United States Navy two-dimensional, long range air search radar that is capable of providing contact bearing and range. It was used on Perth-class destroyers, Forrest Sherman-class destroyers, Charles F. Adams-class destroyers, Spruance-class destroyers, Belknap-class cruisers, Leahy-class cruisers, Knox-class frigates, Bronstein-class frigates, Hamilton-class cutters, Raleigh-class amphibious transport docks and many other ship classes. Its "basket" antenna with the over-the-top feed line was a familiar sight throughout the Navy even into the late 1980s. It was replaced by the AN/SPS-49 on newer ships and on ships that received the New Threat Upgrade.
The AN/SPS-43 was a long-range air-search United States Navy radar system introduced in March 1961 that had a range of 500+ km. This radar could provide bearing and distance information, but no altitude information. The small-ship antenna (AN/SPS-29) looked like a bedspring. Larger ships used the 12.8 m wide AN/SPS-37 antenna - about twice as wide and half the height of the SPS-29 antenna - and designed with a much narrower beam. Targets were much more accurately displayed when using the -37 antenna. The -43 operated at VHF frequency - somewhat unusual for any radar - mostly in the bandwidth of television channel 13. The main difference to the SPS-37 was the greatly improved ECCM performance, as the AN/SPS-43 could jump between 20 different frequencies to frustrate jamming attempts. A sea-skimming missile could be detected at a range distance of 30 km, a large high-flying aircraft at 500 km.
The AN/SPY-1 is a United States Navy 3D radar system manufactured by Lockheed Martin. The array is a passive electronically scanned system and a key component of the Aegis Combat System. The system is computer controlled and uses four complementary antennas to provide 360-degree coverage. The system was first installed in 1973 on USS Norton Sound and entered active service in 1983 as the SPY-1A on USS Ticonderoga. The -1A was installed on ships up to CG-58, with the -1B upgrade first installed on USS Princeton in 1986. The upgraded -1B(V) was retrofitted to existing ships from CG-59 up to the last, USS Port Royal.
An antenna array is a set of multiple connected antennas which work together as a single antenna, to transmit or receive radio waves. The individual antennas are usually connected to a single receiver or transmitter by feedlines that feed the power to the elements in a specific phase relationship. The radio waves radiated by each individual antenna combine and superpose, adding together to enhance the power radiated in desired directions, and cancelling to reduce the power radiated in other directions. Similarly, when used for receiving, the separate radio frequency currents from the individual antennas combine in the receiver with the correct phase relationship to enhance signals received from the desired directions and cancel signals from undesired directions. More sophisticated array antennas may have multiple transmitter or receiver modules, each connected to a separate antenna element or group of elements.
AN/SPS-6 is a two-dimensional radar manufactured by Bendix and Westinghouse Electric. It was used by the US Navy as a first-generation air-search radar after World War II, and was widely exported to allies. In addition, the improved AN/SPS-12 is the derivative types developed in other countries.
AN/SPS-10 is a two-dimensional radar manufactured by Raytheon Technologies. It was used by the US Navy as a surface-search radar after World War II, and was equipped aboard naval ships during the Cold War. Variants include AN/SPS-10B, AN-SPS/10E and AN/SPS-10F.
AN/SPS-8 is a two-dimensional radar manufactured by General Electric. It was used by the US Navy as a height finding radar after World War II, and was equipped aboard naval ships during the Cold War. Variants include AN/SPS-8A, AN-SPS/8B, AN/SPS-8C and AN/SPS-8D After modernization, it was redesignated as AN/SPS-30.
AN/SPS-39 is a three-dimensional radar was manufactured by Hughes Aircraft Company. It was used by the US Navy as a parabolic-cylinder reflector antenna after World War II, and was equipped aboard naval ships during the Cold War. It was mass-produced based on AN/SPS-26, and was also the first 3D radar deployed by the US Navy in the fleet. It later evolved into an improved AN/SPS-52.
