This is a list of different types of radar. Detection and search radars Search radars scan great volumes of space with pulses of short radio waves. They typically scan the volume two to four times a minute. The waves are usually less than a meter long. Ships and planes are metal, and reflect radio waves. The radar measures the distance to the reflector by measuring the time of the roundtrip from emission of a pulse to reception, dividing this by two, and then multiplying by the speed of light. To be accepted, the received pulse has to lie within a period of time called the range gate. The radar determines the direction because the short radio waves behave like a search light when emitted from the reflector of the radar set's antenna. Search Early Warning (EW) Radar Radar Systems Ground Control Intercept (GCI) Radar Airborne Early Warning (AEW) Airborne ground surveillance (AGS) Over-the-Horizon (OTH) Radar Target Acquisition (TA, TAR) Radar Systems Surface-to-Air Missile (SAM) Systems Anti-Aircraft Artillery (AAA) Systems Surface Search (SS) Radar Systems Surface Search Radar Coastal Surveillance Radar Harbour Surveillance Radar Antisubmarine Warfare (ASW) Radar Height Finder (HF) Radar Systems Gap Filler Radar Systems Targeting radars Targeting radars utilize the same principle but scan smaller volumes of space far more often, usually several times a second or more, while a search radar will scan a larger volume less frequently. Missile lock-on describes the scenario where a targeting radar has acquired a target, and the fire control can calculate a path for the missile to the target; in semi-active radar homing systems, this implies that the missile can "see" the target that the targeting radar is "illuminating". Some targeting radars have a range gate that can track a target, to eliminate clutter and electronic countermeasures. Missile guidance systems Air-to-Air Missile (AAM) Air-to-Surface Missile (ASM) Surface-to-air missile (SAM) Systems Surface-to-Surface Missiles (SSM) Systems Others Target Tracking (TT) Systems AAA Systems Multi-Function Systems Fire Control (FC) Systems Acquisition Mode Semiautomatic Tracking Mode Manual Tracking Mode Airborne Intercept (AI) Radars Search Mode TA Mode TT Mode Target Illumination (TI) Mode Missile Guidance (MG) Mode Active electronically scanned array (AESA) Battlefield and reconnaissance radar Battlefield Surveillance Systems Counter-battery radar Battlefield Surveillance Radars Tactical Radar Identification and Location System Countermortar/Counterbattery Systems Shell Tracking Radars Air Mapping Systems Side looking airborne radar (SLAR) Synthetic Aperture Radar (SAR) Perimeter Surveillance Radar (PSR) Red Dawn Radar System