A fire-control radar (FCR) is a

radar Radar is a system that uses radio waves to determine the distance ('' ranging''), direction ( azimuth and elevation angles), and radial velocity of objects relative to the site. It is a radiodetermination method used to detect and track ...

that is designed specifically to provide information (mainly target

azimuth An azimuth (; from ) is the horizontal angle from a cardinal direction, most commonly north, in a local or observer-centric spherical coordinate system. Mathematically, the relative position vector from an observer ( origin) to a point ...

elevation The elevation of a geographic location (geography), ''location'' is its height above or below a fixed reference point, most commonly a reference geoid, a mathematical model of the Earth's sea level as an equipotential gravitational equipotenti ...

range Range may refer to: Geography * Range (geographic), a chain of hills or mountains; a somewhat linear, complex mountainous or hilly area (cordillera, sierra) ** Mountain range, a group of mountains bordered by lowlands * Range, a term used to i ...

and

range rate The radial velocity or line-of-sight velocity of a target with respect to an observer is the rate of change of the vector displacement between the two points. It is formulated as the vector projection of the target-observer relative velocity on ...

) to a

fire-control system A fire-control system (FCS) is a number of components working together, usually a gun data computer, a director and radar, which is designed to assist a ranged weapon system to target, track, and hit a target. It performs the same task as a hum ...

in order to direct weapons such that they hit a target. They are sometimes known as narrow beam radars, targeting radars, tracking radars, or in the UK, gun-laying radars. If the radar is used to guide a missile, it is often known as a target illuminator or illuminator radar. A typical fire-control radar emits a narrow, intense beam of

radio wave Radio waves (formerly called Hertzian waves) are a type of electromagnetic radiation with the lowest frequencies and the longest wavelengths in the electromagnetic spectrum, typically with frequencies below 300 gigahertz (GHz) and wavelengths g ...

s to ensure accurate tracking information and to minimize the chance of losing track of the target. This makes them less suitable for initial detection of the target, and FCRs are often partnered with a medium-range

search radar 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 radio waves are usually less than a ...

to fill this role. In British terminology, these medium-range systems were known as

tactical control radar Tactical Control is a term originating in the British Army to refer to a class of medium-range radar systems. They are generally used for controlling the airspace around a set location on the ground, sometimes a dispersed battery of anti-aircraft a ...

s. Most modern radars have a

track-while-scan Track-while-scan (TWS) is a mode of radar operation in which the radar allocates part of its power to tracking a target or targets (up to forty with modern radar) while part of its power is allocated to scanning. It is similar to but functions diff ...

capability, enabling them to function simultaneously as both fire-control radar and search radar. This works either by having the radar switch between sweeping the search sector and sending directed pulses at the target to be tracked, or by using a

phased-array 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 th ...

antenna to generate multiple simultaneous radar beams that both search and track.

Operational phases

Fire-control radars operate in three different phases: ;Designation or vectoring phase: The fire-control radar must be directed to the general location of the target due to the radar's narrow beam width. This phase is also called "lighting up". It ends when lock-on is acquired. ;Acquisition phase: The fire-control radar switches to the acquisition phase of operation once the radar is in the general vicinity of the target. During this phase, the radar system searches in the designated area in a predetermined search pattern until the target is located or redesignated. This phase terminates when a weapon is launched. ;Tracking phase: The fire-control radar enters into the track phase when the target is located. The radar system locks onto the target during this phase. This phase ends when the target is destroyed.

Performance

The performance of a fire-control radar is determined primarily by two factors: radar resolution and atmospheric conditions. Radar resolution is the ability of the radar to differentiate between two targets closely located. The first, and most difficult, is range resolution, finding exactly how far is the target. To do this well, in a basic fire-control radar system, it must send very short pulses. Bearing resolution is typically ensured by using a narrow (one or two degree) beam width. Atmospheric conditions, such as moisture lapse,

temperature inversion In meteorology, an inversion (or temperature inversion) is a phenomenon in which a layer of warmer air overlies cooler air. Normally, air temperature gradually decreases as altitude increases, but this relationship is reversed in an inver ...

, and dust particles affect radar performance as well. Moisture lapse and temperature inversion often cause ducting, in which RF energy is bent as it passes through hot and cold layers. This can either extend or shorten the

radar horizon The radar horizon is a critical area of performance for air traffic, aircraft detection systems, defined by the distance at which the radar beam rises enough above the Earth's surface to make detection of a target at the lowest level possible. I ...

, depending on which way the RF is bent. Dust particles, as well as water droplets, cause attenuation of the RF energy, resulting in a loss of effective range. In both cases, a lower

pulse repetition frequency The pulse-repetition frequency (PRF) is the number of pulses of a repeating signal in a specific time unit. The term is used within a number of technical disciplines, notably radar. In radar, a radio signal of a particular carrier frequency is tu ...

makes the radar less susceptible to atmospheric conditions.

Countermeasures

Most fire-control radars have unique characteristics, such as radio frequency, pulse duration, pulse frequency and power. These can assist in identifying the radar, and therefore the weapon system it is controlling. This can provide valuable tactical information, like the maximum range of the weapon, or flaws that can be exploited, to combatants that are listening for these signs. During the

Cold War The Cold War was a period of global Geopolitics, geopolitical rivalry between the United States (US) and the Soviet Union (USSR) and their respective allies, the capitalist Western Bloc and communist Eastern Bloc, which lasted from 1947 unt ...

Soviet fire control radars were often named and

NATO The North Atlantic Treaty Organization (NATO ; , OTAN), also called the North Atlantic Alliance, is an intergovernmental organization, intergovernmental Transnationalism, transnational military alliance of 32 Member states of NATO, member s ...

pilots would be able to identify the threats present by the radar signals they received.

Surface based

One of the first successful fire-control radars, the

SCR-584 The SCR-584 (short for '' Set, Complete, Radio # 584'') was an automatic-tracking microwave radar developed by the MIT Radiation Laboratory during World War II. It was one of the most advanced ground-based radars of its era, and became one of the ...

, was used effectively and extensively by the Allies during

World War II World War II or the Second World War (1 September 1939 – 2 September 1945) was a World war, global conflict between two coalitions: the Allies of World War II, Allies and the Axis powers. World War II by country, Nearly all of the wo ...

for anti-aircraft gun laying. Since World War II, the U.S. Army has used radar for directing anti-aircraft missiles including the

MIM-23 Hawk The Raytheon MIM-23 HAWK ("Homing All the Way Killer") is an American medium-range surface-to-air missile. It was designed to be a much more mobile counterpart to the MIM-14 Nike Hercules, trading off range and altitude capability for a much sm ...

, the

Nike Nike often refers to: * Nike, Inc., a major American producer of athletic shoes, apparel, and sports equipment * Nike (mythology), a Greek goddess who personifies victory Nike may also refer to: People * Nike (name), a surname and feminine giv ...

series and currently the

MIM-104 Patriot The MIM-104 Patriot is a mobile interceptor missile surface-to-air missile (SAM) system, the primary such system used by the United States Army and several allied states. It is manufactured by the U.S. defense contractor Raytheon and derives it ...

Ship based

Examples of fire-control radars currently in use by the

United States Navy The United States Navy (USN) is the naval warfare, maritime military branch, service branch of the United States Department of Defense. It is the world's most powerful navy with the largest Displacement (ship), displacement, at 4.5 millio ...

: *Mk 95 — Continuous Wave Illuminator (NATO Sea sparrow Surface Missile System) *Mk 92 — Combined Antenna System (Mk 75 Gun, formerly SM-1 missiles) *

AN/SPG-62 The AN/SPG-62 is a continuous wave fire-control radar developed by the United States, and it is currently deployed on warships equipped with the Aegis Combat System. It provides terminal target illumination for the semi-active SM-2MR/ ER and ...

— Continuous Wave Illuminator (

AEGIS The aegis ( ; ''aigís''), as stated in the ''Iliad'', is a device carried by Athena and Zeus, variously interpreted as an animal skin or a shield and sometimes featuring the head of a Gorgon. There may be a connection with a deity named Aex, a ...

) *

AN/SPQ-9 AN/SPQ-9A (sometimes pronounced as "spook nine") is a United States Navy multi-purpose surface search and fire control radar used with the Mk-86 gun fire-control system (MK86 GFCS). It is a two dimensional surface-search radar, meaning it provide ...

B — Pulse Doppler ( Mk 45 lightweight gun)

Aircraft based

After World War II, airborne fire control radars have evolved from the simpler gun and rocket laying AN/APG-36 system used in the F-86D to the

active electronically scanned array An active electronically scanned array (AESA) is a type of phased array antenna, which is a computer-controlled antenna array in which the beam of radio waves can be electronically steered to point in different directions without moving the a ...

-based AN/APG-81 of the

F-35 Lightning II The Lockheed Martin F-35 Lightning II is an American family of single-seat, single-engine, supersonic Stealth aircraft, stealth strike fighters. A multirole combat aircraft designed for both Air superiority fighter, air superiority and att ...

References

* US Navy, Fire Controlman, Volume 02—Fire Control Radar Fundamentals (Revised)

External links

AN/APG Fire Control Systems at GlobalSecurity.org
{{Military and war Military radars