CHAPTER 1
1-2 REFLECTING TARGET TRUE NORTH TRUE BEARING ENERGY PULSES RANGE LOS VERTICAL PLANE ELEVATION ANGLE HORIZONTAL PLANE FCRf0101 Figure 1-1.—Radar surface angular measurements. Term Definition Energy pulses The pulses that are sent out by the radar and are received back from the target. Reflecting target The air or surface contact that provides an echo. True north The direction of the north geographical pole. True bearing/azimuth The angle measured clockwise from true north in the horizontal plane. Line-of-sight range The length of the line from the radar set directly to the object. Vertical plane All angles in the up direction, measured in a secondary imaginary plane. Elevation angle The angle between the horizontal plane and the line of sight. Horizontal plane The surface of the Earth, represented by an imaginary flat plane which is tangent (or parallel) to the Earth’s surface at that location. Table 1-1.—Radar Reference Coordinate Terms
RADAR MEASUREMENTS We stated earlier that radar is used to determine the distance and direction to and the height of distant objects. These three pieces of information are known, respectively, by the standard terms range, bearing, and altitude. The use of these standard terms allows anyone interested in a specific target to establish its position quickly and accurately. Radar operators determine a target’s range, bearing, and altitude by interpreting its position displayed on a specially designed cathode-ray tube (CRT) installed in a unit known as a plan position indicator (PPI). While most radars are used to detect targets, some types are used to guide missiles to targets and to direct the firing of gun systems; other types provide long-distance surveillance and navigation information. Range and bearing (and in the case of aircraft, altitude) are necessary to determine target movement. To be a successful radar operator, you must understand the capabilities and limitations of your radar system in determining range, bearing, and altitude. Range The radar measurement of range (or distance) is possible due to the properties of radiated electromagnetic energy. This energy normally travels through space in a straight line, at a constant speed, and varies only slightly due to atmospheric and weather conditions. The frequency of the radiated energy causes the radar system to have both a minimum effective range and a maximum effective range. MINIMUM RANGE .—Radar duplexers alternately switch the antenna between the transmitter and the receiver so that one antenna can be used for both functions. The timing of this switching is critical to the operation of the radar and directly affects the minimum range of the radar system. A reflected pulse will not be received during the transmit pulse and subsequent receiver recovery time. The minimum range of a radar, therefore, is the minimum distance between the radar’s antenna and a target at which a radar pulse can be transmitted, reflected from the target, and received by the radar receiver. If the antenna is closer to the target than the radar’s minimum range, any pulse reflected from the target will return before the receiver is connected to the antenna and will not be detected. MAXIMUM RANGE.—The maximum range of a pulse-radar system depends on carrier frequency; peak power of the transmitted pulse; pulse-repetition frequency (PRF) or pulse-repetition rate (PRR) (PRF and PRR are synonymous terms); and receiver sensitivity, with PRF/PRR as the primary limiting factor. The peak power of a pulse determines how far the pulse can travel to a target and still return a usable echo. A usable echo is the weakest signal that a receiver can detect, process, and present on a display. The PRR determines the rate at which the range indicator is reset to zero. As the leading edge of each pulse is transmitted, the indicator time base used to measure the returned echo is reset, and a new sweep appears on the screen. RANGE ACCURACY.—The shape and width of the radio-frequency (RF) pulse influences minimum range, range accuracy, and maximum range. The ideal pulse shape is a square wave that has vertical leading and trailing edges. The vertical edge provides a definite point from which to measure elapsed time on the indicator time base. A sloping trailing edge lengthens the pulsewidth. A sloping leading edge provides no definite point from which to measure elapsed time on the indicator time base. Other factors affecting range are the antenna’s height, beamwidth, and rotation rate. A higher antenna will create a longer radar horizon, allowing a greater range of detection. An antenna with a narrow beamwidth, provides a greater range capability, since it provides more concentrated beam with a higher energy density per unit area. A slower antenna rotation rate, providing more transmitted pulses during the sweep, allows the energy beam to strike each target more times, providing stronger echo returns and a greater detection range. From the range information, the operator knows the distance to an object. He now needs bearing information to determine where the target is in reference to the ship. Bearing Radar bearing is determined by the echo’s signal strength as the radiated energy lobe moves past the target. Since search radar antennas move continuously, the point of maximum echo return is determined either by the detection circuitry as the beam passes the target or visually by the operator. Weapons control and guidance radar antennas are positioned to the point of maximum signal return and 1-3
are maintained at that position either manually or by automatic tracking circuits. You need to be familiar with two types of bearing: true and relative. TRUE BEARING .—True bearing is the angle between true north and a line pointed directly at the target. This angle is measured in the horizontal plane and in a clockwise direction from true north. RELATIVE BEARING.—Relative bearing is the angle between the centerline of the ship and a line pointed directly at the target. This angle is measured in a clockwise direction from the bow. Most surface-search radars provide only range and bearing information. Both true and relative bearing angles are illustrated in figure 1-2. Altitude Altitude or height-finding radars use a very narrow beam in the vertical plane. This beam is scanned in elevation, either mechanically or electronically, to pinpoint targets. Tracking and weapons-control radar systems in current use scan the beam by moving the antenna mechanically or the radiation source electronically. Most air-search radars use electronic elevation scanning techniques. Some older air-search radar systems use a mechanical elevation scanning device; but these are being replaced by electronic scanning radar systems. RADAR TRANSMISSION METHODS Radar systems are normally divided into two operational categories (purposes) based on their method of transmitting energy. The most common method, used for applications from navigation to fire control, is the pulse-modulation method. The other method of transmitting is continuous-wave (CW). CW radars are used almost exclusively for missile guidance. Pulse Modulation In the pulse method, the radar transmits the RF in a short, powerful pulse and then stops and waits for the return echo. By measuring the elapsed time between the end of the transmitted pulse and the received echo, the radar can calculate a range. Pulse radars use one antenna for both transmitting and receiving. While the transmitter is sending out its high-power RF pulse, the antenna is connected to the transmitter through a special switch called a duplexer. As soon as the transmitted pulse stops, the duplexer switches the antenna to the receiver. The time interval between transmission and reception is computed and converted into a visual indication of range in miles or yards. Pulse-radar systems can also be modified to use the Doppler effect to detect a moving object. The Navy uses pulse radars to a great extent. Continuous Wave In a CW radar the transmitter sends out a “continuous wave” of RF energy. Since this beam of RF energy is “always on,” the receiver requires a separate antenna. One disadvantage of this method is that an accurate range measurement is impossible because there is no specific “stop time.” This can be overcome, however, by modulating the frequency. A frequency-modulated continuous wave (FM-CW) radar can detect range by measuring the difference between the transmitted frequency and the received frequency. This is known as the “Doppler effect.” The continuous-wave method is usually used by fire-control systems to illuminate targets for missile systems. RADAR SYSTEM ACCURACY To be effective, a radar system must provide accurate indications. That is, it must be able to determine and present the correct range, bearing, and, in some cases, altitude of an object. The degree of accuracy is primarily determined by two factors: the resolution of the radar system and existing atmospheric conditions. 1-4 TRUE BEARING 90 DEGREES RELATIVE BEARING 45 DEGREES SHIP CENTER LINE TRUE NORTH OWN SHIP TARGET FCRf0102 Figure 1-2.—True and relative bearings.
Range Resolution Range resolution is the ability of a radar to distinguish between two targets on the same bearing, but at slightly different ranges. The degree of range resolution depends on the width of the transmitted pulse, the types and sizes of the targets, and the efficiency of the receiver and the indicator. Bearing Resolution Bearing, or azimuth, resolution is the ability of a radar system to separate objects at the same range, but at slightly different bearings. The degree of bearing resolution depends on the radar’s beamwidth and the range of the targets. The physical size and shape of the antenna determines beamwidth. Two targets at the same range must be separated by at least one beamwidth to be distinguished as two objects. Atmospheric Conditions Several conditions within the atmosphere can have an adverse effect on radar performance. A few of these are temperature inversion, moisture lapse, water droplets, and dust particles. The temperature and moisture content of the atmosphere normally decrease uniformly with an increase in altitude. However, under certain conditions the temperature may first increase with height and then begin to decrease. Such a situation is called a temperature inversion. An even more important deviation from normal may exist over the ocean. Since the atmosphere close to the surface over large bodies of water may contain more than a normal amount of moisture, the moisture content may decrease more rapidly at heights just above the sea. This effect is referred to as moisture lapse. Either temperature inversion or moisture lapse, alone or in combination, can cause a large change in the refraction index of the lowest few-hundred feet of the atmosphere. The result is a greater bending of the radar waves passing through the abnormal condition. This increase in bending, referred to asducting, may greatly affect radar performance. The radar horizon may be extended or reduced, depending on the direction in which the radar waves are bent. The effect of ducting is illustrated in figure 1-3. Water droplets and dust particles diffuse radar energy through absorption, reflection, and scattering. This leaves less energy to strike the target, so the return echo is smaller. The overall effect is a reduction in usable range. Usable range varies widely with such weather conditions. The higher the frequency of the radar system, the more it is affected by weather conditions, such as rain or clouds. Other Factors Some other factors that affect radar performance are operator skill; size, composition, angle, and altitude of the target; possible Electronic Attack (EA) activity; readiness of equipment (completed planned maintenance system requirements); and weather conditions. BASIC RADAR SYSTEMS Radar systems, like other complex electronics systems, are composed of several major subsystems and many individual circuits. Although modern radar systems are quite complicated, you can easily understand their operation by using a basic block diagram of a pulse-radar system. FUNDAMENTAL (PULSE) RADAR SYSTEM Since most radars used today are some variation of the pulse-radar system, this section discusses components used in a pulse radar. All other types of radars use some variation of these units. Refer to the block diagram in figure 1-4. Synchronizer The heart of the radar system is thesynchronizer.I t generates all the necessary timing pulses (triggers) that start the transmitter, indicator sweep circuits, and ranging circuits. The synchronizer may be classified as either self-synchronized or externally synchro- nized. In a self-synchronized system, pulses are generated within the transmitter. Externally synchronized system pulses are generated by some 1-5 NORMAL RANGE ACTUAL RANGEWARM AIR COLD AIR SURFACE DUCT NO DUCT ACTION FCRf0103 Figure 1-3.—Ducting effect on the radar wave.
type of master oscillator external to the transmitter, such as a modulator or a thyratron. Transmitter The transmitter generates powerful pulses of electromagnetic energy at precise intervals. It creates the power required for each pulse by using a high-power microwave oscillator (such as a mag- netron) or a microwave amplifier (such as a klystron) supplied by a low power RF source. For further information on the construction and operation of microwave components, review NEETS Module 11, Microwave Principles , NA VEDTRA 14183. Duplexer The duplexer is basically an electronic switch that permits a radar system to use a single antenna to transmit and receive. The duplexer disconnects the antenna from the receiver and connects it to the transmitter for the duration of the transmitted pulse. The switching time is called receiver recovery time , and must be very fast if close-in targets are to be detected. Receiver The receiver accepts the weak RF echoes from the antenna system and routes amplified pulses to the display as discernible video signals. Because the radar frequencies are very high and difficult to amplify, a superheterodyne receiver is used to convert the echoes to a lower frequency, called theintermediate frequency (IF), which is easier to amplify. Displays Most of the radars that FCs operate and maintain have a display, or multiple displays, to provide the operator with information about the area the radar is searching or the target, or targets, being tracked. The usual display is a cathode-ray tube (CRT) that provides a combination of range, bearing (azimuth), and (in some cases) elevation data. Some displays provide raw data in the form of the signal from the radar receiver, while others provide processed information in the form of symbology and alphanumerics. Figure 1-5 shows four basic types of displays. There are other variations, but these are the major types encountered in fire control and 3-D search radars. TYPE A .—The type A sweep, or range sweep, display shows targets as pulses, with the distance from the left side of the trace representing range. Variations in target amplitude cause corresponding changes in the displayed pulse amplitude. The display may be bipolar video when used with Moving Target Indicator (MTI) or pulse Doppler radars. TYPE B.—The type B sweep, or bearing sweep, is mostly found with gunfire control radars and is used with surface gunfire to spot the fall of shot. The range may be full range or an interval either side of the range gate. TYPE E.—Two variations of type E are shown. Both provide range and elevation (or height) of a target. These are associated with height-finding radars and are generally used to determine the height or elevation angle only. Range is determined from processing or a type P display. TYPE P.—This display is commonly called a PPI (plan position indicator). Own ship is usually the center. Range is measured radially from the center. The range display can be selected, and the radar source is usually selectable. The PPI can display raw video or symbology and alphanumerics, or both. The type P display is most commonly found in the Combat Information Center (CIC) and in weapons control stations. 1-6 DUPLEXERDUPLEXER RECEIVER SYNCHRONIZER TRANSMITTER DISPLAY TRANSMITTED PULSE ECHO RETURN ANTENNA SUPPORT SYSTEMS COOLING AIR POWER CONTROL GROUP FCRf0104 Figure 1-4.—Basic radar block diagram.
Additional information on how individual displays are produced is available in NEETS modules 6, 9, and 18. Antenna System The antenna system routes the pulse from the transmitter, radiates it in a directional beam, picks up the returning echo, and passes it to the receiver with a minimum of loss. The antenna system includes the antenna; transmission lines and waveguide from the transmitter to the antenna; and transmission lines and waveguide from the antenna to the receiver. Before we discuss some types of antennas used in fire control, we need to review the basic principles of electromagnetic wave radiation and reflectors. The radar energy that forms the target-tracking and illumination beams is transmitted by an antenna at the control point. Radiated energy tends to spread out equally in all directions, as shown in figure 1-6. Figure 1-6 compares the radiation from a radio antenna with that from a lamp. Both light waves and radio waves are electromagnetic radiation; the two are believed to be identical, except in frequency of vibration. From both sources, energy spreads out in spherical waves. Unless they meet some obstruction, these waves will travel outward indefinitely at the speed of light. The energy at any given point decreases with range since the wave, and therefore the energy, is spreading out to cover a larger area. Because of its much higher frequency, light has a much shorter wavelength than a 1-7 TYPE A RANGE SIGNALINTENSITY TYPE B AZIMUTH (BEARING) RANGE TYPE E RANGE ELEVATION ANGLE RANGE (RANGE-HEIGHT INDICATION) ELEVATION RANGE (MEASURED RADIALLY FROM CENTER) TYPE P (PPI) AZI M UTH FCRf0105 Figure 1-5.—Types of radar displays.
radio wave. This is suggested in figure 1-6 but it cannot be shown accurately to scale. The wavelength of a radar transmission may be measured in centimeters, whereas the wavelength of light varies from about three to seven ten-thousandths of a millimeter. We mentioned earlier that radio wave energy must be concentrated to be useful. We can concentrate this energy by mounting a suitable reflector behind the antenna, to form a large part of the radiated energy into a relatively narrow beam. The following paragraphs discuss the more commonly used reflectors. PARABOLIC REFLECTORS.—You should be familiar with the use of polished reflectors to form beams of light. An automobile headlight uses a parabolic reflector to produce a fairly wide beam. A spotlight uses a slightly differently shaped parabolic reflector to produce a more narrow beam. A type of reflector generally used in missile fire- control radars is the parabolic dish . It is similar in appearance to the reflector used in an automobile headlight. Since radar operates in the microwave region of the electromagnetic spectrum, its waves have properties and characteristics similar to those of light. This permits radar antennas to be designed using well-known optical design techniques. A basic principle of optics is that a light ray striking a reflecting surface at a given angle will reflect from that surface at the same angle. Now refer to figure 1-7. Think of the circular wavefronts generated by source F as consisting of an infinite number of rays. The antenna’s parabolic reflecting surface is designed, using the reflection principle, so that as the circular wavefronts strike the reflector, they are reflected as straight wavefronts. This action concentrates them into a narrow circular beam of energy. HORN RADIATORS.— Horn radiators (fig. 1-8), like parabolic reflectors, may be used to create concentrated electromagnetic waves. Horn radiators are readily adaptable for use with waveguides because they serve both as an impedance-matching device and as a directional radiator. Horn radiators may be fed by coaxial or other types of lines. Horns are constructed in a variety of shapes, as illustrated in figure 1-8. The shape of the horn, along with the dimensions of the length and mouth, largely determines the beam’s shape. The ratio of the horn’s 1-8 LIGHT WAVES LAMP RADIO WAVES ANTENNA LIGHT RADIO FCRf0106 Figure 1-6.—Radiation waves from a radio antenna and a lamp. WAVEFRONTS OF DIRECTLY RADIATED WAVE WAVEFRONTS AFTER REFLECTION F FCRf0107 Figure 1-7.—Principles of the parabolic reflector. RECTANGULAR PYRAMIDAL CONICAL FCRf0108 Figure 1-8.—Horn radiators.
length to mouth opening size determines the beamwidth and thus the directivity. In general, the larger the opening of the horn, the more directive is the resulting field pattern. FEEDHORNS.—A waveguide horn may be used to feed into a parabolic dish. The directivity of this horn, or feedhorn, is then added to that of the parabolic dish. The resulting pattern (fig. 1-9, view A) is a very narrow and concentrated beam. Such an arrangement is ideally suited for fire control use. In most radars, the feedhorn is covered with a window of polystyrene fiberglass to prevent moisture and dirt from entering the open end of the waveguide. One problem associated with feedhorns is the shadow introduced by the feedhorn if it is in the path of the beam. (The shadow is a dead spot directly in front of the feedhorn.) To solve this problem the feedhorn can be offset from center (fig. 1-9, view B). This takes it out of the path of the RF beam, thus eliminating the shadow. LENS ANTENNA .—Another antenna that can change spherical waves into flat plane waves is the lens antenna. This antenna uses a microwave lens, which is similar to an optical lens to straighten the spherical wavefronts. Since this type of antenna uses a lens to straighten the wavefronts, its design is based on the laws of refraction, rather than reflection. Two types of lenses have been developed to provide a plane-wavefront narrow beam for tracking radars, while avoiding the problems associated with the feedhorn shadow. These are the conducting (acceleration) type and the dielectric (delay) type. The lens of an antenna is substantially transparent to microwave energy that passes through it. It will, however, cause the waves of energy to be either converged or diverged as they exit the lens. Consider the action of the two types of lenses. The conducting type of lens is illustrated in figure 1-10, view A. This type of lens consists of flat metal strips placed parallel to the electric field of the wave and spaced slightly in excess of one-half of a wavelength. To the wave these strips look like parallel waveguides. The velocity of phase propagation of a wave is greater in a waveguide than in air. Thus, since the lens is concave, the outer portions of the transmitted spherical waves are accelerated for a longer interval of time than the inner portion. The spherical waves emerge at the exit side of the conducting lens (lens aperture) as flat-fronted parallel waves. This type of lens is frequency sensitive. The dielectric type of lens, shown in figure 1-10, view B, slows down the phase propagation as the wave passes through it. This lens is convex and consists of dielectric material. Focusing action results from the difference between the velocity of propagation inside the dielectric and the velocity of propagation in the air. The result is an apparent bending, or refracting, of the waves. The amount of delay is determined by the dielectric constant of the material. In most cases, artificial dielectrics, consisting of conducting rods or spheres that are small compared to the wavelength, are used. In this case, the inner portions of the transmitted 1-9 PARABOLIC REFLECTOR FEEDHORN AXIS REFLECTED ENERGY TRAVELS PARALLEL TO AXIS A(A) REFLECTED ENERGY OFFSET FROM AXIS MECH AXIS (B) FCRf0109 Figure 1-9.—Reflector with feedhorn. FEEDHORN (A) FEEDHORN (B) FCRf10110 Figure 1-10.—Antenna lenses: A. Conducting (acceleration) type of microwave lens; B. Dielectric (delay) type of microwave lens.
waves are decelerated for a longer interval of time than the outer portions. In a lens antenna, the exit side of the lens can be regarded as an aperture across which there is a field distribution. This field acts as a source of radiation, just as do fields across the mouth of a reflector or horn. For a returning echo, the same process takes place in the lens. ARRAY ANTENNAS .—An array type of antenna is just what the name implies—an array or regular grouping of individual radiating elements. These elements may be dipoles, waveguide slots, or horns. The most common form of array is the planar array, which consists of elements linearly aligned in two dimensions—horizontal and vertical—to form a plane (fig. 1-11). Unlike the lens or parabolic reflector, the array applies the proper phase relationship to make the wavefront flat before it is radiated by the source feed. The relative phase between elements determines the position of the beam; hence the often used term, phased array. This phase relationship is what allows the beam to be rotated or steered without moving the antenna. This characteristic of array antennas makes it ideal for electronic scanning or tracking. (We will discuss scanning shortly.) Radomes The term radome is a combination of the words radar and dome. Radomes are used to cover and protect radar antennas from environmental effects such as wind, rain, hail, snow, ice, sand, salt spray, lightening, heat, and erosion. The ideal radome is transparent to the RF radiation from the antenna and its return pulses and protects the antenna from the environment. A radome’s design is based on the expected environmental factors and the mechanical and electronic requirements of the RF antenna. Although, in theory, a radome may be invisible to RF energy, in real life the radome effects the antenna’s performance in four ways. These are; beam deflection, transmission loss , reflected power , and secondary effects. Beam deflection is the shift of the RF beam’s axis. This is a major consideration with tracking (i.e., FC) radar. Transmission loss is the loss of energy associated with reflection and absorption within the radome. Reflected power can cause antenna mismatch in small radomes and sidelobes in large radomes. Depolarization and increased antenna noise are a result of secondary effects . As an FC, you will be primarily responsible for maintaining the radome associated with your equipment. This normally will include routine cleaning and inspection according to your prescribed preventive maintenance schedule. Some minor repairs may be authorized by your technical manuals, but most repairs will normally be done by an authorized factory representative. You may be required to repaint the radome because of normal environmental wear and tear. If so, be especially careful to use only paint(s) authorized by the manufacturer and to follow the authorized step-by-step procedures. Figure 1-12 is an example of a radome in use in today’s Navy. Other systems that use radomes include, the Combined Antenna System of the Mk 92 Fire Control System, the AN/SPQ-9 series antenna for the Mk 86 Gun Fire Control System, and the Mk 23 Target Acquisitioning System for the SEASPARROW missile system. Control Group The Control Group provides computer control for an equipment group, processes target detections to develop and maintain a track file, and interfaces with the specific weapon system being used. The Control Group normally consists of the following equipment: a computer, data terminal set, magnetic tape unit, and test set. Support Systems The equipment we discussed above composes the core of the radar system. To operate properly and efficiently, it requires a certain amount of support 1-10 HORIZONTAL LINEAR SUBARRAY TRANSMITTER AND RECEIVER SLOT ANTENNA FCRf0111 Figure 1-11.—Planar array antenna.
equipment. Examples of such equipment include power supplies (some also have frequency converters), chilled water systems, and dry air systems. Although your radar system normally receives 440 V AC directly from the ship’s primary power source, it has other voltage requirements that may be stepped up, stepped down, or converted in order to make the radar fully operational. High-voltage amplifiers and peripheral equipment associated with producing RF energy create tremendous amounts of heat. Chilled water systems remove excessive heat from such equipment. Cooling systems may be either liquid-to-liquid or liquid-to-air types that use either sea water, or chilled water provided by the ship itself. Another important support system is the dry air system. Dry air is used for keeping the internal part of the waveguide assembly moisture free and to aid in properly conducting the RF energy being transmitted. The dry air may be either air taken from ship spaces and circulated through various filters or dehydrated air provided by the ship. Some systems use a special gas for their waveguides. An example of this is the Mk 92 Fire Control System, which uses the gas SF6 for its Continuous Wave Illumination (CWI) mode. These are very important support systems to your radar. As you know, any system is only as good as its weakest link. Therefore, you must be sure to maintain the support equipment as required by the equipment’s technical manuals and maintenance instructions. Stable Elements Hitting a target on a regular basis requires that the gun or launcher be stable in relation to the target. Ideally, the platform on which the gun or launcher is mounted is stable throughout the target acquisition and destruction cycle. Unfortunately Navy ships, on which the guns and launchers are mounted, are seldom stable. In even the calmest sea, they pitch and roll to some extent. The solution lies in stabilizing the guns and launchers while the ship continues to pitch and roll. This is done with gyroscopes (gyros) installed in the fire control systems. Gyros provide a stable platform, called the horizontal plane , as an unvarying reference from which the fire control problem is computed. The basic fundamentals and functions of gyros are covered in NEETS Module 15 —Principles of Synchros, Servos, and Gyros, NA VEDTRA 14187. In fire control, we call the stabilizing unit a stable element. As its name implies, the stable element uses a stabilizing gyro. The stabilizing gyro is also the primary reference for navigation of the ship. It gives the ship a true North reference for all navigational equipment. The WSN-2 or WSN-5 are examples of stabilizing gyros used in today’s ships. The maintenance and operation of these gyros is the responsibility of the Interior Communications (IC) technicians. Figure 1-13 shows a phantom view of a gyro you might see on your ship. The primary purpose of the stable element for fire control equipment is to measure accurately any deviation of the reference element (antenna, director, launcher, etc.) from the horizontal plane. Deviation measurements are sent to the fire control computer to create a stationary foundation from which to solve the fire control problem. They are also sent to the gun director, radar antenna, or optical equipment, depending upon the fire control system, to stabilize these units of the fire control system. 1-11 3A1A1 SEARCH RADAR RADOME ASSEMBLY 3A1A2 SEARCH RADAR ANTENNA ASSEMBLY 3A1A7 TRACK ANTENNA FORWARD 3A1A13 TRACK RADAR RADOME CABLING DETAILS OMITTED FOR CLARITY N OTE: LEFT SIDE CUTAWAY VIEW FCRf0112 Figure 1-12.—Example of a search and track radome.
TYPES OF RADAR SYSTEMS Because of different design parameters, no single radar set can perform all the many radar functions required for military use. The large number of radar systems used by the military has forced the development of a joint-services classification system for accurate identification of radars. Radar systems are usually classified according to their specific function and installation vehicle. The joint-service standardized classification system divides these broad categories for more precise identification. Since no single radar system can fulfill all the requirements of modern warfare, most modern warships, aircraft, and shore installations have several radar sets, each performing a specific function. A shipboard radar installation may include surface-search and navigation radars, a 3D radar, an air-search radar, and various fire-control radars. Figure 1-14 is a listing of equipment identification indicators. You can use this table and the radar nomenclature to identify the parameters of a particular radar set. The example given explains the equipment indicators for the AN/SPY-1A radar system. The letters AN were originally adopted by the Joint Army-Navy Nomenclature System, also known as the AN system, to easily classify all military electronic equipment. In 1985, Military Standard MIL-STD-196D changed the name of the Joint Army-Navy Nomenclature System to the “Joint Electronics Type Designation System (JETDS)”, but the letters AN are still used in identifying military electronics equipment. AIR-SEARCH RADAR The primary function of an air-search radar is to maintain a 360-degree surveillance from the surface to high altitudes and to detect and determine ranges and bearings of aircraft targets over relatively large areas. The following are some uses of an air-search radar: • Give early warning of approaching enemy aircraft and missiles, by providing the direction from which an attack could come. This allows time to bring antiaircraft defenses to the proper degree of readiness and to launch fighters if an air attack is imminent. • Observe constantly the movement of enemy aircraft. When it detects an enemy aircraft, guide combat air patrol (CAP) aircraft to a position suitable for an intercept. • Provide security against attacks at night and during times of poor visibility. • Provide information for aircraft control during operations that require a specific geographic track (such as an antisubmarine barrier or a search and rescue pattern). Together, surface- and air-search radars provide a good early-warning system. However, the ship must be able to determine altitude to effectively intercept any air target. This requires the use of another type of radar. MULTI-DIMENSIONAL RADAR The primary function of a multi-dimensional radar is to compute accurate ranges, bearings, and altitudes of targets detected by an air-search radar. This information is used to direct fighter aircraft during interception of air targets. The multi-dimensional radar is different from the air-search radar in that it has a higher transmitting frequency, higher output power, and a much narrower vertical beamwidth. In addition, it requires a stabilized antenna for altitude accuracy. The following are some applications of a multi-dimensional radar: • Obtain range, bearing, and altitude data on enemy aircraft and missiles to assist in the guidance of CAP aircraft. 1-12 FLOTATION TANK PICKUP COIL P1 P2 MAGNET MAG 1 TORSION WIRES NORTH PICKUP COIL P1 P2 MAGNET MAG 2 GIMBAL RING TORSION WIRES NOTE: FOR CLARITY, GIMBAL RING IS SHOWN SQUARE FCRf011 3 Figure 1-13.—Phantom view of a gyro.
• Provide precise range, bearing, and height information for fast and accurate initial positioning of fire-control tracking radars. • Detect low-flying aircraft. • Determine the range to distant landmasses. • Track aircraft over land. • Detect certain weather phenomena. • Track weather balloons. The modern warship has several radars. Each radar is designed to fulfill a particular need, but it may also be capable of performing other functions. For example, most multi-dimensional radars can be used as secondary air-search radars; in emergencies, fire-control radars have served as surface-search radars. A multi-dimensional air-search radar is shown in figure 1-15. MISSILE GUIDANCE RADAR The purpose of a guidance subsystem is to direct the missile to target intercept regardless of whether or not the target takes deliberate evasive action. The guidance function may be based on information 1-13 A -- AIRBORNE (INSTALLED AND OPERATED IN AIRCRAFT). B -- UNDERWATER MOBILE, SUB- MARINE. C -- AIR TRANSPORTABLE (IN- ACTIVATED, DO NOT USE). D -- PILOTLESS CARRIER. F -- FIXED. G -- GROUND, GENERAL GROUND USE (INCLUDES TWO OR MORE GROUND-TYPE IN- STALLATIONS). K -- AMPHIBIOUS. M -- GROUND, MOBILE (INSTALL- ED AS OPERATING UNIT IN A VEHICLE WHICH HAS NO FUNCTION OTHER THAN TRANSPORTING THE EQUIP- MENT). P -- PACK OR PORTABLE (ANI- MAL OR MAN). S -- WATER SURFACE CRAFT. T -- GROUND, TRANSPORTABLE. U -- GENERAL UTILITY (IN- CLUDES TWO OR MORE GEN- ERAL INSTALLATION CLASSES, AIRBORNE, SHIP- BOARD, AND GROUND). V -- GROUND, VEHICULAR (IN- STALLED IN VEHICLE DE- SIGNED FOR FUNCTIONS OTHER THAN CARRYING ELECTRONIC EQUIPMENT, ETC., SUCH AS TANKS). W -- WATER SURFACE AND UNDERWATER. A -- INVISIBLE LIGHT, HEAT RADIATION. B -- PIGEON. C -- CARRIER. D -- RADIAC. E -- NUPAC. F -- PHOTOGRAPHIC. G -- TELEGRAPH OR TELE- TYPE. I -- INTERPHONE AND PUBLIC ADDRESS. J -- ELECTROMECHANICAL OR INERTIAL WIRE COVERED. K -- TELEMETERING. L -- COUNTERMEASURES. M -- METEOROLOGICAL. N -- SOUND IN AIR. P -- RADAR. Q -- SONAR AND UNDERWATER SOUND. R -- RADIO. S -- SPECIAL TYPES, MAGNET- IC, ETC., OR COMBINA- TIONS OF TYPES. T -- TELEPHONE (WIRE). V -- VISUAL AND VISIBLE LIGHT. W -- ARMAMENT (PECULIAR TO ARMAMENT, NOT OTHER- WISE COVERED). X -- FACSIMILE OR TELEVISION. Y -- DATA PROCESSING. A -- AUXILIARY ASSEMBLIES (NOT COMPLETE OPER- ATING SETS USED WITH OR PART OF TWO OR MORE SETS OR SETS SERIES). B -- BOMBING. C -- COMMUNICATIONS (RE- CEIVING AND TRANS- MITTING). D -- DIRECTION FINDER, RE- CONNAISSANCE, AND/OR SURVEILLANCE. E -- EJECTION AND/OR RE- LEASE. G -- FIRE-CONTROL OR SEARCHLIGHT DIRECTING. H -- RECORDING AND/OR RE- PRODUCING (GRAPHIC METEOROLOGICAL AND SOUND). K -- COMPUTING. L -- SEARCHLIGHT CONTROL (INACTIVATED, USE G). M -- MAINTENANCE AND TEST ASSEMBLIES (INCLUDING TOOLS). N -- NAVIGATIONAL AIDS (IN- CLUDING ALTIMETERS. BEACONS, COMPASSES. RACONS, DEPTH SOUND- ING, APPROACH, AND LANDING). P -- REPRODUCING (INACTI- VATED, DO NOT USE). Q -- SPECIAL, OR COMBINATION OF PURPOSES. R -- RECEIVING, PASSIVE DE- TECTING. S -- DETECTING AND/OR RANGE AND BEARING, SEARCH. T -- TRANSMITTING. W -- AUTOMATIC FLIGHT OR RE- MOTE CONTROL. X -- IDENTIFICATION AND RECOGNITION. Y -- MULTI-FUNCTION. INSTALLATION TYPE OF EQUIPMENT PURPOSE "AN" SYSTEM WHERE IT IS WHAT IT IS WHAT IT DOES MODEL NO. MOD. LETTER AN / S P Y 1 A SET ORE QUIPMENT INDICAT OR LETTERS NOT FOR U.S. USE EXCEPT FOR ASSIGNING SUFFIX LETTERS TO PREVIOUSLY NOMENCLATURED ITEMS.1 1 FCRf0114 Figure 1-14.—AN equipment indicator system. FCRf0115 Figure 1-15.—Multi-dimensional (3-D) radar.
provided by a signal from the target, information sent from the launching ship, or both. Every missile guidance system consists of two separate systems—an attitude control system and a flight path control system. The attitude control system maintains the missile in the desired attitude on the ordered flight path by controlling it in pitch, roll, and yaw (fig. 1-16). This action, along with the thrust of the rocket motor, keeps the missile in stabilized flight. The flight path control system guides the missile to its designated target. This is done by determining the flight path errors, generating the necessary orders needed to correct these errors, and sending these orders to the missile’s control subsystem. The control subsystem exercises control in such a way that a suitable flight path is achieved and maintained. The operation of the guidance and control subsystems is based on the closed-loop or servo principle (fig. 1-17). The control units make corrective adjustments to the missile control surfaces when a guidance error is present. The control units also adjust the wings or fins to stabilize the missile in roll, pitch, and yaw. Guidance and stabilization are two separate processes, although they occur simultaneously. Phases of Guidance Missile guidance is generally divided into three phases (fig. 1-18). As indicated in the figure (view A), the three phases are boost, midcourse, and terminal. STANDARD SM-2 missiles (MR & ER) use all three of these phases. Not all missiles, however, go through the three phases. As shown in figure 1-18 (view B), some missiles (STANDARD SM-1, SEASPARROW) do not use midcourse guidance. With that thought in mind, let’s examine each phase, beginning with boost. INITIAL (BOOST) PHASE .—Navy surface- launched missiles are boosted to flight speed by the booster component (which is not always a separate component) of the propulsion system. The boost period lasts from the time the missile leaves the launcher until the booster burns up its fuel. In missiles with separate boosters, the booster drops away from the missile at burnout (fig. 1-18, view A). Discarding the burnt-out booster shell reduces the drag on the missile and enables the missile to travel farther. SMS missiles with separate boosters are the STANDARD SM-2 and HARPOON. The problems of the initial (boost) phase and the methods of solving them vary for different missiles. The method of launch is also a factor. The basic purposes, however, are the same. The missile can be either pre-programmed or physically aimed in a specific direction on orders from the fire control computer. This establishes the line of fire (trajectory or flight path) along which the missile must fly during the boosted portion of its flight. At the end of the boost period, the missile must be at a precalculated point. There are several reasons why the boost phase is important. If the missile is a homing missile, it must “look” in a predetermined direction toward the target. The fire control computer (on the ship) calculates this predicted target position on the basis of where the missile should be at the end of the boost period. Before launch, this information is fed into the missile. When a beam-riding missile reaches the end of its boosted period, it must be in a position where it can be captured by a radar guidance beam. If the missile does not fly along the prescribed launching trajectory as accurately as possible, it will not be in position to acquire the radar guidance beam and continue its flight to the target. The boost phase guidance system keeps the missile heading exactly as it was at launch. This is primarily a stabilizing function. 1-14 PITCH ROTATES ON LATERAL AXIS YAW ROTATES ON VERTICAL AXIS CENTER OF GRAVITY ROLL ROTATES ON LONGITUDINAL AXIS FCRf0116 Figure 1-16.—Missile axes: pitch, roll, yaw. RECEIVER COMPUTER DETECTOR SERVO MOTOR STABILIZATION CONTROL SURFACE GUIDANCE SIGNAL GUIDANCE SUBSYSTEM CONTROL SUBSYSTEM FCRf0117 Figure 1-17.—Basic missile guidance and control systems.
During the boost phase of some missiles, the missile’s guidance system and the control surfaces are locked in position. The locked control surfaces function in much the same manner as do the tail feathers of a dart or arrow. They provide stability and cause the missile to fly in a straight line. MIDCOURSE PHASE.— Not all guided missiles have a midcourse phase; but when present, it is often the longest in both time and distance. During this part of flight, changes may be needed to bring the missile onto the desired course and to make certain that it stays on that course. In most cases, midcourse guidance is used to put the missile near the target, where the final phase of guidance can take control. The HARPOON and STANDARD SM-2 missiles use a midcourse phase of guidance. TERMINAL PHASE .—The terminal or final phase is of great importance. The last phase of missile guidance must have a high degree of accuracy, as well as fast response to guidance signals to ensure an intercept. Near the end of the flight, the missile may be required to maneuver to its maximum capability in order to make the sharp turns needed to overtake and hit a fast-moving, evasive target. In some missiles, maneuvers are limited during the early part of the terminal phase. As the missile gets closer to the target, it becomes more responsive to the detected error signals. In this way, it avoids excessive maneuvers during the first part of terminal phase. Types of Guidance As we mentioned earlier, missiles have a path control system and an attitude control system. Guidance systems are usually classified according to their path control system, since many missiles use the same type of attitude control. The type of attitude control used in the fleet is inertial. The following is a discussion of the types of path control (guidance) in use in SMS missiles. INERTIAL GUIDANCE.—An inertial guidance system is one that is designed to fly a predetermined path. The missile is controlled by self-contained automatic devices called accelerometers. Accelerometers are inertial devices that measure accelerations. In missile control, they measure the vertical, lateral, and longitudinal accelerations of the controlled missile (fig. 1-19). Although there may not be contact between the launching site and the missile after launch, the missile is able to make corrections to its flight path with amazing precision. During flight, unpredictable outside forces, such as wind, work on the missile, causing changes in speed 1-15 TERMINAL TERMINAL BOOST (UNGUIDED) TERMINALBOOST (GUIDED) BOOSTER BURNOUT A. B. FCRf0118 BOOSTER BURNOUT AND DROPOFF MIDCOURSE Figure 1-18.—Guidance phases of missile flight.
commands. These commands are transmitted to the missile by varying the characteristics of the missile tracking or guidance beam, or by the use of a separate radio uplink transmitter. BEAM-RIDER GUIDANCE .—A beam-rider guidance system is a type of command guidance in which the missile seeks out the center of a controlled directional energy beam. Normally, this is a narrow radar beam. The missile’s guidance system receives information concerning the position of the missile within the beam. It interprets the information and generates its own correction signals, which keep the missile in the center of the beam. The fire control radar keeps the beam pointed at the target and the missile “rides” the beam to the target. Figure 1-20 (view B) illustrates a simple beam- rider guidance system. As the beam spreads out, it is more difficult for the missile to sense and remain in the center of the beam. For this reason, the accuracy of the beam-rider decreases as the range between the missile and the ship increases. If the target is crossing (not heading directly at the firing ship), the missile must follow a continually changing path. This may cause excessive maneuvering, which reduces the missile’s speed and range. Beam-riders, therefore, are effective against only short- and medium-range incoming targets. HOMING GUIDANCE .—Homing guidance systems control the path of the missile by means of a device in the missile that detects and reacts to some distinguishing feature of (or signal from) the target. This may be in the form of light, radio, heat, sound waves, or even a magnetic field. The homing missiles use radar or RF waves to locate the target while air-to-air missiles sometimes use infrared (heat) waves. Since the system tracks a characteristic of the target or energy reflecting off the target, contact between the missile and target is established and maintained. The missile derives guidance error signals based on its position relative to the target. This makes homing the most accurate type of guidance system, which is of great importance against moving air targets. Homing guidance methods are normally divided into three types:, active homing, semi-active homing, and passive homing (fig. 1-21). Active Homing.—With active homing, the missile contains both a radar transmitter and a receiver. The transmitter radiates RF energy in the direction of the target (fig. 1-21, view A). The RF energy strikes the target and is reflected back to the missile. (This process is referred to as “illuminating the target.”) The missile seeker (receiving) antenna detects the reflected energy and provides it as an input to the missile guidance system. The guidance system processes the input, usually called the homing error signal, and develops target tracking and missile control information. Missile control causes the missile to fly a desired flight path. The effective range of the missile transmitter is somewhat limited because of its size (power output). For this reason, relatively long-range missiles, such as HARPOON, do not switch to active guidance until after midcourse guidance has positioned the missile so that the transmitter is within its effective range. Semiactive Homing .—In a semiactive homing system, the target is illuminated by a transmitter (an illuminator) on the launching site (fig. 1-21, view B). As with active homing, the transmitted RF is reflected by the target and picked up by the missile’s receiver. The fact that the transmitter’s size is not limited, as with active homing, allows a much greater range. 1-16 VERTICAL ACCELEROMETER UP RIGHT LATERAL ACCELEROMETER LONGITUDINAL ACCELEROMETER DOWN LEFT BACKWARD FCRf0119 FORWARD Figure 1-19.—Accelerometers in a guided missile.
The missile, throughout its flight, is between the target and the radar that illuminates the target. It will receive radiation from the launching ship, as well as reflections from the target. The missile must therefore have some means of distinguishing between the two signals, so that it can home on the target rather than on the launching ship. This can be done in several ways. For example, a highly directional antenna may be mounted in the nose of the missile; or the Doppler principle may be used to distinguish between the transmitter signal and the target echoes. Since the missile is receding from the transmitter and approaching the target, the echo signals will be of a higher frequency. Most SMS missiles use both of these methods. A drawback of this system is that the shipboard illumination is not free to engage another target while the missile is in flight. STANDARD SM-1 and SEA- SPARROW all use semi-active homing as their primary guidance; they do not use midcourse guidance. The STANDARD SM-2 uses midcourse guidance, and then semi-active homing only for terminal guidance (fig. 1-20, view A). As a result, the SM-2 needs illumination from the ship only for the last few seconds of flight. Passive Homing .—Passive homing requires that the target be a source of radiated energy (fig. 1-21, view C). Typical forms of energy used in passive homing are heat, light, and RF energy. One of the most common uses of passive homing is with air-to-air missiles that use heat-sensing devices. It is also used with missiles that home on RF energy that originates at the target (ships, aircraft, shore-based radar, and so forth). An example of this is the STANDARD ARM (anti-radiation missile) used for both air-to-surface and surface-to-surface engagements. An advantage of this type of homing is that the target cannot detect an attack because the target is not illuminated. Several missiles that normally use other homing methods (active or semi-active) are capable of switching to the passive home-on-jamming (HOJ) mode in a countermeasure environment. That is, if the target detects that it is being illuminated by an active or semiactive guidance radar and initiates jamming (RF interference), the missile will home on the jamming signal if it is unable to maintain track on the reflected illumination signal. Tracking Radar/Fire-Control Radar Radar that provides continuous positional data is called tracking radar. Most tracking radar systems used 1-17 MISSILE DOWN LINK RECEIVER COMPUTER UPLINK COMMAND TRANSMITTER TARGET TRACKER TARGET TRACKING & GUIDANCE RADAR BOOSTER FCRf0120 A. B. Figure 1-20.—Simplified command guidance systems: A. Radar/radio command; B. Beam rider.
by the military are also called fire-control radars, the two names being interchangeable. A fire-control tracking radar system produces a very narrow, circular beam. PHASES OF RADAR OPERATION The three sequential phases of radar operation (designation, acquisition, and track) are often referred to as modes and are common to the target-processing sequence of most fire-control radars. Designation Phase During the designation phase, the fire-control radar is directed to the general location of the target. Acquisition Phase The fire-control radar switches to the acquisition phase once its beam 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 it either locates the target or is redesignated. Track Phase The fire-control radar enters into the track phase when it locates the target. The radar system locks on to the target during this phase. Typical fire-control radar characteristics include high pulse-repetition frequency, a very narrow pulsewidth, and a very narrow beamwidth. A typical fire-control antenna is shown in figure 1-22. 1-18 REFLECTED RADAR SIGNALS TARGET RADAR WAVES FROM MISSILE MISSILE TARGET RADAR WAVES FROM LAUNCHING SHIP A. B. C. REFLECTED RADAR SIGNALS RF / INFRARED WAVES FROM TARGET MISSILE TARGET MISSILE FCRf0121 Figure 1-21.—Homing guidance: A. Active homing; B. Semiactive homing; C. Passive homing. CAS RADOME ENTRANCE HATCH SEARCH ANTENNA FCRf0122 Figure 1-22.—Typical fire-control radar.
Detect-to-Engage Sequence The basic sequence can be divided into six fundamental operations: detection, acquisition and tracking, prediction, launcher/gun positioning, guidance (missiles), and evaluation (intercept and target destruction). Figure 1-23 illustrates the fire control problem sequence. DETECTION.—In this phase, the radar looks for a target. After the radar (usually a search radar) detects a target, the system obtains precise target position information. This information can be provided by the same source that detected the target, or it can be provided from some other source, such as another radar. In the majority of the cases, a second radar, a fire control radar, is used. The search radar establishes the target’s initial position and transmits this information to the designated fire control system. ACQUISITION AND TRACKING .—During this phase, the fire control radar director/antenna is aligned with the search radar’s target position information until it locks on the reflected target signal (acquisition). Either an operator or an automatic control circuit maintains that alignment (track) while the ship and target are moving. In this way, continuous, accurate target position information is available to the weapon system for processing. Not only is the continuous present position of the target obtained, but its movement (course and speed) is also determined. 1-19 DETECTION ACQUISITION AND TRACKING PREDICTION GUN OR LAUNCHER POSITIONING GUIDANCE EVALUATION FCRf0123 Figure 1-23.—Fire-control problem sequence.
Data other than target data is equally important for weapon flight path (trajectory) determination. Wind, for example, could blow the weapon off its flight path. Appropriate corrections would require that wind direction and velocity be determined. The course and speed of the launching ship and its motion, because of the sea (pitch and roll), are also important considerations. If this type of data is not included in the flight path determinations, it could cause large errors in the flight path (trajectory). Data of this nature, along with target data, is transmitted to the fire control system’s computer. The computer performs the necessary calculations for computing the launcher or gun mount position angles and the weapon’s flight path. After target detection and target acquisition have occurred, the fire control system provides three operations for the tracking, computation (prediction), and positioning functions. The first operation tracks the target and provides all necessary data on the target. The fire control radar performs this function by establishing a tracking Line Of Sight (LOS) along which it receives the returned or reflected energy from the target. It also provides accurate range data. Since the speed of the propagated RF energy is about 186,000 miles per second (the same as the speed of light), and since the target ranges involved are relatively small, the time for the energy to travel to and from the target can be considered as instantaneous. Therefore, the radar indications of the target can be considered as instantaneous, present-target positions. PREDICTION.—The second operation of the fire control problem that must be performed is the computation of the gun/launcher positioning angle (line of fire) and the weapon flight path trajectory. This operation consists of two parts. First, the system processes received data into a usable form. Then the fire control computer performs arithmetic operations to predict the future position of the target. LAUNCHER/GUN POSITIONING .—The third operation that must be performed is the positioning of the gun/launcher, based on the calculated line of fire to the future target position. This amounts to using the gun/launcher drive mechanism to offset the gun/launcher axis from the LOS by the amount of the predicted lead angle. In some cases, the missile is positioned (guided) in flight by the fire control system. GUIDANCE (MISSILES) .—For the Guided Missile Fire Control System (GMFCS), additional functions must be performed during the time the missile is in flight. Prior to launching, the fire control computer performs certain computations to provide the missile with information about the target and its own flight path. If the target maneuvers during the missile’s flight, the computer can send course correction data to the missile via the fire control radar or the missile can correct itself. EV ALUATION.—The fire control radar displays are used to evaluate the weapon’s destruction of the target. If the missile misses the target or causes only minor damage, additional weapons can be used. In missile fire control, another missile is fired. In gun fire control, corrections are made to bring the fall of shot onto a target using the radar indicators, optical devices, or spotter corrections. Normally, a target will be fired at until it is evaluated as either destroyed or damaged to the point it is no longer a threat. RADAR SYSTEMS IN TODAY’S NA VY There are too many radar systems used in today’s Navy to cover in this volume. However, table 1-2 provides an overview of the radars and sensors in use, by AN system designator, ship class, and related FC systems. SUMMARY Radio, detecting, and ranging (radar) uses radio frequency (RF) energy and a complex integration of computers, displays, and support equipment to detect a target. However, radar is just one type of sensor that is available to the modern Fire Controlman. Other types of sensors (e.g., infrared and optical) use different parts of the electromagnetic spectrum. It is important that you, as a modern Fire Controlman, understand the basic concepts of the sensors used on your ship and other ships in the Navy. These sensors play a key part in accomplishing the ship’s mission. As sensor technology improves, the Fire Controlman of the future will be expected to have a broader spectrum of knowledge and experience in order to keep our Navy on the cutting edge of naval warfare. 1-20
1-21 Designator Type Ship Class Range Weapon/Function Related FC System SEARCH SPS 48 C/E/F 3D Air Search, phased array CV/CVN, LHA, LCC, LHD 220 NM Primary Search SYS-1,SYS-2 SPS 52 C 3D Air Search LHD 240 NM Primary Search SYS-1 FIRE CONTROL Mk 92 CAS (Combined Antenna System) Fire Control, Track-While-Scan, Search FFG 25 NM Mk 75 Gun, SM-1 missiles Part of Mk 92 FCS Mk 95 radar Fire Control, CW tracker, illuminator DD (Spruance), CV/CVN 20 NM SEASPARROW missiles Mk 23 TAS, Part of Mk 91 FCS SPG 51 D Fire Control, pulse-doppler, COSRO tracker, CWI DDG (Kidd) 100 NM SM-1(MR) missiles, SM-2 missiles Part of Mk 74 FCS SPG 60 Fire Control DD (Spruance), DDG (Kidd) 50 NM SM-1/2 missiles, Mk 45 LWG SPY-1, Mk 86 GFCS SPG 62 Fire Control, CW, illuminator DDG (Arleigh Burke), CG (Ticonderoga) 20 NM SM-2 missiles SPY-1, Part of Mk 99 FCS SPQ 9 Series Fire Control, Track-While-Scan, (Surface), pulse-doppler DD (Spruance), DDG (Kidd), CG (Ticonderoga), LHA 20 NM SM-1/2 missiles Mk 45 LWG SPY-1 Mk 86 GFCS STIR (Separate Target Illuminating Radar) Fire Control, monopulse tracker- illuminator FFG 50 NM Mk 75 Gun, SM-1 missiles Part of Mk 92 FCS OTHER CIWS (Close-In Weapon System) Combined (search and track), pulse-doppler ALL 5 NM Search 1 NM track Anti-ship missile and air defense None HF Surface Wave FM CW LSD 6-12 NM Anti-ship missiles Sea Skimmer missile Detection/Air (This radar is still in development) Mk 23 TAS (Target Acquistion System) Air search, CW, tracker/illuminator DD (Spruance), CV/CVN, LCC, LHD, LHA, LPD 17 20 NM SEASPARROW missiles Part of Mk 91 FCS/Mk 95 Radar SPY 1 Series Multi-function, phased array D for DDG (Arleigh Burke), D for CG (Ticonderoga) >100 NM SM-2 missiles; search, track, and missile guidance, Mk 45 LWG AEGIS, Mk 34 GWS, Mk 86 GFCS, Mk 99 FCS Table 1-2.—Radar Systems in the U. S. Navy
1-22 Designator Type Ship Class Range Weapon/Function Related FC System OTHER—Continued SSDS Mk 1 (Ship Self-Defense System) Integrated use of multiple ship sensors FFG, LHD, LSD, LPD 17, AOE 6 Range as per each sensor CIWS/RAM, SLQ 32, SPS 49, SEASPARROW missiles Mk 2 replaces NATO SEASPARROW with ESSM (Evolved SEASPARROW missile) OPTRONICS SYSTEMS Optical Sighting System (OSS) or Remote Optical Sighting System (ROS) Sensor/View finder Arleigh Burke (DDG), Ticonderoga (CG) 20 km surface, 10 km air Mk 45 LWG MK 34 GWS, MK 86 GFCS FLIR (Forward Looking Infra- red) Sensor All ships upgraded to Block 1B Surface/Air Mk 15 Mods 11-14 CIWS Block 1 B TISS (Thermal Imaging Sensor System) Sensor Arleigh Burke (DDG), Ticonderoga (CG), AOE-6, CV/CVN, LPD-17, LSD-41, LHD/LKA, DDG 993, DD 963 55 kyd/air, 45 kyd surface Mk 31 RAM (Rolling Airframe Missile), CIWS, SSDS AEGIS, Mk 86 GFCS Table 1-2.—Radar Systems in the U.S. Navy—Continued
CHAPTER 2 FIRE CONTROL SYSTEMS INTRODUCTION In the preceding chapter, you read about the basic principles of radar operation. You also read about the basic components of a radar system and their relationship to each other. This chapter deals with specific radar systems and terms associated with those systems. You must understand those terms to get the maximum benefit from the information contained in this chapter. If you don’t have a good understanding of radar operation and theory, we suggest that you review the following Navy Electricity and Electronics Training Series (NEETS) modules: Microwave Principles , Module 11, NA VEDTRA 14183, and Radar Principles , Module 18, NA VEDTRA 14190. We also suggest that you refer to the Functional Description section in your own technical manuals for the specific operation of your radar equipment. The Fire Controlman rating deals with a large number of different radar systems, but you will probably be trained in only one or two of these systems. To help you develop a broad understanding of Fire Control radar, we will first discuss the Fire Control radars and sensors used in the fleet today. We will do this by category: search radar, missile direction/illumination radar, multi-function radar, and optronics systems. Then we will give you an overview of upcoming developments in radar. SEARCH RADAR You may think the function of Fire Control radar is to lock on to and identify a specific hostile target to direct a weapon to destroy it. That is the function of most FC radars. However, most FC radars use a narrow beam to perform their function. This makes using FC radar for locating a target impractical, since a narrow beam can easily miss targets. Locating targets requires using a radar with a wide beam. Search radar has such a beam. Search radar provides long-range (200 nautical miles or more), 360-degree coverage. It can determine a target’s range, bearing, and elevation, and can then hand over that information to the more accurate narrow-beamed FC radar. Some Fire Control systems have built-in search and track radar; others rely on completely separate search radar. In this section, we will cover the separate search radars you will see in the surface Navy. These are the AN/SPS-52C and the AN/SPS-48 series search radars. AN/SPS-48 RADAR The AN/SPS-48 radar is a complete system upgrade of the AN/SPS-52C including all component elements—transmitter, receiver, computer (radar and automatic detection and tracking), frequency synthesizer and height display indicator. Figure 2-1 shows an antenna for the SPS-48 radar on the USS Nimitz CVN-68 (see arrow). 2-1 LEARNING OBJECTIVES Upon completing this chapter, you should be able to do the following: 1. Identify and describe search radar systems associated with fire control radar. 2. Identify and describe missile and gun fire control radar systems. 3. Identify and describe other related sensor systems associated with fire control radar. 4. Describe the detect-to-engage scenario. 5. Describe the fire control problem in relationship to the detect-to-engage scenario. 6. Identify and describe cruise missile systems.