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ABSTRACT

The Duke of Wellington in 1845:‘The whole art of war consists in getting at what is on the other side of the hill or, in other words, in learning what we do not know from what we do. ” Wellington was talking about exquisite knowledge on what a potential enemy is doing with his military equipment and forces at any moment in time, anywhere on the globe. Winning future conflicts will require both this superb information and the long-range projection of force. [1] The information revolution of the past hundred years can provide us with a dramatic enhancement in military capabilities. Radar plays a key role in this information process.

RADAR (RAdio Detection And Ranging) is basically a means of gathering information about distant objects by transmitting electromagnetic waves at them and analyzing the echoes. Radar has been employed on the ground, in air, on the sea and in space. Radar finds a number of applications such as in airport traffic control, military purposes, coastal navigation, meteorology and mapping etc. The development of the radar technology took place during the World War II like Chain Home Radar as in Fig.1, in which it was used for detecting the approaching aircraft and then later for many other purposes which finally led to the development of advanced military radars being used these days. Military radars have a highly specialized design to be highly mobile and easily transportable, by air as well as ground. The need for all-weather, long-range, wide-area surveillance mandates that radar play the critical sensing role in these future military systems.

. In this report the advanced features and benefits of military radar, system configuration of a typical military radar, operating the radar, system functions, various terminal equipments used along with their functions and some of the important parts of the radar such as transmitter, receiver, antenna, AFC (Automatic Frequency Control), Identification Friend or Foe and Counter–battery Radar (Weapons Locating Radar) are discussed.

Fig.1 British Chain Home Radar used in World War 2

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1. INTRODUCTION

Military radar should be an early warning, altering along with weapon control functions. It is specially designed to be highly mobile and should be such that it can be deployed within minutes.

Military radar minimizes mutual interference of tasks of both air defenders and friendly air space users. This will result in an increased effectiveness of the combined combat operations. The command and control capabilities of the radar in combination with an effective ground based air defence provide maximum operational effectiveness with a safe, efficient and flexible use of the air space. The increased operational effectiveness is obtained by combining the advantages of centralized air defence management with decentralized air defence control.

2. ADVANCED FEATURES AND BENEFITS

Typical military radar has the following advanced features and benefits: -

All-weather day and night capability. Multiple target handling and engagement capability. Short and fast reaction time between target detection and ready to fire moment. Easy to operate and hence low manning requirements and stress reduction under

severe conditions. Highly mobile system, to be used in all kind of terrain Flexible weapon integration, and unlimited number of single air defence weapons can

be provided with target data. High resolution, which gives excellent target discrimination and accurate tracking. The identification of the targets as friend or hostile is supported by IFF (Identification

Friend or Foe), which is an integral part of the system.

During the short time when the targets are exposed accurate data must be obtained. A high antenna rotational speed assures early target detection and a high data update rate required for track accuracy.

The radar can use linear (horizontal) polarization in clear weather. During rains, to improve the suppression of rain clutter, provision exists to change to circular polarization at the touch of the button from the display console.

3. THE SYSTEM CONFIGURATION

A typical military radar system can be split up into three parts:

1) Radar groupThe radar group consists of antenna, mast unit, remote control, high tension unit,

LO/AFC (Local Oscillator/Automatic Frequency Control) unit, radar transmitter, radar receiver, video processor and IFF interrogator. The transmitter and receiver are the active part of the system. The integrated radar/IFF antenna is fitted on the collapsible mast, mounted on the container. The container is connected by cable to the operator/control shelter.

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2) ShelterShelter contains display unit, processor unit, TV monitor, colour PPI (Plan

Position indicator), IFF control unit, air conditioner, battery charger with battery, Radio set with antenna for data link, radio set with antenna for voice transmission i.e. communication, filter box for radios.

3) Motor generatorThe motor generator supplies the power to the whole radar system.

3.1 SETS OF TERMINAL EQUIPMENT

These are the sets of lightweight man portable units, which can be easily be stacked together and consists of: -

1) TDR (Target Data Receiver)The TDR is either connected to a VHF-FM radio receiver or to a LCA to receive transmitted target data. The TDR itself is intelligent, it performs parallax correction, threat evaluation and it displays the result in a threat sequence, enabling the weapon commander to make the correct decision.

2) Radio Receiver or LCA (Line Connection Adapter)A radio receiver or LCA (with standard 2 wire telephone line) can be used to receive target data. In principle any VHF-FM radio receiver can be used as a part of the terminal equipment set. In case line connection is applied, no radio receiver is required. An LCA connects the 2-wire telephone line to the TDR cable.

3.2 FUNCTIONAL DESCRIPTION OF RADAR SUBSYSTEM

The detection of air targets is accomplished by the search radar, the video processor and the colour PPI unit. The colour PPI unit provides the presentation of all moving targets down to very low radial speeds on a PPI screen

The search radar is pulse Doppler radar (also called MTI radar) i.e. it is capable of distinguishing between the echo from a fixed target and that of a moving target. The echoes from fixed target are eliminated, so that the echoes from the moving targets are presented on the screen.

The great advantage of this is that it is possible to distinguish a moving target among a large number of fixed targets, even when the echoes from these fixed targets are much stronger. To achieve this the search radar makes use of the Doppler effect, if the target having a certain radial speed with respect to the search antenna is hit by a series of transmitter pulses from the search radar antenna, the change in range between this target and antenna is expressed by successive echo pulses in phase shifts with respect to the phase of the transmitter pulses.

For moving targets the phase difference from echo pulse to echo pulse is continually subject to change, whereas for fixed targets this is a constant. The distinction between the echo signals from a fixed target and moving target is obtained by detecting the above phase differences.

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HT UNIT

High Voltage Supply

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Fig. 2 Block Diagram of Radar

The main units of radar subsystem as shown in Fig.2 are:

1) HT UnitThe high tension unit converts the phase mains voltage into a DC supply voltage

of about in the order of kV for the transmitter unit.

2) Transmitter Unit The transmitter unit as shown in Fig.3 comprises of:a. Modulator

The modulator consists of the following components: -

o Start Pulse AmplifierThe start pulse amplifier unit comprises of an amplifier which

amplifies the pulses from the video processor, a thyratron for discharging the pulse-shaping network. These pulses then trigger a monostable multivibrator.

o Pulse Unit

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The pulse unit comprises of pulse shaping network and pulse transformer. The pulse discharge of the pulse- shaping network will occur only if the magnetron impedance transformed by the pulse transformer is about equal to the characteristic impedance of the pulse-shaping network.The thyratron diodes ensure that the remaining negative voltage, caused by the mismatch, on the pulse-forming network is directed to earth. If the mismatch is too large, capacitor is charged by the discharge current to such an extent that relay (reflection coefficient too high) is activated. This relay switches off the high voltage.

b. MagnetronThe magnetron is a self-oscillating RF power generator. It is supplied

by the modulator by high voltage pulses, whereupon it produces band pulses. The generated RF pulses are applied to the receiver unit. The PRF of the magnetron pulses is determined by the synchronization circuit in the video processor, which applies start pulses to the sub-modulator of the transmitter unit.

This sub modulator issues start pulses of suitable amplitude to trigger the thyratron in the modulator. On being triggered, the modulator which is supplied by the high tension unit producing high voltage pulses.

As a magnetron is self oscillating, some kind of frequency control is required. The magnetron is provided with a tuning mechanism to adjust the oscillating frequency between certain limits. This tuning mechanism is operated by an electric motor being part of AFC control circuit. Together with circuits in LO+AFC (Local Oscillator/Automatic Frequency Control) unit, a frequency control loop is created, thus maintaining a frequency difference i.e. the intermediate frequency of the receiver between the output frequency of the SSLO (Solid State Local Oscillator) and the magnetron output frequency. The magnetron unit comprises a coaxial tunable magnetron, servo motor driving an adjustable plunger.

Fig.3 Block Diagram of Transmitter Unit

3) Local Oscillator and Automatic Frequency Control Unit

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The LO+AFC unit determines the frequency of the transmitted radar pulses. It comprises of: -

Lock pulse mixer AFC discriminator Solid State Local Oscillator (SSLO) Coherent Oscillator (COHO)

The SSLO generates a very stable low power RF signal lower than the desired transmitter frequency. This signal is split in two branches and distributed as local oscillator signal to two mixers. These are: -

Image rejection mixer in the receiver unit Lock pulse mixer

The lock pulse mixer mixes the SSLO signal with a fraction of the magnetron power. The mixer output consists of AFC lock pulse, provided that the magnetron is correctly tuned. The AFC lock pulses are applied to an AFC discriminator, which checks their frequency.

If the frequency of the AFC lock pulses is unequal to IF, a positive or negative control voltage for the AFC control circuit in the transmitter unit is developed, to force the magnetron frequency to the desired value. Thus the AFC loop is closed.

The AFC lock pulses are also applied to COHO. The COHO outputs a signal with a frequency of AFC lock pulse, and is synchronized with the phase of each transmitter pulse. In this way a phase reference signal is obtained required by the phase sensitive detector in the receiver unit.

4) Receiver Unit

The receiver unit converts the received RF echo signals to IF level and detects the IF signals. By detecting the IF signals in two different ways, two receiver channels are obtained called MTI channel and linear channel.

The RF signals received by radar antenna are applied to the low noise amplifier. The image rejection mixer mixes the amplified signals with the SSLO signal, to obtain an IF signal. After amplification the IF signal is split into two branches viz. a MTI channel and a linear channel. A fraction of amplified received signal is branched off and applied to broadband jamming detector (BJD).

In the MTI channel, the IF signal is amplified again by the MTI main amplifier, and applied to the Phase Sensitive Detector (PSD). The second signal applied to the PSD is the phase reference signal from the COHO.

The output of the PSD is the function of the phase difference between the two inputs to the PSD. The polarity pulses indicate whether the phase difference is positive or negative.

The phase differences between the COHO signal and IF echo signals from a fixed target is constant whereas those between the COHO signals and IF echo signals from a moving target is subject to change.

The PSD output signal is applied to the canceller in video processor. In the linear channel, the IF signal is amplified again by the linear main amplifier and subsequently applied to the linear detector. The linear detector output signals are passed on to the colour PPI drive unit.

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5) Antenna

The search antenna is a parabolic reflector, rotating with a high speed. In the focus of the reflector is a radiator, which emits the RF pulses, and which receives the RF echo pulses.

In the waveguide is the polarization shifter, which causes the polarization of the RF energy to be either horizontally or circularly.

6) Video processor

The video processor processes the MTI video from the MTI receiver channel, to make the video suitable for the presentation on the colour PPI screen.

7) Protection Units

There are some protection units such as arc sensor to protect the magnetron against arcing and RF power sensor maintaining the RF power.

4. OPERATING THE RADAR

The operator’s main task is to watch the PPI (Plan Position Indicator) display, which presents only moving targets in the normal mode (MTI-MODE). Detected target can be assigned with the joystick controlled order marker to initiate target tracking. Target tracking is started and a track marker appears over the target echo. A label is displayed near the track marker. The system computer in the processor unit processes data on this tracked target. When an aircraft does not respond to the IFF interrogation, it is considered to be unknown.

4.1. SYSTEM FUNCTIONS

The main task of the radar is to provide individual weapon systems, after an alert, with accurate target data. Therefore, the system has to perform certain functions as shown in the Fig.4:

Fig.4 Data flow in a typical military radar system

Detection

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Target detection by Radar

Target Initiation and Identification

Automatic Target Tracking and IFF status

Target Track data put in encoded message

Message transmitted to weapons system

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The detection function is supported by the search radar, the MTI processor and the PPI. On the PPI all moving targets, even those flying at low radial speeds, are displayed to the operator.

Automatic Target TrackingAfter target detection a track is initiated by indicating the target with the

joystick controlled order marker. The computer starts generating a track on the basis of the joystick data. A target track marker is displayed on the PPI over the target echo. Search radar information is gathered and extracted by video extractor as plots. The computer evaluates the plot information, determines the position and speed of the target and updates the generated track.

IdentificationThe identification function comprises: -

Interrogation of a target detected Decoding IFF responses Display of the decoded IFF responses on the PPI

Reporting Function to External Terminal EquipmentThe data of the tracked targets is automatically converted to X and Y grid

co-ordinates, with respect to preset co-ordinates of the radar location. The data is included in digital data message made up for all targets being tracked. The computer-originated message is encoded and automatically transmitted by VHF-FM radio or by line communication.

IFF AlarmThe IFF alarm function alerts the operator that the IFF code setting has to be

changed. The valid code is displayed to the operator. The IFF codes and their validity period are entered into the system in advance.

4.2 TERMINAL EQUIPMENT FUNCTIONS

Fig.5 Data flow at weapon systems

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Message Decoded and Parallax Correction

Threat Evaluation and display of results as

advice

Target

Selection

Target Tracking, fire control and

weapon aimingFiring at target

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Target DecodingThe target information is received and decoded. In case no, or disturbed target

information is received, it is indicated on the TDR.

Parallax CorrectionThe parallax correction function is performed by the TDR. Through this

function the target data received in the X and Y co-ordinates is transferred into polar co-ordinates, with respect to the entered weapon position.

Threat EvaluationThe data of the targets received is processed by a threat evaluation program,

built in to the TDR. This program places all the targets in a sequence according to their threat priority and displays the result (azimuth angle of four most threatening targets) as an engagement advice. [10]

5. SURVELLIANCE RADAR / IDENTIFICATION FRIEND OR FOE (SSR/IFF)

SSR is currently being used in the military and in civilian air traffic control systems. It was developed during the World War 2 by Watson-Watt, with the development of Mark I and Mark II IFF sets. The first universal system known as Mark III was devised by F.C. Williams. [2] In the military, the need to identify friendly aircrafts positively first arose during the Second World War. Military use of SSR is known as IFF. The information from the IFF system forms part of the decision aid process, which must be followed before a weapon is fired, or action is taken against a non-friendly target.

5.1 OPERATION OF IFF

In SSR, the purpose is not to detect the presence of a target or to determine its position accurately, as in primary radar, but rather to identify the target positively and to distinguish it from others. Primary and secondary surveillance radar is often used jointly, and in most cases their antennas rotate simultaneously. During military training or conflict, a secure IFF mode is used to identify friendly targets, using the Cryptographic Computers (CCs) connected to the interrogator and the transponder (TxP). The Interrogator CC (ICC) typically generates encrypted interrogation pulses and informs the interrogator when to expect a reply, if a friendly platform has successfully decrypted the interrogation. When the TxP receives an encrypted interrogation, it passes it to the attached Transponder CC (TCC), and if the TCC successfully decrypts the interrogation, it informs the TxP when to generate the reply “mission capable”. The technical characteristics of SSR/IFF are governed by a Standardization Agreement, known as the STANAG-4193 document, created by the North Atlantic Treaty Organization (NATO) military agency for standardization. The box created by the dashed lines and arrows in Fig.6 illustrates the top level project scope. Interrogations and replies to/from the targets bypass the RF link and feed directly into the interrogator signal processor. [3]

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Fig.6 Block Diagram of IFF operation

Each IFF transponder also has a KIR or KIT cryptography computer associated with it. The KIR (designed for interrogators) and the KIT (designed for transponders) have an access port where the encryption keys are inserted. The military IFF system will not function without a valid key.

An IFF transponder receives interrogation pulses at one frequency (1,030 MHz), and sends the reply pulses at a different frequency (1,090 MHz). The IFF interrogation is a long series of bits that contains the encrypted message and parity, and the reply is just three pulses.

The IFF message is encrypted with a secret key. IFF transponders with the same secret key will be able to decode the IFF message. Once decoded, the IFF transponder will execute the message and send back a three-pulse reply. The interrogator then compares each reply to the challenge messages, and marks these targets friendly while also storing their azimuth and range.

A second possibility is a target being marked as a spoof target. That is, the target replies, but fails to process the IFF message correctly on a significant number of challenges. Targets marked as a “spoofer” can be declared hostile and, if inside a battle-space, are often destroyed if possible.

If no reply is received from the IFF transponder, the target continues to be an unknown. The IFF system is not used to declare a target hostile if it does not reply. Very often pilots can have the wrong code (encryption key) selected, or the code has expired, and they will have an audible and visual alarm every time they are interrogated by IFF. If they can't clear the alarm they follow the pre-briefed safe passage procedures.

The major military benefits of IFF include preventing "friendly fire" and being able to positively identify friendly forces.

5.2 MODES OF OPERATION OF IFF

Several different RF communication protocols have been standardized for aviation transponders as shown in Table.1:

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Military Mode Description1 provides 2-digit 5-bit mission code (cockpit selectable)2 provides 4-digit octal unit code (set on ground for fighters, can be changed

in flight by transport aircraft)3 provides a 4-digit octal identification code for the aircraft, assigned by the

air traffic controller. 4 provides a 3-pulse reply to crypto coded challenge5 provides a cryptographically secured version of Mode S (designed to help

avoiding over-interrogation of the transponder in busy areas) and GPS position.

Table.1 Different Modes of Operation of Transponders

6. TYPES OF MILITARY RADAR

There are different types of Radar used by the military. These are:

Detection and Search Radar

Search radars scan a wide area with pulses of short radio waves. They usually scan the area two to four times a minute. The waves are usually less than a meter long. 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. Its sub-types are:

Early Warning Radar Ground Control Intercept (GCI) Radar Airborne Early Warning (AEW) Airborne Ground Surveillance (AGS) Over-the-Horizon (OTH) Radar Anti-Aircraft Artillery (AAA) Systems Surface Search (SS) Radar Systems Surface Search Radar Coastal Surveillance Radar Antisubmarine Warfare (ASW) Radar

Targeting radars

Targeting radars have similar principle to Search Radar, but scan a much smaller area far more often, usually several times a second or more, where a search radar might scan a few times per minute. Some targeting radars have a range gate that can track a target, to eliminate clutter and electronic counter-measures.

Missile guidance systems Air-to-Air Missile (AAM) Air-to-Surface Missile (ASM) SAM Systems Surface-to-Surface Missiles (SSM) Systems

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Battlefield and reconnaissance radar Battlefield Surveillance Radars Counter-mortar/Counter-battery Systems Shell Tracking Radars Ground Surveillance Radar Man portable radar

7. SHELL TRACKING (WEAPONS LOCATING RADAR)

A Weapons Locating Radar (Counter-battery / Counter-Mortar Radar) detects artillery projectiles fired by one or more guns, howitzers, mortars and rocket launchers and from their trajectories locates the position on the ground of the gun, etc. that fired it. Alternatively, or in addition, it may determine where the projectile will land. The normal purpose of counter-battery radar is to locate hostile batteries up to about 50 km away depending on the radar's capabilities.

7(a) 7(b)

Fig.7 (a) Israeli counter-battery radar, 7(b) ARTHUR (Artillery Hunting Radar)

If the radar is fast and has fast communications, then it may be possible to provide some warning to troops targeted by the incoming projectiles. However, many projectiles have a time of flight under a minute, which makes it difficult to give warnings without a highly automated communication system, unless the target is in the vicinity of the radar. Weapon locating radars can also be used to observe the fire of friendly artillery and calculate corrections to adjust its fire onto a particular place.

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Radar is the most recently developed means of locating hostile artillery. The emergence of indirect fire in World War I saw the development of sound ranging, flash spotting and air reconnaissance, both visual and photographic. Radars, like sound ranging and flash spotting, require hostile guns, etc., to fire before they can be located.

Low angle trajectories normally used by guns, howitzers and rockets were more difficult. They could be detected but their shape, a segment of an ellipse, was impossible to resolve until efficient algorithms were developed and digital computers, usable on the battlefield, had achieved the necessary performance.

7.1 TECHNICAL ISSUES

There are challenging technical issues associated with the design of a weapon locating radar. The Key issues are:

Radar Cross Section: Fig.8 shows the variation of radar cross section (RCS) of an artillery shell with the aspect angle of the projectile. When the nose of the projectile is pointing directly towards the radar, the aspect angle is 0 deg. There are many aspect angles where the radar cross section is less than 0.0001 m². This is equivalent to the radar cross section of a metallic sphere that is one centimetre in diameter. As a reference point the radar cross section of a small aircraft is about one square meter.

Fig.8 The variation of RCS of an artillery shell with the aspect angle of the projectile

Radar Clutter: A very important issue associated with low radar cross section is radar clutter, i.e., reflections from objects such as terrain, precipitation, birds and insects.

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The birds have a radar cross section between 1 cm² up to 1000 cm². The velocities relative to the wind of birds span from 0 m/s up to 30 m/s and with an average of about 15 m/s. The birds are distributed in height from ground level up to several kilometres above the terrain. With these properties one realizes that birds constitute a major problem for weapons locating radar. At surveillance, the radar has the possibility of using its MTI (Moving Target Indicator). This will of course prevent the slowest birds from being detected but there will still be a considerable number of birds not rejected by the MTI. [4]

The figure of merit for detection of a target in the presence of clutter is known as sub clutter visibility (SCV), i.e., the ratio of the amplitudes of the clutter and target. The SCV required for an effective weapon locating radar is at least 60 db. Earlier the state of the art for SCV was still less than 30 db.

Angle Tracking Accuracy: To achieve the location accuracy needed to bring effective counter fire on a hostile weapon, precision tracking of a projectile over a portion of its trajectory is required. The track data are smoothed to obtain estimates of position, velocity, and acceleration at the centre of the track. The estimates are then extrapolated back to the ground plane. The main contributors to location errors are the radar azimuth and elevation angle tracking errors. To a large extent the radar transmitter power, and the size, weight and cost of the antenna are driven by the requirements for angle tracking accuracy. A popular measure of location error is the circular error probable (CEP). The CEP is the radius of a circle that contains 50% of the location errors. The goal for CEP has been between 50 and 100 m. The location error is a function of the angle tracking errors, the radar to target range, the elevation angle of the weapon tube, and the track and back track times. The required angle accuracy varies from 5 mrads in the case of a mortar trajectory at a range of 10 km and a tube elevation angle of 1200 mrads, to 0.25 mrads for an artillery trajectory at a range of 40 km and a tube elevation angle of 300 mrads.

Low Elevation Angle Tracking: For an artillery weapon firing at an elevation angle of 300 mrads, and located 30 Km from the radar, the maximum elevation angle is less than 100 mrads. Hence the radar will need to complete detection and track while the projectile is still close to the horizon and as a consequence the radar will be exposed to reflections from terrain, birds and insects. [5]

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Fig.9(a) Mortar Fig.9(b) Artillery Gun [8]

Fig.9(c) Difference in trajectory of Mortar and Artillery Gun

The location of artillery presents a much more difficult task than location of mortars. The required range of an effective mortar locator was less than 10 km compared to 30 km for an artillery locator. Also since the minimum tube elevation of a mortar is 800 mrads versus 200 mrads for artillery giving flatter trajectory to artillery compared to high-arcing trajectory of mortar as shown in Fig.9(c), the elevation angle tracking accuracy requirement to locate artillery is much more stringent than for mortars.

7.2 OPERATION

The basic technique is to track a projectile for sufficient time to record a segment of the trajectory. This is usually done automatically, but some early and not so early radars required the operator to manually track the projectile. Once a trajectory segment is captured it can then be processed to determine its point of origin on the ground. Before digital terrain databases this involved interaction with a paper map to check the altitude at the coordinates, change the location altitude and re-compute the coordinates until a satisfactory location was found.

The additional problem was finding the projectile in flight in the first place. The conical shaped beam of a traditional radar had to be pointing in the right direction, and to have sufficient power and accuracy the beam couldn't have too large an angle, typically about 25 degrees, which made finding projectile quite difficult. One technique was to deploy listening posts that told the radar operator roughly where to point the beam, in some cases the radar didn't switch on until this point to make it less vulnerable to electronic counter-measures (ECM). However, conventional radar beams were not notably effective. Since a parabola is defined by just two points then tracking a segment of the trajectory was not notably efficient.

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Fig.10 (a) – Two Point Location Method [6]

Fig.10 (b) – Plan of Area Scanned [6]

The Royal Radar Establishment in UK developed a different approach. The Foster scanner converted the conical beam into one about 40 degrees wide and 1 degree vertical with an antenna that had only two predefined vertical positions as shown in Fig.10 (b). A mortar bomb was plotted as it passed through each of the beam positions to provide the necessary two points that could be processed by an analogue computer.

Fig.11 Radar Process of locating Artillery System Ground Position using Phased Array [6]

However, once phased array radars compact enough for field use and with reasonable digital computing power appeared they offered a better solution as shown in Fig.11 Phased array radar has many transmitter/receiver modules. These are electronically controlled and cover a 90 degree arc without moving the antenna. They can detect and track anything in their field of view, providing they have sufficient computing power. They can filter out the targets of no interest (e.g.: aircraft) and depending on their capability track a useful proportion of the rest.

Counter battery radars are used mostly in X band (between 7.0 to 11.2 GHz) because this offers the greatest accuracy for the small radar targets. However, in the radars produced today C (between 4 to 8 GHz) and S (between 2 to 4 GHz) is the common. Ku (between 12 to

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18 GHz) bands have also been used. Projectile detection ranges are governed by the radar cross section (RCS) of the projectiles. Typical RCS are:

Mortar bomb 0.01 m Artillery shell 0.001 m Light rocket (e.g. 122 mm) 0.009 m Heavy rocket (e.g. 227 mm) 0.018 m

The best modern radars can detect howitzer shells at around 30 km and rockets/mortars at 50+ km. Of course the trajectory has to be high enough to be seen by the radar at these ranges, and since the best locating results for guns and rockets are achieved with a reasonable length of trajectory segment close to the gun, long range detection does not guarantee good locating results. The accuracy of location is typically given by a circular error probable (CEP) (the circle around the target in which 50% of locations will fall) expressed as a percentage of range. Modern radars typically give CEPs around 0.3 - 0.4% of range. However, with these figures long range accuracy may be insufficient to satisfy the Rules of Engagement for counter-battery fire in counter insurgency operations.

Radars typically have a crew of 4 – 8 soldiers, although only one is needed to actually operate the radar. Older types were mostly trailer mounted with a separate generator, so took 15-30 minutes to bring into action and need a larger crew. However, self-propelled are being used today. To produce accurate locations radars have to know their own precise coordinates and be precisely oriented. Until about 1980 this relied on conventional artillery survey, although gyroscopic orientation from the mid 1960s helped.

Radars can detect projectiles at considerable distances, and larger projectiles give stronger reflected signals (RCS). Detection ranges depend on capturing at least several seconds of a trajectory and can be limited by the radar horizon and the height of the trajectory. For non-parabolic trajectories it is also important to capture a trajectory as close as possible to its source in order to obtain the necessary accuracy.

Action on locating hostile artillery depends on policy and circumstances. In some armies, radars may have authority to send target details to counter-battery fire units and order them to fire, in others they may merely report data to an HQ that then takes action. Modern radars usually record the target as well as the firing position of hostile artillery. However, this is usually for intelligence purposes because there is seldom time to alert the target with sufficient warning time in a battlefield environment, even with data communications. However, there are exceptions. The new Lightweight Counter Mortar Radar (LCMR – AN/TPQ 48) has crew of two soldiers and is designed to be deployed inside forward positions, in these circumstances it can immediately alert adjacent troops as well as pass target data to mortars close by for counter-fire.

7.3 THREATS

Radars are vulnerable and high value targets; they are easy to detect and locate if the enemy has the necessary ELINT/ESM capability. The consequences of this detection are likely to be attack by artillery fire or aircraft (including anti-radiation missiles) or ECM. The usual measures against detection are using a radar horizon to screen from ground based detection, minimizing transmission time and using alerting arrangements to tell the radar when hostile artillery is active. Deploying radars singly and moving frequently reduces exposure to attack. [9]

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However, in low threat environments, such as the Balkans in the 1990s, they may transit continuously and deploy in clusters to provide all-around surveillance. In other circumstances, particularly counter-insurgency, where ground attack with direct fire or short range indirect fire is the main threat radars deploy in defended localities but do not need to move, unless they need to cover a different area.

7.4 MODERN COUNTER-BATTERY SYSTEMS

1L259/1L259M Zoopark-1/-1M AN/MPQ 10 (mortar locating) AN/MPQ 4 (mortar locating) AN/KPQ 1 (mortar locating) AN/TPQ-36 Fire finder radar AN/TPQ-37 Fire finder radar AN/TPQ-48 Lightweight Counter Mortar Radar ARSOM 2P - NATO reporting name SMALL YAWN ARTHUR (ARTillery Hunting Radar) BEL Weapon Locating Radar BL904 radar COBRA Radar FA No 15 (Cymbeline) (mortar locating) EL/M-2084 combined air surveillance and counter-battery radar [12]

8. CONCLUSION

Military radars are one of the most important requirements during the wartime, which can be used for early detection of ballistic missile and also for accurate target detection and firing. Radar system has a built in threat evaluation program which automatically puts the target in a threat sequence, and advises the weapon crew which target can be engaged first. Most essential, the target data is available to the weapon crew in time, so they can prepare themselves to engage the ‘best’ target for their specific weapon location. [7]

Modern military radar faces four main threats:1. Low Radar Cross Section (RCS), i.e., stealth crafts2. Electronic Counter Measures (ECM)3. Anti Radiation Missiles4. Low-altitude flying vehicles.

In the future, information will play a key role in military operations, therefore radar will be required to detect, locate, and identify numerous targets accurately, in all weather conditions and over wide areas. [11]

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Military Radar 19

REFERENCES

1) W.P. Delaney, Lincoln Laboratory, Massachusetts Institute of Technology,“Changing World - Changing Nature of Conflicts - A Critical Role for Military Radar”

2) Lord Bowden of Chesterfield, M.A., Ph.D., M.Sc. Tech., D.S., L.L.D., C.Eng., Fellow I.E.E.E., F.I.C.E., F.I.E.E. “The story of IFF (identification friend or foe)”

3) Sharef Neemat & Michael Inggs, University of Cape Town,“Design and Implementation of a Digital Real-Time Target Emulator for Secondary Surveillance Radar / Identification Friend or Foe”

4) Nils-Inge Franzen, Ericsson Radar Electronics AB “The Use of a Clutter Map in the Artillery Locating Radar: ARTHUR”

5) William Fishbein, Life Senior Member, “Firefinder, a Radar Forty Years in the Making”

6) J.G. Milner, M.B.E., C. Eng., M.I.E.E., “Radar mortar locator development in the UK: the first 30 years”

7) McKinney, J. E. “Radar, a case history of an invention” IEEE Aerospace and Electronics Systems Magazine, 21, 8 (Aug. 2006)

8) School of Anti-Aircraft Artillery handbook of radar techniques, Appendix B, 1952; unpublished MOD report

9) Black” S. S., Multiple Hypothesis Tracking for Multiple Target Tracking, IEEE Aerospace and Electronic Systems Magazine, V01.19, No.1 2044.

10) P.M .Jeliazov, M .P. Jeliazov, M.S.Marinov “Influence of Information Technology on Military Radar Systems”

11) Zhang Xixong, Xian Research Institute of Navigation Technology “The Future of Military Radar: A Perspective”

12) www.globalsecurity.org

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