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Military Radar System Detailed Report


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Seminar Report Military Radar System ABSTRACT 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 finds a number of applications such as in airport traffic control military purposes coastal navigation meteorology and mapping etc. Military radars have a highly specialized design to be highly mobile and easily transportable by air as well as ground. This report discusses about the military radar system. Radar system uses the general antenna properties. Radar is used in early warning altering along with weapon control functions. This report gives the view of configuration of a typical military radar data flow in a typical radar system operating the radar system functions various terminal equipments used along with their functions functional description of radar subsystem some of the important parts of the radar such as transmitter unit receiver unit antenna AFC Automatic Frequency Control etc. advanced features of the radar advantages and limitations of the military radar system. This report also describes the target tracking firing control weapon aiming process using military radar.

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Seminar Report Military Radar System INTRODUCTION Radar is an acronym for Radio Detection And Ranging. A radar is an electro-magnetic device capable of transmitting a electro-magnetic wave near 1-110 Ghz receives back a reflection from a target and based on the characteristics of the returned signal determine things about the target. Radar is an electromagnetic system for the detction and location of reflecting objects such as aircraft ship spacecraft vehicles people and the natural environment. it operates by radiating energy into space and detecting the echo signal reflected from an object or target. The reflected energy that is returned to the radar not only indicates the presence of a target but by comparing the received echo signal with the signal that was transmitted its location can be deterined along with othertarget –related information. Radar can perform its function at long or short distences and under the conditions impervious to optical and infrared sensors. It can operate in darkness haze fog rain and snow. Its ability to measure distance with very high accuracy and in all wheather is on of its most important attributes. RADAR Radio Detection and Ranging is basically a means of gathering information about distant objects. 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 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. 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 defense provide maximum operational effectiveness with a safe efficient and flexible use of the air space. The increased operational

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Seminar Report Military Radar System effectiveness is obtained by combining the advantages of centralized air defense management with decentralized air defense control. BASIC PRINCIPLE OF RADAR A transmitter generates an electromagnetic signal such as sine wave that is radiated into the space by using an antenna. A portion of the transmitted energy is intercepted by the target and reradiated in many directions. The reradiation directed back towards the radar is collected by the radar antenna which delivers it to the receiver. There it is processed to detect the presence of the target and determine is location. Figure 1. Basic principle of radar Range to a target The most common radar signal or waveform is a series of short-duration somewhat rectangular-shaped pulses modulating a sine wave carrier. “The range to a target is determined by the time TR is takes the radar signal to travel to the target and back.” The range to a target then ………………..1 Transmitter Receiver Transmitted signal Echo signal Range to target Antenna Target detection and information extraction R - 2

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Seminar Report Military Radar System Here c the velocity of light 3×10 8 ⁄ TR the time taken by signal to reach the target and back to radar in μ sec. R in km i.e. Rkm .15 T μs .………………2 Radar equation By using the radar equation we can find range beyond which a radar cannot detect any object. Radar equation is √ 2 4 2 4 ……………3 Here Pt transmitted power by antenna A e effective area of receiving antenna radar cross section of the target wavelength of transmitted signal Smin mininum power of signal detectable to antenna. Radar frequencies Band designation Nominal frequency range L-band 1-2 GHz S-band 2-4 GHz C-band 4-8 GHz X-band 8-12 GHz Ku-band 12-18 GHz Ka-band 27-40 GHz

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Seminar Report Military Radar System FIRST USE OF RADAR IN MILITARY During the 1930s efforts to use radio echoes for aircraft detection were initiated independently and almost simultaneously in eight countries that were concerned with the prevailing military situation and that already had practical experience with radio technology. The United States Great Britain Germany France the Soviet Union Italy the Netherlands and Japan all began experimenting with radar within about two years of one another and embarked with varying degrees of motivation and success on its development for military purposes. Several of these countries had some form of operational radar equipment in military service at the start of World War II. The first observation of the radar effect at the U.S. Naval Research Laboratory NRL in Washington D.C. was made in 1922. NRL researchers positioned a radio transmitter on one shore of the Potomac River and a receiver on the other. A ship sailing on the river unexpectedly caused fluctuations in the intensity of the received signals when it passed between the transmitter and receiver. The first radars developed by the U.S. Army were the SCR-268 at a frequency of 205 MHz for controlling antiaircraft gunfire and the SCR-270 at a frequency of 100 MHz for detecting aircraft. Both of these radars were available at the start of World War II as was the navy’s CXAM shipboard surveillance radar at a frequency of 200 MHz. It was an SCR-270 one of six available in Hawaii at the time that detected the approach of Japanese warplanes toward Pearl Harbor near Honolulu on December 7 1941 however the significance of the radar observations was not appreciated until bombs began to fall. In the present time radar is an important part of air defense system as well as operations of offensive missiles and other weapon. In air defense it performs the function of surveillance and weapon control. The Surveillance system includes target detection target recognition target tracking and designation to a weapon system. Weapon- control radars track targets direct the weapon to an intercept and assess the effectiveness of the engagement called battle damage assessment. A missile system might employ radar methods for the guidance and fuzing of the weapon. High-resolution imaging radar such as synthetic aperture radar has been used for the reconnaissance purposes and for detecting the fixed and moving targets on the battlefield.

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Seminar Report Military Radar System ADVANCED FEATURES OF RADAR  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 several condition.  Highly mobile system to be used in all kind of terrain.  Highly accurate angle tracking of targets.  Flexible weapon integration and unlimited number of single air defense weapons can be provided with target data.  High resolution which gives excellent target discrimination and accurate tracking.  Radar can make in-storm measurements. The identification of the targets as friend or hostile is supported by IFF 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.

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Seminar Report Military Radar System THE SYSTEM CONFIGURATION A typical military radar system can be split up into three parts: 1 Radar group The 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 waveguide drier and IFF interrogator. The transmitter and receiver form 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. 2 Shelter Shelter 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 generator The motor generator supplies power to the whole radar system. 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. In the parallax correction function the target data received in the X and Y co-ordinates is transferred into the polar co-ordinates with respect to the entered weapon position.

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Seminar Report Military Radar System 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. 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. 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 following block diagram: - Figure 2. Data flow in a typical military radar system. Target detection by radar Track initiation and Identification Automatic target tracking and IFF Status Message transmitted to weapon systems Target track data put in encoded message

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Seminar Report Military Radar System  Detection 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. PPI Plan Position Indicator:- A typical radar display for a radar is the PPI. The PPI is a presentation that maps in polar co-ordinates the location of the target in azimuth and range. Figure 3. Example of a PPI display  Automatic Target Tracking After target detection a track is initiated by indicating the target video 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.  Identification The identification function comprises: - 1 Interrogation of a target detected 2 Decoding IFF responses

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Seminar Report Military Radar System 3 Display of the decoded IFF responses on the PPI IFF Identification Friend or Foe: The IFF interrogator sends a coded challenge in the form of pulse pairs. The selected mode of operation determines the spacing between the pulses. A friendly target’s IFF will automatically reply to the coded challenge with an omni-directional transmission. It sends a different sets of pulses at a slightly different frequency than the interrogator. The IFF interrogator receives the coded reply and process it for display. Recognition of the target is based on PPI display. The coded reply from a friendly normally appears as a dashed line just beyond the target pulse. figure 4. a Pulse sent by interrogator b Reply pulse by object response  Reporting Function to External Terminal Equipment The 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 Alarm The 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.

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Seminar Report Military Radar System TERMINAL EQUIPMENT FUNCTIONS Figure 5. Data flow at weapon systems  Target Decoding The target information is received and decoded. In case no or disturbed target information is received it is indicated on the TDR.  Parallax Correction The 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 Evaluation The 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. Message decoded and parallax correction Firing at Target Target tracking fire control and weapon aiming Target Selection Threat evaluation and display of results as advice

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Seminar Report Military Radar System 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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Seminar Report Military Radar System Figure 6. block diagram of radar TRANSMITTER UNIT ANTENNA VIDEO PROCESSOR RECEIVER UNIT LO + AFC UNIT Modulator Magnetron AFC Control Circuit Sub-Modulator BJD MTI Main Amplifier Linear Detector PSD IF Preamplifier Linear Main Amplifier Image Rejection Miser COHO SSLO AFC Discriminator Lock Pulse Mixer HT UNIT Main Supply High Voltage Supply PPI Unit

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Seminar Report Military Radar System The main units of radar subsystem are: - 1 HT Unit The 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 comprises: a Modulator The modulator consists of the following components: -  Start Pulse Amplifier The start pulse amplifier unit comprises: - 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.  Pulse Unit 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 Magnetron The 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

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Seminar Report Military Radar System 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 produces 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 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 and the magnetron output frequency. The magnetron unit comprises a coaxial tunable magnetron servo motor driving an adjustable plunger. Figure 7. Transmitter Unit AFC circuit and servo amplifier ARC Sensor Readout Module Start Pulse Amplifier Pulse Unit RF Power Sensor Thyratron Magnetron

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Seminar Report Military Radar System 3 LO+AFC Unit The LO+AFC unit determines the frequency of the transmitted radar pulses. It comprises of: - 1 Lock pulse mixer 2 AFC discriminator 3 Solid State Local Oscillator SSLO 4 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: - 1 Image rejection mixer in the receiver unit 2 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

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Seminar Report Military Radar System 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. 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.

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Seminar Report Military Radar System APPLICATION OF RADAR IN MILITARY  Radar is used for the multiple target detection.  Radar is used to direct the weapon to an intercept.  High-resolution imaging radars are used to detect fixed or moving targets in the battlefield.  Radar is used for the guidance of the missile systems. 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 discussed here 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. A magnetron radar system is relatively simple and reliable. As a consequence minimum maintenance is required and thus the system life cycle costs can be kept low. REFERENCES 1 2 3 Merril I. Skolnik ‘Introduction to Radar System’ Tata McGRAW-HILL

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