UNIT-1 RADAR -PULSE RADAR OPERATION AND ADVANTAGES

RADAR BASICS UNIT-1 PULSE RADAR SYSTEMS

1. RADAR ENGINEERING IV B . T ec h II sem e ster Dr.K.SANTOSH KUMAR . Assist a nt P r o f e s sor ELECT R O NICS AN D C O MM UN I C A T I O N ENGINE E RING

2. Unit I BASICS OF RADAR

3. BASICS OF RADAR Unit I

4. Radar Ra dio D etection A nd R anging RADIO Means it is using RADIO WAVES(we are working signals in Radio frequency i.e., RF SIGNALS all in GHZ of frequency i.e.,very high frequency) DETECTION main purpose of RADAR is to identify the objects (wheather object is in visinity of radar system or not) RANGING means DISTANCE ,along with identification it finds distance between the object and radar system.

5. RADAR DEFINATION In simpleway RADAR uses Radio frequiencies in order to identify the presence of objects and also calculate the distance between object and radar system (if target is identified) THIS IS MAIN MOTO OF RADAR

6. INTRODUCTION TO RADAR RADAR is all about using radio waves to detect the presence of objects and to find their position(distance) Radar can see through conditions such as darkness, haze, fog, rain, and snow which is not possible for human vision. Radar has the advantage of being able to measure the distance (Range) to the object.

7. Radar simple operation It operates by radiating energy into space and detecting the echo signal reflected from an object or target . In other words It sends the signal and collects back the reflected signal , depending upon the reflected signal strength it identifies what is distance that the target is located (if echo signal is there then we can say target is there)

8. SUMMARY Antenna transmits high power signal( kwatts ) -EM signal when signal touches the object it scattered in many directions because of shape of object A part of the waveform is reflected back to the antenna and it is collected by receving antenna Here reflected signal (recevied signal) is very low power signal is 10^-13 watts (because of scattering so it is amplified to get information

9. Types of Radar systems Pulse radar system - It uses pulse wave CW Radar system - It uses continuous wave,without modulation FM-CW Radar sytem - It uses frequency modulated with continious wave Moving Target Indicator (MTI) Radar system - used for identification of moving targets Pulse Doppler Radar system (PDR) - used for identification of moving targets Tracking Radar -used to identify the future position of the target.

10. BASIC PRINCIPLE OF RADAR For any Radar system has TRANSMITTER SECTION , RECEIVER SECTION and ANTENNA Transmitter transmits signal through antenna (here single antenna for Tx & Rx) it touches the object and it reflects. Here reflected signal is collected back by antenna Transmitted signal strength is more (because transmitted signal has to be travelled very long distance to identify the object, as we dont know where is the exact location of the target, sometimes target may be there or may not be there) so we need to transmit the signal towards the target ,if target is there it is reflected, if not signal goes like that only.

11. Reflected signal is collected back by antenna single antenna here in one time it is acting as transmitting and in OFF time it is acting as receiving antenna and it sends to receiver Recevied signal is processed to identify “R” ( distance between target and Radar system)

12. Duplexer How to provide isolation using single antenna- acting as transmitting and receving antenna Duplexer separates transmitting and receving from damage It protects Receiver section from damage If no duplexer then receiver damages as high power enters into it ,as we know Receiver sensitivity is very high(10^-13 watts) To prevent this we use duplexer.

13. RANGE MEASUREMENT Distance is determined by measuring time taken for radar signal to travel to target and back. what is velocity of the signal travelling between radar system and object is EM velocity i.e.., velocity of light -3x10^8 m/sec The direction of the target may be determined from the direction of arrival of the reflected wave.

14. DISTANCE = VELOCITY X TIME 2R= C X TR R= C * TR/2 where R is distance from radar system to object TR is time taken by signal from radar system to object and from object to radar system C is velocity of EM wave= 3x10^8m/sec

15. Range measurement Radar op e r a t e s b y r a d i a ti n g e n e r g y 1 Nautical mile=1.852 km

16. Radar Waveforms It uses pulse waveform

17. Maximum Unambiguous Range The maximum unambiguous is also called as maximum usable range Echoes that arrive after the transmission of the next pulse are called second-time- around(or multiple-time-around) echoes. The range beyond which targets appear as second-time-around echoes M a x im u m un a m b i g u ous range

18. Radar Range Equation If the power of the radar transmitter is denoted by Pt I f an isotropic antenna is used (one which radiates uniformly in all directions), The power density radiated by antenna at a distance R from the radar is equal to the transmitter power divided by the surface area 4Π R2 of an imaginary sphere o f r ad i u s R • The power density at the target from an antenn a with a transmitting gain G is The measure of the amount of incident power intercepted by the target and reradiated back in the direction of the radar is denoted as the radar cross section σ, and is defined by the relation

19. Radar Range Equation If the effective area of the receiving antenna is denoted Ae, the power Pr, received by the radar is The maximum radar range Rmax is the distance beyond which the target cannot be detected. It occurs when the received echo signal power P, just equals the minimum detectable signal Smin, Antenna theory gives the relationship between the tra n smitting gain and the receiving effective area of an antenna as • T w o othe r f o rm s o f the r ad a equ a r tion

20. Pulse Radar Block Diagram

21. The operation of a typical pulse radar is described with the help of a simple block diagram shown in the figure below. There are two sections of Radar system i ) Transmitter section ii) Receiver Section Transmitter : The transmitter in Fig consists of pulse modulator which generates pulse waveform for transmission. Duplexer : The duplexer acts as a rapid switch to protect the receiver from damage when the high-power transmitter is on. Antenna : The transmitter power is radiated into space by antenna Low noise RF Amplifier : The receiver is almost always a Superheterodyne. Mixer and Local oscillator: The mixer and local oscillator convert the RF signal to the Intermediate Frequency ( IF ). IF Amplifier : It amplifies the IF pulse. IF amplifier is designed as matched filter which maximizes the output peak signal to mean noise ratio.

22. Second Detector : The IF Amplifier followed by the second detector or demodulator. Its purpose is to assist in extracting the signal modulation from the carrier. Video Amplifier : Video amplifier is designed to provide the sufficient amplification or gain to raise the level of the input signal to a magnitude where it can be seen on a display Display : The most common form of cathode-ray tube display is the Plan Position Indicator , or PPI (Fig. a) which maps in polar coordinates the location of the target in azimuth and range. The beam rotates in angle in response to the antenna position. Another form of display is the A-scope , shown in Fig. which plots target amplitude (y axis) vs. range (x axis), for some fixed direction.

23. ELECROMAGNETIC SPECTRUM

24. Table 1.1: Standard radar-frequency letter-band nomenclature

25. Radar Frequencies

26. Radar Applications Air T r a ffi c C o n t r o l ( A T C ) A i r c r a f t N a vi g a tio n Ship Safety R e mo t e Sensing Space L a w E n f o r ceme n t Military

27. Applications of Radar: General Ground-based radar is applied chiefly to the detection, location and tracking of aircraft of space targets Shipborne radar is used as a navigation aid and safety device to locate buoys, shorelines and other ships. It is also used to observe aircraft Airborne radar is used to detect other aircraft, ships and land vehicles. It is also used for mapping of terrain and avoidance of thunderstorms and terrain. Spaceborne radar is used for the remote sensing of terrain and sea.

28. Air Traffic Control : Used to provide air traffic controllers with position and other information on aircraft flying within their area of responsibility (airways and in the vicinity of airports) High resolution radar is used at large airports to monitor aircraft and ground vehicles on the runways, taxiways and ramps. GCA (ground controlled approach) or PAR (precision approach radar) provides an operator with high accuracy aircraft position information in both the vertical and horizontal. The operator uses this information to guide the aircraft to a landing in bad weather. MLS (microwave landing system) and ATC radar beacon systems are based on radar technology

29. Air Navigation : Weather avoidance radar is used on aircraft to detect and display areas of heavy precipitation and turbulence Terrain avoidance and terrain following radar (primarily military) Radio altimeter (FM/CW or Pulse) – to measure height Doppler navigator Ground mapping radar of moderate resolution sometimes used for navigation

30. Ship Safety : These are one of the least expensive, most reliable and largest applications of radar Detecting other craft and buoys to avoid collision Automatic detection and tracking equipment (also called plot extractors) are available with these radars for collision avoidance Shore based radars of moderate resolution are used from harbour surveillance and as an aid to navigation Space : Radars are used for rendezvous and docking and was used for landing on the moon Large ground based radars are used for detection and tracking of satellites Satellite-borne radars are used for remote sensing (SAR, synthetic aperture radar)

31. Prediction of Range Performance (Assumed Range equation may not be accurate) The simple form of the radar equation expressed the maximum radar range Rmax, in terms of radar and target parameters Above equation is just assumption but effected with noise , target cross section (not constant ),gain may not be constant etc.. All the parameters are to some extent under the control of the radar designer, except for the target cross section σ.

32. Minimum Detectable Signal Th e w ea k e s t signa l the r ece i v e r c a n d e t ec t is c al l ed the minimum detectable signal. If target is far away we get minimum detectable signal. Detection is based on establishing a threshold level at the output of the receiver. If the r e c e i v e r outp u t e x ceed s the th r esh o l d , a signa l is assumed to be present. This is called threshold detection.

33. Minimum D e t e ctab l e Signal The weakest signal the receiver can detect is called the minimum detectable signal. when we get minimum detectable signal? If targrt is far way we get Smin Probability of Miss. Probability of False Alarm.

34. case1: If threshold level is very high A,B,C are treated as noisy component case2: If threshold level is low level Noise also treated as original target case3: so there is need to choose threshold level properly so threshold level determined by expert radar engineeer.

35. Receiver Noise Noise is nothing but unwanted signal It may be present in any stage in receiver (RF,IF,DETECTOR..) Noise can enter from environment to antenna Noise can be generated within receiver. Because of heat noise is generated at receiver input due to ohmic portion of receiver,such noise is thermal noise

36. Receiver Noise where k = Boltzmann's constant = 1.38 x 10-23 J/deg. The available thermal-noise power generated by a receiver of bandwidth Bn, (in hertz) at a temperature T (degrees Kelvin)

37. NOISE FIGURE Noise figure ( Fn) = Noise out of practical receiver/Noise out of ideal reciver

38. Receiver Noise and SNR

39. INTEGRATION OF RADAR PULSES Summing of all Recevied signal pulses is called Integration Number of hits/scan is n b = θ b f p / θ s where θ b= beam width( angle b/w two half power points) f p=pulse repetation frequency θ s=scanning rate Consider there are ‘n’ number of pulses , grouped together (SNR)n=n.(SNR)

40. WHERE TO PERFORM INTEGRATION If integration is performed before second detector it is known as predetection integration or coherent Integration . If integration is performed after second detector , it is known as post detection interation or Non coherent Integration.

41. INTEGRATION OF RADAR PULSES

42. RADAR CROSS SECTION OF TARGET

43. Integration of Radar puls e s

44. Radar Cross Section

45. T ran smitt e d P o w e r

46. c ies Pulse Repetition Frequen

47. THANKS