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Dr. Moataz Elsherbini

Benha University Faculty of Engineering- Shoubra Electrical Engineering Department Msc (Communications) CME612

1st semester Final Exam Date: 24/1/ 2017 Radar Systems Duration : 3 hours

Radar - Model Answer Q1 – 30 Marks

(a) What is the operation of radar, classify the types of Radar systems. (5marks) It is an object detection system that uses electromagnetic waves to identify the range ,altitude ,direction or speed of both moving and fixed objects such as aircrafts ,ships ,motor vehicles ,weather formations and terrain. RADAR is an acronym for RAdio Detection And Ranging 1- Reflection of electromagnetic waves 2-Measurement of running time of transmitted pulses

(b) Write the radar equation and the maximum detection range, state what equation is Similar to radar equation and used in radio telecommunication link. (4marks)

Similar to ferris equation in antennas Tranmitter – receiver system

(c) Show how to determine the following parameters using radar systems: (10 marks)

Distance – Direction - Range resolution - Elevation angle - Range Ambiguities Distance

Slant range: is the line of sight distance between the radar and the object illuminated. R = c0· t/2 where: c0 = speed of light = 3·108 m/s

t = measured running time [s] R = slant range antenna - aim [m]

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The distances are expressed in kilometers or nautical miles (1 NM =1.852 km) Direction

The angular determination of the target is determined by the directivity of the antenna. Directivity, directive gain: is the ability of the antenna to concentrate the transmitted energy

in a particular direction. Range resolution

Range resolution : is the ability of a radar system to distinguish between two or more targets on the same bearing but at different ranges.

The degree of range resolution depends on the width of the transmitted pulse, the types and sizes of targets, and the efficiency of the receiver and indicator. Pulse width is the primary factor in range

resolution. Δ R = R 2 − R 1 = c τ / 2 .

where: c0 = speed of light = 3·108 m/s τ = pulse width time

Elevation angle

The elevation angle :is the angle between the horizontal plane and the line of sight, measured in the vertical plane. The Greek letter Epsilon (ε) describes the elevation angle

Range Ambiguities

(d) What are the radar timing parameters. (3marks)

Pulse Repetition Frequency. Duty Cycle. Dwell Time.

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(e) Write on the following terms: (Pulse Repetition Frequency - Duty Cycle - Drwell Time – Noise – Thermal noise power – Clutter – Jamming). ( 8 marks)

- Pulse Repetition Frequency :The Pulse Repetition Frequency (PRF) of the radar system is the number of pulses that are transmitted per second.

- Duty Cycle : Duty cycle is the proportion of time during which component, device, or system is operated.

- Drwell Time : The time that an antenna beam spends on a target is called dwell time TD. The dwell time of a 2D–search radar depends predominantly on: 1) the antennas horizontally beam width ΘAZ and 2) the turn speed n of the antenna (rotations per minute).

- Thermal noise power:

- Clutter: Radio frequency (RF) echoes returned from targets which are uninteresting to the radar

operators. - Jamming: Radio frequency signals originating from sources outside the radar, transmitting in the

radar's frequency and thereby masking targets of interest .

Q2 (15 marks)

(a) Define : Doppler Radar, what is meant by Doppler effect, what is the importance of Doppler effect?

• is a specialized radar that uses the Doppler effect to produce velocity data about objects at a distance. • Most modern weather radars use the pulse-doppler technique to examine the motion of precipitation. • Doppler effect: is the change in frequency or wavelength of a wave for an observer moving relative to

its source. Sometimes called doppler shift. • Importance of doppler effect:

It detects severe weather events that threaten life .

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It detects large hail, damaging winds, tornadoes, and locally heavy, flooding rain. More importantly, this severe weather is seen by the Doppler radar more definitively than with the old conventional radar. The severe weather is often detected minutes quicker than with the old radar, and seen in a more specific area.

(b) Explain the operation of Doppler radar.

• It obtains weather information (wind and precipitation) based upon returned energy. Then it emits a burst of energy. If the energy strikes an object (rain drop, bug, bird, etc.), the energy is scattered in all directions. A small fraction of that scattered energy is directed back toward the radar.

(c) If the maximum unamiguous range of Radar system operates is 500Km, the wavelength is (1 decimeter), calculate:

- Pulse Repetition Frequency (PRF). - The maximum unamiguous velocity ( m/s ). - The beam hight (Km), for an elevation angle of 30o , refractive index of 1.5 and slant range of 180Km.

Rmax = 500Km , λ = 1 Decimeter = 10cm = 0.1m Pulse Repetition Frequency (PRF): C/2Rmax = 3*108/2*500*103= 300 S-1 Vmax = PRF* λ/4 = 300*0.1/4 = 7.5 ms-1 H = SR* Sin(PHI) + (SR*SR)/(2*IR*RE) = 180*sin(30) + (180*180)/(2*1.5*6371)= 91.695Km If angle = 0.3, H = 2.63Km

Q3 ( 15 marks)

(a) Compare between continous wave radar system and pulsed radar system, then list some disadvantages of CW radar systems.

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(b) " CW radar can be used as a speed monitor device" , discuss.

(c) Draw a simple CW radar system which the flicker noise can be reduced.

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Q4 ( 15 marks) (a) Draw the block diagram of FMCW radar, showing the basic features of FMCW radar.

Ability to measure very small ranges to the. Ability to measure simultaneously the target range and its relative velocity. Very high accuracy of range measurement. Signal processing after mixing is performed at a low frequency range, considerably

simplifying the realization of the processing circuits. Safety from the absence of the pulse radiation with a high peak power.

(b) Show the uses of different modulation patterns in FMCW radar measurements.

(c) Discuss the application of FMCW radar in tracking transit.

Ability to detect stationary and moving

objects Only need ONE radar Environmental factors won’t affect the

accuracy of the radar Detects speed and direction

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Q5 ( 15 marks) (a) Explain the concept of operation for sequential lobing and conical scan for a single target Tracking.

B. Conical scan - It’s an extension of sequential lobbing. - The feed of antenna is rotating around the antenna axis .

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(b) Show that the amplitude compression monopulse is more accurate than sequential and conical scanning for a single target Tracking.

(c) "Track while scanning (TWS) is one type pf multiple targets radar systems", discuss the operation Of TWS radar, showing the different gate types generated.

This type of radar is used for multiple targets It scans for new targets while its tracking old targets When TWS scan a new target it initiates a new track file Track file store position and gate data

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Gate Types

1-Acquisition gate 2-Tracking gate 3-Turning gate