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1、雷达系统雷达系统 大作业大作业一一 汉译英汉译英1.线性调频信号2.二相编码信号3.侦察和监视雷达4.杂波抑制5.恒虚警检测6.合成孔径雷达7.干涉合成孔径雷达8.匹配滤波9.脉冲压缩10.多普勒滤波器组二二 英译汉英译汉1.RCS2.DPCA3.GMTI4.GMTD5.Discrete Fourier Transform6.in-phase and quadrature components7.PRF8.Doppler frequency of ground return9.Pulse compression10.Detection probability and the false-ala
2、rm probability三 12 选 31The velocity of the airborne radar is 100m/s,the beamwidth of the radaris 3 deg.(constant for different look direction),the wavelength of thetransmitted signal is 0.03m,compute the clutter Doppler bandwidth of themain beam for the following look direction:(a)0 deg(relative to
3、thevelocity direction);(b)30 deg(relative to the velocity direction);(c)60deg(relative to the velocity direction);If the radar antenna is a phased-array antenna,and the broadside of theantenna is parallel to the velocity direction,then compute the clutterDopplerbandwidthofthemainbeamforthefollowingl
4、ookdirection(Assume that the beamwidth of the phased-array at 0 deg is 3deg):(a)0 deg(relative to the velocity direction);(b)30 deg(relative tothe velocity direction);(c)60 deg(relative to the velocity direction).2 2The moon as a radar target may be describe as followings:averagedistance to the moon
5、 is3.844 108m(about 208,000 nmi);experimentally112measured radar cross section is6.6410 m(mean value over a range ofradar frequencies);and its radius is1.73810m.(a)(a)What is the round-trip time(seconds)of a radar pulse to the moon andback?(b)(b)What should the pulse repetition frequency(prf)be in o
6、rder to haveno range ambiguities?(c)(c)For the purpose of probing the nature of the moons surface,a muchhigher prf could be used than that found in(b).How high could the prf beif the purpose is to observe the echoes from the moons half?(d)(d)If an antenna with a diameter of 60 ft and aperture effici
7、ency of 0.6were used at a frequency of 430MHz with a receiver having a minimumdetectable signal of1.51016W,what peak power is required?Doesyour answer surprise you；andifso，why?(e)(e)The radar cross section of a smooth perfectly conducting sphere ofradius a is6a2.What would be the radar cross section
8、 of the moon if itwere a sphere with a perfectlysmoothconducting surface?Why mightthe measured cross section of the moon(given above)be different fromthis value?3 3A radar mounted on all automobile is to be used to determine the distanceto a vehicle traveling directly in front of itThe radar operate
9、s at afrequency of 9375 MHz(Xband)with a pulse width of l0 ns(108s)Themaximum range is to be 500ft(a)(a)What is the pulse repetition frequency that corresponds to a range of500 ft?(b)(b)What is the range resolution(meters)?(c)(c)If the antenna beamwidth were6what would be the cross-rangeresolution(m
10、eters)at a range of 500 ft?Do you think this value ofcross-range resolution is sufficient?(d)(d)If the antenna dimensions were 1 ft by 1 ft and the antenna efficiencywere 0.6,what would be the antenna gain(dB)?(e)(e)Find the average power required to detect a 10m2radar cross sectionvehicle at a rang
11、e of 500 ft,if the minimum detectable signal is51013W.4 4(a)(a)What signal-to-noise ratio is required for a radar that makes adetection on the basis of a single pulse,when the probability of detectionis 0.50 and the probability of false alarm is106?Assume anonfluctuating target echo.(b)(b)Repeat for
12、 a 0.99 probability of detection and the same probability offalse alarm.(c)(c)Repeat parts(a)and(b),but for a Swerling Case 1 fluctuating target.(d)(d)Compare your results in a table.What conclusions can you obtainfrom this?5 5A civil marine radar is employed on boats and ships for observingnavigati
13、on buoys,detecting land-sea boundaries,piloting,and avoidingcollisions.Consider the following civil-marine radar:Frequency:9400MHz(X band)Antenna:horizontal beamwidth=0.8Vertical beamwidth=15Gain=33dBAzimuth rotation rate=20rpmPeak power:25kWPulse width:0.15sPulse repetition rate:4000HzReceiver nois
14、e figure:5dBReceiver bandwidth:15MHzSystem losses:12dBAverage time between false alarms:4 hours(a)(a)Plot the single-scan probability of detection as function of range(nmi),assuming a constant cross-section target of 10m2(a navigation buoy)and free-space propagation.You will find it easier to select
15、 theprobability of detection and find the corresponding single-to-noiseratio,rather than the reverse.You need only consider probabilities ofdetection from 0.30 to 0.99.You may,for purposes of this problem,selecta single(average)value of the integration improvement factor rather thantry to find it as
16、 a function ofPd(since the curve in the text does notpermit otherwise).(b)(b)Repeat(a)for a Swerling Case 1 target fluctuation model withaverage cross section of 10m2.Plot on the same diagram as(a).(c)(c)Comment on whether the average power of this radar is too low,justright,or too high for the job
17、it has to perform here.(d)(d)Why do you think this ship-mounted radar antenna has a15elevation beamwidth when all the targets are located on the surface of thesea?6 6Consider the following air-surveillance radar:Frequency:2.8GHz(S band)Peak power:1.4MWPulse width:0.6sPulse repetition rate:1040HzRece
18、iver noise figure:4dBAntenna rotation rate:12.8rpmAntenna gain:33 dBAntenna azimuth beamwidth:1.35 degSystem losses:12dBAverage false-alarm time:20 minTarget cross section:2m2Plot each of the following on the same coordinates(with range as theabscissa):(a)(a)The free-space single-scan probability of
19、 detection as a function ofrange(in nautical miles)for a constant cross-section target.You will findit easier to select the probability of detection and find the correspondingsingle-to-noise ratio,rather than the reverse.You need only considerprobabilities of detection from 0.30 to 0.99.You may,for
20、purposes of thisproblem,select a single(average)value of the integration improvementfactor rather than try to find it as a function ofPd(since the curve in thetext does not permit otherwise).(b)(b)The probability of detection as a function of range for the samesituation as part(a)but with the detect
21、ion criterion that the target must befound on at least 2 out of 3 scans of the rotating antenna.You mayassume that the range and the received signal power do not changeappreciably over the three scans.For convenience of this calculation,youmay assume that the single-scan false-alarm probability is t
22、he same asused in part(a).(c)(c)Repeat(a)for a Swerling Case 1 with average target cross section of2m2.(d)(d)Repeat(b)for a Swerling Case 1 with average target cross section of2m2.(e)(e)Is theprfadequateforavoidingrangeambiguities?(The radar in this problem is similar to the airport surveillance rad
23、arknown as the ASR.)7 7(a)(a)What is the probability of detecting a target on at least 2 out 4 scanswhen the single-scan probability of detection is 0.8?(b)(b)What is the corresponding probability of false alarm in this case whensingle-scan false-alarm probability is10?(c)(c)What should be the singl
24、e-scan false-alarm probability if the overallfalse-alarm probability with a detection criterion of 2 out 4 scans is10?(d)(d)When the higher single-scan probability of false alarm of part(c)isemployed rather than a10single-scan probability of false alarm,whatreduction in the single-to-noise ratio can
25、 be obtained?8 8An S-band(3.1 GHz)air-surveillance radar utilizes a staggered waveformwith four different prfs,which are 1222,1031,1138,and 1000Hz.(a)(a)What is the first blind speed(knots)if a constant prf is used which hasa pulse repetition period equal to the average of the four periods of thesta
26、ggered waveform?(b)(b)What is the first blind speed(knots)of the staggered prf waveform?888Note that thenifor these four frequencies are 27,32,29,33respectively.(c)(c)What is the maximum unambiguous range of the staggered prfwaveform?(d)(d)What is the depth(dB)of the first null of the staggered prf
27、waveform?(e)(e)What is the maximum MTI improvement factor for the staggered prfwaveform,assuming a gaussian clutter spectrum with a standarddeviation of 10Hz?9 9Consider an MTI radar with a frequency of 440MHz flying in an aircraftat a speed of 320kt.Its azimuth beamwidth is 6 degrees and its prf is
28、330Hz.(a)(a)What is the Doppler frequency of the clutter echo and the spread inthe clutter Doppler at azimuth angles of 0,45,and 90 degrees,where 0 isthe head-on and 90 is the broadside?(You may assume that the elevationangle is zero,which is unrealistic of course,but it makes the problemsimpler.)(b
29、)(b)Assume that TACCAR is applied so that the Doppler clutter frequencyis fully compensated along the center of the main beam(that is,the centerfrequency of the clutter Doppler spectrum is at zero Doppler frequency).DPCA is not applied.Sketch the Doppler space(the resulting clutterspectrum as a func
30、tion of Doppler frequency)for the case where the radarantenna is pointing broadside at 90 degrees azimuth angle.For thisproblem you may assume thatcis the same as fc/2.(Drawapproximately to scale along the frequency axis.)(c)(c)What is the value ofc/fpwhen the antenna is pointing broadsideas it is i
31、n part(b),wherefp=prf andc=standard deviation of theclutter spectrum which can be approximated here by fc/2?(d)(d)How well do you think a radar of this type detects moving aircrafttargets in clutter?1010Derivetheerrorsignalinoneanglecoordinatefortheamplitude-comparison monopulse.Show that for small
32、angular errors,theerror signal is proportional to,whereis the angle of the targetmeasured from the antenna pointing direction.The angular separationbetween the two squinted antenna beams is 2the one-way(voltage)pattern of the two antenna beams when not squinted can be approximated2by the normalized
33、gaussian function exp(a22/2);wherea2 2.776/B,andBis the half-power beamwidth.Note that the hyperbolic cosine canbe expressed as coshx(exex)/2and the hyperbolic sine as sinhx(exex)/2;and for small values of x,sin x x and cosh x 1.Also,sinh 2x=2sinh x cosh x.1111This problem involves range glint.(a)(a
34、)A dumbbell target at a long range from the radar has its twounresolved equal cross-section isotropic scatterers located in line in theradial(range)direction and separated by 10m.What is the phase differentbetween the echoes from these two scatterers when viewed by a radar at afrequency of 3GHz?What
35、 is the range glint error in this case?(b)(b)What change in aspect angle(such as might be caused by a rotation oftarget about its center)will cause the two echoes to be by180out ofphase,resulting is a severe glint error in range?(c)(c)What change in frequency is needed to decorrelate the echo when t
36、hetarget is oriented as in(b)?(d)(d)What must be the pulse width in(a)in order to resolve the twoscatterers(so that glint may be avoided)?1212There are two methods for finding the radial velocity of a target.One isbased on the Doppler shiftfd2vr/;the other is based on the rate ofchange of range with
37、 time R/t.They give different measurementaccuracies.(a)(a)What is the expression for the radial velocity error,vd,found bymeasuring the Doppler frequency shift of a long quasi-rectangular pulseof widthand RF frequencyf0?(b)(b)What is the expression for the radial velocity error,vr,found fromthe rate
38、 of change of range based on two range measurementsR1andR2separated by a time,so that the velocity isvr(R2R1)/,andisthe same as the pulse width of the Doppler measurements?The pulses inthis range-rate measurement are of Gaussian shape with a half-powerbandwidthTR1.18(2E/N0)1/2Buseright-handsideofequ
39、ation1.18.Assume the total value of2E/N01/2B(2E/N0)in each of these two methods for radial velocity measurement(a)and(b)is the same.(c)(c)What is the value ofvd/vr?(d)(d)Based on your answer in(c),which is the more accurate method ofvelocity measurement,the Doppler method or the range-rate method?(e
40、)(e)Under what conditions will these two methods give comparableaccuracies(assuming the same total2E/N0)?(f)(f)Why do you think the Doppler method has not been used very oftenfor a velocity measurement?167424523583494851291661177458811112912610674115101112936135291471215596169371787118119120921322323102410251026102732811295304314329332345352361137738839440551052116762129631495917891041132118349733129436125108106