ECEN5633 Radar TheoryECEN5633 Radar TheoryLecture #19 24 March 2015Lecture #19 24 March 2015Dr. George ScheetsDr. George Scheetswww.okstate.edu/elec-eng/scheets/ecen5633www.okstate.edu/elec-eng/scheets/ecen5633

ECEN5633 Radar TheoryECEN5633 Radar TheoryLecture #19 24 March 2015Lecture #19 24 March 2015Dr. George ScheetsDr. George Scheetswww.okstate.edu/elec-eng/scheets/ecen5633www.okstate.edu/elec-eng/scheets/ecen5633 Read 13.3, 9; 9.1Read 13.3, 9; 9.1 Problems Web 4, 5, & 6Problems Web 4, 5, & 6 Corrected quizzes due 1 week after returnCorrected quizzes due 1 week after return Exam #2, 31 March 2014 (Exam #2, 31 March 2014 (<< 4 April DL) 4 April DL) Design problem due 7 April Design problem due 7 April Exam 1 Final StatsExam 1 Final Stats

Hi = 94, Low = 46, Average = 75.83, Hi = 94, Low = 46, Average = 75.83, σσ = 17.83 = 17.83A A >> 86, B 86, B >> 72, C 72, C >> 62, D 62, D >> 52 52

ECEN5633 Radar TheoryECEN5633 Radar TheoryLecture #20 26 March 2015Lecture #20 26 March 2015Dr. George ScheetsDr. George Scheetswww.okstate.edu/elec-eng/scheets/ecen5633www.okstate.edu/elec-eng/scheets/ecen5633

ECEN5633 Radar TheoryECEN5633 Radar TheoryLecture #20 26 March 2015Lecture #20 26 March 2015Dr. George ScheetsDr. George Scheetswww.okstate.edu/elec-eng/scheets/ecen5633www.okstate.edu/elec-eng/scheets/ecen5633

Read 10.1 & 2Read 10.1 & 2 Problems Web 7, 13.2 &10Problems Web 7, 13.2 &10 Exam #2, 31 March 2014 (Exam #2, 31 March 2014 (<< 4 April DL) 4 April DL) Design problemDesign problem

Due 7 April (Live) & 9 April DLDue 7 April (Live) & 9 April DL

Radar Design ProblemRadar Design Problem

Hypothetical Fighter Search RadarHypothetical Fighter Search Radar F-45 SpitwadF-45 Spitwad

Examine some of issues Examine some of issues associated with specifyingassociated with specifyinga designa design

Due in 2 weeksDue in 2 weeks

Radar Design ProblemRadar Design Problem

Search 40º x 40º sectorSearch 40º x 40º sector5 km to 80 km5 km to 80 km

Standard Pulse Radar or Chirp RadarStandard Pulse Radar or Chirp Radar Coherent or Non-coherentCoherent or Non-coherent Single Pulse, M pulse integration, K of MSingle Pulse, M pulse integration, K of M

Use a Spread Sheet!!!Use a Spread Sheet!!! Tie in costs to design choicesTie in costs to design choices

Can see how changes affect costCan see how changes affect cost Get a system (any system) that worksGet a system (any system) that works

P(Hit) = 0.68P(Hit) = 0.68 RCS = 0.005130 mRCS = 0.005130 m22

Distance = 80 KmDistance = 80 Km Adjust parameters to reduce CostsAdjust parameters to reduce Costs

Get some of those extra credit points!Get some of those extra credit points!

GradingGrading Real World RFP: Real World RFP:

1 team gets full credit1 team gets full credit Everyone else gets a zeroEveryone else gets a zero

Partial credit Partial credit Awarded on Quizzes & TestsAwarded on Quizzes & Tests NOT AWARDED ON DESIGN PROJECT!NOT AWARDED ON DESIGN PROJECT!

Real world designs don't get partial creditReal world designs don't get partial credit Either Work or They Don'tEither Work or They Don't

Double check your work!!! Double check your work!!! Use a spreadsheetUse a spreadsheet

Moving Target IndicatorMoving Target Indicator r(t) = feed from specific azimuth & elevationr(t) = feed from specific azimuth & elevation y(t) = r(t) – r(t – T)y(t) = r(t) – r(t – T) Y(f) = R(f) – R(f)eY(f) = R(f) – R(f)e-j-jωωTT

Has a null at 0 HzHas a null at 0 HzWill suppress low frequency Doppler echoes Will suppress low frequency Doppler echoes (Ground clutter, waves, etc.)(Ground clutter, waves, etc.)

Has nulls at integer multiples of PRF = 1/T HzHas nulls at integer multiples of PRF = 1/T HzHas Doppler Blind Speeds at n(PRF*Has Doppler Blind Speeds at n(PRF*λλ/2 m/sec)/2 m/sec)n a positive or negative integern a positive or negative integer

Clutter MapClutter Map

Source: www.radartutorial.eu

Stationary Radar?Stationary Radar?After a few scans clutter stats knownAfter a few scans clutter stats known For every Azimuth & Range cell (pixel)For every Azimuth & Range cell (pixel) Mean & Standard DeviationMean & Standard Deviation

Can be blanked outCan be blanked out Unless cell echo > mean + standard deviationUnless cell echo > mean + standard deviation

Look Down, Shoot DownLook Down, Shoot Down Standard Pulse RadarStandard Pulse Radar

Low Altitude target Low Altitude target obscured by ground obscured by ground clutter.clutter.

Pulse Doppler RadarPulse Doppler Radar Can detect target if Can detect target if

Doppler off aircraft Doppler off aircraft differs enough from differs enough from Doppler off groundDoppler off ground

400 knots

Low Altitude

High Altitude

Frequency Domain ProcessingFrequency Domain Processing

Doppler shift is 0 Hz here.Dashed Line Sinc Function: Set by Pulse ShapeInside smaller Sinc Function: Set by Pulse train LengthDistance between small Sinc Functions: Set by PRF

PRF

Source: Communication and Radar Systems. Nicolaos Tzannes

Main lobe is 1/(2Window) Hz wide

1/tp

Measuring Doppler (Frequency Domain)Measuring Doppler (Frequency Domain)

Measure middle sinc's deviation from 0 Hz.

PRF

Source: Communication and Radar Systems. Nicolaos Tzannes

Main lobe is 1/(2Window) Hz wide

1/tp

Max Doppler Shift

Measuring Doppler (Time Domain)Measuring Doppler (Time Domain)

Coherent DetectionCoherent Detection Ideally, get a baseband pulseIdeally, get a baseband pulse

Not a function of Doppler ShiftNot a function of Doppler Shift

Examine PLL error voltage to VCOExamine PLL error voltage to VCO Examine VCO output sinusoidExamine VCO output sinusoid

Noncoherent DetectionNoncoherent Detection Baseband Pulse is function of Doppler ShiftBaseband Pulse is function of Doppler Shift Matched Filter out has time varying amplitudeMatched Filter out has time varying amplitude

Can compute Doppler if Nyquist Criteria MetCan compute Doppler if Nyquist Criteria Met

Direct Conversion ReceiverDirect Conversion Receiver

RCVR Local Oscillator Sinusoid on-frequencyRCVR Local Oscillator Sinusoid on-frequency Stationary targets Stationary targets

Result in baseband echo with noise Result in baseband echo with noise Moving targets with Doppler shift Moving targets with Doppler shift ++ f fdd Hz Hz

Pulses, AM modulated by low frequency sinusoid, with noisePulses, AM modulated by low frequency sinusoid, with noise

X

cos(2πfct)

Low PassFilter

p(t)cos(2πfct) + n(t)

p(t)cos(2π(fc + fd)t + n(t)

Negligible Doppler Shift

Negligible Doppler Shift

fd = 0.01 Hzθ = 0.0 degreestp = 0.3

Small Doppler Shift

Small Doppler Shift

fd = 1.67 Hzθ = 270 degreestp = 0.3

Small Doppler Shift

Small Doppler Shift

fd = 1.67 Hzθ = 90 degreestp = 0.3

Sample voltage way below anythreshold.

Small Doppler Shift

Small Doppler Shift

fd = 1.8 Hzθ = 148 degreestp = 0.3

Sample voltage way below anythreshold.

I Doppler ShiftDoppler Shift

fd = 5 Hzθ = 0 degreestp = 0.3

Q

Energy not in I component?Then it's in Q component.

Ambiguity FunctionAmbiguity Function

X(X(ττ,f) = g(t)g*(t - ,f) = g(t)g*(t - ττ) e) ej2j2ππft ft dtdt

|X(0,0)| = Matched Filter output envelope|X(0,0)| = Matched Filter output envelope value at ideal sample time value at ideal sample time

ifif perfectly matched to echo perfectly matched to echo

|X(0,0)| = Return from desired target|X(0,0)| = Return from desired target

∫-∞

+∞

Ambiguity FunctionAmbiguity Function

X(X(ττ,f) = g(t)g*(t - ,f) = g(t)g*(t - ττ) e) ej2j2ππft ft dtdt

|X(0,0)| = Return from desired target|X(0,0)| = Return from desired target |X(|X(ττ1,f1)| = Interference cause by 2nd target1,f1)| = Interference cause by 2nd target |X(|X(ττ1,f1)| = 1,f1)| = Matched Filter output envelopeMatched Filter output envelope

value from 2nd target whose echo arrives value from 2nd target whose echo arrives ττ1 seconds early/late, with Doppler shift of1 seconds early/late, with Doppler shift off1 Hzf1 Hz

ττ1 = RTT 1 = RTT differencedifference

∫-∞

+∞