ECEN5633 Radar Theory Lecture #25 14 April 2015 Dr. George Scheets n Read 5.3 n Problems 5.3, Web10...
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Transcript of ECEN5633 Radar Theory Lecture #25 14 April 2015 Dr. George Scheets n Read 5.3 n Problems 5.3, Web10...
ECEN5633 Radar TheoryECEN5633 Radar TheoryLecture #25 14 April 2015Lecture #25 14 April 2015Dr. George ScheetsDr. George Scheetswww.okstate.edu/elec-eng/scheets/ecen5633www.okstate.edu/elec-eng/scheets/ecen5633
ECEN5633 Radar TheoryECEN5633 Radar TheoryLecture #25 14 April 2015Lecture #25 14 April 2015Dr. George ScheetsDr. George Scheetswww.okstate.edu/elec-eng/scheets/ecen5633www.okstate.edu/elec-eng/scheets/ecen5633 Read 5.3Read 5.3 Problems 5.3, Web10 & 11 Problems 5.3, Web10 & 11 Reworked Exams Reworked Exams
Due 16 April (Live)Due 16 April (Live) Due 23 April (DL)Due 23 April (DL)
Quiz #3Quiz #3 Live on 21 AprilLive on 21 April DL DL << 28 April 28 April
ECEN5633 Radar TheoryECEN5633 Radar TheoryLecture #26 16 April 2015Lecture #26 16 April 2015Dr. George ScheetsDr. George Scheetswww.okstate.edu/elec-eng/scheets/ecen5633www.okstate.edu/elec-eng/scheets/ecen5633
ECEN5633 Radar TheoryECEN5633 Radar TheoryLecture #26 16 April 2015Lecture #26 16 April 2015Dr. George ScheetsDr. George Scheetswww.okstate.edu/elec-eng/scheets/ecen5633www.okstate.edu/elec-eng/scheets/ecen5633 Read 5.5, 6.1Read 5.5, 6.1 Problems Web 12, 13, & 14Problems Web 12, 13, & 14 Reworked Exams Reworked Exams
Due 16 April (Live)Due 16 April (Live) Due 23 April (DL)Due 23 April (DL)
Quiz #3Quiz #3 Live on 21 AprilLive on 21 April DL DL << 28 April 28 April
h(t) Delays Low Frequency Outputh(t) Delays Low Frequency Output
x(α) h(α)
x(t-α)
Impulse Response h(t)Impulse Response h(t)
h(t)
Impulse In
MatchedFilter
(FIR Filter)
FIR weights = sampled values of h(t)
How does Chirping affect…How does Chirping affect… … … the Ambiguity Function?the Ambiguity Function? … … a doppler shifted waveform?a doppler shifted waveform? … … the P(Hit)?the P(Hit)?
x(t)
What you might see at:Direct Conversion ReceiverOutput of Mixer Low Pass FilterUp ChirpLocal Oscillator tuned to flow
Phases happen to match
Down Chirp Ambiguity FunctionDown Chirp Ambiguity Function
How does Chirping affect…How does Chirping affect…
… … the Ambiguity Function?the Ambiguity Function? Tilts itTilts it
x(t)
Chirp: No DopplerChirp: No Doppler Top: Matched Filter OutputTop: Matched Filter Output Middle: InputMiddle: Input Bottom: Matched Filter Bottom: Matched Filter
Impulse ResponseImpulse Response
ttpp = 1 second = 1 second
(Δf/2) *t(Δf/2) *t2 2 = 3t= 3t2 2
(rate of phase change)(rate of phase change)Instantaneous Frequency Instantaneous Frequency
= 6 Hz at t= 6 Hz at tpp seconds seconds
= = ΔΔf*tf*tpp at t at tpp seconds seconds
Chirp: 0.1 Hz DopplerChirp: 0.1 Hz Doppler Top: Matched Filter OutputTop: Matched Filter Output Middle: InputMiddle: Input Bottom: Matched Filter Bottom: Matched Filter
Impulse ResponseImpulse Response
Chirp: 1 Hz DopplerChirp: 1 Hz Doppler Top: Matched Filter OutputTop: Matched Filter Output Middle: InputMiddle: Input Bottom: Matched Filter Bottom: Matched Filter
Impulse ResponseImpulse Response
Chirp: 4 Hz DopplerChirp: 4 Hz Doppler Top: Matched Filter OutputTop: Matched Filter Output Middle: InputMiddle: Input Bottom: Matched Filter Bottom: Matched Filter
Impulse ResponseImpulse Response
Chirp RadarChirp Radar Transmit a long pulseTransmit a long pulse
Get range resolution of short pulseGet range resolution of short pulse Long pulse has > energy than short pulseLong pulse has > energy than short pulse Can get by with lower voltagesCan get by with lower voltages Doppler Shift → Wrong rangeDoppler Shift → Wrong range Can get around this by…Can get around this by…
Matching up chirp with down chirpMatching up chirp with down chirp
Down Chirp Ambiguity FunctionDown Chirp Ambiguity Function
source: Levanon, Radar Principles
How does Chirping affect…How does Chirping affect… … … the Ambiguity Function?the Ambiguity Function?
Tilts itTilts it
… … a doppler shifted waveform?a doppler shifted waveform? MF peak is at MF peak is at
wrong timewrong time Up Chirp
How does Chirping affect…How does Chirping affect… … … the Ambiguity Function?the Ambiguity Function?
Tilts itTilts it
… … a doppler shifted waveform?a doppler shifted waveform? MF peak is at wrong timeMF peak is at wrong time
… … the P(Hit)?the P(Hit)?
x(t)
Some Equivalent E signalsSome Equivalent E signals 1 vp Square Pulse, t1 vp Square Pulse, tpp = 1 microsecond = 1 microsecond
Power = 1 watt, Energy = 1 Power = 1 watt, Energy = 1 μμ joule joule 220.50.5 vp sinusoid, t vp sinusoid, tpp = 1 microsecond = 1 microsecond
Power = 1 watt, Energy = 1 Power = 1 watt, Energy = 1 μμ joule joule 2 vp Square Pulse, t2 vp Square Pulse, tpp = 0.25 microsecond = 0.25 microsecond
Power = 4 watt, Energy = 1 Power = 4 watt, Energy = 1 μμ joule joule 0.2 vp sinusoid, t0.2 vp sinusoid, tpp = 25 microsecond = 25 microsecond
Power = 0.04 watts, Energy = 1 Power = 0.04 watts, Energy = 1 μμ joule joule
Matched Filter Output SNRMatched Filter Output SNR SNR SNR << 2E/ 2E/No No
= at optimum sample time= at optimum sample time& input signal is perfectly matched& input signal is perfectly matched
SNR = 2PSNR = 2Prrttpp//NNoo = P = Prr/(/(NNooWWNN) [Baseband Pulse]) [Baseband Pulse]
SNR does depend on WSNR does depend on WNN
WN depends on pulse WN depends on pulse envelopeenvelope shape shape
SNR does depend on TSNR does depend on Toosyssys
Considerable Flexibility for Pulse ShapeConsiderable Flexibility for Pulse Shape What matters is the EnergyWhat matters is the Energy
Radar EquationRadar Equation Yields RF power at antenna outputYields RF power at antenna output No Chirp? No doppler?No Chirp? No doppler?
Direct Conversion ReceiverDirect Conversion ReceiverBaseband pulse (out of Mixer LP Filter)Baseband pulse (out of Mixer LP Filter)
Chirp? Chirp? Time Varying SinusoidTime Varying Sinusoid
Sinusoid packs less energySinusoid packs less energy Do we need to adjust P(Hit) equations?Do we need to adjust P(Hit) equations?
How does Chirping affect…How does Chirping affect…
… … the Ambiguity Function?the Ambiguity Function? … … a doppler shifted waveform?a doppler shifted waveform? … … the P(Hit)?the P(Hit)?
Direct Conversion Receiver?Direct Conversion Receiver? PPrr effectively takes a 3 dB hit effectively takes a 3 dB hit