ECEN5633 Radar Theory Lecture #19 24 March 2015 Dr. George Scheets n Read 13.3, 9; 9.1 n Problems Web 4, 5, & 6 n Corrected quizzes due 1 week after return n Exam #2, 31 March 2014 (< 4 April DL) n Design problem due 7 April n Exam 1 Final Stats Hi = 94, Low = 46, Average = 75.83, σ = A > 86, B > 72, C > 62, D > 52

ECEN5633 Radar Theory Lecture #20 26 March 2015 Dr. George Scheets n Read 10.1 & 2 n Problems Web 7, 13.2 &10 n Exam #2, 31 March 2014 (< 4 April DL) n Design problem Due 7 April (Live) & 9 April DL

Radar Design Problem n Hypothetical Fighter Search Radar u F-45 Spitwad n Examine some of issues associated with specifying a design n Due in 2 weeks

Radar Design Problem n Search 40º x 40º sector 5 km to 80 km n Standard Pulse Radar or Chirp Radar n Coherent or Non-coherent n Single Pulse, M pulse integration, K of M

Use a Spread Sheet!!! n Tie in costs to design choices u Can see how changes affect cost n Get a system (any system) that works u P(Hit) = 0.68 u RCS = m 2 u Distance = 80 Km n Adjust parameters to reduce Costs u Get some of those extra credit points!

Grading n Real World RFP: u 1 team gets full credit u Everyone else gets a zero n Partial credit u Awarded on Quizzes & Tests u NOT AWARDED ON DESIGN PROJECT! n Real world designs don't get partial credit u Either Work or They Don't n Double check your work!!! Use a spreadsheet

Moving Target Indicator n r(t) = feed from specific azimuth & elevation n y(t) = r(t) – r(t – T) n Y(f) = R(f) – R(f)e -jωT u Has a null at 0 Hz Will suppress low frequency Doppler echoes (Ground clutter, waves, etc.) u Has nulls at integer multiples of PRF = 1/T Hz Has Doppler Blind Speeds at n(PRF*λ/2 m/sec) F n a positive or negative integer

Clutter Map Source: n Stationary Radar? After a few scans clutter stats known u For every Azimuth & Range cell (pixel) u Mean & Standard Deviation n Can be blanked out u Unless cell echo > mean + standard deviation

Look Down, Shoot Down n Standard Pulse Radar u Low Altitude target obscured by ground clutter. n Pulse Doppler Radar u Can detect target if Doppler off aircraft differs enough from Doppler off ground 400 knots Low Altitude High Altitude

Frequency Domain Processing Doppler shift is 0 Hz here. Dashed Line Sinc Function: Set by Pulse Shape Inside smaller Sinc Function: Set by Pulse train Length Distance between small Sinc Functions: Set by PRF PRF Source: Communication and Radar Systems. Nicolaos Tzannes Main lobe is 1/(2Window) Hz wide 1/t p

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/t p Max Doppler Shift

Measuring Doppler (Time Domain) n Coherent Detection u Ideally, get a baseband pulse F Not a function of Doppler Shift u Examine PLL error voltage to VCO u Examine VCO output sinusoid n Noncoherent Detection u Baseband Pulse is function of Doppler Shift u Matched Filter out has time varying amplitude F Can compute Doppler if Nyquist Criteria Met

Direct Conversion Receiver n RCVR Local Oscillator Sinusoid on-frequency n Stationary targets Result in baseband echo with noise n Moving targets with Doppler shift + f d Hz Pulses, AM modulated by low frequency sinusoid, with noise X cos(2πf c t) Low Pass Filter p(t)cos(2πf c t) + n(t) p(t)cos(2π(f c + f d )t + n(t)

Negligible Doppler Shift f d = 0.01 Hz θ = 0.0 degrees t p = 0.3

Small Doppler Shift f d = 1.67 Hz θ = 270 degrees t p = 0.3

Small Doppler Shift f d = 1.67 Hz θ = 90 degrees t p = 0.3 Sample voltage way below any threshold.

Small Doppler Shift f d = 1.8 Hz θ = 148 degrees t p = 0.3 Sample voltage way below any threshold.

I Doppler Shift f d = 5 Hz θ = 0 degrees t p = 0.3 Q Energy not in I component? Then it's in Q component.

Ambiguity Function n X(τ,f) = g(t)g*(t - τ) e j2πft dt n |X(0,0)| = Matched Filter output envelope value at ideal sample time if perfectly matched to echo n |X(0,0)| = Return from desired target ∫ -∞ +∞

Ambiguity Function n X(τ,f) = g(t)g*(t - τ) e j2πft dt n |X(0,0)| = Return from desired target n |X(τ1,f1)| = Interference cause by 2nd target n |X(τ1,f1)| = Matched Filter output envelope value from 2nd target whose echo arrives τ1 seconds early/late, with Doppler shift of f1 Hz τ1 = RTT difference ∫ -∞ +∞