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ECEN5633 Radar Theory Lecture #1 13 January 2015 Dr. George Scheets www.okstate.edu/elec-eng/scheets/ecen4533 n Read Chapter 1.1 – 1.4 n Ungraded Homework Problems: 1.1, 2, & 4 Technical Problems? Call (405)744-7234

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ECEN5633 Radar Theory Lecture #2 15 January 2015 Dr. George Scheets www.okstate.edu/elec-eng/scheets/ecen5633 n Read Chapter 1.5 – 1.7 n Problems 1.5, 1.6, 1.9 n Quiz #1, 29 January

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Big Bang n 13.84 + 0.04 billion years ago Picture of Universe Moments Before the Big Bang

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James Clerk Maxwell n Born 1831 n Died 1879 n Scottish Mathematical Physicist n 1865 Maxwell's Equations u Electricity, magnetism, & optics part of same phenomena Source: Wikipedia

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Heinrich Hertz n Born 1857 n Died 1894 n German Physicist n Provided conclusive experimental proof EM waves reflect off some materials Source: Wikipedia

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Radio waves deflected off a RAF Bomber n Robert Watson-Watt u Head, UK Radio Research Station n February 1935 u 6 MHz BBC signal Source: Wikipedia

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Chain Home Radar n Pulse Radar n f c = 22-25 MHz n P peak = 200 Kw n T pulse = 5 - 25μsec n PRF = 25 or 50 pps Source: Wikipedia

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WWII German Radars n "Freya" Pulse Radar n f c = 120 -130 MHz n P peak = 15 -20 Kw n T pulse = 3 μsec n PRF = 500 pps n Could not detect altitude Source: Wikipedia

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WWII German Radars n "Wurzburg" Pulse Radar n f c = 560 MHz n P peak = 8 Kw n T pulse = 2 μsec n PRF = 1,875 pps n Height Finding & Gun Laying Source: Wikipedia

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German Night Fighters circa 1942 - 1943 n Very Short Range Source: Wikipedia

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U.S. Night Fighter n P-61 Black Widow n Deployed Operationally in 1944 n Crew of 3 Source: Wikipedia

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Proximity Fuze n n CW radar inside an AAA projectile n n Operated on Doppler Effect n n 1 st kill in January, 1943 Source: Wikipedia

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WWII Window (Chaff) Source: aess.cs.unh.edu n PPI display of chaff Several minutes after drop u Cut to ½ λ n WWII Lancaster dropping chaff

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Rapid Blooming Chaff n Now standard defensive gear u Against Radar Guided Missiles u Navy Ships u Combat Aircraft Source: Wikipedia & Aerospaceweb.org

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Airborne Jammer Radar Set AN/APT-1 P out < 240 watts Source: lonesentry.com

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Phased Array Radar n Electronically Steerable Beams n 1944 German Mammut u 6 to 8 fixed Freya antennas u Steerable over 100 degree arc n Rare until 70's n Common Now u Pave Paws u Aegis Source: Wikipedia

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Steerable Beam Example fc = 300 MHz λ = 1 meter Same signal fed to both antennas. Beam shoots out both sides at 90 degree angle. Directivity Strength λ/2

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MIMO Example fc = 300 MHz λ = 1 meter Signal to left antenna advanced by 333.3 picosecond ( = 10% wavelength) with respect to right antenna. λ/2 Directivity Strength

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MIMO Example fc = 300 MHz λ = 1 meter Signal to left antenna delayed by 333.3 picosecond ( = 10% wavelength) with respect to right antenna. λ/2 Directivity Strength

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MIMO Example fc = 300 MHz λ = 1 meter Signal to left antenna delayed by 833.3 picosecond ( = 25% wavelength) with respect to right antenna. λ/2 Directivity Strength

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MIMO Example fc = 300 MHz λ = 1 meter Signal to left antenna delayed by 1 2/3 nanosecond ( = 50% wavelength) with respect to right antenna. λ/2 Directivity Strength

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Look Down, Shoot Down n Standard Pulse Radar u Low Altitude target obscured by ground clutter. n Pulse Doppler Radar u Subtract out anything inbound at 400 knots u Moving Target will stick out u Unless… 400 knots Low Altitude High Altitude

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Synthetic Aperture Radar n 1 st Successful Image 15 meter resolution Willow Run Airport, Michigan Source: Wikipedia

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SAR Image (4" resolution) Source: aess.cd.unh.edu

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F-117 Nighthawk Source: Wikipedia

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Impulse Response Non-stealth vs Stealth Source: Cheville & Grischkowsky, "Time Domain THz Impulse Response Studies", Applied Physics Letters, October 1995

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Christian Doppler n Austrian Mathematician & Physicist n Born 1803 n Died 1853 n Paper "On the coloured light of the binary stars and some other stars of the heavens" postulated speeds of stars changed the color of their light. Source: Wikipedia

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Last Time n Selected Historical Radar Highlights n Speed of EM waves u Vacuum: 299.8(10 6 ) m/sec u Air: ≈ 299.7(10 6 ) m/sec u Approximation OK to use: 3(10 8 ) m/sec n Fourier Transform Theory u x(at) ↔ X(f/a)/|a| F a < 1 → freq spread ↓ & center frequency goes down F a > 1 → freq spread ↑ & center frequency goes up

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Previous Class – Doppler Shift n s(t) transmitted? n r(t) = As(t – RTT) if target stationary u A << 1.0 n r(t) = As(αt – RTT + n r(t) = As(αt – RTT + 2v r t o /c) if radial v r ≠ 0 u u α = 1 – 2v r /c transmitted u u α = 1 + 2v r /c > 1.0 if target approaching Received pulse length < transmitted u u Yellow terms = time delay Phase shift in frequency domain t o = time leading pulse edge hits target F F Pulse transmitted at t = 0 seconds

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Frequency Domain n Car approaching at 50 mph = 22.35 m/sec n x(at) ↔ X(f/a)/|a|; a = 1 2v r /c F - if moving closer F + if moving away n a =1 - 2v r /c = 1 – 2(22.34)/(2.997*10 8 ) = 0.99999985 n f transmitted = 10.52 GHz? n f received = 10.52 GHz/0.999999851 = 10,520,001,568 Hz - +

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Doppler Effect 60 mph (26.8 m/sec), 2 m offset, 1.2 GHz

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Parabolic Directional Antennas Source: Web

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