Haystack Radar
Haystack Radar
Haystack Radar
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<strong>Haystack</strong> <strong>Radar</strong> (HY)<br />
<strong>Haystack</strong> Auxiliary <strong>Radar</strong> (HAX)<br />
Millstone Hill <strong>Radar</strong> (MHR)<br />
OUTLINE<br />
More history<br />
Index of Refraction<br />
More basic radar<br />
<strong>Haystack</strong> 2003-1<br />
AJC 7/20/11<br />
MIT <strong>Haystack</strong> Observatory
It is frequently said that,<br />
although the atomic bomb<br />
ended World War II, it was<br />
radar that won the war.<br />
<strong>Haystack</strong> 2003-2<br />
AJC 7/20/11<br />
MIT <strong>Haystack</strong> Observatory
MIT Radiation Laboratory<br />
<strong>Haystack</strong> 2003-3<br />
AJC 7/20/11<br />
• The primary technical barrier to<br />
developing UHF systems was the lack of a<br />
usable source for generating high-power<br />
microwaves.<br />
• In February 1940, John Randall and<br />
Harry Boot at Birmingham University in the<br />
UK built a resonant cavity magnetron.<br />
• Bombing of London Sept 1940 – May<br />
1941 (The Blitz)<br />
• Britain was interested in developing<br />
practical applications for airborne<br />
microwave radar, but did not have the<br />
large-scale manufacturing ability to mass<br />
produce magnetrons.<br />
• In1940, Britain partnered with the US<br />
National Defense Research Committee<br />
(NDRC)<br />
•<br />
MIT <strong>Haystack</strong> Observatory
MIT Radiation Laboratory<br />
Over the course of five years, MIT researchers designed 50 percent<br />
of the radar used in World War II and invented over 100 different<br />
radar systems.<br />
Including:<br />
• Airborne bombing radars<br />
• Shipboard search radars<br />
• Harbor and coastal defense radars<br />
• Interrogate-friend-or-foe beacon systems<br />
• Long-range navigation (LORAN) system<br />
• Critical contributions of the Radiation Laboratory were:<br />
– the microwave early-warning (MEW) radars, which effectively<br />
nullified the V-1 threat to London, and<br />
– air-to-surface vessel (ASV) radars, which turned the tide on the U-<br />
boat threat to Allied shipping.<br />
<strong>Haystack</strong> 2003-4<br />
AJC 7/20/11<br />
MIT <strong>Haystack</strong> Observatory
Millstone<br />
The BMEWS Prototype<br />
First in Space Surveillance<br />
Transmitter<br />
Pulse<br />
Echo<br />
Amplitude<br />
Range<br />
Millstone <strong>Radar</strong><br />
1957<br />
Sputnik<br />
A-Scope Trace<br />
<strong>Haystack</strong> 2003-5<br />
AJC 7/20/11<br />
MIT <strong>Haystack</strong> Observatory
Outline<br />
• More History<br />
• Index of Refraction<br />
• More Basic <strong>Radar</strong><br />
Appleton - Hartree<br />
but also …<br />
<strong>Haystack</strong> 2003-6<br />
AJC 7/20/11<br />
MIT <strong>Haystack</strong> Observatory
<strong>Radar</strong> Range Measurement<br />
Target<br />
• Target range =<br />
cτ <br />
2<br />
where c = speed of light<br />
τ = round trip time<br />
<strong>Haystack</strong> 2003-7<br />
AJC 7/20/11<br />
MIT <strong>Haystack</strong> Observatory
Phase Velocity, Group Velocity, Index of<br />
Refraction<br />
<strong>Haystack</strong> 2003-8<br />
AJC 7/20/11<br />
MIT <strong>Haystack</strong> Observatory
Illustration of Atmospheric Effects<br />
Elevation Refraction<br />
Range<br />
Delay<br />
<strong>Haystack</strong> 2003-9<br />
AJC 7/20/11<br />
MIT <strong>Haystack</strong> Observatory
<strong>Haystack</strong> 2003-10<br />
AJC 7/20/11<br />
MIT <strong>Haystack</strong> Observatory
Outline<br />
• More History<br />
• Index of Refraction<br />
• More Basic <strong>Radar</strong><br />
<strong>Haystack</strong> 2003-11<br />
AJC 7/20/11<br />
MIT <strong>Haystack</strong> Observatory
RADAR<br />
RAdio Detection And Ranging<br />
Antenna<br />
Propagation<br />
Transmitted<br />
Pulse<br />
Reflected<br />
Pulse<br />
(“echo”)<br />
Target<br />
Cross<br />
Section<br />
<strong>Haystack</strong> 2003-12<br />
AJC 7/20/11<br />
<strong>Radar</strong> observables:<br />
• Target range<br />
• Target angles (azimuth & elevation)<br />
• Target size (radar cross section)<br />
• Target speed (Doppler)<br />
• Target features (imaging)<br />
MIT <strong>Haystack</strong> Observatory
<strong>Radar</strong> Block Diagram<br />
Propagation<br />
Medium<br />
Transmitter<br />
Waveform<br />
Generator<br />
Target<br />
Cross<br />
Section<br />
Antenna<br />
Receiver<br />
A / D<br />
Signal Processor<br />
Pulse<br />
Compression<br />
Doppler<br />
Processing<br />
Main Computer<br />
Detection<br />
Tracking &<br />
Parameter<br />
Estimation<br />
Console /<br />
Display<br />
Recording<br />
<strong>Haystack</strong> 2003-13<br />
AJC 7/20/11<br />
MIT <strong>Haystack</strong> Observatory
<strong>Radar</strong> Range Equation<br />
Antenna Aperture A<br />
Transmit Power P T<br />
Transmitted Pulse<br />
Target Cross Section σ <br />
Received Pulse<br />
R<br />
Received Signal<br />
Energy<br />
=<br />
Transmit<br />
Power<br />
P T<br />
Transmit<br />
Gain<br />
4πA <br />
λ 2 <br />
Spread<br />
Factor<br />
1<br />
4πR 2 <br />
Losses<br />
1<br />
L <br />
Target<br />
RCS<br />
σ <br />
Spread<br />
Factor<br />
1<br />
4πR 2 <br />
Receive<br />
Aperture<br />
A<br />
Dwell<br />
Time<br />
τ <br />
<strong>Haystack</strong> 2003-14<br />
AJC 7/20/11<br />
MIT <strong>Haystack</strong> Observatory
Pulsed <strong>Radar</strong><br />
Terminology and Concepts<br />
Pulse length<br />
100 µsec<br />
Power<br />
Peak power<br />
1 Mwatt<br />
Target<br />
Return<br />
1 µwatt<br />
Pulse repetition interval<br />
(PRI) 1 msec<br />
Time<br />
Duty cycle =<br />
Pulse length<br />
Pulse repetition interval<br />
10%<br />
Average power = Peak power * Duty cycle<br />
100 kWatt<br />
Pulse repetition frequency (PRF) = 1/(PRI)<br />
1 kHz<br />
<strong>Haystack</strong> 2003-15<br />
AJC 7/20/11<br />
Continuous wave (CW) radar: Duty cycle = 100% (always on)<br />
MIT <strong>Haystack</strong> Observatory
<strong>Radar</strong> Waveforms<br />
What do radars transmit?<br />
Waves?<br />
or Pulses?<br />
Waves, modulated<br />
by “on-off” action of<br />
pulse envelope<br />
<strong>Haystack</strong> 2003-16<br />
AJC 7/20/11<br />
MIT <strong>Haystack</strong> Observatory
Properties of Waves<br />
Relationship Between Frequency and Wavelength<br />
λ <br />
Speed of light, c<br />
c = 3x10 8 m/sec<br />
= 300,000,000 m/sec<br />
Frequency (1/s) =<br />
Speed of light (m/s)<br />
Wavelength λ (m)<br />
Examples: Frequency Wavelength<br />
<strong>Haystack</strong> 2003-17<br />
AJC 7/20/11<br />
100 MHz 3 m<br />
1 GHz 30 cm<br />
3 GHz 10 cm<br />
10 GHz 3 cm<br />
MIT <strong>Haystack</strong> Observatory
Properties of Waves<br />
Phase and Amplitude<br />
Amplitude (volts)<br />
A<br />
Phase, θ <br />
Amplitude (volts)<br />
A<br />
90° phase offset<br />
Phase, θ <br />
<strong>Haystack</strong> 2003-18<br />
AJC 7/20/11<br />
MIT <strong>Haystack</strong> Observatory
Properties of Waves<br />
Constructive vs. Destructive Addition<br />
Σ<br />
Σ<br />
Constructive<br />
(in phase)<br />
Partially Constructive<br />
(somewhat out of phase)<br />
Σ<br />
Σ<br />
Destructive<br />
(180° out of phase)<br />
<strong>Haystack</strong> 2003-19<br />
AJC 7/20/11<br />
Non-coherent signals<br />
(noise)<br />
MIT <strong>Haystack</strong> Observatory
Polarization<br />
Electromagnetic Wave<br />
y<br />
Electric Field<br />
Magnetic Field<br />
x<br />
Vertical Polarization<br />
y<br />
Horizontal Polarization<br />
y<br />
E<br />
x<br />
<strong>Haystack</strong> 2003-20<br />
AJC 7/20/11<br />
z<br />
x<br />
E<br />
MIT <strong>Haystack</strong> Observatory<br />
z
Doppler Effect<br />
<strong>Haystack</strong> 2003-21<br />
AJC 7/20/11<br />
MIT <strong>Haystack</strong> Observatory
Doppler Shift Concept<br />
λ <br />
c<br />
v<br />
λ f = c<br />
λ f <br />
c<br />
<strong>Haystack</strong> 2003-22<br />
AJC 7/20/11<br />
λ ’<br />
f ’ = f ± (2v/λ) <br />
Doppler<br />
shift<br />
MIT <strong>Haystack</strong> Observatory
Resolving Doppler<br />
Tx signal: cos(2πf o t)<br />
Doppler shifted: cos[2π(f o + f D )t]<br />
Multiply by cos(2πf o t) -> Low pass filter -> cos(2πf D t)<br />
BUT, the sign of f D is lost (cosine is an even<br />
function)<br />
So, instead use<br />
exp(j2πf D t) = cos(2πf D t) + jsin(2πf D t)<br />
Generate this signal by mixing cos and sin via two<br />
oscillators (same frequency, 90 o out of phase)<br />
<strong>Haystack</strong> 2003-23<br />
AJC 7/20/11<br />
Components are called I (In phase) and Q<br />
(Quadrature): Aexp(j2πf D t) = I + jQ<br />
MIT <strong>Haystack</strong> Observatory
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