Haystack Radar

Haystack Radar (HY) 

Haystack Auxiliary Radar (HAX) 

Millstone Hill Radar (MHR) 

OUTLINE 

More history 

Index of Refraction 

More basic radar 

Haystack 2003-1 

AJC 7/20/11 

MIT Haystack Observatory

It is frequently said that, 

although the atomic bomb 

ended World War II, it was 

radar that won the war. 


AJC 7/20/11 


MIT Radiation Laboratory 


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• The primary technical barrier to 

developing UHF systems was the lack of a 

usable source for generating high-power 

microwaves. 

• In February 1940, John Randall and 

Harry Boot at Birmingham University in the 

UK built a resonant cavity magnetron. 

• Bombing of London Sept 1940 – May 

1941 (The Blitz) 

• Britain was interested in developing 

practical applications for airborne 

microwave radar, but did not have the 

large-scale manufacturing ability to mass 

produce magnetrons. 

• In1940, Britain partnered with the US 

National Defense Research Committee 

(NDRC) 

• 


MIT Radiation Laboratory 

Over the course of five years, MIT researchers designed 50 percent 

of the radar used in World War II and invented over 100 different 

radar systems. 

Including: 

• Airborne bombing radars 

• Shipboard search radars 

• Harbor and coastal defense radars 

• Interrogate-friend-or-foe beacon systems 

• Long-range navigation (LORAN) system 

• Critical contributions of the Radiation Laboratory were: 

– the microwave early-warning (MEW) radars, which effectively 

nullified the V-1 threat to London, and 

– air-to-surface vessel (ASV) radars, which turned the tide on the U- 

boat threat to Allied shipping. 


AJC 7/20/11 


Millstone 

The BMEWS Prototype 

First in Space Surveillance 

Transmitter 

Pulse 

Echo 

Amplitude 

Range 

Millstone Radar 

1957 

Sputnik 

A-Scope Trace 


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Outline 

• More History 

• Index of Refraction 

• More Basic Radar 

Appleton - Hartree 

but also … 


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Radar Range Measurement 

Target 

• Target range = 

cτ 

2 

where c = speed of light 

τ = round trip time 


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Phase Velocity, Group Velocity, Index of 

Refraction 


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Illustration of Atmospheric Effects 

Elevation Refraction 

Range 

Delay 


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Outline 

• More History 

• Index of Refraction 

• More Basic Radar 


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RADAR 

RAdio Detection And Ranging 

Antenna 

Propagation 

Transmitted 

Pulse 

Reflected 

Pulse 

(“echo”) 

Target 

Cross 

Section 


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Radar observables: 

• Target range 

• Target angles (azimuth & elevation) 

• Target size (radar cross section) 

• Target speed (Doppler) 

• Target features (imaging) 


Radar Block Diagram 

Propagation 

Medium 

Transmitter 

Waveform 

Generator 

Target 

Cross 

Section 

Antenna 

Receiver 

A / D 

Signal Processor 

Pulse 

Compression 

Doppler 

Processing 

Main Computer 

Detection 

Tracking & 

Parameter 

Estimation 

Console / 

Display 

Recording 


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Radar Range Equation 

Antenna Aperture A 

Transmit Power P T 

Transmitted Pulse 

Target Cross Section σ 

Received Pulse 

R 

Received Signal 

Energy 

= 

Transmit 

Power 

P T 

Transmit 

Gain 

4πA 

λ 2 

Spread 

Factor 

1 

4πR 2 

Losses 

1 

L 

Target 

RCS 

σ 

Spread 

Factor 

1 

4πR 2 

Receive 

Aperture 

A 

Dwell 

Time 

τ 


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Pulsed Radar 

Terminology and Concepts 

Pulse length 

100 µsec 

Power 

Peak power 

1 Mwatt 

Target 

Return 

1 µwatt 

Pulse repetition interval 

(PRI) 1 msec 

Time 

Duty cycle = 

Pulse length 

Pulse repetition interval 

10% 

Average power = Peak power * Duty cycle 

100 kWatt 

Pulse repetition frequency (PRF) = 1/(PRI) 

1 kHz 


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Continuous wave (CW) radar: Duty cycle = 100% (always on) 


Radar Waveforms 

What do radars transmit? 

Waves? 

or Pulses? 

Waves, modulated 

by “on-off” action of 

pulse envelope 


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Properties of Waves 

Relationship Between Frequency and Wavelength 

λ 

Speed of light, c 

c = 3x10 8 m/sec 

= 300,000,000 m/sec 

Frequency (1/s) = 

Speed of light (m/s) 

Wavelength λ (m) 

Examples: Frequency Wavelength 


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100 MHz 3 m 

1 GHz 30 cm 

3 GHz 10 cm 

10 GHz 3 cm 



Phase and Amplitude 

Amplitude (volts) 

A 

Phase, θ 

Amplitude (volts) 

A 

90° phase offset 

Phase, θ 


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Constructive vs. Destructive Addition 

Σ 

Σ 

Constructive 

(in phase) 

Partially Constructive 

(somewhat out of phase) 

Σ 

Σ 

Destructive 

(180° out of phase) 


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Non-coherent signals 

(noise) 


Polarization 

Electromagnetic Wave 

y 

Electric Field 

Magnetic Field 

x 

Vertical Polarization 

y 

Horizontal Polarization 

y 

E 

x 


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z 

x 

E 

MIT Haystack Observatory 

z

Doppler Effect 


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Doppler Shift Concept 

λ 

c 

v 

λ f = c 

λ f 

c 


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λ ’ 

f ’ = f ± (2v/λ) 

Doppler 

shift 


Resolving Doppler 

Tx signal: cos(2πf o t) 

Doppler shifted: cos[2π(f o + f D )t] 

Multiply by cos(2πf o t) -> Low pass filter -> cos(2πf D t) 

BUT, the sign of f D is lost (cosine is an even 

function) 

So, instead use 

exp(j2πf D t) = cos(2πf D t) + jsin(2πf D t) 

Generate this signal by mixing cos and sin via two 

oscillators (same frequency, 90 o out of phase) 


AJC 7/20/11 

Components are called I (In phase) and Q 

(Quadrature): Aexp(j2πf D t) = I + jQ

Haystack Radar

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