haystack auxiliary radar (hax) millstone hill radar … auxiliary radar (hax) millstone hill radar...
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MIT Haystack Observatory Haystack 2003-1
AJC 7/20/11
Haystack Radar (HY)
Haystack Auxiliary Radar (HAX)
Millstone Hill Radar (MHR)
OUTLINE
More history Index of Refraction More basic radar
MIT Haystack Observatory Haystack 2003-2
AJC 7/20/11
It is frequently said that, although the atomic bomb ended World War II, it was
radar that won the war.
MIT Haystack Observatory Haystack 2003-3
AJC 7/20/11
MIT Radiation Laboratory • 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 Haystack Observatory Haystack 2003-4
AJC 7/20/11
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.
MIT Haystack Observatory Haystack 2003-5
AJC 7/20/11
Millstone
The BMEWS Prototype
Millstone Radar 1957
Sputnik A-Scope Trace
Transmitter Pulse
Echo
Range
Am
plitu
de
First in Space Surveillance
MIT Haystack Observatory Haystack 2003-6
AJC 7/20/11
Outline
• More History • Index of Refraction • More Basic Radar
Appleton - Hartree
but also …
MIT Haystack Observatory Haystack 2003-7
AJC 7/20/11
Radar Range Measurement
Target
• Target range = cτ 2
where c = speed of light τ = round trip time
MIT Haystack Observatory Haystack 2003-8
AJC 7/20/11
Phase Velocity, Group Velocity, Index of Refraction
MIT Haystack Observatory Haystack 2003-9
AJC 7/20/11
Illustration of Atmospheric Effects
Elevation Refraction Range Delay
MIT Haystack Observatory Haystack 2003-10
AJC 7/20/11
MIT Haystack Observatory Haystack 2003-11
AJC 7/20/11
Outline
• More History • Index of Refraction • More Basic Radar
MIT Haystack Observatory Haystack 2003-12
AJC 7/20/11
RADAR RAdio Detection And Ranging
Radar observables: • Target range • Target angles (azimuth & elevation) • Target size (radar cross section) • Target speed (Doppler) • Target features (imaging)
Antenna
Transmitted Pulse
Target Cross
Section
Propagation
Reflected Pulse
(“echo”)
MIT Haystack Observatory Haystack 2003-13
AJC 7/20/11
Radar Block Diagram
Transmitter
Pulse Compression
Recording
Receiver
Tracking & Parameter
Estimation
Console / Display
Antenna
Propagation Medium
Target Cross
Section Doppler Processing A / D
Waveform Generator
Detection
Signal Processor
Main Computer
MIT Haystack Observatory Haystack 2003-14
AJC 7/20/11
Radar Range Equation
R
Transmitted Pulse
Received Pulse
Received Signal Energy
Transmit Power
Transmit Gain
Spread Factor
Target RCS
Spread Factor
Receive Aperture
Dwell Time
Target Cross Section σ
Antenna Aperture A Transmit Power PT
PT 4πA λ2 4πR2
1 σ 4πR2
1 A τ
Losses
L 1
=
MIT Haystack Observatory Haystack 2003-15
AJC 7/20/11
Pulsed Radar Terminology and Concepts
Pow
er
Duty cycle =
Average power = Peak power * Duty cycle
Peak
pow
er
Time
Pulse length
Pulse repetition interval (PRI)
Pulse length Pulse repetition interval
Pulse repetition frequency (PRF) = 1/(PRI)
Continuous wave (CW) radar: Duty cycle = 100% (always on)
Target Return
1 Mwatt
100 kWatt
10%
100 µsec
1 msec
1 kHz
1 µwatt
MIT Haystack Observatory Haystack 2003-16
AJC 7/20/11
Radar Waveforms
Waves?
or Pulses?
Waves, modulated by “on-off” action of
pulse envelope
What do radars transmit?
MIT Haystack Observatory Haystack 2003-17
AJC 7/20/11
Properties of Waves Relationship Between Frequency and Wavelength
Speed of light, c c = 3x108 m/sec = 300,000,000 m/sec
λ
Frequency (1/s) = Speed of light (m/s) Wavelength λ (m)
Examples: Frequency Wavelength 100 MHz 3 m
1 GHz 30 cm 3 GHz 10 cm
10 GHz 3 cm
MIT Haystack Observatory Haystack 2003-18
AJC 7/20/11
Properties of Waves Phase and Amplitude
Amplitude (volts)
Phase, θ
90° phase offset
A
Amplitude (volts)
Phase, θ
A
MIT Haystack Observatory Haystack 2003-19
AJC 7/20/11
Properties of Waves Constructive vs. Destructive Addition
Σ
Constructive (in phase)
Destructive (180° out of phase)
Σ
Partially Constructive (somewhat out of phase)
Σ
Σ
Non-coherent signals (noise)
MIT Haystack Observatory Haystack 2003-20
AJC 7/20/11
Polarization
x
y Electric Field
Magnetic Field
Electromagnetic Wave
x
y
z E
Horizontal Polarization
Electric Field
Magnetic Field
Electromagnetic Wave
x
y
z
E
Vertical Polarization
MIT Haystack Observatory Haystack 2003-21
AJC 7/20/11
Doppler Effect
MIT Haystack Observatory Haystack 2003-22
AJC 7/20/11
Doppler Shift Concept
c v
λ λ = c f
c v
λ f = c λ
c
λ’
f’ = f ± (2v/λ) Doppler shift
MIT Haystack Observatory Haystack 2003-23
AJC 7/20/11
Resolving Doppler
Tx signal: cos(2πfot) Doppler shifted: cos[2π(fo+ fD)t]
Multiply by cos(2πfot) -> Low pass filter -> cos(2πfDt)
BUT, the sign of fD is lost (cosine is an even function)
So, instead use exp(j2πfDt) = cos(2πfDt) + jsin(2πfDt)
Generate this signal by mixing cos and sin via two oscillators (same frequency, 90o out of phase)
Components are called I (In phase) and Q (Quadrature): Aexp(j2πfDt) = I + jQ