75 Years of Radar

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75 Years of Radar
A short history of Radar 1935-1945 How some
mathematical calculations, plus a lot of science,
won the war Chris Budd
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• Some significant
  anniversaries this year
• 75 years 1935 Invention of Radar
• 70 years 1940 Invention of the Cavity
  Magnetron
• Battle of
  Britain
• Tizard Mission
  to the USA
• Wednesday Statue for Keith Park

• Invention of Radar
• Chain Home
• Battle of Britain
• Cavity Magnetron
• Airborne Radar
• German developments and how the UK found out
• Other uses of Radar
• What radar led to.

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Where Radar Started
Maxwell and the discovery of electromagnetic waves
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Radar before Radar
Hertz Practical demonstration of radio waves and
that they were reflected from metallic
objects Marconi Invention of radio communication
In 1899 he proposed used of CW Radio to detect
ships in fog and demonstrated by Christian
Huelsmeyer 1904 then used on the Normandie
1930s Set up of commercial radio
stations Complaints by listeners of interference
when aeroplanes flew near. Report on reflected
radio waves by Post Office Engineers 1933.
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The British Invention of Radar
Problem vulnerability of UK to bombing
attack The bomber will always get through
Baldwin 1934 Defence committee set up under
Henry Tizard and A. Rowe
Q. 1935 Could a bomber be destroyed by a radio
death ray
Watson Watt (NPL), showed by calculation that
this was not possible, as it required 5 GW of
power BUT calculations (by Wilkins) showed that
radio waves scattered by an aircraft could be
detected. This indicated that the aircraft and
its range could be found
Worried about a factor of 10
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12th Feb 1935

• 'Detection and location of aircraft by radio
  methods
• Watson-Watt
• Strength of radar reflection
• Optimum wavelength
• Range estimation using pulses
• Position by three ranges
• Cathode ray tube

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The basic physics behind the early radar
Dipole aerial . This is a transmitter and also a
reflector of radio waves current I_0
Radiation pattern
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The maths behind the memorandum how maths won
the war!
25m
A. Wilkins
50m wavelength
6km
Height 18m optimises ground reflection
18m
Field at target per
amp of antenna current Current in target wing I
1.5 mA per amp of antenna current Received field
per amp of antenna
current Amp 15A .. So received field
which is detectable!
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26th Feb 1935 Daventry Experiment
Sir Hugh Dowding 10 000
49.8m
Heyford bomber
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1935-1939 Orfordness, Bawdsey and pulsed radar
Pulsed radar gives range c t
Taffy Bowen .. Airborne radar 200Mhz
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Chain Home Good Friday 1939
20 stations operational 100 mile range Gave 30
mins warning
13m Horizontal polarisation
350ft
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Estimation of height
elevation angle deg h height in feet R
range in nMiles
R
h
Curvature of earth correction
Operator measures strength of two signals at
antennae at two different heights to find
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Chain Home and the Battle of Britain
July-Sept 1940. 15th Sept Battle of Britain Day
K. Park and H. Dowding
600 RAF vs. 2000 Luftwaffe
Germans dismissed Radar thinking that a ground
station could only control one aircraft at a
time!!
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In contrast Radar was part of a major organisation
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Never in the field of human conflict was so much
owed by so many to so few.
Operations room 11 Group Uxbridge
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Problems with the original Radar Systems

• 12m wavelength gave poor resolution
• lots of ground clutter
• poor directional finding RDF
• too large to fit easily in an aircraft

Solution .. Use much smaller wavelength eg. 10cm
But .. Problems with existing Klystron valves
(TRE) generating enough power at microwave
frequencies
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The Birmingham Connection The Cavity Magnetron
Oliphant, Randall and Boot 21/02/1940 University
of Birmingham/GEC
Kilowatts of power at centimetric wavelengths!
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Tizard Mission
September 1940 British scientific secrets taken
to America 15kW Magnetron no. 12 .. Taffy
Bowen (Jet Engine and Atomic Bomb)
Developed in the MIT radiation lab 10cm airborne
radar (Lawrence)
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Airborne Interception Radar (AI)
1 micro second pulse width .. 1 mile/speed of
light
Early 1.5m/200MHz radar AI mark IV
German Ai radar
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H2S Radar April
1942 Blumlein, Dee, Rowe, Lovell
TRE Malvern A Rowe
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German Radar
Freya
Wurzburg
Bruneval
R V Jones
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Other uses of Radar
Anti Submarine Radar Radar based navigation
Oboe Jamming Window/Chaff
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What RADAR led to
Radio Astronomy Microwave cooking
Hey Radio interference from the sun
Lovell Jodrell Bank