1. A short history of Radar 1935-1945
75 Years of Radar
A short history of Radar
How some mathematical calculations, plus a lot of science, won the war
Chris Budd

2. Some significant anniversaries this year
75 years: Invention of Radar
70 years: 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.

3. Where Radar Started
Maxwell and the discovery of electromagnetic waves

4. 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.

5. 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 : 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

6. 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

7. 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

8. The maths behind the memorandum: how maths won the war!
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!

9. 26th Feb 1935: Daventry Experiment
Sir Hugh Dowding
£10 000
49.8m
Heyford bomber

10. 1935-1939 Orfordness, Bawdsey and pulsed radar
Pulsed radar gives range = c t
Taffy Bowen .. Airborne radar 200Mhz

11. Chain Home: Good Friday 1939
20 stations operational
100 mile range … Gave 30 mins warning
13m Horizontal polarisation
350ft

12. Estimation of height R h 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

13. Chain Home and the Battle of Britain
July-Sept th Sept = Battle of Britain Day
K. Park and H. Dowding
600 RAF vs Luftwaffe
Germans dismissed Radar thinking that a ground station could only control one aircraft at a time!!

14. In contrast Radar was part of a major organisation

15. Operations room 11 Group Uxbridge
Never in the field of human conflict was so much owed by so many to so few.
Operations room 11 Group Uxbridge

16. 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

17. The Birmingham Connection: The Cavity Magnetron
Oliphant, Randall and Boot: 21/02/1940
University of Birmingham/GEC
Kilowatts of power at centimetric wavelengths!

18. Tizard Mission September 1940
British scientific secrets taken to America
15kW Magnetron no Taffy Bowen
(Jet Engine and Atomic Bomb)
Developed in the MIT radiation lab: 10cm airborne radar
(Lawrence)

19. 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

20. H2S Radar April 1942
Blumlein, Dee, Rowe, Lovell
TRE Malvern: A Rowe

21. German Radar
Freya
Wurzburg
Bruneval
R V Jones

22. Other uses of Radar
Anti Submarine Radar
Radar based navigation: Oboe
Jamming: Window/Chaff

23. What RADAR led to Radio Astronomy Microwave cooking
Hey: Radio interference from the sun
Lovell: Jodrell Bank