A short history of Radar 1935-1945 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

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.

Where Radar Started Maxwell and the discovery of electromagnetic waves

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.

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

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

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

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!

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

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

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

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

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!!

In contrast Radar was part of a major organisation

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

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

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

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)

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

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

German Radar Freya Wurzburg Bruneval R V Jones

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

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