A short history of Radar up to 1945 How some mathematical calculations, plus a lot of science helped to win the war Chris Budd, G4NBG

Where Radar Started Maxwell and the discovery of electromagnetic waves The best equation of all

Radar before Radar Hertz: Practical demonstration of radio waves (50cm) and that they were reflected from metallic objects Marconi: Invention of radio communication (long wave) 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: Tizard. Rowe, Blackett, Wimperis Q : Could a bomber be destroyed by a radio ‘death ray’ Sir Robert 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

'Detection and location of aircraft by radio methods’ Watson-Watt 12th Feb 1935

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! 25m 6km 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! A. Wilkins 30 MHz

A question of power P: Transmitter power (100 kW) wavelength Power reaching aircraft at range r: Reflected power: Power reaching receiver: Power received: If r = 10km then received power is in pico Watts!

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

Orfordness, Bawdsey and pulsed radar E G Bowen.. Airborne radar 200MHz Pulsed radar gives range = c t

Chain Home: Good Friday ft 13m Horizontal polarisation 20 stations operational: 400kW 100 mile range … Gave 30 mins warning

Estimation of height h elevation angle deg h height in feet R range in nMiles R Operator measures strength of two signals at antennae at two different heights to find Curvature of earth correction

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

In contrast Radar was part of a major organisation

Aircraft detected using a mixture of statistics and trigonometry Last known position of German aircraft Projected position using trigonometry Estimates of position from Radar stations Position combining the two

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

Problems with the original Radar Systems 13m / 30 MHz 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, 3GHz 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 E G Bowen (Jet Engine and Atomic Bomb) Developed in the MIT radiation lab: 10cm airborne radar (Lawrence)

Airborne Interception Radar (AI) Bowen!! Early 1.5m/200MHz radar AI mark IV German Ai radar 1 micro second pulse width.. 1 mile/speed of light

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

German Radar Freya Wurzburg BrunevalR V Jones Major use of Bletchley Intercepts!!

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

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