Presentation on theme: "A short history of Radar"— Presentation transcript:
1A short history of Radar 1935-1945 75 Years of RadarA short history of RadarHow some mathematical calculations, plus a lot of science, won the warChris Budd
2Some significant anniversaries this year 75 years: Invention of Radar70 years: Invention of the Cavity MagnetronBattle of BritainTizard Mission to the USAWednesday: Statue for Keith ParkInvention of RadarChain HomeBattle of BritainCavity MagnetronAirborne RadarGerman developments and how the UK found outOther uses of RadarWhat radar led to.
3Where Radar StartedMaxwell and the discovery of electromagnetic waves
4Radar before RadarHertz: Practical demonstration of radio waves and that they were reflected from metallic objectsMarconi: Invention of radio communicationIn 1899 he proposed used of CW Radio to detect ships in fog and demonstrated by Christian Huelsmeyer 1904 then used on the Normandie1930s Set up of commercial radio stationsComplaints by listeners of interference when aeroplanes flew near. Report on reflected radio waves by Post Office Engineers 1933.
5The British Invention of Radar Problem: vulnerability of UK to bombing attack:‘The bomber will always get through’ Baldwin1934: Defence committee set up under Henry Tizard and A. RoweQ : 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 powerBUT calculations (by Wilkins) showed that radio waves scattered by an aircraft could be detected.This indicated that the aircraft and its range could be foundWorried about a factor of 10
612th Feb 1935 'Detection and location of aircraft by radio methods’ Watson-WattStrength of radar reflectionOptimum wavelengthRange estimation using pulsesPosition by three rangesCathode ray tube
7The basic physics behind the early radar Dipole aerial …. This is a transmitter and also a reflector of radio wavescurrent I_0Radiation pattern
8The maths behind the memorandum: how maths won the war! A. Wilkins50m wavelength6kmHeight = 18m optimises ground reflection=18mField at target per amp of antenna currentCurrent in target wing I = 1.5 mA per amp of antenna currentReceived field per amp of antenna currentAmp = 15A .. So received field which is detectable!
926th Feb 1935: Daventry Experiment Sir Hugh Dowding£10 00049.8mHeyford bomber
101935-1939 Orfordness, Bawdsey and pulsed radar Pulsed radar gives range = c tTaffy Bowen .. Airborne radar 200Mhz
11Chain Home: Good Friday 1939 20 stations operational100 mile range … Gave 30 mins warning13m Horizontal polarisation350ft
12Estimation of height R h elevation angle deg h height in feet R range in nMilesRhCurvature of earth correctionOperator measures strength of two signals at antennae at two different heights to find
13Chain Home and the Battle of Britain July-Sept th Sept = Battle of Britain DayK. Park and H. Dowding600 RAF vs LuftwaffeGermans dismissed Radar thinking that a ground station could only control one aircraft at a time!!
14In contrast Radar was part of a major organisation
15Operations 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
16Problems with the original Radar Systems 12m wavelength gave poor resolutionlots of ground clutterpoor directional finding … RDFtoo large to fit easily in an aircraftSolution .. Use much smaller wavelength eg. 10cmBut .. Problems with existing Klystron valves (TRE) generating enough power at microwave frequencies
17The Birmingham Connection: The Cavity Magnetron Oliphant, Randall and Boot: 21/02/1940University of Birmingham/GECKilowatts of power at centimetric wavelengths!
18Tizard Mission September 1940 British scientific secrets taken to America15kW Magnetron no Taffy Bowen(Jet Engine and Atomic Bomb)Developed in the MIT radiation lab: 10cm airborne radar(Lawrence)
19Airborne Interception Radar (AI) 1 micro second pulse width .. 1 mile/speed of lightEarly 1.5m/200MHz radar AI mark IVGerman Ai radar
20H2S Radar April 1942Blumlein, Dee, Rowe, LovellTRE Malvern: A Rowe