Introduction History

19 th Century EM radiation propagating through atmosphere can be reflected, scattered or transmitted at reduced speed –Development of radio technologies bring these effects to light –Realization that information buried in these effects

History Heinrich Hertz discovers wave form of EM radiation –EM waves can be reflected by certain objects –Proves electrical wave identical to optical wave (James Clerk Maxwell’s thesis) 1900 – Nikola Telsa Century Magazine “when we make sound wave we can hear echo – likewise electrical waves also bounce off an object and the echo potentially can tell us the distance and velocity of that object”

History (Continued) 1904 – Christian Holsmeyer – Patent issued by Germany and England after 1 st recorded demonstration of detection of objects by radio –Public demonstration 18 May, 1904 of detection of ships passing under bridge through beam of radio waves Early 1900s – Development of pulsed technology –Under development for detection of submarines using acoustic waves in WWI –EM waves needed new technologies in short wave generation

History (Continued) 1922 – Important studies on propagation of radio waves by Gugliemo Macroni lead to advances in electromagnetic detection 1922 – Navy testing high frequency radio transmission across Potomac river interrupted by passing wooden ship the “Dorchester” –Researchers Albert Hoyt Taylor and Leo C. Young noticed this and suggested that these interruptions be used to detect ships in the night. Later, in 1934 Young and Taylor have similar experience with passing aircraft!

History (Continued) 1925 – First pulsed device making ranging possible 1925 – G. Briet and M Tuve (Dept. of Terrestrial Magnetism of the Carnegie Institution) demonstrate first ranging –In cooperation with radio engineers of the US NRL pulsed a 71.3 m wavelength –NRL transmitter located 10 km southeast of their laboratory and detected echos 150 km from above –Was this first radar??? Yes: because they detected No: because reflection height a function of wavelength and not well defined position of an object

History (Continued) – 1 st real attempts to measure Ionosphere heights by pulsed radar –British physicist W. F. G. Swann came to Univ. of Minnesota where Breit was Assistant Professor and Tuve was Research Fellow. They were unsuccessful but their work led to later work – Atmospheric Scientists brought in Britian –CSSAD Committee for the Scientific Survey of Air Defense approached Robert A. Watson Watt about use of radio waves to find aircraft –Watt was pioneering detection of thunderstorms by detecting radio emissions of lightning –Inquiry triggered Watson-Watt and Collegue A. F. Wilkns to propose a radar system to detect local aircraft –5 months later Watson-Watt demonstrate radio detection and ranging of aircraft – led to a radar network that provided British early detection of approaching German aircraft

History (Continued) 1930’s – Development inUS, Germany, England, Italy, France, Holland, Japan and Hungry 1936 – –April 28 - NRL first definitive detection and ranging of aircraft –14 December Us Army Signal Corp locate airplane by pulse method

History (Continued) Development of Multi-Resonant Cavity Magnetron – High frequency oscillator –1924 – Add split anode design allows generation of ultra-high frequency waves Eric Habann –1924 – August Zacek discovers split anode produces considerable microwave power at wavelengths as short as 29 cm –1927 – Japanese independently develop split anode design with microwave power at 40 cm –1940 – Breakthrough Randall and Vooth achieve 400 Watts of continuous power at 10 cm wavelength! Combined resonant cavity feature of Klystron with high current feature of magnetron cathode to create mulit-resonant cavity structure –1940 – 10 cm Radar developed by GE Research Laboratory in Wembley England and goes into operation

History (Continued) Cowell and Friend detect air mass boundary with 5 cm radar – Friend (1939) showed very good correlation with in situ measurements by aircraft Early 1940’s Pulsed radar developed to better detect aircrtaft in presence of echos from sea and land – frequency shift allows detection…Doppler effects rediscovered, polarization technologies Ryde (1946) publishes work on attenuation and echoing properties of cloud and rain..radar was detecting WEATHER!

Types of Radars Monostatic vs. Bistatic Continuous vs. Pulsed Doppler