Introduction

History

19th 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

• 1886 - 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 1st 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)

• 1918- 1923 – 1st 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.

• 1935 – 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– 1921 - 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)

• 1935-1936 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

• 1946 - 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