Transcript Power Point Lecture

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