The first observation of the radar effect at the U.S. Several of these countries had some form of operational radar equipment in military service at the start of World War II. The United States, Great Britain, Germany, France, the Soviet Union, Italy, the Netherlands, and Japan all began experimenting with radar within about two years of one another and embarked, with varying degrees of motivation and success, on its development for military purposes. First military radarsĭuring the 1930s, efforts to use radio echoes for aircraft detection were initiated independently and almost simultaneously in eight countries that were concerned with the prevailing military situation and that already had practical experience with radio technology. None of these, however, proved effective. Researchers also experimented with infrared sensors. These included listening for the acoustic noise of aircraft engines and detecting the electrical noise from their ignition. Most of the countries that developed radar prior to World War II first experimented with other methods of aircraft detection. This prompted the major countries of the world to look for a means with which to detect the approach of hostile aircraft. There was simply no economic, societal, or military need for radar until the early 1930s, when long-range military bombers capable of carrying large payloads were developed. Hülsmeyer built his invention and demonstrated it to the German navy but failed to arouse any interest. In 1904 a patent for “an obstacle detector and ship navigation device,” based on the principles demonstrated by Hertz, was issued in several countries to Christian Hülsmeyer, a German engineer. The potential utility of Hertz’s work as the basis for the detection of targets of practical interest did not go unnoticed at the time. Hertz demonstrated these properties in 1888, using radio waves at a wavelength of 66 cm (which corresponds to a frequency of about 455 MHz). Maxwell’s work led to the conclusion that radio waves can be reflected from metallic objects and refracted by a dielectric medium, just as light waves can. Maxwell had formulated the general equations of the electromagnetic field, determining that both light and radio waves are examples of electromagnetic waves governed by the same fundamental laws but having widely different frequencies. Hertz set out to verify experimentally the earlier theoretical work of Scottish physicist James Clerk Maxwell. Serious developmental work on radar began in the 1930s, but the basic idea of radar had its origins in the classical experiments on electromagnetic radiation conducted by German physicist Heinrich Hertz during the late 1880s.
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