Evan Chipley



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Evan Chipley

Fred Orsaia

Fred, Evan, You’ve made nice progress on identifying technical and military considerations for Radar, and I have a better sense of context for this technology now. You say nothing about policy issues, what leaders of what countries knew about Radar, supported its development, used it in their military operations and planning and so forth. It’s a missing dimension in your development. Still you’ve built a base for further development, and I’m persuaded that you are on your way to a substantive set of papers and web site.
Grade for this stage: B
-RPDS
RADAR

(Radio detecting and ranging)



Radar development


Most of the countries that developed radar prior to World War II first experimented with other methods of aircraft detection. These included listening for the noise of aircraft engines and detecting the electrical noise from their ignition. Researchers also experimented with infrared sensors, however none proved to be useful.

The development of radar came about nine years prior to the start of World War II.  provide the date. The first military developmental work on radar began in the 1930s, but the basic idea of radar had its origins in the experiments on electromagnetic radiation conducted by the German physicist Heinrich Hertz during the late 1880s. Hertz set out to verify experimentally the earlier theoretical work of the Scottish physicist James Clerk Maxwell. 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. Maxwell's work led to the conclusion that radio waves can be reflected from metallic objects and refracted by a medium just like light waves. Hertz demonstrated these properties in 1888, using radio waves at a wavelength of 66 centimeters (a frequency of about 455 MHz).< In this paragraph, are these your words, or have you quoted from a source? If it’s the latter, you’re obliged to say so by way citing a reference.

The potential use of Hertz's work as the basis for the detection of targets of practical interest did not go unnoticed at the time. 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 Hulsmeyer, a German engineer. Hülsmeyer built his invention and demonstrated it to the German navy, but failed to arouse any interest. There was simply no economic, societal, or military need for radar until the early 1930s, when a long-range military bomber capable of carrying large payloads was developed. This prompted the major countries of the world to look for a means with which to detect the approach of hostile aircraft.

First Military Radar


During the 1930s, efforts to use radio echo for aircraft detection were initiated independently and almost simultaneously in several countries that were concerned with the existing military situation and that already had practical experience with radio technology. The United States, Great Britain, Germany, France, the Soviet Union, Italy, and Japan all began experimenting with radar within about two years of one another and embarked, with varying degrees of success, on its development for military purposes. Most of these countries had some form of operational radar equipment in military service at the start of World War II in 1939.

The first observation of the radar effect at the U.S. Naval Research Laboratory (NRL) in Washington, D.C., was made in 1922. NRL researchers positioned a radio transmitter on one shore of the Potomac River and a receiver on the other. A ship sailing on the river caused fluctuations in the intensity of the received signals when it passed between the transmitter and receiver. In spite of the promising results of this experiment, U.S. Navy officials were unwilling to sponsor further work.

The principle of radar was "rediscovered" at the NRL in 1930 when L.A. Hyland observed that an aircraft flying through the beam of a transmitting antenna caused a fluctuation in the received signal. Although Hyland and his associates at the NRL were enthusiastic about the prospect of detecting targets by radio means and were anxious to pursue higher technology, the authorities showed little interest. Not until it was learned how to use a single antenna for both transmitting and receiving (now termed monostatic radar) was the value of radar for detecting and tracking aircraft and ships fully recognized. Such a system was demonstrated at sea on the battleship USS New York in early 1939.< Note how much persuasion technical people must supply before policy people concede the potential value of new technology for military purposes here. This is frequently the case.

First radars developed by the U.S. Army


  1. SCR-268 (at a frequency of 205 MHz) for controlling antiaircraft gunfire

  2. SCR-270 (at a frequency of 100 MHz) for detecting aircraft.

*Both of these radars were available at the start of World War II.

Britain commenced radar research for aircraft detection in 1935. The British government encouraged engineers to proceed rapidly because they were quite concerned about the growing possibility of war. By September 1938, the first British radar system, the Chain Home, went into 24-hour operation and remained operational throughout the war. The Chain Home radars allowed Britain to successfully deploy its limited air defenses against the heavy German air attacks conducted during the early part of the war. They operated at about 30 MHz--in what is called the short-wave, or high-frequency (HF), band--which is actually quite a low frequency for radar. It might not have been the most favorable solution, but the inventor of British radar, Sir Robert Watson-Watt, believed that something that worked and was available was better than an ideal solution that was only a promise or might arrive too late.

The Soviet Union also started working on radar during the 1930s. At the time of the German attack on their country in June 1941, the Soviets had developed several different types of radars and had in production an aircraft-detection radar that operated at 75 MHz (in the very-high-frequency [VHF] band). The development and manufacturing of radar equipment was disrupted by the German invasion, and the work had to be relocated.

At the beginning of World War II, Germany had progressed further in the development of radar than any other country. The Germans employed radar on the ground and in the air for defense against Allied bombers. Radar was installed on a German pocket battleship as early as 1936. The Germans halted radar development in late 1940 because they believed the war was almost over.< source for this assertion? The United States and Britain, however, accelerated their efforts. By the time the Germans realized their mistake, it was too late to catch up.

Except for some German radar that operated at 375 and 560 MHz, all of the successful radar systems developed prior to the start of World War II were in the VHF band, below about 200 MHz. The use of VHF frequencies posed several problems. First, beam widths are broad. (Narrow beam widths yield greater accuracy, better resolution, and the exclusion of unwanted echoes from the ground or other clutter.) Second, the VHF portion of the electromagnetic spectrum does not permit the wide bandwidths required for the short pulses that allow for greater accuracy in range determination. Third, VHF frequencies are subject to atmospheric noise, which limits receiver sensitivity. In spite of these drawbacks, VHF represented the frontier of radio technology in the 1930s, and radar development at this frequency range constituted a genuine pioneering accomplishment. It was well understood by the early developers of radar that operation at even higher frequencies was desirable; particularly since narrow beam widths could be achieved without excessively large antennas. (The beam width of an antenna of fixed size is inversely proportional to the radar frequency).

Uses during World War II

The opening of higher frequencies (those of the microwave region) of radar, with its apparent advantages, came about in late 1939 when British physicists at the University of Birmingham invented the cavity magnetron oscillator. In 1940 the British generously disclosed to the United States the concept of the magnetron, which then became the basis for the work undertaken by the newly formed Massachusetts Institute of Technology (MIT) Radiation Laboratory at Cambridge, Mass. It was the magnetron that made microwave radar a reality in World War II. < Again I’m concerned that I’m not reading your words, but the words of your sources.

The successful development of innovative and important microwave radars at the MIT Radiation Laboratory has been attributed to the urgency for meeting new military capabilities as well as to the enlightened and effective scientific management of the laboratory and the recruiting of talented, dedicated scientists. Approximately 150 different radar systems were developed as a result of the laboratory's program during the five years of its existence (1940-45).

One of the most notable microwave radars developed by the MIT Radiation Laboratory was the SCR-584, a widely used gunfire-control system. It employed narrowed scan tracking, and, with its four-degree beam width, it had sufficient angular accuracy to place antiaircraft guns on target without the need for searchlights or optics, as was required with the older VHF SCR-268 gun-laying radar, which had very wide beam widths. The SCR-584 operated in the frequency range from 2.7 to 2.9 GHz (in the S band) and had a parabolic reflector antenna with a diameter of nearly two meters (six feet). It was first used in combat early in 1944 on the Anzio beachhead in Italy. Its introduction was timely, since the Germans by that time had learned how to jam its predecessor, the SCR-268. The introduction of the SCR-584 microwave radar caught the Germans unprepared.



Conclusion

The use of radar was vital < vital how? For which countries? In what circumstances? in the second world war. We plan to dig further into the vast information provided on radar by literature and the internet. < You surely don’t cite many of those sources in this report. What are they? Concentrating on the United States, Great Britain and Germany, we hope to determine the apparent consequences if this technology was not developed and utilized. In order to find this information, my partner and I will examine exactly what the use of radar did to prevent losses< Loss of what? Of People, materials, battles? in each country we have discussed. What is the debatable issue toward which you and your partner are working, the issue that will form the basis of your individual final papers ?



Bibliography

1. Fisher, David E. A Race on the Edge of Time :Radar – the decisive weapon of World War II. Paragon House, 1988.



2. www.Encarta.com

  • Information on all aspects of radar from development to modern uses.



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