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Efficient Design and Analysis of Airborne Radomes
What specific moment and event destined Maryland to flourish as a hotbed of microwave innovation? Scientific discovery is a continuum that often defies an exact beginning. But this account of the who, what, how and why that made this years’ International Microwave Symposium host city of Baltimore the center of so much multi-generational achievement and microwave commerce begins in New Jersey in May 1915.
It was then that Thomas Edison, speaking to a New York Times correspondent about the Great War in Europe, argued that the nation should look to science for help and that “The Government should maintain a great research laboratory.” The Secretary of the Navy seized upon this sediment to enlist the famous inventor’s support, requesting him to serve as the civilian head of a Naval Consulting Board, advising the Navy on science and technology and overseeing the creation of modern research facility.1 Edison lent his name to board activities, personally engaged in sonic research for submarine detection, and vigorously promoted the creation of a Naval Research Laboratory.2 Working closely with this newly formed board was the Assistant Secretary of the Navy, Franklin D. Roosevelt.1
Two years before Edison’s New York Times interview, a high-school graduate, self-educated in early radio technology by the name of Leo C. Young joined the Naval Communications Reserves. When the Navy Reserve was activated in World War I, Young was assigned to the District Communications Office in Illinois, working for Director Albert Hoyt Taylor. In 1918, when Taylor was sent to head the Navy's Trans-Atlantic (formerly Marconi) Communications System, followed by an assignment to the Navy's Aircraft Radio Laboratory (ARL) at Anacostia, Washington, DC; Taylor arranged for Young to follow him. By 1919, both Young and Taylor returned to civilian life, but continued as employees at the ARL in Washington.
In the autumn of 1922, Taylor and Young were investigating the use of short radio waves for secure communication between nearby ships. While making measurements with a transmitter located at the ARL and a receiver on the opposite shore of the Potomac River, the two observed a wavering in the strength of the received signal as a ship crossed the signal path. In effect, they had demonstrated the first multi-static radar, a system that uses separate transmitting and receiving antennas to detect targets. Taylor reported this to higher authorities as a potential method of detecting ships intruding into a formation, "destroyers located on a line a number of miles apart could be immediately aware of the passage of an enemy vessel between any two destroyers of the line, irrespective of fog, darkness, or smoke screen." No action was taken on this report and no further tests were authorized, but those involved remembered what they had seen.3
On July 2, 1923, the United States Naval Research Lab (NRL) envisioned by Edison began operations in Bellevue, a residential neighborhood located in Southwest Washington, DC. The Lab absorbed several existing research facilities including the ARL. The two original divisions of the NRL– radio and sound, performed research in the fields of high-frequency radio and underwater sound propagation. Taylor was named Superintendent of the Radio Division with Young as his assistant. Over the next decade, Young had a major role in most of the early radio developments of the NRL, including their 1925 round-the-world high-frequency experiment, communicating 10,000 miles between Radio in Virginia and a US Navy ship in Australia.
Further NRL experiments once again led to the witnessing of “re-radiations” as the phenomena was referred to by Lawrence ‘Pat’ Hyland during the field testing of an aircraft direction finder. Hyland was an accomplished ex-Navy radio recruited by a Navy Lieutenant to work at the NRL under Young. Later in his career, Hyland would become best known as the man who transformed Hughes Aircraft from an aviation "hobby shop" into a leading technology company. Note - In 1954, Hyland was hired as Vice President/General Manager of Hughes Aircraft and ultimately became the President and CEO after Howard Hughes' death in 1976.
While working on a direction finder for the NRL, Hyland observed wild detector current readings after firing up a CW transmitter pointed towards an airplane two miles away. Hyland eventually realized that every time an airplane taxied out to the runway for take off, the meter reacted. Contacting Young, Hyland excitedly exclaimed “My gosh, we’re getting re-radiations” from the airplanes. Young confirmed this from his experience with wavering signals off ships on the Potomac, and they immediately went to the top brass at NAVAIR, only to be told “Well, not much we can do about it, but OK, that’s nice.” Young went to the Director of the Lab who went to Bureau of Ships, which responded in a similar discouraging manner, “We want nothin’ to do with that”.4
Radio Research and the Founding of Bendix Radio Corp.
Within his first two years at the NRL, Hyland had designed a faraday shield to address the impact of engine ignition noise on aircraft receivers for which he received $10,000 from Bendix for the rights to his invention. By 1928, Young and Hyland applied this seed money to set up a side business known as Radio Research. The non-incorporated company included Hyland and Young, as unpaid employees and a technician whom they hired because he had a cellar that they could use to work in. At this time, commercial radio was growing significantly and frequency control technology was in high demand. And so, Hyland and Young began designing and selling crystal-controlled oscillators, built by their technician in his basement for customers that included the government.
Meanwhile, Hyland kept investigating radio reflections off aircraft while working on the NRL’s direction finder. After his boss found out about his efforts and told him to cease, Hyland and Young decided to continue the experiments on Radio Research time. By 1931, Hyland left the NRL to devote full time to Radio Research, quickly expanding the business with a novel crystal frequency indicator (later known as an LM frequency meter) and a contract to build tunable frequency sources for the Navy. The company built ten for the production run, none of which worked. Wondering what happened; Hyland took apart the prototype, checked it against everything and put it back together again. This time the prototype also failed to work.
The design consisted of a condenser and a holding screw on the rotor. Recalling that there was a loose screw when he took it apart, Hyland soon realized that when he tightened the screw, it actually changed the capacity by putting pressure on it. So he loosened the screw, and once again the prototype worked! Applying this finding to the rest of the devices he got them all to work. Keeping quiet about his discovery, Hyland put them all together with loose screws and shipped them. Unwittingly, Hyland become an early practitioner of screw tuning, a technique commonly found in the cavity filters developed in Maryland and around the world.
That same year Hyland’s work on direction finder multipath interference fields –reflections or re-radiations for the detection of aircraft by using radio waves, resulted in two patents being filed in his and Leo Young’s name and they were awarded to Radio Research in 1932. The company grew from a cellar operation to increasingly larger buildings, adding a machinist and a draftsman, paying them each $15 a week. And then disaster struck.
Despite the ongoing depression, Radio Research had been able to leverage the founder’s technical prowess, the burgeoning commercial radio market and Navy business to grow at a tremendous rate. However, when Franklin Roosevelt was sworn in as President and declared a bank holiday in 1933, the company found itself without enough operating money. Hyland and Young were not accountants and they had simply grown too fast without proper concern for cash flow. The economic situation set in motion the acquisition of Radio Research by Bendix, which was flush with cash and interested in the direction finder work done by Hyland as well as the company’s push into the commercial market with its oscillator and frequency detection technology.
In 1936, the Bendix Radio Corp. was formed as a result of the sale of an interest in the Radio Research Company to the Bendix Aviation Corporation. As a fully owned subsidiary of Bendix Aviation Corp., Radio Research was joined by the W. P. Hilliard Co., the Jenkins & Adair Corporation and Industrial Instruments Inc., all of Chicago, and the Radio Products Co., of Dayton, Ohio.
Initially, the Bendix Radio plant was placed in Chicago where the majority of the acquired firms were already located nearby. Chicago was also closer to the Aircraft Radio Labs at Wright Field with which the new corporation had significant established business through its component companies. Since Radio Research was already set up in Washington, close to the Naval Research Laboratories as well as the government procurement agencies, the Washington factory was maintained and functioned actively both as a research and production center. In short order, the demands on research and production became too heavy for the new company’s Washington plant and it was moved to a former General Motors plant located at 920 East Fort Avenue in Baltimore in November of 1937.
Radar Takes Off
The Navy’s initial lack of understanding or interest in the use of radio wave reflections was not universal. Reflection of Hertzian or radio waves had been in the literature for over fifty years at this point in time. Tesla had predicted radar in 1900, Hulsmeyer patented a non-ranging but working 600 MHz spark gap detector in 1904 and in 1922 Marconi's spoke to engineers about the deflection of waves off metal objects miles away.
Elsewhere, Major W.R. Blair, the Director of the Signal Corps Labs (SCL) at Fort Monmouth, New Jersey, had decided to pursue aircraft detection with the short Hertzian waves, now termed microwaves that he studied at the University of Chicago.
The Corps of Engineers and the Ordnance Corps were working on infrared aircraft detection, a subject of 1918 research by Master Signal Electrician S.A. Hoffman, at Columbia University but Blair was able to get the infrared research transferred to the Signal Corps Laboratories, by February of 1931. By 1933, this particular device could measure Doppler reflections from moving automobiles and railroad cars. That same year at the Century of Progress Exposition in Chicago, Westinghouse demonstrated a complete microwave communications system that used a magnetron tube developed by Kilgore.
To be fair to the Navy naysayers, the wave interfering phenomena discovered by Taylor, Young and Hyland was only capable of detecting objects, lacking information about the object’s location or velocity. With the NRL unsuccessful at getting the Navy interest in its “interference radio”, Young suggested that they use pulsing techniques to determine the target range. This led NRL researcher to develop a system capable of detecting a plane flying over the Potomac using a transmitter operating at 60 MHz with a 10 us, 10 percent duty cycle pulse in December of 1934, representing the world’s first successful demonstration of Radar.
Evolving aerospace technology and faster planes would help establish the need for radar. The Douglas DC-3 and the Boeing B-17 Flying Fortress were flying at speeds that exceeded some of the fighter aircraft on hand and this tended to render acoustic detection of aircraft less than useful. Although in common use at this time, the use of sound detection apparatus to locate aircraft was becoming increasingly useless due to the relatively slow speed of sound waves in the atmosphere - (700 odd MPH). The main use of sound locators in World War Two seemed to be misinformation.
Meanwhile, pulsed radar experiments continued with a receiver improved for handling short pulses. In June 1936, a new prototype radar system from the NRL, operating at 28.3 MHz (using readily available communication antennas), successfully tracked aircraft at distances up to 25 miles, yet the relatively large antennas made them impractical for ship or aircraft mounting and so efforts were made to increase the frequency (thus requiring a smaller antenna). A new 200 MHz system was successfully tested at the NRL in April 1937, the same month that the first sea-borne testing was conducted and the equipment was temporarily installed on the USS Leary, with a Yagi antenna mounted on a gun barrel for sweeping the field of view.
In 1929, G. Ross Kilgore, an engineer at Westinghouse in Pittsburgh, generated microwave energy with an experimental split-anode magnetron vacuum tube, eventually reaching a wavelength of 1.6 cm (18 GHz).5 In the absence of wartime needs or market pressures, Kilgore's work took place in the context of a gentlemanly competition among radio engineers. Breaking power and frequency records served as a means of keeping score in the game, and anyone who broke either with a new vacuum tube held the prize among radio enthusiasts until the next record-breaking device was demonstrated.6
At the time, radio and later radar transmitters were designed around the most efficient vacuum tube that was otherwise qualified. In the case of early radar equipment, high power at ever increasing frequencies was the quest of nearly every tube designer.
A look at the mid nineteen-thirties helps put things in perspective. "The war to end all wars" had been over for nearly two decades, the great depression of the thirties had followed the stock market crash of 1929 and money was tight. With the inevitable shortage of tax dollars, many Government workers at every level were laid off. Meanwhile, the stage was being set for World War Two. Japan had invaded mainland China and occasionally fighting Russia. Hitler was helping the fascists win the war in Spain, while his "ally" Stalin, was doing likewise for the Republican opposition.
In 1938, Westinghouse Electric Corp. joined Bendix by moving its 250 employee Radio Division from Massachusetts and Pittsburgh to Baltimore. Westinghouse had entered the broadcast industry in the 20s. What brought Westinghouse to the region was managements’ desire to expand the company’s radio business and to be closer to the federal government in Washington.
Five years later in 1943, the Westinghouse Radio Division was brought into the Navy carrier based night fighter radar program. At that time, the Radiation Laboratory of the Massachusetts Institute of Technology requested Westinghouse to design and build twenty RF heads to be used in aircraft radar set then being developed by the Laboratory for the Navy. The RF Head is a composite unit containing the transmitter and the front end of the receiver and appropriate switching mechanisms to permit them to operate from a single antenna. The new equipment was expected to displace AIA equipment then being manufactured by the Sperry Gyroscope Company, and which had been Jointly designed by Sperry and the Radiation Laboratory.
Westinghouse accepted this commission and divided the responsibility between the Research Laboratories and the Baltimore Works. The Research Laboratories were to design the electrical components and Baltimore was to do the mechanical engineering and manufacturing. Work began immediately and early in April, 1943, a semi-operative model was taken to the Radiation Laboratory for discussion. Comment on the unit was very favorable.
In one year the company more than doubled its manufacturing area in its Baltimore location to accommodate production of the then highly-secret SCR-270 aircraft warning radar, the very radar that detected the December 7th attack on Pearl Harbor. The US Army's various histories are very candid about the fact that the SCR-270 was built at the expense of the Army's Coast Artillery Corps SCR-268 searchlight control radar. In fact, the first version of the prototype SCR-270 used a transmitter borrowed the SCR-268, slowing down the latter’s development program. According to the Historical Electronic Museum, near Baltimore, Maryland, the Army SCL ordered key SCR-270/1 model and prototype components from Westinghouse Electric, in January of 1940. The equipment was deployed in the original Panama Canal SCR-271 installations, in late 1940, which bore Westinghouse nameplates.
Despite its warnings, they went unheeded because of high-level uncertainty about the new technology's reliability. The first ground-based radar built for the Army Signal Corps, the SCR-270 proved to be the only model to stay in action throughout all of World War II. From 1941–1945 the Westinghouse Radio Division manufactured approximately 50 products during the war. Until 1942, most of this was radio equipment; later production shifted to radar products. Wartime production included ground-based and naval radio and radar, electronic fuses, and torpedoes.
At the meeting held at the Bureau of Ships, it was proposed by the Navy that Westinghouse accept a production contract to include not only the RF Head but the complete radar system. It was stipulated that Westinghouse would purchase the Modulator and the Antenna, which were already under development on contracts previously issued to Stromberg-Carlson and Dalmo-Victor respectively. The proposition was accepted by Westinghouse and contracts were issued eventually for four models and 50 equipments. Delivery of the models was expected in the fall and it was estimated that the production units would start about the beginning of 1944.
After the war and through the cold-war, Westinghouse had a distinguished history of achievements, developing radar system for the US military as well as NASA. In 1953, the unit patented key technologies for Pulse-Doppler radar, making possible airborne systems that can detect both stationary and moving targets, determine range, and distinguish targets from background "clutter." Pulse-Doppler is the basis for all airborne radars in use today. By 1966, the division designed and developed a miniaturized black-and-white camera that captured images from the Project Apollo Lunar Module that landed on the Moon on July 20, 1969. In 1967, The world's first solid-state radar, the AN/APQ-120 for the F-4 Phantom II fighter, was produced by the division. In 1974, the division began development of the AN/APG-66 radar for the F-16; to date the unit has produced over 6,000 radars for various versions of the F-16. In 1976, Westinghouse Electronic Systems delivered the first E-3 Sentry AWACS long-range airborne surveillance radar. In 1996, Westinghouse was selected to design, build and test the radar for the F-35 Joint Strike Fighter, what became the AN/APG-81.
The post-Cold War decline in US defense spending chilled Electronic Systems' output. However, the company maintained an attractive book of business. F-16 radars are still being produced for foreign air forces, and the division won the contract to produce radar for the F-22.
Northrop Grumman Electronic Systems was created by Northrop Grumman's acquisition of Westinghouse Electronic Systems Group in December 1995. The sale ended Westinghouse's 57-year history as a Maryland defense contractor that started with a small plant on Wilkens Avenue, where a few hundred workers made radar tubes. By the late 1980s, Electronic Systems was one of the state's largest private employers with 17,000 workers. These included hundreds of highly educated mechanical, electrical, software and systems engineers as well as thousands of skilled manufacturing employees. They designed and built sophisticated radars for F-16 fighters, AWACS radars, anti-submarine and electronic warfare systems.
Maryland also has a rich history in filters. Much of this is tied to the radar systems being developed by Bendix and Westinghouse for the NRL and Army SCL. Development of distributed element filters began in the years before World War II. A major paper on the subject was published by Mason and Sykes in 1937. Mason had filed a patent much earlier, in 1927, and that patent may contain the first published design which moves away from a lumped element analysis. Mason and Sykes' work was focused on the formats of coaxial cable and balanced pairs of wires – the planar technologies were not yet in use. Much development was carried out during the war years driven by the filtering needs of radar and electronic counter-measures. A good deal of this was at the MIT Radiation Laboratory.
It was the policy of the Radiation Lab to get industrial firms like Bell Labs, General Electric, Westinghouse, Raytheon, and others, up to speed in microwaves. That was their policy. The government was trying to get the whole operation going from a manufacturing standpoint as well. So they had a policy of bringing in people, or having people nominated, to come in and learn the technology, according to Coltman, head of Westinghouse research.
The introduction of printed planar technologies greatly simplified the manufacture of many microwave components including filters, and microwave integrated circuits then became possible. It is not known when planar transmission lines originated, but experiments using them were recorded as early as in 1936. The inventor of printed stripline, however, is known; this was Robert M. Barrett who published the idea in 1951. This caught on rapidly, and Barrett's stripline soon had fierce commercial competition from rival planar formats, especially triplate and microstrip. The generic term stripline in modern usage usually refers to the form then known as triplate.
Early stripline directly-coupled-resonator filters led to the introduction of parallel-coupled line filters, interdigital filters, and comb-line filters. Much of this work was published by the group at Stanford led by George Matthaei, and Leo Young in a landmark book which still today serves as a reference for circuit designers. The hairpin filter was first described in 1972. By the 1970s, most of the filter topologies in common use today had been described.
The initial non-military application of distributed element filters was in the microwave links used by telecommunications companies to provide the backbone of their networks. These links were also used by other industries with large, fixed networks, notably television broadcasters. Such applications were part of large capital investment programs. However, mass-production manufacturing made the technology cheap enough to incorporate in domestic satellite television systems.
Leo Young, author, co-author, or editor of 14 books, including Microwave Filters, Impedance-Matching Networks, and Coupling Structures (Artech House Publishers, 1964). Considered "the bible" by those in the field, Young’s reference book has been translated into Russian and Japanese, and it still sells well decades after its initial publication. Young has a passing influence on Maryland’s microwave legacy. He was born in Austria to a prominent Jewish family and moved to England in 1938 to escape the Nazis. After graduating from Cambridge University in 1949 [a B.A. in physics (1947), and a B.A. in mathematics (1945)], he moved to Maryland where he received his doctorate in engineering from the Johns Hopkins University (1959) as well as an M.A. (1950).
As an engineer at Westinghouse from 1953 to 1960, Young worked on military radar research and development, including microwave components and antennas. He left Baltimore to work at SRI International and later at the Naval Research Laboratory in Washington. He later was in the Pentagon administrating the Defense Department Basic Research Program.
From 1930 to 1940, NRL explored the use of radio for detection and ranging, and in 1935 the Committee on Naval Appropriations of the US House of Representatives allocated $100,000 to NRL for the development of radar. This led to NRL's invention and development of the first US radar, the XAF (installed on the battleship USS New York in 1939), and led eventually to its commercial production form, the CXAM. By the time of Japan's attack on Pearl Harbor, 20 radar units were in operation on selected vessels. These radars contributed to the victories of the US Navy in the battles.
3. History of radar
4. Bendix Radio Foundation Oral History: Cramer Bacque Interview http://www.bendixradiofoundation.com/documents/BacqueTranscipt.pdf
6. Experts at Play: Magnetron Research at Westinghouse, 1930-1934 Technology and Culture - Volume 42, Number 4, October 2001, pp. 737-749.
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