The Development of Radar

By By John R. Page

Dr. Robert M. Page (1903-1992), Eden Prairie, Minnesota. Retired as Director of Research, U.S. Naval Research Laboratory, 1966.

Dr. Robert M. Page was the original inventor of monopulse radar, preceding the work of the British by at least nine months (1934). One or two encyclopedias at least mention him. Most still give credit to Sir Watson Watt (England), especially where his son wrote the articles! Early British developments in radar used existing ham technology, as they could string wire antennae by the mile along their coast facing France. They could also separate transmitter and receiver antennae as required. My dad worked as a physicist at the U.S. Naval Research Laboratory in Washington D.C.

Earlier experiments by NRL scientists discovered that ship and plane traffic along the Potomac River interfered with radio transmissions, but further experiments with CW transmissions (ham technology) proved fruitless for determining range, bearings, or altitude. Leo C. Young suggested radio pulses. But no one had the technology to transmit or receive signals in this manner.

My father was assigned the task of inventing something, anything, that might demonstrate whether this was feasible. He not only succeeded, but also quickly went to high frequencies and high power, never dreamed possible in the 1930's, to get equipment small enough and powerful enough to work aboard ships.

He used the most powerful ham radio transmitter tubes of the day (Eimac, Palo Alto, CA) and got 10-20 times the rated power out of them by designing circuits that turned them on and off for milliseconds at a time in a sequenced, 6-tube ring oscillator. The first sea trials of the XAF were held aboard the U.S.S. Leary in 1937 and allowed range calculations. An improved 200 MHz system was tested on the U.S.S. York in the Chesapeake Bay in 1938. The very first test spotted an airplane 45 miles away, over the horizon! 19 such sets were aboard ships in Pearl Harbor when it was attacked. Not one was turned on.

See "Tora! Tora! Tora!" for the Army unit and the rest of that story. Trainee, George Elliot, saw the echoes 15 minutes ahead of the attack and reported them, but was ignored. Higher command thought the echoes were from an inbound flight of bombers from 'Frisco. Too bad. Those are the quirks of history. Elliot passed away in December of 2003.

Among his 75 or more patents, Dr. Page was the first to come up with the rotating display for cathode ray tubes (PPI or Plan Position Indicator) and the "duplexer" which allowed both transmitter and receiver to use the same antenna. Imagine standing next to a powerful searchlight which is turned on for a fraction of a second, after which you are supposed to see reflections from the sky with your own two eyes. Impossible--you have just been blinded for the next 20 or 30 minutes because of the brilliant flash.

This duplexer solution to a vexing problem (blinding and destabilizing a sensitive receiver) came to my father while in a Sunday morning church service (he certainly wasn't paying attention to the minister). The idea so impressed him that he stopped off at the Laboratory and recorded the idea into his workshop log books. His assistant went to work on it immediately, and several days later a working prototype was installed and tested in a wave guide. It worked the first time. It took 20 years for other physicists and mathematicians to come up with the correct explanation for why this device worked as it did.

After the British invented the magnetron it was combined with the duplexer, allowing high power and even higher frequency equipment to be installed on board British fighter-bombers. This was just in the nick of time to break the back of the German wolf packs in the Atlantic. I think it was in May of 1943 that Allied aviation sunk over 40 German U-boats. When the German subs surfaced to charge their batteries Allied planes could spot them, even through cloud cover.

The German submarines were equipped with receivers set to scan radar frequencies. Upon hearing warning signals, they would dive. This worked against them in two ways. First of all, the Germans received so many signals from extended distances that they had to ignore all but the loudest signals. Some commanders ordered their radar detectors turned off, since the false signals were unnerving to all aboard.

As losses increased, the subs were forced to use their radar detectors. Only by then we had developed microwave radar, far beyond the frequency detecting capability of the U-boat defensive receivers. So subs got caught under overcasts suddenly and without warning, leading to the Black Month of May. Credit must also be given here to U.S. and British cryptologists, who broke the German communications codes. We knew in advance when subs left on patrol and where they were headed, so we knew where to look for them.

Early in W.W.II, German scientists tried to get Hitler's permission to work on the development of microwave radar. When told this might take several years, Hitler refused. His policy required that scientific research produce usable applications for the military within a year's time.

Still, German intelligence and scientific personal were desperate to discover what the Allies were using. They examined downed Allied bombers for radar equipment, hoping to piece together from the wrecks the secrets of our equipment. As Divine providence would have it, either the bomber crews or the crashes succeeded in destroying enough evidence so that it was not until very late in the war that the German technicians came into possession of more than about half a recoverable microwave radar system.

They finally succeeded, however. Hitler was invited into a tall, darkened building in Berlin in late 1943 or early 1944 to see an operating Allied bomber system. The screen display showed a detailed radar street map of Berlin. Rumors say this was the first night Hitler contemplated committing suicide.

My father also pioneered the development of fire control radar, which was responsible for winning several stunning nighttime naval battles against the Japanese in the Pacific.

Another of my father's technical contributions was the Madre radar system, first installed on the Chesapeake Bay shore. It was a low-frequency system that followed the curvature of the earth (like ham radio transmissions), and proved capable of spying on Russian missile launches by returning a signal off of the flaming ionized exhaust trail as the missile lifted into the sky. System parameters could be set to determine accuracy of location or accuracy of velocity, but not both simultaneously.

During the experimental development of this system, a radar installation in Washington D.C. was tracking a weather balloon that had been launched from a site in Nevada. The electrical signals driving the antenna servomotors at the Naval Research Lab were observed to be oscillating, as if the antenna were hunting an erroneous signal. All circuits were checked and found to be OK. It was later determined that the radar was attempting to track the oscillations of a large crumpled-aluminum foil ball that was swinging while suspended inside the weather balloon. Later functional prototypes were able to distinguish differences of velocity among aircraft flying in formation on the other side of the North American continent; all without benefit of the modern digital computer.

I would like to salute several gentlemen who worked with my father, whose names and contributions will never be known beyond a small circle of people, most of whom have already died. Anthony Stecca (still alive in Illinois), LaVern Philpott, Irving Page, Dr. Robert Guthry, and Dr. Leo C. Young. I had the privilege of knowing these dedicated scientists when I was a small boy. They are all heroes of science, history, and American freedom.

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Copyright 2005 by John R. Page. All rights reserved.