Complete history of microwave technology (part 6). 1937 onwards. William Doherty's development of high power transmitters and the effect such technology had on the battle of Britian.

William Doherty worked for Western Electric's Bell Laboratories in the development of high-power transmitters for trans-oceanic broadcasting when he invented the 'Doherty Amplifier'. His development of a method for greatly improving the efficiency of RF power amplifiers makes his name familiar in the RF industry today.

Doherty was awarded the Morris Liebmann award by the Institute of Radio Engineers in May 1937 for his idea. He was 29 years old! His invention was quickly brought to market by a devoted team of Western Electric engineers. By 1940, Western Electric had incorporated the Doherty concept in 35 commercial radio stations worldwide, at powers up to 50 kilowatts. This concept has been exploited many times by microwave designers in the last 20 years, including MMIC representations.

At the Battle of Britain in 1940, the British were able to detect enemy aircraft at any time of day and in any weather conditions, proving the value of microwaves to the world. The Massachusetts Institute of Technology (MIT) opened the Radiation Laboratory to research applications for radar early in the 1940s.

Two British scientists (HAH Boot and JT Randall) at University of Birmingham, England had devised a valve or tube, which could generate 1,000 times the power of any other existing microwave generator at the time. They named it the 'cavity magnetron'. The problem was that it took them a month to create a dozen of the complex units. Watson-Watt suggested they talk to MIT, and MIT in turn suggested that the British meet with a small company called Raytheon, which had been founded by an ex-MIT professor, Vannever Bush.

One of the engineers, Percy Spencer, took home one of the super-secret magnetrons, and figured out a new manufacturing process that cut manufacturing time to a mere fraction of what it was and improved the power efficiency. Within a month, Raytheon was making thousands of magnetrons a day for the war effort. Throughout the war years, new efficient sources were rapidly developed for transmitting microwave radar pulses, which by the end of the war had reached peak power levels as great as 100,000 watts to several million watts.

Just after the war, Percy Spencer was still working with magnetrons when he noticed that a chocolate bar in his pocket melted when he walked in front of the magnetron. After several experiments, he found that popcorn popped and eggs exploded! You guessed it; Percy Spencer had invented the microwave oven.

For further information on history of the microwave, go to microwaves101.com