The History of Microwave Power Transmission, and all the influencial scientists responsible for progressing this brand of expertise.

Microwave Transmission

The History of Microwave Power Transmission

In, 1864, James Clerk Maxwell predicted the existence of radio waves by means of mathematical model. Twenty-four years later, in 1888, bolstered by Maxwell's theory, Heinrich Hertz first succeeded in showing experimental evidence of radio waves by his spark-gap radio transmitter. This experiment stimulated Marchese Guglielmo Marconi, who first achieved signal transmission by means of radio waves over 10 m in 1895, and over the Atlantic Ocean in 1901.

It was Reginald Fessenden who first succeeded in transmitting continuous wave (CW) for voice telecommunications. The road to modern radio telecommunication was opened up around the turn of the century. Modern radio utilization has been directed into the area of radio telecommunications for transmission of 'intelligence and information' over rather weak radio waves. This is one main stream of radio utilization stemming from the Maxwell-Hertz-Marconi-Fessenden work. However, another stream of work was directed toward a different radio wave application. The second stream of radio utilization was an effort to transmit electrical energy by radio to a distant place.

The idea of radio power transmission was first conceived and experimented on in 1899 by Nikola Tesla. He attempted to distribute ten thousand horse-power under a tension of one hundred million volts. He said: "This energy will be collected all over the globe preferably in small amounts, ranging from a fraction of one to a few horse-power. One of its chief uses will be the illumination of isolated homes". He actually built a gigantic coil, which was connected to a high mast of 200-ft with a three ft-diameter ball at its top. He fed 300 kW power to the Tesla coil resonated at 150 kHz. The RF potential at the top sphere reached 100 MV.

From the turning point of the century on, however, radio has been used mainly for transmitting intelligence and information, and very few attempts have been made to transmit electrical energy over radio following Tesla's work.

The reason for a lack of interest in radio power transmission in the first half of this century is clear. People were waiting for the invention of a high-power microwave device to generate electromagnetic energy of reasonably short wavelength, since efficient focusing toward the power-receiving destination is strongly dependent on the use of technology of narrow-beam formation by small-size antennas and reflectors.

In the 1930's, much progress in generating high-power microwaves was achieved by invention of the magnetron and the klystron. Though the magnetron was invented by A. W. Hull in 1921, the practical and efficient magnetron tube gathered world interest only after Kinjiro Okabe proposed the divided anode-type magnetron in 1928.

It is interesting to note that H. Yagi and S. Uda, who are famous for their invention of Yagi-Uda Antenna, stressed a possibility of power transmission by radio waves in 1926, thereby displaying profound insight into the coming microwave tube era in Japan. Microwave generation by the klystron was achieved by the Varian brothers in 1937 based on the first idea by the Heil brothers in Germany in 1935.

During World War II, development of radar technology accelerated the production of high-power microwave generators and antennas. A CW high power transmission over a microwave beam was investigated in secrecy in Japan. The project, the 'Z-project', was aimed at shooting down air-bombers by a high-power microwave beam from the ground, and involved two Nobel winners H. Yukawa and S. Tomonaga.

An introduction of the Japanese Magnetron appeared in 'Electronics' of USA immediately after World War II. However, the technology of the high-power microwave tube was still not developed sufficiently for the practical continuous transmission of electric power. Further, no power device was available to convert a microwave energy beam back to DC power until the 1960's.