As the radio technology blossomed in the 20th century, there was major investment and infrastructure development in the first half of the century using radio technology.

The household radio (before television) was the major for of broadcasting to millions of Americans. They tuned in daily for news and entertainment. As research and investment progressed, they began finding that different frequencies would provide different characteristics to provide communication.

Microwave Band

Microwaves are widely used for point-to-point communications because their small wavelength allows conveniently-sized antennas to direct them in narrow beams, which can be pointed directly at the receiving antenna. This allows nearby microwave equipment to use the same frequencies without interfering with each other, as lower frequency radio waves do. Another advantage is that the high frequency of microwaves gives the microwave band a very large information-carrying capacity; the microwave band has a bandwidth 30 times that of all the rest of the radio spectrum below it. A disadvantage is that microwaves are limited to line of sight propagation; they cannot pass around hills or mountains as lower frequency radio waves can.

Microwave radio transmission is commonly used in point-to-point communication systems on the surface of the Earth, in satellite communications, and in deep space radio communications. Other parts of the microwave radio band are used for radars, radio navigation systems, sensor systems, and radio astronomy.

The next higher part of the radio electromagnetic spectrum, where the frequencies are above 30 GHz and below 100 GHz, are called “millimeter waves” because their wavelengths are conveniently measured in millimeters, and their wavelengths range from 10 mm down to 3.0 mm. Radio waves in this band are usually strongly attenuated by the Earthly atmosphere and particles contained in it, especially during wet weather. Also, in wide band of frequencies around 60 GHz, the radio waves are strongly attenuated by molecular oxygen in the atmosphere. The electronic technologies needed in the millimeter wave band are also much more difficult to utilize than those of the microwave band.

As science progressed, the possibilities of how to use microwave, millimeter waves and the RF spectrum broke into hundreds of specialty areas of development. Percy Spencer invented the first microwave oven after World War II from radar technology developed during the war when he noticed his chocalate bar melting on equipment. Named the “Radarange”, it was first sold in 1947. Raytheon later licensed its patents for a home-use microwave oven that was first introduced by Tappan in 1955, but these units were still too large and expensive for general home use. The countertop microwave oven was first introduced in 1967 by the Amana Corporation, which was acquired in 1965 by Raytheon.

Microwave in Communication
Beginning in the 1950s and 1960s networks of microwave relay links, such as the AT&T Long Lines system in the U.S., carried long distance telephone calls and television programs between cities. These included long daisy-chained series of such links that traversed mountain ranges and spanned continents. Much of the transcontinental traffic is now carried by cheaper optical fibers and communication satellites, but microwave relay remains important for shorter distances.

Millmeter Wave Bands
The millimeter wave bands would be banned from public use by the FCC and primarily used by research universities and the U.S. military as the century progressed. It’s applications and possibilities until about the mid 90’s when the FCC began making millimeter wave spectrum available to the public.

As the growth of telecommunications and data systems skyrocketed, the use of millimeter wave bands became more apparent as the ability to transmit higher bandwidth data lied in this spectrum.

In February 2013, the Internation Standards organization ratified the 802.11ad specification which is primarily a millimeter wave specification (60Ghz) and paves the way for OEM’s and manufacturers to standardize equipment for public use in many applications.