Overview

The ultra-high-frequency (UHF) band of the electromagnetic spectrum extends from 300 to 1000 MHz (1 GHz), and over that range wavelength decreases from 100 to 30 cm. The microwave band is considered to extend from the upper limit of the UHF band (1 GHz) to the lower limit of the millimeter region at 40 GHz. The wavelengths of all of the frequencies within this band can be measured in centimeters or millimeters. For example, the wavelength at 1 GHz is 30 cm and this decreases to 0.75 cm (7.5 mm) at 40 GHz. The millimeter band begins at 40 GHz and, for practical applications, ends at about 100 GHz. Table 7-1 relates frequency to wavelength and band designation.

The behavior of the radio frequencies at the high end of the UHF band and across the microwave and millimeter bands differs from that of the very high frequency (VHF) band and lower frequencies because different methods are required for generating RF power and transmitting it through conductors or free space. The first practical defensive radar systems developed during World War II operated in the UHF band, and long-range search radars still operate in this band.

Some experimental work was done in the microwave band before the turn of the twentieth century, but it was dropped in favor of lower frequencies because they offered more promise for commercial radio broadcasting and reception. Serious research into the characteristics of microwaves and the technology necessary to produce them with enough power for practical...