# Frequency Spectrum of Microwave and Millimeter Waves

Microwave frequency range spans from ~300 MHz to 30 GHz (3 x 10^{6} HZ – 30 x 10^{9} Hz) corresponding to a wavelength range of 1 m to 0.01 m (1000 mm – 10 mm), respectively. Millimeter waves occupy the frequency range from 30 GHz to 300 GHz (3 x 10^{9} HZ – 300 x 10^{9} Hz) corresponding to a wavelength range of 0.01 m to 0.001 m (10 mm – 1 mm), respectively. From the “microwave engineering” point-of-view there is no distinction between these two ranges other than considering the effect of frequency and wavelength when designing circuits and performing measurements. In other words, at higher frequencies slight geometrical variations cause higher measurement error than the same variation at lower frequencies. There are several waveguide bands that occupy these frequency ranges. Standard waveguides, with rectangular and circular cross-sections, operate in a certain range of frequencies as a function of their broad or radius dimensions, respectively. The former is more commonly used in practice. Table below lists the dimensions, operating frequencies and designations of all rectangular waveguides in the microwave and millimeter wave frequency ranges. For additional information about waveguides the reader may consult one of many available reference textbooks or web sites.