August 15, 2022
Electromagnetic waves are called microwaves; generally between 300 MHz and 30 GHz, which assumes an oscillation period of 3 s (3×10−9 s) to 33 s (33×10−12 s) and a wavelength in the range of 10 mm to 1 m. Other definitions, for example those of the IEC 60050 and IEEE 100 standards, place its frequency range between 1 GHz and 30 GHz, that is, wavelengths between 30 centimeters and 10 millimeters. The microwave range is included in the radio frequency bands, specifically in those of UHF (ultra-high frequency - ultra high frequency) 0.3-3 GHz, SHF (super-high frequency - super high frequency) 3-30 GHz and EHF (extremely high frequency) 30-300 GHz. Other radio frequency bands include waves of lower frequency and longer wavelength than microwaves. Microwaves of higher frequency and shorter wavelength—on the order of millimeters—are called millimeter waves. The existence of electromagnetic waves, of which microwaves are a part, was predicted by Maxwell in 1864 from his famous Maxwell Equations. In 1888, Heinrich Rudolf Hertz was the first to demonstrate the existence of electromagnetic waves by building an apparatus for generating and detecting radio frequency waves. Microwaves can be generated in various ways, generally divided into two categories: solid-state devices and vacuum tube-based devices. Solid-state microwave devices are based on silicon or gallium arsenide semiconductors, and include field-effect transistors (FETs), bipolar junction transistors (BJTs), Gunn diodes, and IMPATT diodes. Specialized versions of standard transistors have been developed for high speeds that are commonly used in microwave applications. Vacuum tube-based devices operate by taking into account the ballistic motion of an electron in a vacuum under the influence of electric or magnetic fields, including the magnetron, the klystron, the TWT, and the gyrotron.