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This article is about the electromagnetic wave. For the cooking appliance, see Microwave oven. A telecommunications tower with a variety of dish antennas for microwave relay links on Frazier Peak, Ventura County, California. The prefix micro- in microwave is not meant to suggest a wavelength in the micrometer range. The atmospheric attenuation of microwaves and far infrared radiation in dry air with a precipitable water vapor level of 0.

The downward spikes in the graph correspond to frequencies at which microwaves are absorbed more strongly. In a microwave beam directed at an angle into the sky, a small amount of the power will be randomly scattered as the beam passes through the troposphere. A sensitive receiver beyond the horizon with a high gain antenna focused on that area of the troposphere can pick up the signal. This technique has been used at frequencies between 0. Waveguide is used to carry microwaves.

Their short wavelength also allows narrow beams of microwaves to be produced by conveniently small high gain antennas from a half meter to 5 meters in diameter. The term microwave also has a more technical meaning in electromagnetics and circuit theory. As a consequence, practical microwave circuits tend to move away from the discrete resistors, capacitors, and inductors used with lower-frequency radio waves. The grey assembly attached to the end of the copper-colored horn antenna is the Gunn diode which generates the microwaves. High-power microwave sources use specialized vacuum tubes to generate microwaves. All warm objects emit low level microwave black-body radiation, depending on their temperature, so in meteorology and remote sensing, microwave radiometers are used to measure the temperature of objects or terrain.

Wireless LAN protocols, such as Bluetooth and the IEEE 802. 11 specifications used for Wi-Fi, also use microwaves in the 2. 16, designed to operate between 2 and 11 GHz. Commercial implementations are in the 2. 9 GHz in the Americas and elsewhere, respectively.

Most satellite communications systems operate in the C, X, Ka, or Ku bands of the microwave spectrum. These frequencies allow large bandwidth while avoiding the crowded UHF frequencies and staying below the atmospheric absorption of EHF frequencies. ASR-9 airport surveillance radar which radiates a narrow vertical fan-shaped beam of 2. Radar is a radiolocation technique in which a beam of radio waves emitted by a transmitter bounces off an object and returns to a receiver, allowing the location, range, speed, and other characteristics of the object to be determined. The short wavelength of microwaves causes large reflections from objects the size of motor vehicles, ships and aircraft. Chile, observes the universe in the millimetre and submillimetre wavelength ranges.

1964 by radio astronomers Arno Penzias and Robert Wilson. Microwaves are widely used for heating in industrial processes. A microwave tunnel oven for softening plastic rods prior to extrusion. A microwave oven passes microwave radiation at a frequency near 2. Microwave heating is used in industrial processes for drying and curing products. Microwaves are used in stellarators and tokamak experimental fusion reactors to help break down the gas into a plasma, and heat it to very high temperatures.

Microwaves can be used to transmit power over long distances, and post-World War 2 research was done to examine possibilities. Less-than-lethal weaponry exists that uses millimeter waves to heat a thin layer of human skin to an intolerable temperature so as to make the targeted person move away. The United States Air Force and Marines are currently using this type of active denial system in fixed installations. Bands of frequencies in the microwave spectrum are designated by letters. Unfortunately, there are several incompatible band designation systems, and even within a system the frequency ranges corresponding to some of the letters vary somewhat between different application fields. The term P band is sometimes used for UHF frequencies below the L band but is now obsolete per IEEE Std 521.

To avoid this problem, the original K band was split into a lower band, Ku, and upper band, Ka. Absorption wavemeter for measuring in the Ku band. Microwave frequency can be measured by either electronic or mechanical techniques. Frequency counters or high frequency heterodyne systems can be used. Here the unknown frequency is compared with harmonics of a known lower frequency by use of a low-frequency generator, a harmonic generator and a mixer. The accuracy of the measurement is limited by the accuracy and stability of the reference source.