Editing Microwave (section)

=== Radar ===
{{main|Radar}}
[[File:ASR-9 Radar Antenna.jpg|thumb|The [[parabolic antenna]] (lower curved surface) of an ASR-9 [[airport surveillance radar]] which radiates a narrow vertical fan-shaped beam of 2.7–2.9&nbsp;GHz ([[S band]]) microwaves to locate aircraft in the airspace surrounding an airport]]

[[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.  Also, at these wavelengths, the high gain antennas such as [[parabolic antenna]]s which are required to produce the narrow beamwidths needed to accurately locate objects are conveniently small, allowing them to be rapidly turned to scan for objects.  Therefore, microwave frequencies are the main frequencies used in radar.  Microwave radar is widely used for applications such as [[air traffic control]], weather forecasting, navigation of ships, and [[speed limit enforcement]].  Long-distance radars use the lower microwave frequencies since at the upper end of the band atmospheric absorption limits the range, but [[millimeter wave]]s are used for short-range radar such as [[collision avoidance system]]s.

{{multiple image
 |direction = vertical
 |align = left
 |width = 270
 |image1=The Atacama Compact Array.jpg
 |caption1= Some of the dish antennas of the [[Atacama Large Millimeter Array]] (ALMA) a radio telescope located in northern Chile. It receives microwaves in the [[millimeter wave]] range, 31 – 1000&nbsp;GHz.
 |image2=BigBangNoise.jpg
 |caption2=Maps of the [[cosmic microwave background radiation]] (CMBR), showing the improved resolution which has been achieved with better microwave radio telescopes}}