Editing Microwave (section)

== Antennas ==
[[File:Diplexer1.jpg|thumb|upright|Waveguide is used to carry microwaves. Example of [[waveguide]]s and a [[diplexer]] in an [[air traffic control]] radar.]]

The short [[wavelength]]s of microwaves allow [[omnidirectional antenna]]s for portable devices to be made very small, from 1 to 20 centimeters long, so microwave frequencies are widely used for [[wireless device]]s such as [[cell phone]]s, [[cordless phone]]s, and [[wireless LAN]]s (Wi-Fi) access for [[laptop]]s, and [[Bluetooth]] earphones.  Antennas used include short [[whip antenna]]s, [[rubber ducky antenna]]s, sleeve [[dipole antenna|dipole]]s, [[patch antenna]]s, and increasingly the printed circuit [[inverted F antenna]] (PIFA) used in cell phones.

Their short [[wavelength]] also allows narrow beams of microwaves to be produced by conveniently small [[antenna gain|high gain]] [[antenna (radio)|antenna]]s from a half meter to 5 meters in diameter.  Therefore, beams of microwaves are used for [[point-to-point (telecommunications)|point-to-point]] communication links, and for [[radar]].  An advantage of narrow beams is that they do not interfere with nearby equipment using the same frequency, allowing [[frequency reuse]] by nearby transmitters.  [[Parabolic antenna|Parabolic ("dish") antennas]] are the most widely used directive antennas at microwave frequencies, but [[horn antenna]]s, [[slot antenna]]s and [[lens antenna]]s are also used.  Flat [[microstrip antenna]]s are being increasingly used in consumer devices.   Another directive antenna practical at microwave frequencies is the [[phased array]], a computer-controlled array of antennas that produces a beam that can be electronically steered in different directions.

At microwave frequencies, the [[transmission line]]s which are used to carry lower frequency radio waves to and from antennas, such as [[coaxial cable]] and [[twin lead|parallel wire lines]], have excessive power losses, so when low attenuation is required, microwaves are carried by metal pipes called [[waveguide (electromagnetism)|waveguide]]s.  Due to the high cost and maintenance requirements of waveguide runs, in many microwave antennas the output stage of the [[transmitter]] or the [[RF front end]] of the [[radio receiver|receiver]] is located at the antenna.