Editing Reflective array antenna (section)

===Gain limits===
As more elements are added to an array, the [[beamwidth]] of the antenna's main lobe decreases, leading to an increase in gain. In theory there is no limit to this process. However, as the number of elements increases, the complexity of the required feed network that keeps the signals in-phase increases. Ultimately, the rising inherent losses in the feed network become greater than the additional gain achieved with more elements, limiting the maximum gain that can be achieved.

 [[File:Standard gain dipole array.png|thumb|Two element dipole array in front of a one wavelength square reflector used as gain standard]]The gain of practical array antennas is limited to about 25–30&nbsp;dB. Two half wave elements spaced a half wave apart and a quarter wave from a reflecting screen have been used as a standard gain antenna with about 9.8 dBi at its design frequency.<ref>{{Cite web | url=http://www.schwarzbeck.de/en/antennas/standard-gain-antennas.html |title = Standard Gain Antennas}}</ref> Common 4-bay television antennas have gains around 10 to 12&nbsp;dB,<ref>{{cite web |url=http://www.channelmaster.com/Digital_HDTV_Outdoor_TV_Antenna_p/cm-4221hd.htm |title= ULTRAtenna 60 |website=Channel Master}}</ref> and 8-bay designs might increase this to 12 to 16&nbsp;dB.<ref>{{cite web |url=http://www.channelmaster.com/CM_4228HD_p/cm-4228hd.htm |title=  EXTREMEtenna 80 |website=Channel Master}}</ref> The 32-element SCR-270 had a gain around 19.8&nbsp;dB.<ref>{{cite book |url={{GBurl|k7g4BQAAQBAJ|p=460}} |title=Radio Wave Propagation |page=460|isbn=978-1-4832-5854-6|last1=Burrows |first1=Chas. R. |date=2013-10-22 |publisher=Academic Press }}</ref> Some very large reflective arrays have been constructed, notably the Soviet [[Duga radar]]s which are hundreds of meters across and contain hundreds of elements. ''Active'' array antennas, in which groups of elements are driven by separate RF amplifiers, can have much higher gain, but are prohibitively expensive.

Since the 1980s, versions for use at [[microwave]] frequencies have been made with [[patch antenna]] elements mounted in front of a metal surface.<ref>{{cite book|last=Huang|first=john|title=Reflectarray antennas}}</ref>