Editing Feed horn

{{Unreferenced|date=December 2009}}

[[Image:Hughes Direcway LNB.jpg|thumb|Feed horn with concentric rings (left) and LNB (right) on a Hughes DirecWay home satellite dish.]]
[[File:LNB 1.JPG|thumb|An LNBF ([[low-noise block downconverter|LNB]] with integrated feed horn) that has been cut into two. Visible is the scalar horn antenna (the funnel with concentric rings), which couples the microwave beam into a short [[waveguide]] (the tube connecting the feed horn to the LNB electronics part of the LNBF).]]
[[Image:Radar-hatzerim-1-1.jpg|thumb|right|Feed horn (right) on a military radar antenna. The feed horn must be shaped to produce a [[radiation pattern]] tailored to adequately illuminate the reflector.]] 
<!-- Not a feedhorn [[File:DualPolarityAntennaFeedHorn.jpg|thumb|right|Dual polarity feed horn]] -->

A '''feed horn''' (or '''feedhorn''') is a small [[horn antenna]] used to couple a [[waveguide]] to e.g. a [[parabolic antenna|parabolic dish antenna]] or [[offset dish antenna]] for reception or transmission of [[microwave]]s. A typical application is the use for [[satellite television]] reception with a [[satellite dish]]. In that case the feed horn can either be a separate part used together with e.g. a "[[low-noise block downconverter]]" (LNB), or more typically today is integrated into a "low-noise block feedhorn" (LNBF).

==Principle of operation==
The feed horn minimizes the [[mismatch loss]] between the antenna and the waveguide. If a simple open-ended waveguide would be used, without the horn, the sudden end of the conductive walls causes an abrupt impedance change at the aperture, between the [[wave impedance]] in the waveguide and the [[impedance of free space]] (see [[horn antenna]] for more details).

When used with a [[offset dish antenna|offset]], [[parabolic reflector|parabolic]] or [[lens antenna]], the [[phase center]] of the horn is placed at the [[Focus (optics)|focal point]] of the reflector. The characteristic of the feed horn is usually selected with the {{no wrap|[[3 dB point]]s}} of the horn's [[radiation pattern]] falling on the edge of the reflector (the [[beamwidth]] of the horn matching the F/D ratio of the dish).{{cn|date=January 2021}} When the shape of the antenna deviates from a circular dish, the feedhorn needs to be shaped accordingly to illuminate the antenna properly.

==Applications==
For [[satellite TV|satellite TV reception]] the feedhorn is mounted at the feed arm of the [[satellite dish]]. The feedhorn then connects via a short waveguide to the "[[low-noise block downconverter]]" (LNB), a small housing containing a part of the reception electronics (also called the "[[RF front end]]"). This LNB converts the high satellite microwave downlink frequencies to lower frequencies, so the TV signals can be more easily transmitted through [[coaxial cable]]s to receivers located anywhere inside a building. For DTH TV typically the LNB and the feedhorn are integrated into one unit called "low-noise block feedhorn" (LNBF), but separate feedhorns and LNBs are used for more specialized applications.

For [[satellite uplink]] (e.g. for transmission of "Direct-To-Home" DTH TV programs, [[satellite news gathering]] SNG, [[satellite internet access]] or [[Very-small-aperture terminal|VSAT]] applications) a [[block upconverter]] (BUC) connects via a waveguide to the feedhorn, in order to transmit via the satellite dish to the [[communications satellite]].

Feedhorns are also used in applications like [[radar]], [[line-of-sight propagation|line-of-sight]] [[microwave transmission]] or [[radio astronomy]].

==See also==
* [[Focal cloud]]
* [[Horn antenna]]

==References==
{{reflist}}

{{Telecommunications}}

{{DEFAULTSORT:Feed Horn}}

[[Category:Radio frequency antenna types]]
[[Category:Satellite broadcasting]]
[[Category:Antennas (radio)]]

[[pl:Konwerter satelitarny]]