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Antenn

Denna artikel handlar om elektromagnetiska antenner. Se känselspröt för djurs antenner.
Flera antenner av Yagi-typ

En antenn för mottagning av radiosignaler är en elektrisk ledning eller annan anordning av elektriskt ledande material där elektromagnetiska vågor, som finns i omgivningen, inducerar en växelström. Den växelströmmen kan matas vidare via en antennledning till en radiomottagare. En sändarantenn fungerar tvärtom; en radiosändare matar då en växelström via en antennledning till sändarantennen. I sändarantennen omvandlas växelströmmen till elektromagnetiska vågor som utbreder sig i rymden. De elektromagnetiska vågorna skapas av att elektroner accelereras i sändarantennen.

En vanlig antenntyp är den så kallade parabolantennen. Den består av en parabolformad, elektriskt passiv reflektor som egentligen inte är någon antenn. I den reflektorns fokalpunkt är själva antennen (så kallad "matare" eller "antennhuvud") monterad. Den "mataren" eller det "antennhuvudet" kan vara av i princip vilken som helst av alla kända antenntyper. Ofta handlar det om en så kallad hornantenn.

Man brukar skilja mellan ståendevåg-antenner och vandringsvåg-antenner.

Ett viktigt mätetal är antennvinst, som uttrycker hur mycket en antenn förstärker den sända eller mottagna signalen jämfört med en given referensnivå. Antennvinsten beror på antennens strålningseffektivitet och direktivitet.[1]

Exempel på ståendevågantenner

Exempel på vandringvågantenner

Definition: En ledning eller antenn som är längre än en våglängd.

Se även

Referenser

  1. ^ Balanis, Constantine A. (2016). Antenna theory : analysis and design (Fourth edition). sid. 61. ISBN 978-1-119-17898-9. OCLC 933291646. https://www.worldcat.org/oclc/933291646. Läst 23 april 2021 

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