Rammeantenne

En rammeantenne (loop-antenne) er en radioantenne, der består af en loop (ring) eller spole af metaltråd eller metalbånd, metalrør, eller en anden elektrisk leder, som typisk er energifødet fra en balanceret elektrisk kilde eller belastet af en balanceret belastning.

En rammeantenne dækker over flere forskellige antennetyper, der bl.a. har forskellige bølgelængdeomkredse og om den evt. anvender en ferritkerne, kaldes den for en helbølge rammeantenne og en ferritantenne.^[1]^[2]^[3]

Denne artikel vedrører rammeantenner, der har en omkreds på mere end 30% af en bølgelængde til typisk omkring én bølgelængde.

Helbølge rammeantenne

En selvresonant rammeantenne, der har en omkreds på omkring én bølgelængde, kaldes for en helbølge rammeantenne. Disse rammeantenner er følsomme for radiobølger i rammens to hulretninger.

Den lineare polarisation bestemmes af signalfødningspunktet i forhold til jordoverfladen. Fødes signalet ind for neden eller oven er rammeantennen vandret polariseret. Fødes signalet ind til venstre eller højre er rammeantennen lodret polariseret.

Eksempler på helbølge rammeantenner omfatter energifødeelementet i quad-antenner og delta-loop-antenner. Disse antenner kan anvendes til både radiosending og radiomodtagelse.

Små rammeantenner

Hovedartikel: Magnetisk dipolantenne.

En lille rammeantenne er også kendt som en magnetisk dipolantenne. En magnetisk dipolantenne kobler til radiobølgens magnetiske felt i antennens nærfelt - i modsætning til monopolantenner og dipolantenner, der kobler til radiobølgens elektriske felt i antennens nærfelt.

Denne kategori omfatter rammeantenner fra under 1% til 30% af én bølgelængde i omkreds. Disse rammeantenner er følsomme for radiobølger langs renden af rammeantennen eller spolen.

Se også

Kilder/referencer

^ antenna-theory.com: Small Loop Antennas, The Loop Antenna Citat: "...The [small] loop antenna feed point does not matter too much - it can be anywhere along the loop perimeter...Note that a balun may be needed...The one-wavelength perimeter loop antenna behaves like a folded dipole antenna, with an impedance that is higher than that of a half-wavelength dipole antenna...", backup. antenna-theory.com: Welcome to Antenna-Theory.com! Citat: "...I am a practicing antenna engineer, with a PhD in antennas and I have worked for many years in defense, university and the consumer electronics field as an antenna engineer. My dissertation in pdf form is available here: Antenna Arrays: Performance Limits and Geometry Optimization...", backup
^ ece.mcmaster.ca: LECTURE 12: Loop Antennas Citat: "...Loop antennas are usually classified as electrically small (C < λ/3) and electrically large (C ≈ λ). Here, C denotes the loop’s circumference...As the circumference of the loop increases, the [radiation] pattern maximum shifts towards the loop’s normal, and when C≈λ, the maximum of the pattern is alongthe loop’s normal...", backup
^ W5QJR, Ted Hart, robkalmeijer.nl: Small, high-efficiency loop antennas Citat: "...polarization component radiated by the [small] loop lies in the plane of the loop...Here's the bad news - the [small] loop is the equivalent of a high-Q tuned circuit, which means it has a narrow bandwidth...A power input to the antenna of 500 W will produce voltages of up to 30,000 V...", backup

[at-1] tenna-theory.com: Small Loop Antennas, The Loop Antenna Citat: "...The [small] loop antenna feed point does not matter too much - it can be anywhere along the loop perimeter...Note that a balun may be needed...The one-wavelength perimeter loop antenna behaves like a folded dipole antenna, with an impedance that is higher than that of a half-wavelength dipole antenna...", backup. antenna-theory.com: Welcome to Antenna-Theory.com! Citat: "...I am a practicing antenna engineer, with a PhD in antennas and I have worked for many years in defense, university and the consumer electronics field as an antenna engineer. My dissertation in pdf form is available here: Antenna Arrays: Performance Limits and Geometry Optimization...", backup

[mcmaster-2] .mcmaster.ca: LECTURE 12: Loop Antennas Citat: "...Loop antennas are usually classified as electrically small (C < λ/3) and electrically large (C ≈ λ). Here, C denotes the loop’s circumference...As the circumference of the loop increases, the [radiation] pattern maximum shifts towards the loop’s normal, and when C≈λ, the maximum of the pattern is alongthe loop’s normal...", backup

[3] W5QJR, Ted Hart, robkalmeijer.nl: Small, high-efficiency loop antennas Citat: "...polarization component radiated by the [small] loop lies in the plane of the loop...Here's the bad news - the [small] loop is the equivalent of a high-Q tuned circuit, which means it has a narrow bandwidth...A power input to the antenna of 500 W will produce voltages of up to 30,000 V...", backup

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