Effective Length
For antennas which are not defined by a physical area, such as monopoles and dipoles consisting of thin rod conductors, the aperture bears no obvious relation to the size or area of the antenna. An alternate measure of antenna gain that has a greater relationship to the physical structure of such antennas is effective length leff measured in metres, which is defined for a receiving antenna as:
where
- V0 is the open circuit voltage appearing across the antenna's terminals
- Es is the electric field strength of the radio signal, in volts per metre, at the antenna.
The longer the effective length the more voltage and therefore the more power the antenna will receive. Note, however, that an antenna's gain or Aeff increases according to the square of leff, and that this proportionality also involves the antenna's radiation resistance. Therefore this measure is of more theoretical than practical value and is not, by itself, a useful figure of merit relating to an antenna's directivity.
Read more about this topic: Antenna Aperture
Famous quotes containing the words effective and/or length:
“The only effective way to help well-intentioned, intelligent persons to do the best they can in raising children is to encourage and guide them always to do their own thinking in their attempts at understanding and dealing with child-rearing situations and problems, and not to rely blindly on the opinions of others.”
—Bruno Bettelheim (20th century)
“A needless Alexandrine ends the song,
That, like a wounded snake, drags its slow length along.”
—Alexander Pope (16881744)