On Thu, 26 Sep 2019 at 15:10, Wolfgang OE1MWW <oe1mww@...> wrote:
David,
yes, SWR (resonance) is fairly pertinent for an antenna. But once again,
this does not
say, if this is a good antenna or not.
SWR and resonance are not the same thing. An antenna can be resonate but
have a VSWR of 100:1. Another antenna may have a 1.5:1 VSWR, but not be
resonate.
Efficiency = good antenna is a matter of antenna
gain and resonance is only a small portion of it.
Efficiency of an antenna has nothing whatsoever to do with resonance. A
lossless dipole of 0.5 wavelengths long has an impedance of around 73 + j
42 ohms, so is not resonate. However, the dipole is 100% efficient as it is
lossless.
The efficiency of an antenna is
(Power radiated) / (Poor accepted by the antenna)
If you have an antenna with a very high SWR, it will not radiate much. But
neither will it absorb much power.
Note also that an antenna with an impedance of 75 ohms will have a VSWR of
1.5:1 in a 50 ohm system, but 1:1 in a 75 ohm system.
I base my above comments on
145-2013 - IEEE Standard for Definitions of Terms for Antennas
You can get a copy without payment using sci-hub.
G8WRB.
--
Dr. David Kirkby,
Kirkby Microwave Ltd,
drkirkby@...
Telephone 01621-680100./ +44 1621 680100
Registered in England & Wales, company number 08914892.
Registered office:
Stokes Hall Lodge, Burnham Rd, Althorne, Chelmsford, Essex, CM3 6DT, United
Kingdom
