On Mon, 08 Dec 2003 00:55:46 +0000, Paul Burridge
wrote:


Hi guys,

How does one go about measuring (with a reasonable degree of
accuracy) the radiation resistance of antennas? And when I say
"antennas" I mean any radiator from a balanced dipole through to a
random length of wet string with a damp matchbox for a ground plane.

Are you really interested in the radiation resistance or are you
actually trying to figure out the efficiency or total radiated power
of the antenna ?

One way would be to first measure the total radiated power. To do
this, you would have to measure the EiRP to all directions and
integrate it. If the measurement is done in the far field, a
calibrated magnetic probe would be enough, but at closer distances,
additionally the electric field would have to be measured with a
reference dipole.

At short wavelengths the antenna can be put on a rotating table but
for instance to measure the radiated power for an LF system, you would
have to fly around in a plane with DGPS navigation and make the
measurements from all directions.

If the antenna has a symmetrical or otherwise well known radiation
pattern, the number of measurements could be greatly reduced.

When you have the total radiated power and then measure the input
power, you can calculate the efficiency and radiating resistance.

Assuming that the radiation resistance is in series with the loss
resistance, it would be enough to measure just the antenna current,
which also flows through the radiation resistance, producing the
already measured total radiated field.

Paul OH3LWR