Hi Richard,

You're discussing the reciprocity of the antenna. I was not.

Thanks,

ac6xg


Richard Clark wrote:
On Thu, 26 Apr 2007 14:27:38 -0700, Jim Kelley
wrote:


Roy Lewallen wrote:


David wrote:

Are the electromagnetic field patterns noticeably different according
to whether antenna is receiving or transmitting?

No. They are the same. This is part of what is known as reciprocity.

I think you would agree the field pattern the antenna sees from a
distant source is different than the field pattern the antenna
generates on transmit. The field is uniform about the vertical axis
on transmit and the phase of the signal in each radial is identical.
But on receive the phase of the induced signal is unique into each
radial.


Hi Jim,

What you describe about the asymmetry of response to a distant source
is all perfectly true (and offers a similar argument in regards to
placing a 3D antenna into 2D null space).

However, your conclusion that there is a difference in field patterns
does not follow. Such patterns infer a multiplicity of loads for
transmit; or, in this case, a multiplicity of sources for receive.
These loads/sources populate a spherical constellation of constant
radius to exhibit the patterns we see in models. Two points do not
render a pattern.

For a one transmit source, one receive antenna, the receive antenna
current asymmetry will ALWAYS be oriented towards the source
regardless of where it is. As long as either moves in a constant
radius, the asymmetry will always follow the shared the axis. Add a
second source, and the receive antenna will similarly develop the same
axial/asymmetry relationship. The net contribution of a constellation
of sources will simple average out the asymmetry back into the rather
pedestrian distribution pattern.

73's
Richard Clark, KB7QHC