Re: NEC-LIST: Definition of Gain

George,

I see that everyone disagrees with me on the question of lumping
impedance mismatch loss and polarization loss in with gain. Let me
give an example to try to support my contention that the definition of
antenna gain should include both mismatch losses.

Let's say that I am the manufacturer of a horn antenna, and I am going
to measure that antenna gain versus frequency over 2 to 8 GHz in an
anechoic chamber. I intend to publish this information in my sales
literature, or perhaps I intend to provide this curve along with each
antenna I ship, because I know that users will then use this horn as a
gain standard in their measurements.

In my anechoic chamber, I measure the performance of my horn using a
network analyzer. That network analyzer's impedance is fixed at 50
ohms. I cannot complex conjugate match the antenna for each frequency
point. I could measure VSWR, and then back out the impedance mismatch
loss from the gain mathematically, but the fact is that no one I know
does this. They report what is currently defined as "realized gain",
i.e. the gain including mismatch loss. Current industry practice
reports realized gain, but they call it "gain". It is not in synch
with the current IEEE definition.

Now, I believe I understand the source of the disagreement. Perhaps
engineers and technicians working with WIRE antennas habitually
complex conjugate match the antenna with a tuner at each frequency,
and only measure a few discrete frequencies. Maybe that is the source
of our disagreement. I usually work with APERTURE type antennas, not
WIRE antennas.

The same sort of argument applies to the issue of polarization
mismatch. You would have to measure axial ratio, then back the
polarization mismatch loss out of the measured gain. I don't see
engineers on antenna ranges and in anechoic chambers doing this. So,
again, we should make the definition fit the defacto standard.

Matt Taylor
Received on Tue Mar 07 2000 - 04:33:58 EST