[Q] Antenna Measurements

Thanks for everyone who replayed to me or to NEC-list about my question
regarding antenna's long range test.

On replying to John Boye's message ...
-------- Start of John's message
>Before any of us can attempt to answer your question we need more info.
>I presume you want to measure radiation patterns and gains??
>What sort of frequncy range are you wanting to work over?
>What sort of site do you have?
>How much money do you have?
>
>Regards John B
-------- End of John's message

Mainly we want to measure the gain of several configurations of an antenna
(various sizes, wires, etc.). The goal of my research is to find the gain
characteristics of this antenna. The radiation pattern is `almost`
known/predicted, of course it is needed to be confirmed by more
measurements.

The frequency range actually is different for deferent configurations. For
now it is in the 30-90 MHz range.

The site that we have is not made for antenna measurements. The basic steps
(input impedance measurements, matching circuits tuning, etc.) are held in
a small lab. But we conduct our "long range test" outside the lab. The
distance between the receiver and the transmitter antennas is about 30
meters.

We compare our antenna to a dipole (each as a receiver), and we use a
dipole as a transmitter.

We have an HP network analyzer that helps us to determine the location of
the resonance frequency of the antenna and its input impedance, also it
helps us in evaluating the S12 parameter.

I have the following questions
------------------------------
1] When we measure the gain of an antenna at a given frequency do we
measure the power at this frequency, or the power of the (modulated)
signal? Is the noise level of the environment a factor?

2] Is there a measuring device (watt meter) to measure the direct power
(with no amplifying) transmitted/received from/by the antenna? Is this a
correct way? What else can measure the gain of an antenna from its
terminals from a power point of view?

3] Is lower SWR is the main measure of a `good` matching circuit? Is SWR is
the ONLY indication of how well the antenna perform at a given frequncy?

4] I understand we have to eliminate reflections. Is there a standard
description of how the site should look like?

5] Is comparing dipole-dipole then dipole-antenna a good way of measuring
the performance of the antenna? Is this a `fair` comparison to ALL
antennas?

I hope that these questions to be relevant to everyone in this mailing
list. Most of antennas' handbooks/references don't discuss these practical
issues. I am looking for something that provides a basic explanation to
antenna measurements from a practical point of view.

Thanks again to everyone who responded to my question

Wael

____________________________________________________________________
 Wael S. Ellithy
 Mechanical and Aerospace Engr. mailto:ellithy_at_coe.wvu.edu
 Engineering Sciences Building http://www.coe.wvu.edu/~ellithy
 West Virginia University Tel: (304)293-6601 Ext. 477
 Morgantown, W.V. 26506-6106 Fax: (304)293-8823
____________________________________________________________________
Received on Fri Mar 22 1996 - 01:24:00 EST