"Massi" wrote in message ...
Hi to everybody,
I got the VSWR of an antenna from a Vector Analyzer and I'd like to know
(and how) if is possible to calculate the Quality Factor from it.
Thanks,
Massimo


You mean the "Q" of the antenna, or how narrow or broad-band it
is.


I would do it like this:

1. Place a short or an open at the end of the test cable,
where the antenna is placed. Measure the return loss in dB, at the
center frequency of interest. This will be the return loss that will
include the losses of the cable too (ideally, it will be pretty close
to 0dB). Let's call this the RLshort.

2. Replace the antenna, and then find the upper and lower
frequencies (immediately off of the center frequency, F_upper and
F_lower) where the
return loss is = RLshort - 3dB.

3. The "Q" of the antenna would be
Fcenter/(F_upper-F_lower).


This all assumes a decently lossless antenna, mind you.

As you can see, it's easier to do this if you change the
measurement from VSWR to Return Loss on your network analyzer.


Dr. Slick