Because of the high maintenance needed to monitor and filter spammers from the RF Cafe Forums, I decided that it would
be best to just archive the pages to make all the good information posted in the past available for review. It is unfortunate
that the scumbags of the world ruin an otherwise useful venue for people wanting to exchanged useful ideas and views.
It seems that the more formal social media like Facebook pretty much dominate this kind of venue anymore anyway, so if
you would like to post something on RF Cafe's
page, please do.
Below are all of the forum threads, including all
the responses to the original posts.
Post subject: S-parameters of Matching Unit with Different Port Impedances
Sun Mar 20, 2005 9:56 pm
The ultimate objective of this exercise is to be able to determine the input
impedance of an antenna when it is connected to the output port of an antenna matching unit (AMU). The reason for
making the measurement in this way because it is not possible to make the measurement directly at the input
terminals of the antenna.
I have characterized the AMU on the bench (which includes a 50:100 ohm
transformer) in a 50 ohm environment with a network analyser. What I would like some help with is, how to convert
the S-parameters the I have measured in the 50 ohm environment, to a new set with 50 ohms on the input port and
100 ohms on the output port. (i.e. where the output is loaded with 100 ohms and not 50 ohms).
offer any advice?
Post subject: Antenna Matching & Network analyzer
postPosted: Sun Mar 20, 2005 10:40 pm
It seems that what you need to do is to characterize the AMU
with the 50 Ohm port of the AMU connected to the 50 Ohm port of the network analyzer, and the 100 Ohm port of the
AMU connected to a minimum-loss pad to convert the impedance to 50 Ohms. You will, of course, have to compensate
for the loss of the pad.
Or it could be that I'm misinterpreting what you're trying to do, and that you're
expecting an antenna load impedance (rather far) away from 100 Ohms, and want to be able to know what that is from
the appearance at the 50 Ohm impedance side. Any reason not to use theory there, based on the topology and values
of the AMU?
Unread postPosted: Mon Mar
21, 2005 12:56 am
Thanks for your advice.
My strategy was to characterise the AMU at its nominal
output impedance of 100 ohms and to then indirectly measure the complex input impedance of the antenna by
measuring the input reflection coefficient at the AMU. The antenna's input impedance will, for part of the
frequency range, deviate significantly from the nominal value of 100 ohms.
I have made a measurement as
you've suggested with a 50:100 ohm pad. I wanted to know if there's a way of transforming the S-parameter
measurements made in a 50 ohm environment. I could then check the results I have obtained using the 50:100 ohm
Unread postPosted: Mon Mar 21,
2005 10:30 am
I have an excel spreadsheet that will perform the conversion you are looking for , but I
have been able to figure out how to place an attachment. If you could tell me how to place an attachment on the
forum I will be happy to do so..
Unread postPosted: Mon
Mar 21, 2005 4:15 pm
I'm not sure how to attach documents to replies in the forum.
If you would
email it to me I would be most grateful. My email address is: email@example.com
Thanks for your