Copyright: 1996 - 2024
BSEE - KB3UON
RF Cafe began life in 1996 as "RF Tools" in an AOL screen name web space totaling
2 MB. Its primary purpose was to provide me with ready access to commonly needed
formulas and reference material while performing my work as an RF system and circuit
design engineer. The World Wide Web (Internet) was largely an unknown entity at
the time and bandwidth was a scarce commodity. Dial-up modems blazed along at 14.4 kbps
while tying up your telephone line, and a nice lady's voice announced "You've Got
Mail" when a new message arrived...
All trademarks, copyrights, patents, and other rights of ownership to images
and text used on the RF Cafe website are hereby acknowledged.
My Hobby Website:
S-parameters of Matching Unit with Different Port Impedances - RF
RF Cafe Forums closed its virtual doors in 2012 mainly due to other social media
platforms dominating public commenting venues. RF Cafe Forums began sometime around
August of 2003 and was quite well-attended for many years. By 2010, Facebook and
Twitter were overwhelmingly dominating online personal interaction, and RF Cafe
Forums activity dropped off precipitously. If the folks at
phpBB would release a version with integrated
sign-in from the major social media platforms, I would resurrect the RF Cafe Forums,
but until then it is probably not worth the effort. Regardless, there are still
lots of great posts in the archive that ware worth looking at.
Below are the old forum threads, including responses to the original posts.
|-- Amateur Radio
Gripes & Humor
-- CAE, CAD, &
Test & Measurement
Post subject: S-parameters of Matching Unit with Different
Unread postPosted: 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).
Can anyone offer any advice?
Post subject: Antenna Matching & Network analyzer
Unread postPosted: Sun Mar 20, 2005 10:40 pm
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
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 pad.
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: firstname.lastname@example.org
Thanks for your assistance.