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:
Stability circles questions - RF Cafe Forums
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: Stability circles
Unread postPosted: Tue Mar
29, 2005 8:52 am
I have 2 questions regarding
For example the input stability circle contains
the input impedances that cause to Gin<1. To make the network stable
in the input domain means to find passive load impedances that would
cause to Gin<1.
The intersection of the Gload domain with
Gin domain splits the Gload domain into 2 regions: Unstable one and
stable one. I saw in a tutorial that the discussion over stability is
divided into 2 cases: One for S11<1 and the other for S11>1. According
to S-parameters definitions:
Gin=S11 If ZO=Zload. If Zload=Zo then
S11=0 and that must be a stable region. For each of these 2 conditions
2 possible situations are possible:
1) The Gin circle covers
the center of the Smith chart
2) The Gin circle doesn't cover the
center of the Smith chart
For the first condition the area of
the Smith chart outside Gin circle is the unstable region.
second condition the entire Gin circle is defined as the unstable region.
My queation is regarding the second condition: Why is the entire Gin
circle is unstable and not the area outside the Gin circle as in the
Also why the network is defined as unconditionally
stable when there is no intersection between the Gin circle and the
Gload circle (Smith chart).