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: open shunt stub phase Posted: Thu Jan 12, 2006 4:26 am
Hi i asked earlier about
quarter-wave form Tlines and you guys helped out a lot. i've another question to ask: i used ideal transmission
line models and it told me that I need 23 deg. electrical length for a line series tranmission line and i plotted
the mag. and phase of s21 and saw yes the phase is 23 deg (in fact it was -23 deg, why is that?).
my main question is this: the model also told me that i need 47 deg. of electrical length for an open shunt stub
for something. i then plotted its mag. and phase of s21 but saw that the phase was only 24 deg at the given
frequency? why is that? i don't know the concept clearly to know why the phase was 24 deg.--something to do with
open stub??. there is nothing special i am doing here. i just took completely ideal models in a CAD program and
put two 50 ohms terminations and simulated them. your answer will be much appreciated. how wold be shunt
short-circuited stub different? thanks
Post subject: Posted: Thu Jan 12, 2006
one more question: one can have open circuit single shunt stub but it said that when doing layout it
is a good idea to have balanced shunt stubs, meaning half the length on either side of a series line, like a +
sign. i calculated exactly how to convert one shunt stub to balanced stub...my question is when one simulates this
should you get exactly the same response, what i am getting is that the phase are same but the magnitude are
opposite. in the single shunt open stub i have phase starting from 1 (or 0 dB) and decreasing a bit throughout he
frequency sweep but for balanced shunt open stub it start from 0 magnitude and approaches like .6 through its
frequency sweep!! doesn't make sense. please provide explanation. my layout is i think ok, its like a + with both
sides open and then placed ports on the sides where the signal enters and exits
Post subject: Posted: Thu Jan 12, 2006 2:09 pm
the phase are same but the magnitude are opposite
that what you meant to say? I am almost ready to answer all of your questions and more! After 3 more cups of
Post subject: Posted: Fri Jan 13, 2006 5:35 am
yeah....that's what i
meant but i think i figure out the problem but would still like to know your feedback and the answer to the first
Post subject: 23 or 24Posted: Wed Jan 18, 2006 2:47 am
Joined: Tue Dec 13, 2005 2:42 am
Location: Czech Rep.
I think that this
misunderstanding comes from the model/software you used.
1) Why -23 and not +23deg? ..I guess that the SW
calculates the phase as decreasing quantity with increasing distance from the port on which the fictive signal
generator is applied.
2) Why 24 deg and not 23 deg? (I HOPE I understood your question well - that after adding
a shunt line the phase of s21 changed from 23 to 24 deg.) It is sure that some added line MUST change phase
relationships in the system - if the added line has some significant length in comparison with the rest of the
network. ...You can see this fact if you use Smith chart. Try to put some serial line with parallel line and see
what will happen with the phase