rat-race coupler / 180 degree phase shifter - RF Cafe Forums
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: rat-race coupler / 180 degree phase shifter Posted: Wed Sep 07, 2005 7:45 am
I need to take a single ended signal at 8GHz and convert it to a balanced signal. i.e. two outputs are
180 degrees out of phase. This is in order to drive a PLL differentially.
I've simulated a microstrip
rat-race coupler in order to achieve this. It seems to work ok.
Another option is to use a microstrip
wilkinson power divider, then after the divider, have a meandering line on one leg which basically delays the
signal to give the 180 degree phase shift necessary.
Any opinions on which is better? From my sims, the
isolation with the wilkinson power divider is good, whereas the S11 is about -9dB - only ok. With the rat-race
coupler, the isolation is poor, but the S11 is pretty good.
Post subject: Posted: Wed Sep 07, 2005 7:48 am
I guess the real question is - how
important is isolation between the two lines? They're carrying the same signal, 180 degrees out of phase....
Post subject: Posted: Wed Sep 07, 2005 12:01 pm
I would say use the rat-race. No,
actually use the Wilkinson.
Post subject: Wilkinson vs.
rat-race for differential conversionPosted: Wed Sep 07, 2005 12:34 pm
If I "read between the lines"
accurately, the single-ended signal is coming from a VCO.
The important factor here is going to be
minimizing the effects of the following circuitry on the VCO (noise, detuning, pulling, etc). So either a very
uniform S11 over the band of interest, or a very low S11, would be important.
If the S11 is very low, it
can't vary very much and stay very low. That would tend to point to the rat-race coupler - IF the input impedance
of the driven stage is constant. But, again, "reading between the lines", the driven stage might be a divider.
Depending on its input structure, "digital" circuits (like dividers) don't always present a constant S11
themselves... which would tip the stage toward the Wilkinson. Enough? good question.
So the "devil is in
the details" - as always.
Post subject: reg: coupler 180
degPosted: Thu Sep 08, 2005 5:43 pm
Joined: Wed Jul 06, 2005 5:54 pm
if ur familiar with genesys then this tool provides a synthesis option
for 180 coupler. mebbe u can optimise to get the required S11 and then mebbe introduce non-ideality into the
all the best