Directional Coupler Ratings - 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: Directional Coupler Ratings Posted: Thu Feb 24, 2005 10:19 am
I'm pretty new to RF engineering and have a question about ratings on RF directional couplers. When the spec says
something like 2W max power, does that mean only when properly terminated, or for any port termination (like
open)? I need an answer pretty quick, please, because I need to place an order ASAP. Thanks
Post subject: Posted: Thu Feb 24, 2005 10:59 am
The parameter of power
handling is ususally given for rpoperly terminated ports.
subject: Posted: Thu Feb 24, 2005 12:08 pm
The power rating is for average power. There should also be a
rating for peak power. The power rating of a direction coupler refers to the input signal only.
also have ratings for insertion loss and tolerance (dBm and %, respectively). The directional coupler should be
specified for frequency range and coupling (GHz and dB). Other ratings can include frequency sensitivity,
directivity, VSWR on both the main path and coupled path, coupled losss, impedance, operating temperatures and
Post subject: selecting 20-dB or 30-dB directional coupler and using
it...Posted: Tue Aug 21, 2007 6:49 am
Joined: Thu Mar 08, 2007 10:29 am
Could i ask, are there procedures that i need to take in general in order to make sure that i connect the
directional coupler to a properly terminated port please?
I intend to use a dual directional coupler to
measure the reflected and forward power into a cavity on an oscilloscope. i intend to connect a signal
generator(MO) feeding power via a power amplifier(PA) into a cavity via a loop coupler. PA has max output power of
1) to ensure proper termination, am i correct to first use a VNA to make sure that the loop
coupler is matched to the cavity, and then disconnect the VNA and feed power into the cavity with the MO and PA
please? would this be enough to ensure proper termination for the directional coupler please?
2) say for
example i feed in 50W from the PA, for a 20dB directional coupler, i'll couple out about 0.5W into the
oscilloscope. having Z0=50ohms, i suppose i'll observe a V=sqrt(0.5*50)=5V average OR 7V peak voltage waveform on
BUT, assuming my above calculation is correct, if i use a 30dB directional coupler,
0.05W couples into the oscilloscope, i observe a V=1.6V average voltage on oscilloscope.....
Would using a
30dB directional coupler be too much?? i am thinking in terms of VSWR and insertion losses, bcos i see that 30dB
directional couplers have better performance than 20dB directional couplers, but then will the small voltage
amplitude on the scope be too small and consequently noise dominates the reading on the scope.
forward to hear from anyone for comments or suggestions. Thank you for your kind attention.