Directional Coupler Ratings - RF Cafe Forums
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
Post subject: Posted: Thu Feb 24, 2005 12:08 pm
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
You should 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 connectors.
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
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 60W CW.
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 the oscilloscope...
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.
i look forward
to hear from anyone for comments or suggestions. Thank you for your