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Directional Coupler Ratings - RF Cafe Forums

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Post subject: Directional Coupler Ratings Posted: Thu Feb 24, 2005 10:19 am

Hi All:

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.

- IR


PSL Tech

Post 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.

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

Posts: 6

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 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...

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.

i look forward to hear from anyone for comments or suggestions. Thank you for your kind attention.



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