directional coupler

Hi,

I want to use a Spectrum Analyzer to measure the return loss of an Antenna at certain frequencies. I've read that this can be achieved using directional couplers. Can anyone explain how the directional coupler will extract the reflected signal from the antenna, and what specifications are needed in the design of such a coupler (isolation, directivity, etc)?

Thanks in advance

http://www.satori-technology.com/doc...al_coupler.pdf

Thank you vfone, but this paper gives the general points, and I need something more specific and more explanatory... something that can explain how the refelected signal is separated from the incident signal using a directional coupler, and how such a coupler can be designed?

Regards

Saludos, espero no sea tarde, fijate si esto te sirve.
Luis.