One would start by defining what the exact frequency range is, the coupling value, maximum input power, altitude, the directivity required, and the media desired (coax, waveguide, microstrip, stripline).
For the detector, one would define what is the dynamic range required and response time.
use overlay coupler, about 20dB (so u gona have good directivity)
put att after the coupler, and then Analog devive comp. made agood ditector 0-18GHz. (i teset it, and it is ok).