Positive S11 S21 in free space meas. with VNA Agilient

I posted it before, anyone can give a clear answer? thanks

I have some planar samples and designed a free space measurement, I calibrated the rectangular horn antennas THRU-REFLECT than put the sample in the middle of system. The result gives S11 and S21, at some frequencies S11 and/or S21 have/has positive values. Is it correct ? does it have any physical meaning?
Thanks for your valuable helps...

I also have similar problem with coaxial waveguide measurement?

positive S21 means that there is extra power added in the free space ,
make sure that ur measurements frequency is away from the wireless standards like GSM and WiFi and all these signals.

positive S11 also can results from these signals

so check ur frequencies
another this , check ur calibration procedures

Khouly

hi

Certainly it's a calibration error, so try your Ecal (Electric Calibration)

/Open/Short/Loads calibration.

Good luk

if the circuit is under oscillation then also you will get similar problem.