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VNA starts with S12=S21=-50dB?

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I'm doing my measurement on LNA using Agilent's VNA. After calibrating the VNA with a ECal kit, the values of the S11=S22=0dB but the S12=S21=-50dB. Is these values of S12 and S21 normal? Or should it starts at 0dB as well?

Please advise.
 

Hi
This is true if You disconnect VNA ports
You are measuring reflections from open ports and isolation of ports
 

S21 & S12 represent signals from port1 to port2 and from port2 to port1. If you do not connect them toghether you see a large attenuation (-50 dB) that is the lower limit you VNA can measure.
I hope it can help.
Mazz
 

no,it is nor normal,it is something wrong!
 

Hi there,
After calibration of a network analyzer I always do a simple check with a 3dB attenuator: should measure -6dB Sii when connected either to Port1 or to Port2, and should measure -3dB Sij and Sji when connected between Port1 and Port2. If this doesn't work, then no point going any further...
It could also be a problem with the trigger if your measurement is pulsed. If you use Agilent 8753 series, the trigger is done on the falling edge and doesn't work above 50Hz...
Mosieur_Oiso
 

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