Scattering parameter interpretation

i am a bit confused on interpreting the scattering parameter results shown by network analyzer

for example the S11 shown by network analyzer for any antenna is in dB.

now if i want to calculate the abosulte values which formula should i use

S11(dB)=20 log ( S11)

or

S11(dB)=10 log (S11)


any help will be highly appreciated

regards

S-paramters are theoretically calculated as voltage ratios. So you would use 20log instead of 10log.

In general, if you want to transfer to dB values from voltage, current, and field intensity quantities, you could use 20log; however, use 10log for power, radiation intensity, gain, and directivity quantities