"The cross polarization may be specified for an antenna as a power level in negative dB, indicating how many decibels below the desired polarization's power level the x-pol power level is."

db is a ratio of powers,what amplitudes and why its negative ,if you could show an example with numbers showing negative dB.

thanks

I don't know any exemple for polarization, but this one about attenuation:

If power level of incident wave of Port 1(a1) is 100 W, and power level of reflected wave of Port 2 (a2) is 1W, it means: |S21|=10log10(1/100)=-20 dB

But I don't know exactly what situation with polarization

thank i understand :-)

the thing is the amplitude of the undesired polariZation