1-how can i measure the air impedance
2- i have a circuit (RF circuit ) i want to make matching with the air impedance
can any body help me to make the output impedance of the circuit = to that of the air ?
The magnetic permeability does not change with conditions. It is the capacitive permittivity that changes. You can measure the capacitance of parallel plates and back out the permittivity to do the impedance calculations.
the impedance of Free Space is about 377 Ohms. and when the conditions change this amount will be less than 377 Ohms.
You can't measure this impedance by an Ohm meter or something like that. This impedance is used to express the relation between Electric and Magnetic Field Traveling as a Wave.
Why do you want to match your circit to air? Do need to transmit the signal to some where? If the answer is yes you should use an antenna.
We are well known that Characteristic Impedance of the air is calculated by:
Z0 = sqrt(u0/e0) =~ 120pi.
I think, if you want to measure this characterisctic impedance, you should measure pemitivity and permeability of the air, that provides you air characteristic impedance.
You can not measure it directly, I think because, simple, it's characteristic quantity.