antenna-theory.com

[Ahsan]

I have measured antenna data in far field and I want to analyze it using matlab. I have theta and phi values of  E field for a particular frequency. How can I calculate Gain of an antenna with the help of this data. So far what I know that I can calculate total E by adding these two components and then squaring it and integrating it over a sphere will give me radiated power. But for antenna gain calculation you need input power information which I dont have. Also if I suppose that data is already calibrated internally from the instrument, does that mean that by finding maximum value from Etotal will be the maximum gain of the antenna ? 

[Parna]

I don't think the maximum radiated power will give you the gain of the antenna. The VNA calibration is to account for cables, connectors, etc..

To find the gain for your antenna, you need to measure another antenna that you know the gain for. Then, you can compare the maximum received power for that antenna to the maximum received power of your AUT and calculate the gain of your AUT from that difference ...

If you don't have such an antenna, you will need two other antennas with unknown gains (one can be your probe) and then you will need to do three measurements for any two combination of the three antennas. If you are using your probe as one of those other two antennas, you already have done one of those three measurements (you will need to be able to change your probe for one of the other measurements to one of the other antennas). Then you can solve three Friis equations to get your three unknowns (the unknown gains of the three antennas). This is called three antenna gain measurement.