Total E field gain calculation from anechoic chamber

Hi, I have radiation pattern results from anechoic chamber which I need to plot. The data which I have are the XY, XZ and the YZ plan each with co and cross pol data. I did the necessary calculation using the horn antenna(source) gain values.

Now, how do I calculate the total E field gain? Example, in XY co pol at 5GHz, I have 360 values since the step angle of rotation is 1 degree. How do I calculate using this values to find the gain? I understand its something like Etotal = Etheta + Ephi, but how do I do this from my data?

This is the data for XY co pol at 5GHz:

Angle Gain
-180 -25.617dB
.
.
.
.
180 -23.372dB



Does total E field gain means the combination of all the planes? Or just each XY co and cross have their own total E field gain?

Your help is greatly appreciated!