Antenna coupling measurement

Hi,

I want to know how to measure the Antenna coupling in MIMO 2X2.

for example, I inject a signal in the feed of antenna 1 and receive a signal in the feed of antenna 2 (using network analyzer). Is this a measurement of coupling between antennas?

For the simplicity of the argument, lets consider the coupling of the antennas in the transmitter. how would you measure the coupling using Network analyzer?

Thanks,