Watched this from Ericsson.
Coupler-based AC for c1 and C2 FDD AAS Radios
Antenna calibration is to detect and compensate between antenna branches due to temperature variations and other effects.
The phase response of the analog RF parts (PA, FUs, etc. ) cannot be assumed to be stable over time, so we need to do antenna calibration over time to achieve desired system performance.
In AAS Product, AC is the precondition of Beamforming function, which adjusts the antenna phases to shape downlink beams and analyzes phase differences of uplink transmissions to detect beams.
Ideally, the beam directions of two polarizations are the same. However, in practice, radios in the field have uncalibrated antennas, hence their phase are random, so it makes it impossible to align their beam directions.
As a consequence, due to this cross polarization, the [[notes/Downlink||DL]] throughout is not 100% efficient. Radios without phase calibration suffer from performance losses. Uncalibrated Antennas have random phases.
We can however maximize the throughput by finding the optimal various phase offsets between two polarizations of the antenna (which compensates for the random phases between the antennas).
We call this Antenna Calibration, trying to find the optimal phase for each station.