What is IQ calibration?
The I/Q calibration adjusts the DC offsets into the I/Q modulator to minimize carrier leakage. It also insures that the I/Q modulator is in Quadrature to help minimize images. It may be possible to reduce the carrier leakage even further by using the I and Q offset adjustments on the PSG/MXG/EXG/ESG.
What is gain imbalance?
IQ gain imbalance is the ratio of the gain of the in-phase (I) portion of the signal to the gain of the quadrature phase (Q) portion of the signal at a point in the time signal. Because Gain Imbalance is expressed as a logarithmic value, it may have a positive or negative value.