In an ideal world, users should be able to achieve perfect image rejection. This plot shows how much image rejection is limited if the I and Q LO components are not exactly shifted 90 degrees. The other concept to take into account, which is as equally important as phase shift compensation, is gain mismatch on the I and Q mixer paths, which has not been discussed at all. Gain mismatch will affect the cancellation of the I and Q signals and can be a limiting factor in image rejection just as much as phase mismatch.