Quadrature transceivers utilize complex signal processing in the analog front-end (AFE) to tackle the image problem in frequency up/downconversion. The image-rejection performance is limited by the unavoidable I/Q imbalance throughout the AFE. In this paper, an in-depth analysis and modeling of I/Q mismatch effects in 3 different AFE frequency up/downconverters in SIMULINK are presented to better illustrate their image-rejection performance and to establish the most effective solution to improve it. The modeled AFEs include the conventional quadrature up/down-converter, double-quadrature up/downconverter with passive quadrature generator and the analog-double quadrature sampling (A-DQS) scheme for IF-to-baseband downconversion in complex-IF receiver path.