Calibration methods for microwave imaging (MI) systems are disclosed. According to an aspect, an MI system has a plurality of Vector Network Analyzer (VNA) ports operatively connected to a plurality of antennas. A multiple state calibration network having predetermined parameters is operatively connected between a first VNA port of the plurality of VNA ports and a first antenna of the plurality of antennas. A method of calibrating the MI system includes determining first, second, and third pluralities of reflection coefficients associated with the plurality of VNA ports using first, second, and third calibration scenarios removing a measurement effect of the multiple calibration network from the first, second and third pluralities of reflection coefficients and determining error parameters for each VNA port using the first, second, and third pluralities of reflection coefficients.
