In this paper antenna measurements in the presence of multipath waves are discussed. Methods are proposed to diagnose the degradation sources of a compact range measurement system operating at a frequency much lower than the designed frequency range. A range-gating technique is employed to improve the capability of the compact range measurement system. With this technique, the field responses over a bandwidth for each rotation angle are coherently measured, and the fast Fourier transform is applied to obtain the range profile. A suitable window function is applied to extract the desired path and eliminate all other undesired paths. The antenna pattern is plotted according to the filtered response of the desired path. We have expressed the receiving voltage of a testing antenna in terms of its gain pattern and input impedance of the testing antenna operating in multipath environment. If the bandwidth of the testing antenna is very narrow and the mismatch problem is very serious over the required bandwidth, an algorithm is proposed to compensate the mismatch effect so that the obtained radiation pattern and the antenna gain are more accurate. Numerical and experimental results have verified the effectiveness of our method.