The mathematical expressions of the joint fractional Fourier transform correlator(JFRTC) are demonstrated,according to which,the properties of the JFRTC are discussed.It is shown that the properties of a JFRTC are different from that of a conventional JTC.In a conventional JTC,the distance between the two desired correlation signals at the output plane is fixed and is depended on the distance between the target and the reference images.However,by shifting the fractional orders,the distance between the two desired correlation signals at the output plane of a JFRTC can be changed larger or smaller than that of a conventional JTC.Besides,when the fractional order is shifted appropriately,the distortion of the fractional spectrum derived from the dimension distortion of the target image can be offset.Thus the JFRTC is predicted having the capability of distortion-invariant pattern recognition.On the other hand,the intensity of the desired correlation signals at the output plane of a JFRTC is always lower than tha