The short wavelength of millimeter-waves in fifth-generation (5G) mobile communications enables the implementation of multi-element antenna arrays in relatively small space, e.g., in user devices and small base stations. Joint communication and sensing (JCAS) is a scheme which utilizes the beamsteering capabilities of the multi-element antenna arrays for simultaneously maintaining a communication link and sensing the surroundings with a radar beam and receiving it with the same device. The simultaneous transmission and reception requires a beam weighting algorithm which cancels the self-interference while at the same time maintaining the integrity of both beams. In this paper, the performance of different linear patch antenna array architectures is studied in terms of self-interference cancellation performance and obtained maximum gain in the beamsteering range. A mirror-beam problem in the self-interference cancellation algorithm for parallel arrays is studied and novel coupling randomization is introduced for the arrays to prevent the forming of the mirror beams.