Integrated wireless communications and radar detections have so far mainly relied on phased-array (PA) antennas with only considering the beampatterns in angle domain. By applying the frequency diverse array (FDA) into radar and communications (RadComm) systems, a compact dual-functional structure of joint PA and FDA is designed. Based on the built joint PA and FDA channel models, different beamformer designs are proposed by jointly optimizing the signal-to-interference-noises of the communications and radar. Numerical simulations demonstrate the performances of both communications and the radar with the proposed approaches are over than that of the conventional PA RadComm systems.