  Dual-functional radar communication (DFRC) system has recently attracted
significant academic attentions as an enabling solution for realizing
radar-communication spectrum sharing. During the DFRC transmission, however,
the critical information could be leaked to the targets, which might be
potential eavesdroppers. Therefore, the physical layer security has to be taken
into consideration. In this paper, fractional programming (FP) problems are
formulated to minimize the signal-to-interference-plus-noise ratio (SINR) at
targets under the constraints for the SINR of legitimate users. By doing so,
the secrecy rate of communication can be guaranteed. We first assume that
communication CSI and the angle of the target are precisely known. After that,
problem is extended to the cases with uncertainty in the target's location,
which indicates that the target might appear in a certain angular interval.
Finally, numerical results have been provided to validate the effectiveness of
the proposed method showing that it is viable to guarantee both radar and
secrecy communication performances by using the techniques we propose.
