## 2 System Model  
We consider a typical wiretap scenario, where a base station Alice and an eavesdropper Eve are equipped with uniform linear arrays (ULA) with \(M\) and \(N\) antenna elements, respectively. A legitimate user [PERSON] is equipped with a single antenna. To facilitate the presentation of location for the users, we adopt the polar coordinate system and Alice is considered as the origin [22]. Then, the locations of [PERSON] and [PERSON] can be denoted as \((d_{ab},\theta_{b})\) and \((d_{ae},\theta_{e})\), respectively. We assume that the location of [PERSON] is known to [PERSON]. To investigate the impact of [PERSON]'s location on eavesdropping performance, we assume that the location of [PERSON] is also known to [PERSON]. Then, an optimal beamforming scheme can be designed using AN. In the case where the location of [PERSON] is unknown to [PERSON], the beamforming scheme can still be used to minimize the area with eavesdropping risk. We note that the CSIs of [PERSON] and [PERSON] are unknown to [PERSON]. Based on the location information of [PERSON], [PERSON] is able to transmit confidential information via a beam aiming to [PERSON]. Moreover, [PERSON] may transmit a jamming signal via another beam aiming to [PERSON]. We assume that all of the channels are subject to quasi-static independent and identically distributed (i.i.d) Rician fading with different Rician K-factors, and that the K-factors are known to [PERSON] via some a priori measurement campaigns. Hence, the channel vector from [PERSON] to [PERSON], denoted as \(\mathbf{H}_{b}\in\mathcal{C}^{1\times M}\), can be written as \[\mathbf{H}_{b}=\sqrt{\frac{K_{b}}{1+K_{b}}}\mathbf{H}_{b}^{o}+\sqrt{\frac{1}{1+K_{b }}}\mathbf{H}_{b}^{r} \tag{1}\]  
where \(K_{b}\) is the Rician K-factor of \(\mathbf{H}_{b}\), \(\mathbf{H}_{b}^{o}\in\mathcal{C}^{1\times M}\) denotes the LOS component, and \(\mathbf{H}_{b}^{r}\in\mathcal{C}^{1\times M}\) denotes the scattered component, the elements of which are assumed to be i.i.d. complex Gaussian random variables with zero mean and unit variance, i.e., \(\mathbf{H}_{b}^{r}\sim\mathcal{CN}(0,\mathbf{I}_{M})\). Moreover, \(\mathbf{H}_{b}^{o}\) can be written as  
\[\mathbf{H}_{b}^{o}=\left[1,e^{\tau_{a}\cos(\theta_{b})},...,e^{i(M-1)\tau_{a} \cos(\theta_{b})}\right] \tag{2}\]  
where \(\tau_{a}=\frac{2\pi f_{0}\rho_{a}}{c}\), \(f_{0}\) is the carrier frequency, \(\rho_{a}\) is the space between two adjacent antenna elements of the ULA of Alice, and \(c\) is the speed of propagation of the plane wave. When \(\rho_{a}\) is equal to a half wavelength, i.e., \(\rho_{a}=\frac{c}{2f_{0}}\), we have \(\tau_{a}=\pi\). Likewise, the channel matrix from [PERSON] to Eve, denoted as \(\mathbf{H}_{e}\in\mathcal{C}^{N\times M}\), can be written as  
\[\mathbf{H}_{e}=\sqrt{\frac{K_{e}}{1+K_{e}}}\mathbf{H}_{e}^{o}+\sqrt{\frac{1}{1+ K_{e}}}\mathbf{H}_{e}^{r} \tag{3}\]  
where \(K_{e}\) is the Rician K-factor of \(\mathbf{H}_{e}\), \(\mathbf{H}_{e}^{o}\in\mathcal{C}^{N\times M}\) denotes the LOS component, and \(\mathbf{H}_{e}^{r}\in\mathcal{C}^{N\times M}\) denotes the scattered component with i.i.d circularly-symmetric complex Gaussian random variables with zero mean and unit variance. Moreover, \(\mathbf{H}_{e}^{o}\) can be written as  
\[\mathbf{H}_{e}^{o}=\mathbf{h}_{e}^{T}\mathbf{h}_{ae} \tag{4}\]  
where \(\mathbf{h}_{e}\) and \(\mathbf{h}_{ae}\) are the array responses at Eve and Alice, respectively, which can be written as  
\[\mathbf{h}_{e}=\left[1,e^{-\tau_{e}\cos(\theta_{e})},...,e^{-i(N- 1)\tau_{e}\cos(\theta_{e})}\right] \tag{5}\] \[\mathbf{h}_{ae}=\left[1,e^{\tau_{e}\cos(\theta_{e})},...,e^{i(M- 1)\tau_{e}\cos(\theta_{e})}\right] \tag{6}\]  
where \(\tau_{e}=\frac{2\pi f_{0}\rho_{e}}{c}\), \(\rho_{e}\) is the space between two adjacent antenna elements of the ULA of [PERSON] and \(\phi_{e}\) is the direction of arrival from [PERSON] to [PERSON].