Can someone please help me determine whether this matrix is positive semi-definite?

Question

I want to demonstrate the convexity of my problem by proving that the matrix $\boldsymbol{A} = \boldsymbol{a}(\theta) \boldsymbol{a}^H(\theta)$, where $$ \boldsymbol{a}(\theta) = \left[1 \quad e^{j\pi\sin(\theta)} \quad e^{j\pi2\sin(\theta)} \quad \cdots e^{j\pi(M-1)\sin(\theta)}\right]^T, \quad \theta\in\mathbb{R} $$ It is positive semi-definite (PSD). However, I am having difficulty proving this and would appreciate any help demonstrating that $\boldsymbol{A}$ is indeed a PSD matrix.