We present an analytical study for the scattering amplitudes (Reflection |R| and Transmission |T|), of the periodic ${\cal {PT}}$PT symmetric optical potential $V(x) = \displaystyle W_0 \left( \cos ^2 x + i V_0 \sin 2x \right)$V(x)=W0cos2x+iV0sin2x confined within the region 0 ⩽ x ⩽ L, embedded in a homogeneous medium having uniform potential W0. The confining length L is considered to be some integral multiple of the period π. We give some new and interesting results. Scattering is observed to be normal (|T|2 ⩽ 1, |R|2 ⩽ 1) for V0 ⩽ 0.5, when the above potential can be mapped to a Hermitian potential by a similarity transformation. Beyond this point (V0 > 0.5) scattering is found to be anomalous (|T|2, |R|2 not necessarily ⩽1). Additionally, in this parameter regime of V0, one observes infinite number of spectral singularities ESS at different values of V0. Furthermore, for L = 2nπ, the transition point V0 = 0.5 shows unidirectional invisibility with zero reflection when the beam is incident from the absorptive side (Im[V(x)] < 0) but with finite reflection when the beam is incident from the emissive side (Im[V(x)] > 0), transmission being identically unity in both cases. Finally, the scattering coefficients |R|2 and |T|2 always obey the generalized unitarity relation : $||T|^2 - 1| = \sqrt{|R_R|^2 |R_L|^2}$‖T|2−1|=|RR|2|RL|2, where subscripts R and L stand for right and left incidence, respectively.