In a coherent radar detector system, if noise in the in-phase phase channel (vI) is Gaussian distributed with a standard deviation of 2 mV, and a target adds a constant signal level determined by A = 10 mV and θ = π/3 to the noise in the vI channel, what is the threshold (θd) for target detections?
a) 2 mV
b) 4 mV
c) 6 mV
d) 8 mV