Why parabolic mirrors are use in search light?

Why are mirror is uded in search ligths parabolic and not concave spherical?

The focus of a parabolic mirror as shown in the figure is at a distance of 5 cm from its vertex. If the mirror is 45 cm deep, find the distance AB.

The focus of a parabolic mirror as shown in the figure is at a distance of 6 m from its vertex. If the mirror is 20 cm deep, show that MN = 8 sqrt30 m.

A ray of light moving parallel to the x-axis gets reflected form a parabolic mirror whose equation is (y-2)^2=4(x+1) . Find the point on the axis of the parabola through which the ray must pass after reflection.

Microwaves are used in RADAR, why ?