Lens systems used in a gigahertz/terahertz imaging system are proposed. Each proposed lens system may include two thin lens elements, spherical or aspherical, in which combined provides gigahertz-terahertz refractive power with a small f-number. The gigahertz-terahertz waves are diverted by the lens systems in such a way that it forms an image of an object, such as a human scale object, on a planar gigahertz-terahertz image sensor. The radius of curvatures, profile, sizes, spacing, and aspherical coefficients of the lens elements may be selected to achieve quality focusing performance. The spacing between the lens elements and the spacing between the lens elements and the image sensor may be adjusted to change both the focal length and the focusing distance to achieve optimum field of view and maximum imaging resolution. The size of the lens may be scaled with the size of the object or the lens aperture stop.