A millimeter wave imaging system. The system includes one or more millimeter wave frequency scanning antenna for collecting frequency dependent beams of millimeter wave radiation from a narrow one-dimensional field of view and millimeter wave amplifier components for amplifying the millimeter wave radiation collected by each antenna. The system includes a beam-former that separates the amplified radiation to produce frequency dependent signals corresponding to the frequency dependent beams. The beam-former includes delay lines, a millimeter wave lens, and an array of millimeter wave power detectors for detecting the power in each frequency dependent beam. A sampling circuit reads out the frequency dependent signals to produce a one-dimensional image of the antenna field of view. A two dimensional image of a target may be obtained by moving the target (or having the target move) across the field of view of the scanning antenna or by moving the antenna in order to scan its line of focus over the target. In preferred embodiments a 2×2 Dicke switch is provided to permit sampling a reference thermal source for gain control while continuing to collect image information. This 2×2 Dicke switch provides a square root of 2 improvement in temperature sensitivity over a single receiver version. Preferred embodiments also include features for focusing the antenna within a range of about 5 feet to infinity.