A millimeter wave imaging system. The system includes at least one millimeter wave frequency scanning antenna for collecting frequency dependent beams of millimeter wave radiation from a narrow one-dimensional field of view; a millimeter wave amplifier for amplifying at the collected frequencies said millimeter wave radiation. A beam-former separates the amplified radiation to produce frequency dependent signals corresponding to the frequency dependent beam. 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 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.times.2 Dicke switch is provided to permit sampling a reference thermal source for gain control while continuing to collect image information. This 2.times.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.