The present invention provides a monolithic superheterodyne detector pixel operable to receive a radio frequency (RF) signal at millimeter wavelength and produce a video output signal with many orders of improved sensitivity when compared with the prior art. This sensitivity improvement is achieved by translating the received RF signal to a intermediate frequency (IF) signal before detection of the video signal. At the lower frequency of the IF signal, monolithic amplification circuitry can be fabricated more easily to provide necessary gain than would be achievable if simple amplification of the RF signal were attempted. Detector pixels constructed in accordance with the invention each contain an antenna for receiving the RF signal. Local oscillator (LO) signal circuitry likewise apply an externally generated LO signal to the pixel. The RF signal and LO signal are then applied by interconnecting conductors to appropriate mixer means to produce the IF signal. An IF amplifier next amplifies the IF signal to a level sufficient for detection of the video output signal by a second detector. In presently preferred embodiments, pixel circuitry is fabricated in microstrip format with impedance matching provided between respective monolithic components. The antenna and local oscillator signal circuitry may each comprise slots defined in the metallized ground plane of the detector substrate. Utilization of a subharmonic mixer permits the external LO signal to be a subharmonic of the "virtual LO" mixed with the received RF signal. The amplifier may comprise a plurality of cascaded field effect transistor (FET) amplifier stages. The second detector, as well as diodes utilized in the mixer, are preferably Schottky barrier diodes.