A design of the input circuit of a millimeter-wave superheterodyne rec
eiver is described. The circuit has the form of a ring-cavity-based wa
veguide directional filter with a built-in mixer (plug-in planar diode
). Devices operating at 36 and 140 GHz were manufactured, whose resona
tors had a approximate to 10(3) quality factor, and losses in the sign
al and heterodyne channels were <1 and 68 dB, respectively.