Picosecond photoconductors in the form of dielectric resonators have been used to generate and detect extremely short bursts of millimeter wave radiation at 55 GHz with a repetition rate of 100 MHz. Both the generator and detector are tuned to a frequency which is determined by the length of the photoconducting dielectric resonators. The detector, which is phase coherent, has an estimated noise equivalent power of only 4×10−11W for an integration bandwidth of 1 Hz, and is capable of resolving time intervals corresponding to a small fraction of one millimeter‐wave cycle.