Linewidth measurement of millimeter wave radiation from a Josephson array source coupled to free space

Radiation from a linear array oscillator with a spiral antenna has been coupled out of the dewar through a Teflon window. Both its linewidth and its power have been measured after coupling the radiation through free space into a second dewar. The linewidth has been determined using a SIS mixer with a spiral antenna which was pumped with an 88 GHz phase-locked Gunn oscillator, and also by Josephson mixing of the array itself. The array oscillator has a distributed array structure of 300 resistively shunted junctions which are placed in groups of 6 junctions. It was fabricated on a silicon wafer and has a two-arm spiral antenna. The chip was attached to a silicon lens with an anti-reflection coating. The linewidth of the array oscillator was determined between 158 GHz and 194 GHz, far below its design frequency of 400 GHz. The measured linewidth and power data of the oscillator reveal interesting information about its phaselocking behavior in the operating range far below its design frequency.