Abstract:
In this paper we study the spectral characteristics of the Josephson junction array oscillator and investigate the possibility of its application as a heterodyne in a superconductor integrated receiver. The array consists of 350 junctions connected in series and embedded into the central electrode of a coplanar line. The radiation from the array is mixed with the higher harmonics of the synthesiser (frequency 16–19 GHz) arising at a single tunnel Josephson junction (harmonic mixer). The signal at intermediate frequency (up to 800 MHz) is visualized by commercial spectrum analyser. The free-running generation linewidth at the best point was less than 1 MHz, with a signal-to-noise ratio of 26.3 dB. The estimates of the linewidth performed within a model that accounts for Josephson junction noise as well as thermal and low-frequency noises are in qualitative agreement with the experimental results. Also at all points where the linewidth is less than 15 MHz, for the first time the phase-locking to a stable external synthesizer was demonstrated.
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