Superconductive convolver with junction ring mixers

A superconductive convolver with tunnel-junction ring mixers has been developed and demonstrated as a programmable matched filter for near 1-GHz-bandwidth chirped waveforms. A low-loss, 14-ns-long superconductive stripline circuit provides temporary storage and relative shifting of signal and reference waveforms. These waveforms are sampled by 25 proximity tap pairs and local multiplication is performed by 25 junction ring mixers. Two short transmission lines coherently sum the local products and deliver the convolution output. The output power level of the convolver has been increased 18 dB by the incorporation of ring mixers and other output circuit improvements. These mixers employ series arrays of niobium/niobium oxide/lead junctions driven by delay-line taps in a quasi-balanced manner. The ring mixer provides higher output power levels (to -58 dBm), improved suppression of undesired mixing products and higher rf impedances than did the single-junction mixers used in the previous device. Convolvers can provide the essential programmable matched-filter component for extremely wide-bandwidth spectral analysis or spread-spectrum communication systems. The current device has a 2-GHz design bandwidth and a time-bandwidth (TB) product of 28. It produced compressed pulses with -7 dB peak-to-side-lobe levels. Design improvements to be discussed include increasing the TB product to 100 and reducing spurious side-lobe levels.