KEYWORDS: Antennas, Superconductors, Magnetism, Transformers, Receivers, Digital electronics, Digital signal processing, Analog electronics, Signal processing, Resistors
Substantial progress in superconductor analog to digital converters (ADCs) and digital circuitry makes possible development and implementing broadband receiving systems with direct signal digitizing and by single ADC and following digital extraction of sub-bands with programmable band location and bandwidth. To provide the overall system performance as high as the superconductor ADC allows, one has to develop and implement a completely superconductive receiving antenna unit with using active superconductor antenna The antenna characteristic and design issues are considered and discussed in the paper.
Serial arrays of two and three Josephson junctions coupled to a high quality oscillator circuit are considered using analytical approach and numerical simulation. Two different oscillation modes, the in phase and anti-phase ones, are possible in the systems above resonance frequency. It is shown that the first mode can be formally described through the same analytic theory as was developed earlier for one-junction system. This approach allows also analysing resonance peculiarities and phase-locking effects caused by external irradiation. However, stability of the mode is upset at low frequency and therefore the system shows abrupt switching either to other mode or to resonance oscillation state or to rest in superconducting state. In the anti-phase mode, the junction oscillations run with high amplitude, although resulting amplitude of the fundamental harmonic of the voltage across the arrays is negligibly small. The upper frequency of the mode stability domain decreases rapidly with McCumber parameter of the junctions and therefore this mode is relevant basically for arrays of overdamped Josephson junctions.
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