Study on the Ultrawide-Band Ultrahighly Sensitive Radio Receiver Based on the Direct Digitization of Radio Signals

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This research directed to develop the receiver frontend based superconducting technology and to prove broad-band capability and high sensitivity of that. Following results were obtained.1. Development of Tunable Analog Bandpass Fitters : In order to develop tunable filters using superconducting films, we first designed and fabricated microstrip resonator as a basic element. Tuning was carried out mechanicaly by moving a dielectric plate placed near the filter using an actuator. Low loss and large shift of center frequency of 3-15% was observed in the experiment. For further flexible tuning, we designed lumped-element-type 3-pole bandpass filter, and confirmed that the center frequency and the bandwidth can be changed separately in wide ranges.2. Design of AD Converter : AD converters that convert radio signals to digital data by direct sampling were analyzed and designed by numerical calculation. We devised a system that enables high performance without making high order structure by separating quantization and sampling. Applicability of high-Tc circuits to such AD converter system was investigated.3. Development of Basic Technology for Digital Circuit Fabrication : We succeeded to suppress the leak currents dramatically by doping small amount of Pr and Ga during the process of the barrier formation. Nonuniformity of the barrier layer of ramp-edge junctions along the thickness direction was suggested as one of the origins of the scattering. Deposition conditions were amended by lowering the nonuniformity of the temperature and introducing gas partial pressure monitor, for reproducibility of superconducting films.4. Investigation of Integration Technology for High-Tc Circuit : Multilayer structure of superconducting layers and insulating layers and superconducting contact, which are necessary for circuit integration, were investigated, and structures applicable to superconducting circuits were obtained.