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

本研究旨在开发基于接收器前端的超导技术，并证明其宽带能力和高灵敏度。取得了以下研究结果：1.可调谐模拟带通滤光片的研制：为了研制超导薄膜可调谐滤光片，我们首先设计并制作了微带谐振器作为基本元件。通过使用致动器移动放置在滤光器附近的介质板来机械地进行调谐。实验中观察到损耗小，中心频率漂移3-15%。为了进一步灵活调谐，我们设计了集总元件型三极点带通滤波器，并证实了中心频率和带宽可以在较大范围内分别改变。AD转换器的设计：通过数值计算对无线电信号直接采样转换成数字数据的AD转换器进行了分析和设计。我们设计了一种系统，通过将量化和采样分离，在不制造高阶结构的情况下实现高性能。研究了高温超导电路在此类AD转换系统中的适用性。数字电路制造基础技术的发展：通过在势垒形成过程中掺杂少量的Pr和Ga，我们成功地抑制了漏电流。斜边结势垒层沿厚度方向的不均匀是引起散射的原因之一。改进了沉积条件，降低了温度的不均匀性，引入了气体分压监测器，提高了超导薄膜的重现性。高温超导电路集成技术研究：对电路集成所需的超导、绝缘层和超导接触的多层结构进行了研究，得到了适用于超导电路的结构。

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.