Research and Development of High-Temperature Superconductor Millimeter-Wave Filters

近年来，人们对小尺寸、低损耗、高频率选择性的高温超导(HTS)滤光片进行了广泛的研究。关于高温超导微带滤光器的报道和出版物很多。另一方面，由于共面波导(CPW)结构的滤波器只需要单面超导薄膜，与使用双面超导薄膜的微带结构的滤波器相比，制作成本更低。本研究旨在开发毫米波超导滤波器的设计和测试方法。2002年，为了准确测量介质衬底(MgO)和超导薄膜(YBa2Cu3O7)的表面电阻与频率的关系，提出了三种测量方法，包括圆腔法、截止圆波导法和蓝宝石棒谐振器中的四种模式。YBCO)在毫米波。结果表明，在30 GHz和70K下，…衬底的最大损耗小于2×10~(-6)，而YBCO薄膜的表面电阻约为铜的五分之一。在此基础上，提出了一种采用共面波导谐振器结构的H槽型谐振器，并对其进行了数值模拟，结果表明其在毫米波具有很高的Q因子。其次，利用H槽型谐振器设计了一种低损耗高温超导共面波导切比雪夫四极点滤波器，为了实现通带低插入损耗、阻带衰减大的高性能滤波器，分析了单交叉耦合通道滤波器的一般电路模型，为阻带具有衰减极点的滤波器的设计提供了新的理论。利用所导出的公式，可以很容易地确定交叉耦合路径中的电抗元件的值。因此，可以在期望的频率上分配衰减极点。研究成果发表在《IEICE电子学报》上5篇论文、IEICE技术报告4篇、IEICE全国会议口头报告6篇、国际研讨会论文3篇、多个技术研讨会论文5篇。较少

Recent years have seen extensive studies on high-temperature superconductor (HTS) filters with small-size, low loss, and high frequency selectivity. There have been numerous reports and publications on HTS microstrip filters. On the other hand, as filters using coplanar waveguide (CPW) structures require only, one side superconductor film, lower fabrication cost is expected compared with filters using microstrip structures using two-sides superconductor films.This research project is aimed at developing design and measuring methods of superconductor filters at millimeter-wave frequencies.In 2002, three measuring methods, including the circular cavity method, the cut-off circular waveguide method, and the four modes in a sapphire rod resonator method, are developed for accurate measurement of the dielectric substrate (MgO) and the frequency dependence of surface resistance of superconductor film (YBa_2Cu_3O_7, i.e., YBCO) at millimeter-waves. The results show that at 30GHz and 70K, the … More loss tangent of the MgO substrate is smaller than 2x10^<-6,> while the surface resistance of YBCO film is about one fifth of that of the copper. Therefore, low loss resonators and filters can be built by using these materials even at millimeter-waves.Based on these measured results, an H-slot type resonator using CPW structure is proposed, and the simulated results show it owns very high Q-factors at millimeter-waves. Next, a low-loss HTS CPW 4-pole Chebyshev filter is designed using the H-slot type resonators.In order to realize a high performance filter with low insertion-loss in its passband and sharp attenuation in its stopband, a general circuit model of a filter having one cross coupling path is analyzed, and a new theory is developed for the design of a filter with poles of attenuation in its stopband. By using the derived formulas, the reactance element values in the cross coupling path are determined readily. The attenuation poles can thus be assigned at desired frequencies. Various design examples are provided, together with simulated results, which validate the proposed theory.The research results have been published with 5 papers in IEICE Transactions on Electronics, 4 technical reports of IEICE, 6 oral presentations at the national conferences of IEICE, 3 papers at international symposiums, and 5 papers at a number of technical workshops. Less