Development of the Fin-Line Superconductive Mixer in the Millimeter and Submillimeter Band

对于毫米波外差接收机，充足、高质量的本振(LO)功率对接收机性能至关重要。尤其是在射电天文应用中，它是决定天文观测质量的主要因素之一，除了高质量的本地源外，如何将本地信号完美地注入混频器也是高性能接收机的关键。一般而言，理想的LO功率注入方法应满足以下条件：(1)为泵浦非线性器件提供足够高质量的LO功率；(2)不增加射频信号的额外损耗；(3)不增加来自本地源的功率的不稳定性；(4)消除本地噪声；(5)注入结构紧凑，对接收系统无重载。在毫米波频段，通常采用交叉波导定向耦合器将LO功率耦合到混频器中，而分束器通常由一种非常薄的聚四氟乙烯薄膜或线栅等制成，安装在与RF/LO路径成45°角的位置，通常用于较短的毫米波和亚毫米波。基于SIS混频器的优点，我们发现LO功率可以通过结的子速率直接注入到SIS结中，即LO信号与DC/IF信号共享路径，而不是传统方法中的RF信号。因此，不需要传统的交叉波导耦合器和分束器。另外，LO信号路径和RF信号路径在结之前完全分开，从而可以最大限度地降低LO路径引起的RF插入损耗。这就是新的LO功率注入方法的基本思想。我们特别针对(亚)毫米波SIS混频器的应用提出了这种方法。

For a millimeter-wave heterodyne receiver, a sufficient, high-quality local oscillator (LO) power is fairly important to the receiver performance. Particularly for radio astronomical applications, it is one of the major factors driving quality astronomical observations.Besides a high-quality local source, how to perfectly inject the local signal into mixers is also determinant for a high performance receiver. In general, an ideal LO power injection method should satisfy following conditions : (1) providing sufficient quality LO power to pump nonlinear device ; (2) adding no additional loss to RF signal ; (3) adding no instability to the power from local source ; (4) eliminating local noise ; (5) resulting an injection structure compact and of no heavy duty to receiver system in any aspect.In millimeter-wave band, cross guide directional couplers are generally used to couple the LO power into mixers, while beamsplitters, which are usually made from a kind of very thin Teflon film or wire grid etc. and are mounted at 45° to the RF/LO paths, are more often used at shorter millimeter-wavelengths as well as submillimeter- wavelengths. Obviously, they all contribute additional loss and are not so compact, sometimes unstable.Based on SIS mixers' the advantage, we find that the LO power can be injected directly into the SIS junction through the junction subsrate, that is the LO signal shares same path with the dc/IF signal, but not with the RF signal as in traditional method. So conventional cross-guide couplers and beam splitters are not needed. Additionally the LO signal path and the RF signal one are completely separated before the junctions so that the RF insertion loss caused by the LO path can be decreased maximally. This is the basic idea of the new LO power injection method. We propose this method particularly for the applications of (sub)millimeter-wave SIS mixers.