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

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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.