Ghassan Yassin

Abstract:

It is well known that the boundary conditions of the electromagnetic fields on the surface of a superconductor are influenced by the field penetration into the material. In a series of recent publications, it has been suggested that this effect substantially influences the wave propagation in high-temperature superconducting waveguides, to the extent that the mode order becomes different than that predicted for perfect conductor waveguides. In this paper, we present experimental investigation of this effect. We show that the effect of superconductivity on the wave propagation in waveguides is very small for temperatures well below the transition temperature and away from cutoff. We also discuss the behavior of the waveguide near cutoff and very close to the transition temperature. © 2001 IEEE.

Abstract:

We describe a procedure for simulating the behavior of partially coherent submillimeter-wave antenna systems. The procedure is based on the principle that the second-order statistical properties of any partially coherent vector field can be decomposed into a sum of fully coherent, but completely uncorrelated, natural modes. Any of the standard electromagnetic analysis techniques-physical optics, geometrical theory of diffraction, etc.-can be used to propagate and scatter the modes individually, and the statistical properties of the total transformed field reconstructed at the output surface by means of superposition. In the case of modal optics-plane waves, Gaussian optics, waveguide mode matching, etc.-the properties of the field can be traced directly by means of scattering matrices. The overall procedure is of considerable value for calculating the behavior of astronomical instruments comprising planar and waveguide multimode bolometers, submillimeter-wave optical components, and large reflecting antennas.

Abstract:

We have developed a 330-370GHz SIS mixer for small-format, heterodyne, astronomical imaging arrays. Fixed-tuned broadband operation is achieved by means of a superconducting radial waveguide probe. A horn-reflector antenna provides high-efficiency optical coupling. Using a variable-temperature cryogenic noise source, we measured a DSB system noise temperature of 32±1K. The mixer contributes 3±3K, supporting the theoretically-predicted result that the noise temperature of a DSB mixer can be less than (Latin small letter hwith stroke)ω/2k (8.6K). © 2001 Plenum Publishing Corporation.

Abstract:

Superconducting detectors are set to become the principal method by which wide-field mapping and deep point-source searches are carried out throughout the whole of the submillimetre-wave frequency range. In the paper, we outline the operation of the basic detector types, and assess the future of superconducting detector technology. We place particular emphasis on distinguishing between single-mode, few-mode, and multi-mode designs, and we explain how similar the superconducting bolometer and mixer technologies have become. We outline the considerable advances that are taking place in the area of superconducting detector technology.

Abstract:

In this paper, we describe the design and operation of a 350-GHz flnline superconductor-insulator-4superconductor mixer. The mixer is fed by a horn-reflector antenna, and the superconducting circuit is fabricated using planar-circuit technology and fully integrated tuning. An important feature of the mixer is that it employs an antipodal flnline section, deposited on one side of a quartz substrate, which transforms the high impedance of the waveguide (300 fi) to the low impedance of the microstrip (-420 II). The Nb/Al-oxide/Nb tunnel junction is fabricated at the same time as the flnline circuit. In this paper, we describe the design procedure in some detail. We pay particular attention to the synthesis of the flnline taper and the electromagnetic design of the horn-reflector antenna. We have tested a flnline mixer over the frequency range of 330-370 GHz and measured a receiver noise temperature of 90 K, which remained unchanged over the whole frequency range. Our investigation has demonstrated that it is possible to make superconducting flnline mixers for frequencies as high as 350 GHz. © 2000 IEEE.