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Associate Professor    KOJIMA, Takafumi

Research Field

  • High frequency and superconducting electronics for radio astronomy

Degree

  • Ph.D.

Summary of Research

  • I have been working on the design, analysis and characterization of heterodyne receivers and their components for next generation ALMA. My research interests are:
    -Ultra-wideband RF and IF superconducting mixers for ALMA
    -Low noise and low power consumption superconducting amplifier

Research Achievements or Papers

  • Development of wideband receiver technologies

    T. Kojima, M. Kroug, A. Gonzalez, K. Uemizu, K. Kaneko, A. Miyachi, Y. Kozuki, S. Asayama, "275–500-GHz Wideband Waveguide SIS Mixers," IEEE Transactions on Terahertz Science and Technology, vol. 8, no. 6, pp. 638-646, Nov. 2018.
    T. Kojima, M. Kroug, K. Uemizu, Y. Niizeki, H. Takahashi and Y. Uzawa, "Performance and Characterization of a Wide IF SIS-Mixer-Preamplifier Module Employing High-Jc SIS Junctions," IEEE Transactions on Terahertz Science and Technology, vol. 7, no. 6, pp. 694-703, Nov. 2017.
    T. Kojima, A. Gonzalez, S. Asayama, and Y. Uzawa, "Design and Development of a Hybrid-Coupled Waveguide Multiplexer for a Multiband Receiver," IEEE Transactions on Terahertz Science and Technology, pp. 1-10, 2016.

  • Development of low-noise SIS mixers for ALMA telescope

    T. Kojima, K. Kuroiwa, Y. Uzawa, M. Kroug, M. Takeda, Y. Fujii, K. Kaneko, A. Miyachi, Z. Wang, and H. Ogawa, "A Low-Noise Terahertz SIS Mixer Incorporating a Waveguide Directional Coupler for LO Injection," Journal of Infrared, Millimeter, and Terahertz Waves, vol. 31, no. 11, pp. 1321-1330, 2010.
    T. Kojima, M. Kroug, M. Takeda, Y. Uzawa, W. Shan, Y. Fujii, Z. Wang, and H. Ogawa, “Three Quanta Sensitivity Superconductor–Insulator–Superconductor Mixer for the 0.78–0.95 THz Band,” Applied Physics Express, 2, 102201, 2009
    T. Kojima, M. Kroug, M. Takeda, S. Wenlei, Y. Fujii, Y. Uzawa, W. Zhen, and S. Shengcai, "Performance of Terahertz Waveguide SIS Mixers Employing Epitaxial NbN Films and Nb Junctions," IEEE Transactions on Applied Superconductivity, vol. 19, no. 3, pp. 405-408, 2009.
    T. Kojima, K. Kuroiwa, T. Takahashi, Y. Fujii, Y. Uzawa, S. Asayama, and T. Noguchi, "Design and performance of mass-produced sideband separating SIS mixers for ALMA band 4 receivers," Superconductor Science and Technology, vol. 28, no. 9, 2015.

  • Basic studies

    T. Kojima, M. Kroug, Y. Uzawa, Y. Kozuki and W. Shan, "Contribution of Quantum Susceptance in SIS Junction Capacitance Measurement," IEEE Transactions on Applied Superconductivity, vol. 29, no. 5, Art no. 1103304. pp. 1-4, 2019.
    T. Kojima, Y. Uzawa, and W. Shan, "Microwave amplification based on quasiparticle SIS up and down frequency converters," AIP Advances, vol. 8, no. 2, 2018.
    T. Kojima, M. Kroug, K. Sato, T. Sakai, and Y. Uzawa, "On-Wafer Capacitance Measurement of Nb-Based SIS Junctions With a 4-K Probe Station," IEEE Transactions on Applied Superconductivity, vol. 27, no. 4, pp. 1-4, 2017.

Academic Society

  • ASJ, JSAP, IEICE, IEEE-MTT

Academic Award

  • IEEE Microwave Theory and Techniques Society Japan Young Engineer Award (2018 November)
    The Astronomical Society of Japan (ASJ) Young Astronomer Awards (2013 March)
    Japanese Society of Applied Physics (JSAP) Superconductors Division Young research award (2011 March)
    The Society of Non-Traditional Technology Superconductivity Science and Technology Award (2010 April)

Web Page

E-mail

  • t.kojima[at]nao.ac.jp
    (In the mailing address, replace [at] with @)

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