Millimeter-Wave Lumped Element
Superconducting Bandpass Filters for Multi-Color Imaging

Shwetank Kumar, Anastasios Vayonakis, Henry G. LeDuc,
Peter K. Day, Sunil Golwala, Jonas Zmuidzinas, Member, IEEE

Abstract—The opacity due to water vapor in the Earth’s atmosphere obscures portions of the sub-THz spectrum (mm/submm wavelengths) to ground based astronomical observation. For maximum sensitivity, instruments operating at these wavelengths must be designed to have spectral responses that match the available windows in the atmospheric transmission that occur in between the strong water absorption lines. Traditionally, the spectral response of mm/sub-mm instruments has been set using optical, metal-mesh bandpass filters [1]. An alternative method for defining the passbands, available when using superconducting detectors coupled with planar antennas, is to use on-chip, superconducting filters [2]. This paper presents the design and testing of superconducting, lumped element, on-chip bandpass filters (BPFs), placed inline with the microstrip connecting the antenna and the detector, covering the frequency range from 209 – 416 GHz. Four filters were designed with pass bands 209 – 274 GHz, 265 – 315 GHz, 335 – 361 GHz and 397 – 416 GHz corresponding to the atmospheric transmission windows. Fourier transform spectroscopy was used to verify that the spectral response of the BPFs is well predicted by the computer simulations. Two-color operation of the pixels was demonstrated by connecting two detectors to a single broadband antenna through two BPFs. Scalability of the design to multiple (four) colors is discussed.

Index Terms—Bandpass Filters, superconductivity, submillimeter camera, multi-color pixels

Manuscript received 19 August 2008. This work was supported in part by the NASA Science Mission Directorate, Jet Propulsion Laboratory, and the Gordon and Betty Moore Foundation
Shwetank Kumar was with Department of Applied Physics, California Institute of Technology Pasadena, CA, 91125, USA. He is now with IBM Watson Research Center, Yorktown Heights, New York, 10598, USA. (Phone: 914-945-2695, E-mail: shwetank@us.ibm.com)
Anatasios Vayonakis, Sunil Golwala and Jonas Zmuidzinas are with Department of Physics, California Institute of Technology, Pasadena, CA, 91125, USA.
Henry G. LeDuc and Peter K. Day are with Jet Propulsion Laboratory, Pasadena, CA, 91109, USA.

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