Short-slot Hybrid Coupler Using Linear Taper in W-band
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Short-slot Hybrid Coupler Using Linear Taper in W-band Koichi Kuroiwa & Alvaro Gonzalez & Makoto Koyano & Takafumi Kojima & Yasunori Fujii & Yoshinori Uzawa & Hideo Ogawa
Received: 24 October 2012 / Accepted: 30 September 2013 / Published online: 20 October 2013 # The Author(s) 2013. This article is published with open access at Springerlink.com
Abstract -We have designed and fabricated a broadband short-slot hybrid coupler using a twostage linear taper in W-band. The coupler consists of two metal pieces split at the edge of the narrow wall of the waveguide, which makes it possible to use simple direct machining for fabrication. The electrical performance of the coupler was measured by a Vector Network Analyzer (VNA) at room temperature. The results showed excellent performance as designed: amplitude imbalance between the two output ports of ≤ 1 dB, phase difference between the output ports with respect to 90° < 3°, input return loss < –15 dB, and isolation < –15 dB across the measured frequency range of 85-110 GHz. The short-slot hybrid coupler was used in a balanced Superconductor-Insulator-Superconductor (SIS) mixer at 4 K. The noise performance was almost the same as that of the two single-ended mixers used in the balanced mixer. These results indicate that our short-slot hybrid coupler has great potential for practical applications, such as at millimeter- and submillimeter-waves. Keywords Short-slot hybrid coupler . Waveguide coupler . Balanced mixer . Superconductor-Insulator-Superconductor mixer
1 Introduction Millimeter- and sub-millimeter-wave technologies have recently become increasingly important in many practical and basic scientific applications such as remote sensing, radio astronomy, plasma diagnostics, imaging, and communication. In particular, high-resolution heterodyne spectroscopy using ultra-sensitive detectors such as Superconductor-InsulatorSuperconductor (SIS) junctions in the millimeter- and sub-millimeter-wave regions is important for astronomical research, since signals provide spatial information. Heterodyne receivers in the latest radio astronomical telescopes such as the Atacama Large K. Kuroiwa (*) : A. Gonzalez : T. Kojima : Y. Fujii : Y. Uzawa Advanced Technology Center, National Astronomical Observatory of Japan, 2-21-1 Osaka( Mitaka, Tokyo 181-8588, Japan e-mail: [email protected] K. Kuroiwa : M. Koyano : H. Ogawa Osaka Prefecture University, 1-1 Gakuen-cho, Naka-ku, Sakai, Osaka 599-8531, Japan
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J Infrared Milli Terahz Waves (2013) 34:815–823
Millimeter/sub-millimeter Array (ALMA) employ sideband-separating (2SB) mixers with about 25% fractional bandwidth to cover the existing atmospheric windows [1]. In these mixers, waveguide quadrature hybrid couplers are used. At terahertz frequencies, where no powerful source is available at the moment, balanced mixers with a quadrature coupler are considered to be useful because the required local oscillator (LO) power can be substantially reduced, as well as the LO sideband noise. Waveguide branch line couplers are wi
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