Presentation Information
[16p-W8E_308-1]A Monolithic Dual-Polarization Sideband-Separating SIS Mixer for the 2-mm Band
〇Wenlei Shan1, Shohei Ezaki1, Yoshinori Uzawa1 (1.NAOJ)
Keywords:
SIS mixer,Multi-beam,Radio astronomy
We demonstrate, for the first time, a monolithic dual-polarization sideband-separation superconductor–insulator–superconductor (SIS) mixer operating in the 2-mm wavelength band (125–163 GHz) based on a silicon substrate. The mixer chip is developed using the hybrid planar integration (HPI) concept, in which superconducting thin-film circuits are integrated onto a single silicon chip to enable compact, scalable heterodyne receiver arrays.
The mixer incorporates a planar turnstile-junction orthomode transducer (OMT) at the chip center, providing dual-linear-polarization signal separation. Each polarization is processed by a sideband-separation SIS mixer. The chip design is derived from a previously demonstrated balanced SIS mixer, allowing the same mixer block to be reused. On-chip lumped-element resistors are realized using nitrogen-deficient NbTiN thin films, optimized to provide appropriate resistivity and a superconducting transition temperature below the SIS operating temperature. The complete mixer chip measures approximately 12 mm × 10 mm.
The device was characterized in a 4-K cryostat. Single-sideband receiver noise temperatures of approximately 80 K at 4 GHz IF and 120 K at 8 GHz IF were measured using the standard Y-factor method. Sideband rejection ratios exceeding 10 dB were achieved across most of the RF band, with performance likely limited by standing waves in the IF circuitry. IF crosstalk among the four output channels was measured to be below −20 dB, and cross-polarization levels of approximately −20 dB were obtained. These results confirm the feasibility of a compact dual-polarization sideband-separating SIS mixer and demonstrate a key step toward large-format heterodyne arrays for millimeter and sub-millimeter radio astronomy.
The mixer incorporates a planar turnstile-junction orthomode transducer (OMT) at the chip center, providing dual-linear-polarization signal separation. Each polarization is processed by a sideband-separation SIS mixer. The chip design is derived from a previously demonstrated balanced SIS mixer, allowing the same mixer block to be reused. On-chip lumped-element resistors are realized using nitrogen-deficient NbTiN thin films, optimized to provide appropriate resistivity and a superconducting transition temperature below the SIS operating temperature. The complete mixer chip measures approximately 12 mm × 10 mm.
The device was characterized in a 4-K cryostat. Single-sideband receiver noise temperatures of approximately 80 K at 4 GHz IF and 120 K at 8 GHz IF were measured using the standard Y-factor method. Sideband rejection ratios exceeding 10 dB were achieved across most of the RF band, with performance likely limited by standing waves in the IF circuitry. IF crosstalk among the four output channels was measured to be below −20 dB, and cross-polarization levels of approximately −20 dB were obtained. These results confirm the feasibility of a compact dual-polarization sideband-separating SIS mixer and demonstrate a key step toward large-format heterodyne arrays for millimeter and sub-millimeter radio astronomy.