Extended-W-band Single Pixel for Cryogenic Array Receiver for Users of the Sardinia Observatory (CARUSO) Astronomical Instrument

This paper describes the design and performance of the single-pixel receiver elements in the Cryogenic Array Receiver for Users of the Sardinia Observatory (CARUSO). CARUSO contains an array of 4x4 extended-W-band pixels, covering astronomical source frequencies from 70 to 116 GHz. CARUSO has recently been installed at the Gregorian focus of the 64 m diameter Sardinia Radio Telescope. Each cryogenic receiver pixel comprises a smooth walled feedhorn and a waveguide orthomode transducer for polarization separation. Each polarization channel comprises two low-noise amplification modules with a waveguide isolator between them, and an image-rejecting sub-harmonic mixer delivering the upper and lower sidebands, with a frequency tripler providing the local oscillator signal. The low noise amplifiers are based on two-stage MMIC amplifiers, incorporating InP high electron mobility transistors.