Design, Development and Characterization of mm/sub-mm wave Receivers at 220-230 & 330-345GHz for radio astronomical applications

This paper presents design, development and characterization of $\mathrm{m m}$ /sub-mm wave receivers at $220-230 \mathrm{GHz}$ and 330-345 GHz for radio astronomical applications. The receivers are designed for observing CO transitions from first $\mathrm{m m} / \mathrm{s u b}-\mathrm{mm}$ wave telescope of India, proposed to be deployed at Hanle, Himalayan region. The receiver comprises of Schottky-diode based RF front-end and Monolithic Microwave Integrated Circuit (MMIC) & Microwave Integrated Circuit (MIC) based IF back-end with two levels of down conversion. In first stage down conversion in RF front-end (FE), double sideband (DSB) configuration is followed whereas sideband separating (2SB) configuration is adopted in second stage down-conversion. Local oscillator (LO) signal at certain offset from band center aids in distinguishing the CO spectral lines in the lower side band (LSB) and upper side band (USB) after sideband separation. RF front-end comprises of Schottky barrier diode (SBD) based sub-harmonic (SHM) mixer at 230 GHz (WR- 4.3 interface) & 345 GHz (WR-2.8 interface) followed by IF low noise amplifier (LNA). The IF back-end receiver has side-band separation mixing circuit, amplification stages, filtering stages and electronic gain control circuitry. Measured results of both 230 and 345 GHz receivers demonstrate side-band separation better than 20 dB across the IF bandwidth.