Initial progress toward planar integrate, low-cost water vapour radiometers

Astronomical, astrometric and geodetic observations by mm-Wave Very Long Baseline Interferometry (VLBI) are adversely affected by precipitable water vapour (PWV) in the troposphere. Current water vapour radiometers (WVRs), such as that deployed at the Large Millimeter Telescope (LMT) site, are difficult to install and maintain, and are prohibitively expensive for surveying promising new sites for telescopes or for wide-spread deployment for a priori calibration. We report here on initial progress towards a Planar Integrated Low-Cost H₂O Atmospheric Radiometric Detector (PILCHARD), which aims to reduce the cost of 22 GHz WVRs for site surveys, whilst eliminating the need for moving antennas. It is found that the required tip curve can be generated by a static antenna using multiple pencil beams from a multi-feed, non-traditional offset reflector, while the necessary system receiver temperature is easily achievable using planar integrated off-the-shelf components alone.