A comparison of radome- and astrodome-enclosed large radio telescopes at millimeter wavelengths: The Large Millimeter Telescope

We present a systematic comparison of the main figures of merit for an open -air radio telescope and two different types of enclosed antennas: (1) an o rdinary radome, with a metal space frame providing the required mechanical rigidity and a dielectric membrane, and (2) an "astrodome," i.e., a corotat ing rigid dome with a large window covered by a tensile membrane structure. The analysis is limited to submillimeter and millimeter wavelengths and la rge (greater than or similar to 30 m) antenna/enclosure systems, where the window tensile structure is very unlikely to be removable and is supported by either a metal space frame or cable networks. As compared with previous studies of this type, here we concentrate on the specific effects that thes e large metallic support structures have on sensitive astronomical observat ions. In particular, we critically discuss how the wind-induced random moti ons of the metal space frame can limit the sensitivity of continuum observa tions, as a result of fluctuating shadowing and spillover effects combined with various beam-chopping techniques. Using the Large Millimeter Telescope as a benchmark, we provide baselines for future projects where a similar c omparison is needed.