The optical system of the Tenerife Microwave Spectrometer: a window for observing the 10-20 GHz sky spectra

TL;DR

This paper presents the design and simulation analysis of the Tenerife Microwave Spectrometer's optical system, achieving low cross-polarization and sidelobe levels over a broad frequency range for precise sky observations.

Contribution

The study provides a detailed design and performance evaluation of a decentered dual-reflector optical system for microwave sky observation, including simulations of polarization and beam stability.

Findings

Achieved low cross-polarization (-30 dB) and sidelobe (-25 dB) levels.

Demonstrated stable beam shape and size across 10-20 GHz bandwidth.

Analyzed effects of cryostat window and sidelobes on system performance.

Abstract

The TMS optical system is based on a decentered dual-reflector system in a Gregorian configuration to observe with an angular resolution of less than $2^\circ$. The primary goal of the present study is to evaluate the final design and verify that it satisfies the design requirements. We aim for low cross-polarization (-30 dB), low sidelobe (-25 dB) levels, and a stable beam in terms of shape (low ellipticity) and size over a full octave bandwidth (10-20 GHz). We performed both ray-tracing and full-wave simulations using the CST Studio software in order to investigate the system behaviour. We gave special attention to the beam frequency variation and polarization leakage. We have characterized the effects on the radiation pattern produced by the cryostat window. We present the final design of the TMS optical system, as well as a complete study of the system's performance in terms of cross-polarization, sidelobes, ellipticity and beamwidth. We discuss the effects of sidelobes and study the need for a baffle.