Development of planar technology for focal planes of future radio to sub-millimetre astronomical instruments

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Abstract

Receiver systems utilising planar technologies are prevalent in telescopes observing at radio to sub-millimetre wavelengths. Receiver components using planar technologies are generally smaller, have reduced mass and are cheaper to manufacture than waveguide-based alternatives. Given that modern-day detectors are capable of reaching the fundamental photon noise limit, increases in the sensitivity of telescopes are frequently attained by increasing the total number of detectors in the receivers. The development of components utilising planar technologies facilitates the demand for large numbers of detectors, whilst minimising the size, mass and manufacturing cost of the receiver. After a review and study of existing concepts in radio to sub-mm telescopes and their receivers, this thesis develops planar components that couple the radiation from the telescope's optics onto the focal plane. Two components are developed; a W- band (75-110 GHz) planar antenna-coupled flat mesh lens designed for the receiver of a Cosmic Microwave Background (CMB) B-mode experiment, and an L-band (1- 2 GHz) horn-coupled planar orthomode transducer designed for the receiver of the FAST telescope. The first developments of a planar antenna-coupled flat mesh lens are presented. The design is driven by the requirement to mitigate beam systematics to prevent pollution of the CMB B-mode signal. In the first instance, a waveguide-coupled mesh lens is characterised. The radiation patterns of the waveguide-coupled mesh lens have -3 dB beam widths between 26 and 19 degrees, beam ellipticity < 10%, and cross-polarisation <-20 dB between 75 and 110 GHz. Subsequently, a dual-band slot antenna that is sensitive to orthogonal linear polarisation states is designed to couple with the flat mesh lens. The horn-coupled planar orthomode transducer is fabricated and characterised. The planar orthomode transducer has a loss of ~ 0.5 dB, a cross-polarisation < -30 dB and an isolation < -40 dB between 1.05 and 1.45 GHz. Measurements of the radiation patterns of the horn-coupled orthomode transducer are also presented.

Keyword(s)

Cosmic Microwave Background instrumentation; FAST telescope; clean room fabrication; electromagnetic modelling; focal plane design; metamaterial lens; multichroic; planar orthomode transducer; planar slot antenna; radio to sub-mm; radio to sub-mm measurements

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