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Optimization of an Offset Receiver Optics for Radio Telescopes

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Abstract

The latest generation of Cassegrain radio astronomy antennas is designed for multiple frequency bands with receivers for individual bands offset from the antenna axis. The offset feed arrangement typically has two focusing elements in the form of ellipsoidal mirrors in the optical path between the feed horn and the antenna focus. This arrangement aligns the beam from the offset feed horn to illuminate the subreflector. The additional focusing elements increase the number of design variables, namely the distances between the horn aperture and the first mirror and that between the two mirrors, and their focal lengths. There are a huge number of possible combinations of these four variables in which the optics system can take on. The design aim is to seek the combination that will give the optimum antenna efficiency, not only at the centre frequency of the particular band but also across its bandwidth. To pick the optimum combination of the variables, it requires working through, by computational mean, a continuum range of variable values at different frequencies which will fit the optics system within the allocated physical space. Physical optics (PO) is a common technique used in optics design. However, due to the repeated iteration of the huge number of computation involved, the use of PO is not feasible. We present a procedure based on using multimode Gaussian optics to pick the optimum design and using PO for final verification of the system performance. The best antenna efficiency is achieved when the beam illuminating the subreflector is truncated with the optimum edge taper. The optimization procedure uses the beam’s edge taper at the subreflector as the iteration target. The band 6 receiver optics design for the Atacama Large Millimetre Array (ALMA) antenna is used to illustrate the optimization procedure.

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Acknowledgements

This work was supported in part by the Fundamental Research Grant Scheme funded by Malaysia Ministry of Education (project: FRGS/2/2013/SG02/UTAR/02/1) and Universiti Tunku Abdul Rahman research fund (project: IPSR/RMC/UTARRF/2014-C1/Y03).

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Authors and Affiliations

  1. Faculty of Engineering and Green Technology, Universiti Tunku Abdul Rahman , Jalan Universiti, Bandar Barat, 31900, Kampar, Perak, Malaysia

    Kim Ho Yeap

  2. School of Science and Technology, Wawasan Open University, 54 Jln. Sultan Ahmad Shah, 10050, Penang, Malaysia

    Choy Yoong Tham

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  1. Kim Ho Yeap
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  2. Choy Yoong Tham
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Correspondence to Kim Ho Yeap.

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Yeap, K.H., Tham, C.Y. Optimization of an Offset Receiver Optics for Radio Telescopes. J Infrared Milli Terahz Waves 39, 64–76 (2018). https://doi.org/10.1007/s10762-017-0449-z

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  • DOI: https://doi.org/10.1007/s10762-017-0449-z

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