Near-Field Radio Holography of Large Reflector Antennas

TL;DR

This paper details a holographic measurement method for large reflector antennas, incorporating Fresnel effects, and demonstrates its application on ALMA prototype antennas to accurately determine their surface profiles.

Contribution

It presents a comprehensive mathematical and practical framework for near-field radio holography, including finite-distance source effects, and applies it to real-world large antenna measurements.

Findings

Successful measurement of ALMA prototype antennas

Inclusion of Fresnel terms improves accuracy

Practical implementation guidelines provided

Abstract

We summarise the mathematical foundation of the holographic method of measuring the reflector profile of an antenna or radio telescope. In particular, we treat the case, where the signal source is located at a finite distance from the antenna under test, necessitating the inclusion of the so-called Fresnel field terms in the radiation integrals. We assume a ``full phase'' system with reference receiver to provide the reference phase. We describe in some detail the hardware and software implementation of the system used for the holographic measurement of the 12m ALMA prototype submillimeter antennas. We include a description of the practicalities of a measurement and surface setting. The results for both the VertexRSI and AEC (Alcatel-EIE-Consortium) prototype ALMA antennas are presented.