Multi-Band Feeds: A Design Study

TL;DR

This paper explores the design of multi-band antenna feeds for radio telescopes that can selectively respond to RFI-free frequency windows over a wide spectrum, improving observational quality.

Contribution

It introduces new multi-band feed designs using simple wire dipoles and coaxial feed-lines, enabling selective frequency response and RFI rejection over a broad range.

Findings

Coaxial line-based design effectively rejects unwanted spectrum parts.

Design achieves controlled resonant band placement.

Simple wire dipoles are effective in multi-band antenna feeds.

Abstract

Broadband antenna feeds are of particular interest to existing and future radio telescopes for multi-frequency studies of astronomical sources. Although a 1:15 range in frequency is difficult to achieve, the well-known Eleven feed design offers a relatively uniform response over such a range, and reasonably well-matched responses in E & H planes. However, given the severe Radio Frequency Interference in several bands over such wide spectral range, one desires to selectively reject the corresponding bands. With this view, we have explored the possibilities of having a multi-band feed antenna spanning a wide frequency range, but which would have good response only in a number of pre-selected (relatively) RFI-free windows (for a particular telescope-site). The designs we have investigated use the basic configuration of pairs of dipoles as in the Eleven feed, but use simple wire dipoles instead of folded dipoles used in the latter. From our study of the two designs we have investigated, we find that the design with feed-lines constructed using co-axial lines shows good rejection in the unwanted parts of the spectrum and control over the locations of resonant bands.