Coaxially fed dual-frequency horn for offset parabolic reflector [geodetic applications]

Geodetic measurements are commonly performed by using very long baseline interferometry (VLBI) when mm-accuracy is required. The number of antennas which can be utilized for geodetic measurements is limited; most often radiotelescopes with multi-frequency capability are used. Furthermore, the geographic distribution of these antennas is uneven which means that for large regions of the Earth there are no high-accuracy data available. The performance of a VLBI antenna system depends to a large degree on the gain to noise ratio. This, together with demand for dual-band operation and circular polarization, makes reflector antennas the only viable solution. Within the framework of a study of small low-cost antennas suitable for VLBI, a dual-frequency feed horn has been developed. In this paper the authors present the configuration of the feed, including the feed network, and they show how waveguide components for the feed network have been designed and analyzed. Finally, measured data for the complete horn are presented.