Dyson conical quad-spiral array as ultrawideband feed system

Abstract

VLBI2010 requires a feed that simultaneously has high efficiency over the full 2-14 GHz frequency range. The simultaneity requirement implies that the feed must operate at high efficiency over the full frequency range without the need to adjust its focal position to account for frequency dependent phase center variations. Two feeds meet this specification with some lacks to be fulfilled [1]: The Eleven Feed developed at Chalmers University and the Quadruple Ridged Flared Horn (QRFH) developed at the California Institute of Technology. In this frame, Universidad Carlos III de Madrid has developed a new topology for complete covering the requirements of the VLBI2010, including two new pretty attractive characteristics: dual circular polarization (versus the dual lineal solutions present in the state of the art) and constant input impedance of the antenna due to its self-complementary geometry, what is highly interesting for the LNA design. This manuscript is divided as follows: first, results of the complete system using an ideal Gaussian feed are summarized. Then, the new topology proposed is presented and analyzed both, isolated and integrated in the radiotelescope. Finally, a closed solution for covering all the requirements has been manufactured and results from full wave electromagnetic simulations together with measurements are presented. Conclusions and future lines are presented at the end of the present manuscript.