64 IEEE ANTENNAS AND WIRELESS PROPAGATION LETTERS, VOL. 8, 2009 Design and Realization of a Linearly Polarized Eleven Feed for 1–10 GHz Jian Yang, Xiaoming Chen, Niklas Wadefalk, and Per-Simon Kildal, Fellow, IEEE Abstract—A new linearly polarized Eleven feed for operation between 1 and 10 GHz is presented. This frequency band is higher than the realized before, and the input reflection coefficient is better than dB over the frequency range, which also is an improvement over previous models. The log-periodic dipole petals have been designed by using a simple one-by-one parameter optimization scheme with a simulation tool based on moment method. The final analysis has been improved by applying an finite-difference time-domain (FDTD)-based solver for the central part of the feed and then a circuit network program to combine the results of the center part with the result of the dipole panels. The antenna has been manufactured by printed circuit board (PCB) technology on a metalized Kevlar sheet in order to obtain better tolerances and smaller dimensions than in previous models. Measurements show agreement with the analysis. Index Terms—Eleven antenna, optimization, reflector feed. I. INTRODUCTION W IDE-FREQUENCY band antenna systems are re- quired for many new and future applications, such as in radio astronomy and ultrawideband (UWB) communi- cation technology [1], [2]. Therefore, research on more than octaves bandwidth antennas has gained a lot of attentions [2]–[5]. The radio astronomy applications are mainly the SKA project ( Square Kilometer Array) and the VLBI2010 project ( Very Long Baseline Interferometry). Both of these projects have reflector antennas as candidates covering 1–13 GHz or even higher, whereas the UWB systems require small direct radiating antennas covering typically 3–10 GHz. Thus, the frequency ranges are similar, although the require- ments are quite different. Chalmers University of Technology in Gothenburg, Sweden, has during the last years been developing a new decade band- width log-periodic dual-dipole antenna referred to as the Eleven antenna [6], which has resulted in dually polarized hardware below 3 GHz for use in different radio telescopes [7]–[9]. The development of Eleven feed has also gained attention from other researchers and been applied to other applications [10]. The Manuscript received November 11, 2008; revised December 04, 2008. First published December 22, 2008; current version published April 17, 2009. This work was supported in part by the Swedish Foundation for Strategic Research (SSF) within the Strategic Research Center Charmant. J. Yang, X. Chen, and P.-S. Kildal are with the Department of Signals and Sys- tems, Chalmers University of Technology, 412 96 Gothenburg, Sweden (e-mail: jian.yang@chalmers.se). N. Wadefalk is with the Department of Microtechnology and Nanoscience, Chalmers University of Technology, 412 96 Gothenburg, Sweden. Color versions of one or more of the figures in this letter are available online at http://ieeexplore.ieee.org. Digital Object Identifier 10.1109/LAWP.2008.2011148 Fig. 1. Configuration of Eleven feed of single polarization. basic geometry of the Eleven antenna is two parallel dipoles separated by half wavelength and located above a ground plane. Both dipoles are cascaded in log-periodic arrays in order to achieve the wide bandwidth (see Fig. 1). The cascading was most easily performed by folded dipoles. The Eleven antenna has very good features: nearly constant beamwidth with about 10 dBi directivity and fixed phase center location over the whole bandwidth, low profile, and simple geometry. Therefore, the Eleven antenna is well-suited to feed reflectors, and at frequen- cies above 1 GHz its size is so small that it would fit into a Dewar and could be cooled together with the low-noise am- plifier (LNA) in low-noise applications such as VLBI2010 and SKA. The Eleven antenna could also provide tracking patterns for use in Earth terminals for satellite communications [11]. The purpose of the present letter is to present a new design of an Eleven antenna with better performance and realized at higher frequencies than before, which can make it a better candidate for the SKA and VLBI2010 projects. In low-noise systems one of the most critical performance parameters is the input reflection coefficient because strong reflection at the antenna input port will cause noise mismatch to the LNA and increase the system noise level. In the present work, we are therefore focusing on optimizing the geometry of the feed to obtain better performance of the reflection coefficient than in previous models. We also introduce a man- ufacturing technology that can be used at 10 GHz and higher. Due to the very wide frequency band, the size of the whole feed becomes very large in terms of wavelength at the highest 1536-1225/$25.00 © 2009 IEEE