IEEE ANTENNAS AND WIRELESS PROPAGATION LETTERS, VOL. 11, 2012 57 Lens-Corrected Axis-Symmetrical Shaped Horn Antenna in Metallized Foam With Improved Bandwidth Anthony Rolland, Artem V. Boriskin, Member, IEEE, Christian Person, Member, IEEE, Cedric Quendo, Member, IEEE, Laurent Le Coq, Member, IEEE, and Ronan Sauleau, Senior Member, IEEE Abstract—A lens-corrected smooth-walled axis-symmetrical dielectric-loaded horn antenna is designed and characterized in Ka-band using the bodies of revolution ﬁnite-difference time domain (BoR-FDTD) technique and genetic algorithm. The joint optimization of the horn and dielectric loading proﬁles enables us to develop a horn with a very good gain performance achieved in a frequency range of about 18%. Compared to earlier results, the bandwidth improvement exceeds a factor two. A lightweight prototype is fabricated in metallized foam. A very good agreement between the numerical and measured data is obtained. Index Terms—Bodies of revolution ﬁnite-difference time domain (BoR-FDTD), genetic algorithm, metallized foam, millimeter waves, smooth-walled shaped horns. I. INTRODUCTION A XIS-SYMMETRICAL horns are widely used as primary feeds for reﬂector and lens antennas of space- and ground- based communication and tracking systems [1]–[6]. Their pop- ularity is explained by the fabrication simplicity and excellent radiation characteristics, like very good beam symmetry, low cross-polarization level, high efﬁciency, etc. (see [7] and refer- ences therein). Very attractive single- and dual-band solutions with corrugated and/or smoothly shaped walls have been pro- posed to improve gain and sidelobe level [2]–[5]. In addition, the bandwidth improvement has been achieved by adding di- electric lenses [6]. Nevertheless, most of the reported horns are long, bulky, and heavy, which is a critical drawback for some ap- plications. To solve this problem, short horns with large ﬂare an- gles have been proposed [7]–[10]. Such feeds have much more compact dimensions, but require metallic or dielectric loading to compensate for the unavoidable phase distortions in the horn mouth. Manuscript received November 24, 2011; accepted December 16, 2011. Date of publication January 02, 2012; date of current version March 19, 2012. This work was supported in part by the “Université Européenne de Bretagne” (UEB), France, under the “International chair” program and the OPTIMISE and GRAPPAS projects, the Conseil Régional de Bretagne (CREATE/CONFOCAL project), and CNRS. This work was performed using HPC resources from GENCI-IDRIS under Grant 2010-050779. A. Rolland, A. V. Boriskin, L. Le Coq, and R. Sauleau are with the Institute of Electronics and Telecommunications of Rennes (IETR), UMR CNRS 6164, University of Rennes 1, Rennes 35042, France (e-mail: ronan.sauleau@univ- rennes1.fr). C. Person and C. Quendo are with the Lab-STICC, Brest 29238, France (e-mail: christian.person@telecom-bretagne.eu). 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.2011.2182596 Fig. 1. Proposed antenna conﬁguration. The metallized and dielectric contours are shown by black and gray solid lines, respectively. The optimized halves of the metallic horn and radiating aperture are denoted by dashed lines. The ﬁxed nodes are marked by hollow circles. In our recent papers [7], [11], we have introduced a design technique based on the bodies of revolution ﬁnite-difference time domain (BoR-FDTD) and genetic algorithm and enabling the analysis and synthesis of axis-symmetrical smooth-walled shaped horns. To validate the accuracy and relevance of this design methodology, a few prototypes have been fabricated in metallized foam using an innovative 3-D fabrication process [7]. Combining the advanced design and fabrication techniques en- abled us to develop lightweight and compact conical horns with very high radiation efﬁciency (up to 90%) in Ka-band. One of the weak points of the horn solutions introduced in [7] is their limited frequency bandwidth, which does not exceed 8%. To design a metallized-foam smooth-walled horn antenna with improved operational bandwidth, we propose here an alternative conﬁguration that consists in loading the horn mouth with an outer phase-correcting lens (Fig. 1). The latter constitutes the main difference compared to [7], where the dielectric lens was placed only inside the horn. The design and fabrication methodologies are the same as in [7], so we omit their description here. II. ANTENNA CONFIGURATION AND OPTIMIZATION GOAL The antenna geometry studied here is represented in Fig. 1. The central frequency is ﬁxed at 29.5 GHz ( mm). In order to produce a short horn and simplify the comparison to ear- lier results, the horn dimensions are the same as in [7], namely 1536-1225/$31.00 © 2012 IEEE