Tridimensional Yagi Antenna J. R. Brianeze Orbisat da Amazônia Indústria e Aerolevantamento S/A Campinas, Brazil jurbrian@yahoo.com.br Arismar Cerqueira S. Jr, A. M. O. Ribeiro, E. Conforti and H. E. Hérnandez-Figueroa Dept. of Microwaves and Optics, School of Electrical and Computer Engineering, University of Campinas Campinas, Brazil {arismar, aribeiro, conforti, hugo}@dmo.fee.unicamp.br Abstract — This work presents the concept and development of the so called Tridimensional Yagi Antenna, which is a novel type of Yagi antenna operating in P band. It was idealized from two other types of Yagi antennas: Quasi-Yagi and Yagi-Uda. The resultant antenna is based on a microstrip balun, as in Quasi- Yagi, and its driver and directors are made from metal tubes, as in Yagi-Uda, both integrated to a reflecting plane. The key point of this new antenna model is its asymmetric and reconfigurable radiation pattern and therefore the possibility of a high rejection between bands in a plane. This feature was accomplished with the new concept of progressive rotation of directors around driver. We present a design methodology to adjust return loss and radiation pattern characteristics. The final prototype presents 9.4 dB gain at 450 MHz and 47% bandwidth centered at 425 MHz. Keywords – antenna; Yagi-Uda; Quasi-Yagi; radiation pattern; trough region; Yagi3D I. INTRODUCTION Creation of trough or cancellation regions in a radiation pattern has been commonly used to eliminate interferences in signal receptions. This can be achieved relocating a number of the pattern nulls into the region of the trough, which must increase if either the required trough width (frequency bandwidth) or depth is increased [1]. Nowadays in modern cellular radio systems this is usually done dynamically, through adaptive or smart antenna systems, or ultimately through Spatial Division Multiple Access (SDMA) [2]. Yagi-Uda (YU) antenna was invented in the 1920s. Today it is the most common and known traveling wave antenna, being largely used in home TV reception. Quasi-Yagi (QY) antenna was first proposed in [3]. Nowadays it is very popular for combining the best features of planar antennas, without compromising any important parameter [4]. It has the same basic structure of a YU antenna: a dipole array with a driver, directors and reflectors. The main difference is the replacement of the reflector by the truncated ground plane. A printed balun ensures a balanced feed to driver and the antenna wide bandwidth [5]. The aim of this work was to develop a new Yagi antenna operating in P band, with the feature of using a reflector plane and non-planar directors to shape the radiation pattern and create trough regions in it. The proposed novel Yagi antenna was called Tridimensional Yagi (Yagi3D) and its main properties were analyzed by means of numerical simulations using Ansoft HFSS and experiments. Finally, a prototype was built and experiments on return loss and radiation pattern have been carried out and compared to numerical simulations. II. YAGI3D CONCEPT Yagi3D antenna is a combination of QY and YU antennas. From the first, the microstrip balun is kept, in order to ensure a large bandwidth. The radiant elements (driver and directors), remain similar to those of YU antenna, in other words, cylindrical metal dipoles. The antenna was designed to be fixed to a reflecting plane, which could be a tower, an airplane fuselage or other metallic surface, depending on the application. Fig. 1 presents the new Yagi3D antenna, installed in a section of an airplane fuselage, which was used as the reflecting plane for the simulations and experiments. A supporting structure to directors is not shown. The resulting construction keeps at the same time features from YU (metal tubes dipoles) and from QY (printed balun) antennas. From a QY antenna designed to operate at P band, initially the amount of substrate used in the balun was optimized to reduce the antenna weight. The borders were reduced and the longer side, which is responsible for the 180º phase difference between the microstrip lines, was bent to (a) Antenna without reflecting plane and balun metal box. (b) Model used for simulations, with a reflecting plane. Figure 1: Yagi3D Antenna. 978-1-4244-5357-3/09/$26.00©2009IEEE 432