Design of Fractal Shape Cross Field Antenna

Abstract

ABSTRACT:The main concept of Cross Field Antenna is getting phase shift between electric fields of the two cylinders of the antenna equals to 90 degrees. This is done by connecting a coil to the antenna circuit. The objective of doing this is to get rid of near field region and make far field region starting from antenna surface. Fractal shape antennas have many characteristics that not find in classical antennas. Among them is, multiband and wide band behaviour, antenna size is not depend on the operating frequency and easy matching of the antenna circuit.Here, combination of cross field antenna and fractal antenna is done; to get fractal shape cross field antenna. The proposed fractal shape is Sierpinski Carpet. Fractal shape cross field antenna has attracted wide band behaviour and self-tuning. KEYWORDS:Cross field antenna, EH antenna, Fractal antenna, Sierpinski Carpet, Poynting vector. I.INTRODUCTIONField set up by any radiating system can be divided into two components: the induction field and the radiation field. The induction field is observed in near field area; the energy associated with it pulsates back and forth between the radiator and near-by space. At large distances the radiation field is dominant; it represents a continual flow of energy directly outward from the radiator, with a density that varies inversely with the square of the distance and, in general, depends on the direction from the source [1]. Antenna is defined as a structure that convert guided waves on a transmission line into free space waves [2]. Cross field antenna (EH) appear around 1988. It consist of two separated cylinders connected to a coil. The diameter of the coil and number of turns differs according to its frequency of operation. Schematic figure of EH antenna is shown in figure 1. Over the past few years EH antenna has been built and put into service for MW broadcasts by the Egyptian Radio and Television Union [3]. Recently, flat EH antenna designs appeared in ham's web pages. They used flat plates instead of cylinders in their designs [4]. In this paper new shape of EH antenna is proposed. Shape of antenna is utilized from fractal geometry. EH antenna with fractal shape exhibit new features not find in previous designs. II. LITERATURE SURVEYAntenna researches has great amount of attention in electromagnetism field. Many designs of wire and microstrip antennas have published in the past years [5,6]. Antennas with fractal shapes have been very useful tools to solve two of the limitations of classical antennas, the single band performance and the dependence of antenna's size on the operating frequency. The first one who worked in this field was Dr.Nathan Cohen, professor at the Applied Science and Telecommunication department at Boston University. He published his first article "Fractal Antennas" in 1995, describing fractal antennas and their properties [7]. Few months later, Dr.Carles Puente at University of Catalonia, Barcelona in Spain published papers about fractal antennas [8]. His work focused on multiband behavior ...