DESIGN OF DUAL DIRECTOR SHORT BACK FIRE ANTENNA FOR UWB APPLICATIOS 1 Anjaneyulu Badugu 1 N.Ananda Rao 2 T.V.Rama Krishna 1 K.Vijaya Vardan 1 K.Satish 1 Assistant Professors, ECE Department, Vignan University, Vadlamudi, Guntur (DT). 2 Professor, ECE Department, Vignan University, Vadlamudi, Guntur (DT). anji.412@gmail.com Abstract: The design proposed in this paper is dedicated to increasing the gain of Short Back Fire Antenna (SBFA) in the 20% bandwidth. A SBFA consists of a round disc of two wavelengths diameter with a quarter wavelength rim. A dipole (or crossed simple) is mounted above the disc with quarter wavelength and a second small disc (disc 1) having half a wavelength diameter is located above the lower disc with a half wavelength. This modified version has a conical reflector with a rim, as well as an additional front disc of more than 15dB and the return loss will be less than -10dB. The designed antenna has a simple and compact construction and high mechanical and electrical characteristic. Hence, it is appropriate for the applications of Ultra Wide Band (UWB) and satellite communications. This proposed antenna presents the input impedance, radiation patterns return loss, VSWR, E-field, H-field current distributions using CST Microwave Studio Software. KEYWORDS: Short Back Fire Antenna (SBFA), Ultra Wide Band (UWB), CST, and VSWR. I. INTRODUCTION Short backfire antenna has gone through a great development since it was conceived by Ehrenspeck in 1960 [1]. It has received much interest for its advantages, such as low cost, compactness, simplicity of construction, and high gain. The conventional SBFA is composed of two parallel reflectors (main and sub reflectors) and a feed, which commonly includes a dipole placed between the reflectors, or an open-ended waveguide [2]. We know that UWB commonly refers to signal or system that either has larger bandwidth or a large absolute bandwidth [3]- [5]. In this paper, a structure scheme is presented to reach the requirement of high gain, appropriate impedance bandwidth and low side-lobe. This improvement is based on some former articles [6]. SBFA combines a microstrip type element with a backfire cavity [7]. Because of its compact construction, good radiation pattern characteristics and high- efficiency, SBFA is widely used in mobile satellite communications, tracking, telemetry, and wireless local-area network systems. Application are as a feed for a reflector or as a single antenna for mobile communications [8]. II. STRUCTURE AND RADIATION OF ANTENNA. The short backfire antenna operates in a resonant mode. It was ascertained from extensive studies of the near field of the SBFA that mechanism of radiation is characterized by multiple reflections of a feed-excited electromagnetic wave between main reflector and sub-reflector. As a result, the power is strengthened and high gain is obtained. A. Structure of Proposed Antenna A short backfire antenna consists of a round disc of two wavelengths diameter with a quarter wavelength rim. A dipole (or crossed dipole) is mounted above the disc with quarter wavelength , and a second small disc (Disc1) having half a wavelength diameter is located above the lower disc with a half wavelength .This modified version has a conical reflector with a rim, as well as an additional front disc (Disc2). The input impedance of the antenna is controlled by the dipole, its location and the dimension of the disc1 and placement of disc2, however, it is advisable to 2014 2nd International Conference on Devices, Circuits and Systems (ICDCS) 1 978-1-4799-1356-5/14/$31.00 ©2014 IEEE