Modified Rectangular Dielectric Resonator Antenna for Circular Polarization S. A. Malekabadi 1,* , M. H. Neshati 2 , J. Rashed-Mohassel 3 1 Electrical Engineering Dept., Ferdowsi University of Mashhad, Mashhad, Iran. * a.malekabadi@gmail.com 2 Electrical Engineering Dept., Sistan & Baluchistan University, Zahedan, Iran. 3 Center of Excellence on Applied Electromagnetic System, University of Tehran, Tehran, Iran. 1. Introduction DRs are widely used in microwave circuits including oscillators, filters and cavity resonators. In recent years, application of these components as a radiator at microwave and millimetre band has been extensively studied [1-7]. These types of antennas provide efficient radiation due to low loss in dielectric materials. DRAs provide different modes of operation leading to different radiation patterns. Moreover, they are small in size, low cost and simple coupling structures such as feed probe, microstrip and microstrip–slot methods could be used in antenna structure. DR Antennas in cylindrical [1], hemispherical, rectangular [6] and other geometries located on top of a ground plane could operate as antennas by proper excitation of the resonator. Rectangular resonators are more suitable compared with other geometries, for their ease of fabrication, and the existence of two independent aspect ratios which lead to a better design flexibility to meet impedance and radiation requirements. Early development of mobile and wireless communication systems such as Bluetooth and Wireless Local Area Network (WLAN) working at 2.4 GHz needs a broadband antenna. Moreover better connectivity could be obtained using circular polarization (CP) especially for indoor communication systems. However, DR antennas suffer from some disadvantages including narrow bandwidth and based on their exciting method they normally radiate linear polarized waves. For CP mode of operation especial techniques have to be used. The method of corner chopped and diagonal rectangular microstrip antenna is reported by Gupta in [8]. In this paper two new and simple, one point feed structure of probe-fed RDRAs including corner chopped RDRA and diagonal fed RDRA are presented to provide CP waves at 2.4 GHz. Antennas are simulated using High Frequency Structure Simulator (HFSS). The results show that AR of nearly 0 dB and impedance bandwidth of 5.6% for VSWR<2 are obtained which could be useful in broadband communication systems application. 2. Antenna Structures Figure 1a shows a top view of the antenna under investigation. The resonator has a relative dielectric constant of ε r and its dimensions are a, b and h along x-, y- and z-direction respectively. The DR is placed on the top of a circular ground plane with a diameter d and feed by a single probe. Two structures are investigated in this paper. The top view of the first structure is shown in Fig. 1a in which the resonator is corner chopped and is excited by a vertically oriented coaxial probe of height h located at x=a/2 and ϕ=0°. In Fig. 1b the top view of the second structure, called diagonal probe-fed RDRA, is shown while the feeding probe is placed at the corner of the resonator in which the resonator width, b , is larger than its length a. Tables 1 and 2 summarize the detailed dimensions of the antenna structures. Proceedings of iWAT2008, Chiba, Japan 978-1-4244-1523-3/08/$25.00 © 2008 IEEE 538 P331