IEEE ANTENNAS AND WIRELESS PROPAGATION LETTERS, VOL. 11, 2012 515 Omnidirectional Cylindrical Dielectric Resonator Antenna With Dual Polarization Longfang Zou, Student Member, IEEE, Derek Abbott, Fellow, IEEE, and Christophe Fumeaux, Senior Member, IEEE Abstract—This letter proposes an annular cylindrical dielectric resonator antenna (DRA) with two-port diversity realizing simul- taneously omnidirectional horizontally and vertically polarized radiation patterns with low cross coupling. The horizontally and vertically polarized radiation patterns are achieved by exciting the orthogonal TE and TM modes in a single cylindrical dielectric resonator (DR). Due to the high -factor of the TE mode, an air gap and multiple feeding lines are introduced to in- crease the impedance bandwidth. The proposed antenna provides an impedance bandwidth of 19.1% in the vertically polarized mode and an overlapping bandwidth of 7.4% in the horizontally polarized mode, with the overlapping band ranging from 3.78 to 4.07 GHz. Antenna diversity and multiple-input–multiple-output (MIMO) performance are examined in terms of envelope correla- tion coefficient and mean effective gain. Index Terms—Dielectric resonator antenna (DRA), multifunc- tion, polarization diversity. I. INTRODUCTION S INCE a dielectric resonator antenna (DRA) was first pro- posed by Long in the 1980s [1], extensive research has been carried out on analyzing DRA shapes, resonant modes, radiation characteristics, and excitation schemes. The results of these investigations have highlighted attractive features of DRAs such as compact size, high radiation efficiency, and ver- satility in shape and feeding mechanism [2], [3]. In particular, the 3-D structure of the DRA offers an additional freedom in ex- citing various modes in one antenna volume. Each mode can be employed for a different application, which makes the DRA a candidate for multifunction, diversity, and multiple-input–mul- tiple-output (MIMO) communication systems. Several multimode usages of a single dielectric res- onator (DR) have been demonstrated recently. Jazi and Denidni proposed an ultrawideband DRA by exciting the fundamental and higher-order modes [4]. Radiator and filter functions were demonstrated in a cylindrical DR by using the HEM and TE modes [5], respectively. A dual-band antenna with two different radiation characteristics in two separate bands was achieved by exciting the HEM and TM modes in a cylindrical DR in [6]. A filter function, operating in the TE mode, was added to the previous design to achieve a dual-band Manuscript received April 18, 2012; accepted May 05, 2012. Date of pub- lication May 14, 2012; date of current version May 22, 2012. The work of C. Fumeaux was supported by the Australian Research Council (ARC) Future Fellowship funding scheme under Project no. FT100100585. The authors are with the School of Electrical and Electronic En- gineering, The University of Adelaide, Adelaide, SA 5005, Australia (e-mail: lfzou@eleceng.adelaide.edu.au; dabbott@eleceng.adelaide.edu.au; cfumeaux@eleceng.adelaide.edu.au). 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.2012.2199277 Fig. 1. Prototype of the proposed dual polarized omnidirectional DRA with schematic field distributions for the two orthogonal modes excited. radiator and filter applications in a DR [7]. A cross-shaped DRA was designed for both multifunction and diversity applications by employing the quasi-TM and TE mode operating in an overlapping frequency band in [8]. A MIMO DRA was illustrated in a split-cylindrical DR by exciting the TE and HE modes in [9]. Due to the high quality ( ) factor of the TE mode in a cylindrical DR, it is traditionally used in filter design [5], [7]. An attempt to obtain a horizontally polarized pattern by ex- citing this TE mode is found in [10]. However, only a 2% impedance bandwidth is achieved in simulation, and the impedance is mismatched in the prototype. By optimizing the feeding network and an air gap between the resonator and the substrate, an impedance bandwidth of 5.6% was demonstrated in both simulation and measurement in [11]. To extend this concept, we propose a dual-mode DRA with a magnetic-monopole-like and electric-monopole-like radiation patterns obtained simultaneously by exciting the TE and TM modes in a single annular cylindrical DR. Two groups of four radially arranged microstrip feeding lines with two different lengths are utilized to increase the bandwidth of the TE mode and suppress the influence of higher-order modes. The overlapping operating band for the two functions makes the proposed antenna suitable for being used in diversity or MIMO communication systems when omnidirectional characteristics are required. II. DUAL POLARIZED DRA DESIGN The prototype of the proposed dual-polarized antenna and schematic TE - and TM - mode field distribution are shown in Fig. 1. An annular cylindrical DR is mounted on a Rogers Ul- tralam substrate with thickness of 1.524 mm and relative permit- tivity of 2.5. The two functions of the antennas are fed through two SMA connector ports located on the left and right sides of substrate. The feeding network is located on the backside of the ground plane and shielded in a metallic cavity. A schematic of the proposed dual-polarized antenna is illustrated in Fig. 2, with all dimensions listed in Table I. The design procedure is explained in the following. 1536-1225/$31.00 © 2012 IEEE