IEEE ANTENNAS AND WIRELESS PROPAGATION LETTERS, VOL. 7, 2008 341 Broadband Microstrip-Fed Dielectric Resonator Antenna for X-Band Applications Yacouba Coulibaly, Tayeb A. Denidni, Senior Member, IEEE, and Halim Boutayeb, Member, IEEE Abstract—A new microstrip fed low profile broadband dielec- tric resonator antenna is proposed. The antenna is composed of a dielectric resonator, a microstrip fed stepped patch and an inter- mediate substrate. The stepped patch and the intermediate sub- strate allow to widen the matching bandwidth. Using a finite inte- gration method (CST Microwave), a parametric investigation was performed for the optimization. To validate the proposed design, a prototype of the optimized antenna was fabricated and measured. The predicted results are compared with the measured data, and a good agreement is achieved. The proposed antenna offers a frac- tional bandwidth of 50% around the center frequency 10.16 GHz, and relatively stable radiation patterns in the matching band. Index Terms—Broadband operation, dielectric resonators (DRs), hybrid structures, patch antennas. I. INTRODUCTION D IELECTRIC RESONATORs (DRs) are important com- ponents for several communication systems operating at microwave- and millimeter-wave bands [1]. These applications include filters, shielded oscillators and antennas. The first di- electric resonator antenna (DRA) was proposed in 1983 [2]. Over the last decade, increasing attention has been paid to the investigation of DRAs due to their attractive features. DRAs have several advantages, such as low losses, high radiation effi- ciency, high integration, reduced size, low cost, and low weight. They also allow to obtain different radiation characteristics by exciting different radiation modes. For a single-mode excitation, the bandwidth of a DRA is often below 10%, which is not enough for ultrawideband appli- cations and spread spectrum systems. Recently, different tech- niques have been proposed to enhance the bandwidth [3]–[10]. In respect to this issue, DRAs with different shapes, such as conical [3], tetrahedron, and triangular [4] shapes have been suggested. Another method for widening the bandwidth con- sists of stacking two or more elements of different sizes with different dielectric constants to improve the coupling between the feed line and the antenna [5]. In addition, coplanar parasitic DRAs can also be used to increase the bandwidth [6]. However, these different techniques are generally difficult to fabricate and the parasitic DRAs can increase the antenna size. An approach Manuscript received November 16, 2007; revised December 19, 2007. This work was supported in part by the National Science Engineering Research Council of Canada (NSERC). The authors are with the Institut National de Recherche Scientifique (INRS)- EMT, Montréal, QC Canada (e-mail: couli@emt.inrs.ca; denidni@emt.inrs.ca; boutayeb@emt.inrs.ca). 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.2008.921326 based on the use of multiple resonances have been also pro- posed [7]–[9]. This method consists of using different radiating structures with different resonant modes and combining them in order to obtain a wideband hybrid structure. For example, a combination of a DRA and slot has been proposed in [7], whereas a combination of a patch antenna and DRA has been proposed in [8]. In [10], a low-profile DRA fed by a stepped microstrip line has been designed, where a bandwidth of 17% has been achieved. In [11], an ultrawideband antenna fed by a coaxial probe has been designed by inserting a dielectric seg- ment between the ground plane and a radiating dielectric res- onator. In this letter, a new broadband dielectric resonator antenna with a fractional bandwidth of 50% is proposed. It is composed of three parts: a DR, an intermediate substrate and a microstrip fed stepped patch. The stepped patch and the intermediate sub- strate allow to increase the matching bandwidth. To optimized the proposed design, a parametric analysis was carried out by using a finite integration method (CST Microwave). Numerical results for the near-field inside the antenna and the return loss are also presented in Section II. To validate our analysis, a proto- type of the antenna was fabricated and measured, and the exper- imental results are presented in Section III. Finally, concluding remarks are given in Section IV. II. ANTENNA DESIGN Fig. 1 shows the topology of the proposed hybrid antenna. It consists of a dielectric resonator, an intermediate substrate and a microstrip fed patch. The parameters of the DR are the height , the width , the length , and the relative permittivity . The intermediate substrate has a thickness , a permittivity , and a width . The feeding circuit is composed of a microstrip line of width connected to a stepped patch constituted of three strips, as illustrated in Fig. 1(b). The width and length of the patch strips are and for the first strip, and for the second, and and for the last one. The distance from the edge of the DRA to the edge of the patch is . A parametric analysis of the proposed hybrid antenna was carried out by using the commercial software CST Microwave [12], which is based on the finite integration method. The initial dimensions of the DRA, which fix the excited mode, can be found by using the modified waveguide model [13]. Using this model, the frequency of the fundamental mode of the DRA , which is a hybrid mode, is around 11 GHz. For the DRA, the following parameters are considered: mm, and mm. The values of the other parameters of the antenna are mm, mm, mm, mm, mm, mm, 1536-1225/$25.00 © 2008 IEEE