DUAL-POLARIZED DIELECTRIC RESONATOR ANTENNAS Chih-Yu Huang, 1 Tzung-Wern Chiou, 2 and Kin-Lu Wong 2 1 Department of Electronic Engineering Yung Ta Institute of Technology and Commerce Pingtung, Taiwan 909, R.O.C. 2 Department of Electrical Engineering National Sun Yat-Sen University Kaohsiung, Taiwan 804, R.O.C. Recei ed 22 May 2001 ABSTRACT: Two feeding designs for achie ing dual orthogonal linear ( ) polarization operations of dielectric resonator DR antennas fed by microstrip lines are demonstrated. The microstrip feedlines can be placed directly under the DR or conformal to the surface of the DR. Good dual-polarization excitation can be obtained for the two feeding designs. Experimental results for the return loss, isolation between two feeding ports, and radiation patterns are presented and discussed.  2001 John Wiley & Sons, Inc. Microwave Opt Technol Lett 31: 222223, 2001. Key words: dielectric resonator antenna; dual polarization; polarization di ersity 1. INTRODUCTION  Studies of DR antennas 1 have been increasing in the last decade for their inherent merits of small size, low cost, and no conductor loss as an efficient radiator. There have been significant efforts in recent years toward various designs of DR antennas. Much of the research to date has been on the feeding methods, different shapes of DR elements, and lin- early polarized or circularly polarized radiation. The designs of dual-polarized DR antennas, however, are not available or are scant in the open literature. Dual-polarized radiation is an important subject for practical applications in wireless communications systems. With the capability of dual-polarized radiation, the antenna can combat the multipath effects of wireless communications and optimize system performances  2 . In this paper, we demonstrate an experimental study of two possible designs of dual-polarized microstrip-line-fed DR antennas. The DR element studied had a low-profile square- disk configuration, and a very high relative permittivity of 79   3, 4 ; two microstrip feedlines for the two feeding ports are  placed directly under the DR 4 or conformal to the surface  of the DR 5 to achieve dual-polarized radiation. For both feeding designs, measured results of dual-polarized perfor- mances are presented and discussed. 2. ANTENNA CONFIGURATIONS The proposed dual-polarized DR antennas are shown in Ž. Ž. Figure 1 a and b , and are denoted as designs A and B, respectively. In design A, the DR element is placed directly on two 50  microstrip feedlines, which are arranged in orthogonal directions for the excitation of two orthogonal linearly polarized waves. The microstrip lines are printed on a microwave substrate of thickness h and relative permittivity 1  . The DR element has a height of h and a square cross r 1 2 section of dimensions L  L, and was constructed from Ž ceramic material of relative permittivity  in this study, r 2 .   79 . The portion of the microstrip lines under the DR r 2 has a length of d . Simply by selecting a proper value of d , 1 1 good impedance matching of the dual-polarization excitation can be obtained. For design B, the two microstrip lines are placed conformal to the surface of the DR, and the length of Figure 1 Geometries of the proposed dual-polarized dielectric res- Ž. Ž. onator antennas. a Design A. b Design B the conformal microstrip-line section is denoted as d in this 2 study. 3. EXPERIMENTAL RESULTS AND CONCLUSIONS Prototypes of designs A and B were constructed and studied. Ž . Ž . The measured return loss S and isolation S for designs 11 21 A and B are shown in Figures 2 and 3, respectively. The dimensions of the DR element studied were 4.9  28.2  28.2 Ž . Ž mm h  L  L , and FR4 microwave substrates h  1.6 2 1 . mm,   4.4 were used. The optimal d and d for designs r 1 1 2 A and B with good impedance matching were found to be 6.5 and 3 mm, respectively. First, note that for design A, the obtained impedance bandwidth is 58 MHz or about 2.6% referenced to the resonant frequency at 2230 MHz. As for the isolation between the two feeding ports, the measured isolation across the entire impedance bandwidth is less than 17.7 dB. For design B, the obtained impedance bandwidth is also 58 MHz or about 2.6% referenced to the resonant frequency at 2220 MHz. The measured isolation between the two feeding ports is less than 21 dB within the impedance bandwidth, which is better than design A. This behavior is probably because the separation between the two feeding ports is larger for design B, which helps improve the port Figure 2 Measured return loss and isolation against frequency for design A; L  28.2 mm, d  6.5 mm,   4.4,   79, h  1 r 1 r 2 1 1.6 mm, h  4.9 mm, ground-plane size  100  100 mm 2 2 MICROWAVE AND OPTICAL TECHNOLOGY LETTERS / Vol. 31, No. 3, November 5 2001 222