Compact wideband dielectric-resonator- on-patch antenna J. Janapsatya, K.P. Esselle and T.S. Bird A method to reduce the size of the dielectric-resonator-on-patch (DRoP) antenna, using a shorting metal wall, is presented. An experimental antenna demonstrates several advantages including better bandwidth, less weight, less volume and a lower profile when compared to the original DRoP antenna without shorting walls. The predicted return loss and radiation patterns of the antenna are compared with measured data. Introduction: The dielectric resonator (DR) antenna is very popular and research is being conducted on broadening its bandwidth using methods such as lateral parasitic DR [1] and shaped DR [2]. However, these methods increase the volume of the DR antenna considerably. Another method of increasing the bandwidth of DR antennas, the concept of a hybrid structure, consisting of a dielectric resonator and a patch resonator has been proposed previously [3, 4]. This so-called dielectric resonator on patch (DRoP) antenna consists of a microstrip patch resonator coupled to a stacked dielectric resonator using a slot (slot 1) in the microstrip patch, as shown in Fig. 1. The patch resonator helps to achieve a wider bandwidth, without contributing significantly to the volume or area of the antenna. slot 1 patch substrate microstrip feed slot 2 stub substrate ground DR patch Fig. 1 Original dielectric-resonator-on-patch antenna In this Letter, we present a method to design a compact DRoP antenna with even smaller volume without compromising the excellent bandwidth of the original DRoP antenna. For this purpose, the full size (half-wavelength) DRoP antenna shown in Fig. 1 is cut in half and a shorting plate is introduced at the plane of the cut. This metal short is a crude approximation to a perfect electric wall and it creates a vertical electrical field null in the microstrip patch and the dielectric resonator. The shorted patch and its image (made by the approximate electric wall) are expected to behave as a full size microstrip DRoP antenna. dielectric resonator patch ground plane SMA connector shorting metal wall slot in middle of patch Fig. 2 Compact DRoP antenna with shorting walls Antenna configuration: For technical demonstration of the proposed concept, we chose an air-filled patch resonator because it can be made easily by simply bending a single piece of metal sheet to form all parts of the patch resonator, namely the ground plane, shorting metal wall for the patch and the patch itself. A probe feed was chosen instead of a microstrip feed to further simplify prototyping. The resulting DRoP antenna with shorting walls is shown in Fig. 2. The substrate used for the DR (TMM) has a copper film on one side. It formed the shorting metal wall for the DR. In our prototype, the DR was glued to the patch by soldering the DR and patch metal walls together. Note that the DR is still coupled to the patch resonator through a slot in the patch that is adjacent to the shorting walls. The inner conductor of the coaxial feedline is attached to the patch, whereas the outer conductor is connected to the ground plane. Results: The dimensions and other parameters of three low-profile DRoP antenna designs with shorting walls are given below. These designs have been achieved with the help of Ansoft HFSS commercial software. Only the DR length is different in the three designs. They are 11, 17, 22 mm, respectively. The other parameters are: DR width ¼ 11 mm, DR height ¼ 6 mm, patch length ¼ 24 mm, patch width ¼ 12 mm, patch height ¼ 2.5 mm, DR dielectric constant ¼ 9.2 (TMM), slot width ¼ 2 mm, slot length ¼ 7 mm, ground plane length ¼ 50 mm, ground plane width ¼ 25 mm. The theoretical return loss of these three antenna designs are shown in Fig. 3. The longer (22 mm) DR is matched at frequencies as low as 4.6 GHz and the shorter DRs are more suitable when matching at higher frequencies is required. The 10 dB RL bandwidths are 5.0–6.9, 4.7–>7 and 4.6–6.7 GHz for the 11, 17 and 22 mm antennas, respectively. |S 11 |, dB 0 –5 –10 –15 –20 –25 –30 –35 theoretical 11 mm 11 mm 17 mm 22 mm theoretical 17 mm theoretical 22 mm measured 11 mm frequency, GHz 4.5 4.7 4.9 5.1 5.3 5.5 5.7 5.9 6.1 6.3 6.5 6.7 6.9 7.1 7.3 7.5 Fig. 3 jS 11 j of DRoP antenna for three DR lengths –10 –10 –20 –20 –30 –30 a b –40 –40 –10 –10 –20 theoretical measured –20 –30 –30 –40 –40 Fig. 4 Radiation patterns of DRoP antenna in H-plane aE y bE j To verify the theoretical results obtained from HFSS, we fabricated a DRoP antenna with a shorting wall. Due to availability of a resonator with required size, we chose the 11 mm design. The experimental return loss of this antenna is compared with the theoretical return loss in Fig. 3 and good agreement can be seen. The theoretical and measured radiation patterns of the reduced-size DRoP antenna with 11 mm dielectric resonator, at the frequency of 5.25 GHz, are shown in Figs. 4 and 5. The radiation patterns are shown at the H-plane (Fig. 4), which is the plane where the shorting metal walls are, and the E-plane (Fig. 5), which is the plane orthogonal to the shorting walls. The normalised radiation patterns in Fig. 4 show how the measured and theoretical results closely match each other. Note that the maximum values of E j and E y are comparable in the H-plane, indicating that this antenna has high cross-polarisation levels in this plane. Fig. 5 shows the measured gain of the DRoP antenna in the E-plane for both E j and E y polarisations. Radiation patterns at this plane have also been checked and found to match the theoretical values closely. The theoretical patterns have not been included in this Figure so as to maintain the clarity of the graph. Unlike in the H-plane, the level of E j polarisation is much smaller compared to the E y polarisation at this plane. Radiation patterns have also been measured at 6.25 and 7.25 GHz but the results are not shown owing to space. Good agreements between the theoretical and measured results were noted for these frequencies also. ELECTRONICS LETTERS 14th September 2006 Vol. 42 No. 19