Compact UWB printed monopole loaded with dielectric resonator antenna O.M.H. Ahmed, A.R. Sebak and T.A. Denidni A novel compact ultra-wideband (UWB) printed monopole loaded with a dielectric resonator (DR) antenna is proposed. The antenna con- sists of a microstrip fed monopole printed on a substrate with a trun- cated ground plane loaded with a DR. The bandwidth is enhanced by making an inner groove inside the DR and controlling the slot width of the truncated ground. Introduction: Since the Federal Communications Commission (FCC) announced the use of the ultra-wideband (UWB) range, i.e. 3.1– 10.6 GHz for commercial purposes, both academic and industrial research into UWB technology has dramatically increased. Two impor- tant techniques for antenna engineering design are bandwidth enhance- ment along with antenna miniaturisation. Recently, many researchers have proposed different techniques to design compact size antennas along with wide-bandwidth performance for several applications. The dielectric resonator antenna (DRA) is considered as an efficient solution to achieve both size reduction and bandwidth enhancement. DRAs have shown several unique characteristics rather than conventional metallic antennas such as high radiation efficiency, low dissipation loss, small size, light weight, and low profile [1–4]. In addition, DRAs have more degrees of freedom in terms of design flexibility than the conven- tional antennas, which allows them to become perfect candidates for high-efficiency, wideband and cost-effective wireless applications. In this Letter, a and compact hybrid printed monopole loaded with a DR for UWB applications is proposed. The proposed antenna consists of a microstrip fed monopole printed on RT5880 substrate with a finite truncated ground plane on the upper side of the substrate. The monopole is then loaded with a DR with a quarter elliptical cylinder of Rogers RO3010. Details of the proposed antenna are described and studied in the following Sections. side view GND DRA DRA GND W2 L1 L2 dx LG L Y R X h B H W A top view a b bottom view Fig. 1 Geometry and photograph of proposed UWB antenna Antenna configuration and design: Fig. 1 shows the geometry and dimensions of the proposed antenna, which is a microstrip fed monopole printed on a Rogers RT5880 substrate with size of 13 × 22.5 mm (0.13 l × 0.21 l at f ¼ 3.1 GHz), thickness h ¼ 0.787 mm, relative permittivity 1 r ¼ 2.2 and loss tangent 0.0009. The DR consists of a quarter elliptical cylinder of Rogers RO3010 with relative permittivity 1 r ¼ 10.2, thickness H ¼ 2.54 mm, minor and major radii of A ¼ 12 mm and B ¼ 14 mm, respectively. The feeding structure, which is installed in the lower side of the substrate, consists of a 50 V transformer with width W 1 ¼ 2 mm and length L 1 ¼ 5 mm and a microstrip fed monopole of width W 2 ¼ 1.24 mm and length L 2 ¼ 14.2 mm, which is located at a distance d x ¼ 4.76 mm from the substrate edge. This hybrid combination of a monopole with finite ground plane of length L G ¼ 10 mm and DR is behind achieving the wide bandwidth required for UWB operation. The ground plane and microsrip line together act as a monopole antenna. Furthermore, the antenna bandwidth was increased by loading the monopole antenna with a DR. It has been shown from the full-wave electromagnetic (EM) simulations that the DR has some modes that could be excited by the monopole. In addition, the antenna impedance bandwidth was enhanced by making an inner groove of radius R inside the DR at distance X ¼ 1.5 mm and Y ¼ 3.5 mm from the DR edges. The tuning arm of length L S in the truncated ground plane is used for matching purposes and increasing the antenna impe- dance bandwidth. Compared to the UWB antenna reported in [4], the proposed antenna design provides a size reduction by 62% while achiev- ing a bandwidth increase of 4%. The optimised antenna parameters for achieving a maximum bandwidth are: R ¼ 7 and L S ¼ 12.5 mm. –40 –30 R = 4 mm R = 5 mm R = 6 mm R = 7 mm L S = 4.5 mm L S = 8.5 mm L S = 6.5 mm L S = 10.5 mm L S = 12.5 mm –20 –10 0 return loss, dB 2 –30 –25 –20 –15 –10 –5 0 3 4 5 6 7 8 frequency, GHz b a return loss, dB 9 10 11 12 Fig. 2 Effect of some antenna parameters on bandwidth enhancement a Effect of air groove radius R inside DR b Effect of tuning arm length L S in truncated ground plane 3 2 –40 –35 –30 –25 –20 –15 reflection coefficent, |S 11 | –10 –5 measurement simulation: HFSS simulation: CST 0 4 5 6 7 8 frequency, GHz 9 10 11 12 Fig. 3 Simulated and measured return losses of proposed antenna Results and discussion: The impedance characteristics of the proposed antenna as well as reference antennas are calculated with two different EM software tools, i.e. Ansoft HFSS and CST MWS. The effect of some antenna parameters on the bandwidth enhancement is presented in Fig. 2. When the air groove is used inside the DR, the bandwidth is increased slightly, especially in the upper frequency band as shown in Fig. 2a, but the effect of the tuning arm in the truncated ground plane is more remarkable especially in the low frequency band, as shown in Fig. 2b. Fig. 3 shows the simulated and measured return loss curves against frequency for the proposed antenna. It is seen that the proposed antenna exhibits a wideband performance from 3.6 to 11.2 GHz (simulated) for return loss less than 210 dB, covering almost the entire UWB frequency band. The measured impedance band- width is from 3.9 to 10.6 GHz except in the 4.4–4.8 GHz frequency band because there is a disagreement with the calculated results. This may be due to the fabrication tolerance or misalignment of the DR when it is mounted on the substrate. The radiation characteristics of the antenna were also studied. Figs. 4a and b show the far field radiation patterns of H-plane and E-plane, respectively, at 4, 6, 8 and 10 GHz. The antenna exhibits a nearly omnidirectional radiation pattern in the H-plane and a dipole-like radiation pattern in the E-plane. In addition, the calculated realised gain and measured antenna group delay are shown in Fig. 5. It can be seen that the proposed antenna shows a stable gain across the whole frequency band with maximum group delay of less than 5 ns. ELECTRONICS LETTERS 6th January 2011 Vol. 47 No. 1 Downloaded 15 Mar 2011 to 132.205.50.31. Redistribution subject to IET licence or copyright; see http://ietdl.org/copyright.jsp