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ireless local area network (WLAN) technology is a rapidly expanding area in modern wireless communications. The trend of integrating a WLAN communication system into mobile electronic products |
requires developing dual-band or multi-band antennas with compact size. The planar coplanar waveguide (CPW)fed monopole antenna is a good candidate because of its simple structure, omni-directional radiation pattern, low cost and ease of integration with active circuits. Many CPW-fed monopole designs, which can fully cover the IEEE 802.11 WLAN bands in both the 2.4 GHz (2400-2484 MHz) and 5.2/5.8 GHz (5150-5350 MHz/5725-5875 MHz) range have been reported. These include the rectangular notched monopole, meandered monopole and modified PIFA structure. In general, these designs either require large antenna size or increase the complexity of the antenna structure.
In this work, a novel dual-band hybrid antenna consisting of a CPW-fed inverted-L monopole and a high permittivity rectangular dielectric resonator (DR) is presented. The inverted-L monopole simultaneously acts as an effective radiator and as a feeding structure of the DR. The high permittivity rectangular DR can be efficiently excited if its dimensions and the relative position on the monopole are properly determined. By connecting the monopole and the DR in parallel, a dualband hybrid antenna with compact size is achieved. A prototype antenna has been designed to satisfy the IEEE 802.11 WLAN standards.
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Contact person
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Assoc Prof BL Ooi
Tel: 6516 7942,
Fax: 6779 1103
E-mail: eleooibl@nus.edu.sg
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The proposed hybrid antenna structure is shown in Figure 1. An inverted-L monopole and the 50-Ω CPW feed line are printed on the same side of the Roger Corporation (RT)/Duroid substrate. The width of the 50Ω CPW center line metal strip is fixed at 3.0 mm, whereas the gap between the strip and the ground plane is 0.5 mm. In this study, a dielectric substrate with thickness of 1.25 mm and relative dielectric constant of 6.1 is chosen. Two ground planes of the same size (15.5 mm × 13 mm) are placed symmetrically on each side of the CPW line. The horizontal length and vertical height of the inverted-L monopole are 8.0 mm and 12.0 mm, respectively. The resonance mode at 2.4 GHz is due to the CPW-fed monopole whose total length is 20mm, approximately λ/4 at 2.4 GHz. The resonance mode at 5 GHz is due to the dielectric resonator which has a higher permittivity of εr=100. In order to improve DRA's bandwidth, the thickness of the DR is minimized to achieve large width/height aspect ratio. With no ground plane underneath the resonator, DR can be efficiently excited by the monopole by adjusting the relative position of the DR. The optimized dimensions of the DR are 7 mm × 6 mm × 1 mm, whereas the optimal distance between the resonator and the feed point is 3.0 mm.
Figure 2 shows the comparison of the simulated and measured input return losses of the proposed antenna whereas Figure 3 shows a photograph of the prototype. The S-parameter measurement was performed using an Agilent 8510C network analyzer and the simulation result was obtained from an inhouse developed finite difference time domain (FDTD) code. In the 2.4 GHz band, the measured 10-dB return loss bandwidth is about 400 MHz (2.30 – 2.70 GHz) or corresponds to a relative bandwidth of 16%. In the 5 GHz band, the 10-dB return loss bandwidth is about 930 MHz (5.12 – 6.05 GHz) or about 16.6% for the center frequency of 5.60 GHz.
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