A dual-band folded shorted patch antenna

Abstract

IntroductionAs is well known, a dual-band antenna is better than a wideband antenna if both of them are required to cover two frequency bands that are far away from each other. Consequently, the researches on dual-band shorted patch antennas are increasing dramatically. In the literature, several methods have been reported to develop this type of antenna. They involved cutting a special slot [1] and using a stacked structure [2] on the traditional quarter-wave shorted patch antenna. Although the new antenna has dual-band characteristic, its impedance bandwidth of each frequency band is narrow (2-10%). In order to tackle this problem, a bandwidth widening technique is utilized. By using proximity-coupled feeds to excite two quarter-wave shorted patches that are in stacked configuration, wide impedance bandwidths of 47-54% are obtained in two frequency bands [3][4]. Nevertheless, they will be reduced to around 10% if the height of the antenna is low (<0.05λ L ). Actually, most of the wideband techniques in the literature are not effective for the low profile antennas. In the last year, a wideband low-profile antenna is proposed. By folding the open (or radiating) edge of a quarter-wave shorted patch antenna backwards, wide impedance bandwidth of 29.4% is acquired at a low profile of 0.046λ C [5].In this paper, a dual-band folded shorted patch antenna with a low profile of 0.05λ L and a small size of 0.25λ L x 0.36λ L is presented. It is operated at both TM 10 mode and TM 30 mode, which is developed by introducing two slots to the patch of our previously proffered folded shorted patch antenna [5]. With the proper choose of the sizes and the positions of these slots, wide impedance bandwidths of 20.4% and 32.2% are measured at the lower and the upper bands, respectively. Antenna performance procured by the measurement is also compared with the simulation and good agreement is observed. Moreover, details of the antenna design are given. Antenna StructureThe geometry of the proposed antenna is shown in Fig. 1. This antenna is mounted in the middle of a rectangular ground plane. It consists of a rectangular patch that is supported by a foam substrate above the ground plane. Along the xaxis, this patch has one end shorted to the ground and the other end folded backwards. The folded part is supported by another foam substrate over the main part of the patch. Also, two slots with different sizes are etched on different 978-1-4244-2042-1/08/$25.00 ©2008 IEEE positions of the patch. Moreover, a coaxial feeding probe and a shorting post are connected to the main part of the patch. Let λ L be the free space wavelength at 0.883GHz. For this antenna, the size of the ground plane is 280.2mm x 318mm (0.82λ L x 0.94λ L ). The thicknesses of the patch and the ground plane are 0.2mm and 2mm, respectively. Dielectric constant of the foam substrate is 1.1. The other dimensions are listed in Table 1 in details. In fact, the lateral size (or projection area) of this antenna is 36% that of a regular half-wave square patch antenna with the...

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