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A printed microstrip-line-fed slot antenna with a pair of parasitic patches for bandwidth enhancement is proposed in this paper. By using the parasitic patches along the microstrip feed line, an additional resonance is excited and a good performance of bandwidth enhancement can be obtained. The proposed antenna is designed and manufactured successfully. The measurement shows a good agreement with the simulation. From the measured results, the enhanced impedance bandwidth, defined by voltage standing wave ratio (VSWR) less than 2, is about 136% ranging from 2.1 to 11.1 GHz. In addition, stable and nearly omnidirectional far-field radiation patterns are observed over the entire operating band.Index Terms-Bandwidth enhancement, microstrip-line-fed antenna, printed slot antenna, parasitic patch.

A wideband dual-polarised patch antenna with high isolation and a low cross-polarisation level is presented. Two orthogonal linearly-polarised modes are excited by the electromagnetic-fed structure. One of the two modes is excited by a pair of hook-shaped probes with a 180 o phase difference; while the other is excited by a magnetic-coupled loop, which is comprised of a metal loop and an open-ended transmission line. By introducing two shorting pins, the isolation between two feeding ports can be enhanced to more than 40 dB. Moreover, the radiation patterns in the ± 45°planes have a cross-polarisation level of less than − 30 dB within the 3 dB beam widths. The measured − 10 dB reflection coefficients bandwidth of the two modes are 40.7% (2.45-3.7 GHz) and 38.7% (2.6-3.85 GHz). The gains of the proposed antenna are about 8.7 and 9.1 dBi over the operating band. Thus, this antenna is highly suitable for the base station antenna that is required to cover the operating bandwidth of 3.5 GHz WiMAX systems.

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A novel coplanar waveguide-fed tri-band monopole antenna with a compact radiator (10 × 23 mm 2 ) for WLAN/WiMAX applications is presented. By etching properly an inverted-L slot on the straight strip loaded with a rectangular tuning patch and further adjusting the dimensions and positions of these structures, three distinct wide bands can be achieved. The measured and simulated results show that the proposed antenna has 10 dB impedance bandwidth of 470 MHz (2.38-2.85 GHz), 360 MHz (3.36-3.72 GHz) and 890 MHz (4.98-5.87 GHz) to cover all the 2.4/5.2/5.8 GHz WLAN bands and 2.5/3.5/5.5 GHz WiMAX bands. Also, the proposed antenna produces good dipole-like radiation pattern over the covering bands.Introduction: Currently, the wireless local area network (WLAN) and the worldwide interoperability for microwave access (WiMAX) have been widely used in mobile devices. To support the WLAN and WiMAX applications in the 2.4 (2.4-2.484 GHz)/5.2 (5.15-5.35 GHz)/5.8 (5.725-5.825 GHz) and 2.5 (2.5-2.69 GHz)/3.5 (3.4-3.69 GHz)/5.5 (5.25-5.85 GHz) bands, respectively, many multiband antennas have been reported. In [1], the antenna with a dual-layer metallic structure is presented for WLAN/WiMAX applications. In [2], three types of structures are used to achieve triple band to cover the WLAN/WiMAX bands. However, these proposed antennas are complicated in structure and the resulting bandwidth is not sufficient to cover the 2.5 GHz WiMAX band. To achieve sufficiently large bandwidth to cover all the 2.4/5.2/5.8 GHz WLAN and 2.5/3.5/5.5 GHz WiMAX bands, several antennas are proposed, including a microstrip-fed rectangular monopole antenna with a large parasitic patch on the back of the substrate [3], a coplanar waveguide (CPW)-fed antenna formed by a triangular monopole and a U-shaped monopole [4], and a CPW-fed monopole antenna with two bent slots [5]. Although the antennas in [3,4] can generate two wide bands to meet the whole WLAN/ WiMAX applications, the dual wideband might cause interference with other communication systems. Moreover, the oversize of the antenna [5] is somewhat large (40 × 40 mm 2 ).In this Letter, the mode method [6] is introduced to design a novel tri-band monopole antenna covering all the 2.4/5.2/5.8 GHz WLAN and 2.5/3.5/5.5 GHz WiMAX bands. The proposed antenna has a small size of 25 × 36 mm 2 , which is smaller than the antenna proposed in [5]. Meanwhile, compared with the antennas presented in [1,2], the proposed antenna is much simpler in structure. The antenna is designed and optimised by using the electromagnetic simulation tool ANSYS HFSS 13. Details of the antenna design and the simulated and measured results are presented and discussed.

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