Frequency-tunable Antenna for Dual-band WLAN Applications

In this paper, a frequency-tunable dual-band antenna for WLAN applications is proposed. The antenna consists of two microstrip branches serving as radiating elements for two frequency bands at 2.4 and 3.5GHz and two variable capacitors on the radiating elements for individually tuning the frequency bands. The antenna is designed on a 40mm £ 40mm substrate with a thickness of 0.8mm, relative permittivity of 3.5 and loss tangent of 0.02. The re∞ection coe-cient S11 of the antenna with difierent capacitance values is studied. Simulation results suggest that the two frequency bands have a tuning range of 2.4{3.5GHz and 3.5{5.9GHz separately. Moreover, simulated radiation patterns, e-ciencies and gains of the proposed antenna are also presented. The rapid development in personal and computer communications technologies demands integration of more than one communication system into a single compact module. This trend leads to the increasing requirement of using a single antenna to cover multiple frequency bands for difierent wireless standards. In literature, many techniques have been proposed for multiband antenna designs. Among these designs, planar monopoles are most often used (1{5), where multiple-mode operations are obtained by modifying the radiators so that multiple current paths are formed. This requires large antenna sizes. Designing a small antenna to operate in several frequency bands is formidably challenging because of the di-culties in impedance matching and volume reduction. Tunable antenna is one of the ways to overcome such problems. Recently tunable antennas have been studied on difierent types of antenna such as patch antennas (6), loop antennas (7,8) and Planar-Inverted-F antennas (PIFA) (9,10). In this paper, a frequency-tunable dual-band antenna is proposed. Two microstrip lines are used as the radiating elements of the antenna to create resonances in two difierent bands, 2.4 and 3.5GHz. Two variable capacitors, each being placed in the proper locations of two radiating elements, are used to achieve the frequency-tunable feature. The performance of the antenna is evaluated using the commercial EM simulation tool CST. Simulation results on the re∞ection coe-cient S11 with difierent capacitance values suggest that the two resonant frequencies can be tuned independently with the tuning ranges of 2.4{3.5GHz and 3.5{5.9GHz.