Frequency‐reconfigurable dual‐band monopole antenna for WiMAX wireless devices

This article proposes a planar monopole antenna with two frequency-tunable bands for wireless devices used in the WiMAX system. The antenna has two radiating branches acting as monopoles and resonating at around 2.4 GHz (lower band) and 3.4 GHz (higher band). By using two varactors on the radiating branches with novel designs of DC-biasing circuits, the two operating bands can be continuously tuned using the corresponding DC-bias voltages. The lower band can be tuned to cover the frequency bands of 2.3-2.4 GHz and 2.5-2.69 GHz, and the higher band can cover the frequency bands of 3.3-3.4 GHz, 3.4-3.6 GHz, and 3.6-3.8 GHz for the WiMAX system. The antenna has a small overall size of 40 x 35 x 0.8 mm(3) with a compact radiator of only 14.5 x 8.2 mm(2). The antenna performance in terms of tuning, reflection coefficient, radiation pattern, efficiency, and peak gain are studied using computer simulation. For verification of simulation results, the antenna is fabricated and measured. The feeding cable used in measurement causes substantial discrepancies between the simulated and measured results. To study the cable effects, a computer model for the cable is included for simulation studies. With the cable model, the simulated and measured results agree very well. Although the WiMAX system is used in our design, the proposed tuning technique may well be used for tuning other frequency bands in different standards. (c) 2014 Wiley Periodicals, Inc. Microwave Opt Technol Lett 56:49-55, 2014