Frequency-Tunable Monopole Antenna for Wimax Applications

This article presents a planar dual-band monopole antenna with a frequency-tunable band for use in wireless devices of the 2.4 and 3.4 GHz worldwide interoperability for microwave access (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). A varactor is placed on the radiating branch responsible for the lower band. A very simple DC biasing circuit is designed for reverse-biasing the varactor. By varying the DC-bias voltages from 0 to 12 V for the varactor, the lower band of the antenna can be continuously tuned from 2.3 to 2.83 GHz, covering the frequency bands from 2.3 to 2.4 GHz and 2.5 to 2.7 GHz for the WiMAX system. The antenna has a small overall size of 40 x 35 x 0.8 mm3 with a compact radiator of only 14.5 x 8.2 mm2. The antenna performance in terms of reflection coefficient, radiation pattern, peak gain, and efficiency is 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 simulation results. To study the cable effects, a computer simulation model is included for studies. With the cable model, the simulated and measured results agree very well. (c) 2013 Wiley Periodicals, Inc. Microwave Opt Technol Lett 55:1902-1907, 2013