A compact tri-band planar monopole antenna suitable for 2.4/5.2/5.8 GHz WLAN and 3.5 GHz WiMAX is presented. The antenna employs a U-shaped parasitic strip and a defect ground-plane structure. By inserting a U-shaped strip as a parasitic strip into a normal monopole which operates at lower band of the WLAN, one more resonance at the higher WLAN band comes out. A defect ground-plane composed of two symmetrical L-shaped slits leads to another resonance operating at WiMAX band. The proposed antenna has a compact size of 22×41×0.8 mm3 and offers good radiation and reflection characteristics in the above frequency bands. The measured VSWR exhibits a good agreement with the simulated one. Detailed design steps, parametric studies and experimental results for the antenna are investigated in this paper.
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