A low-profile planar monopole antenna is proposed to operate within WLAN and WiMax frequency bands. The antenna is composed three radiating elements together with an additional strip to control the antenna performance. An electromagnetic (EM) model of the proposed antenna is developed in CST Microwave Studio for numerical analysis and optimization. The principle of operation and parametric study on the antenna performance are provided. Two dual-band and triple-band antennas are fabricated and experimental results are presented. Index Terms-Compact antenna, multiband antennas, wireless local area network (WLAN), worldwide interoperability for Microwave Access (WiMAX).

Abstract-Besides the return loss and radiation pattern, dispersion characteristic of the antenna is one of the most important factors which should be considered in ultra wideband applications. In this paper, dispersion behavior of two specific Vivaldi antennas has been fully investigated in both frequency and time domains. All simulations are carried out by CST MS software. Moreover, by fabricating the antennas, the simulation results are verified by experimental data.

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