A multiband monopole antenna with modified fractal loop parasitic is presented. Especially, bow-tie stubs and a modified fractal loop are attached to the sides and bottom of a strip line monopole antenna, respectively, in order to generate the multi-resonant frequencies for the applications of wireless communication systems. The characteristics of the presented antenna have been examined by using the simulation software. The comparison between the simulated and measured results confirms the good agreement. The results show good multiband operation with 10 dB impedance bandwidths of 15.55%, 8.75%, and 31.94% at the resonant frequencies of 1.8 GHz, 2.4 GHz, and 3.6 GHz, respectively, which cover the operating band applications of DCS 1800, WLAN (IEEE802.11 b/g), WiMAX, and IMT advanced system (4G mobile communication system).

A double square loop antenna with fractal geometry that supports for multiband operation is proposed. The antenna has multiband operation in that the generator model, which is an initial model to create a fractal loop antenna to operate at the first and second resonant frequencies, is inserted at each center side of a big square loop antenna. It also has a small square loop to operate at the third resonant frequency. The proposed antenna is implemented and shown to effectively support the global system for mobile communication (880-960 MHz), digital communication system (1710-1880 MHz), personal communication system (1850-1990 MHz), universal mobile telecommunication system (1920-2170 MHz), and wireless local area network (2400-2483 MHz) bands. The radiation patterns of the proposed antenna are still similar to a bidirectional radiation pattern. The properties of the antenna such as return losses, radiation patterns and gain are determined via numerical simulation and measurement.