I. Introduction
With the rapid proliferation of various wireless communication standards, the demand for a single wireless platform with multi-band applications is increasing. The monopole antennas have enjoyed proliferated use in many multi-band applications due to their compact size, easy integration and low cost. Consequently, various multi-band monopole antennas receive increasing interest from both industries and academia. For example, a planar dual-band monopole antenna for WiMAX applications is presented in [1]. A compact tri-band antenna with rectangular ring is proposed in [2], which covers the frequency bands 2.34-2.74GHz, 3.04-3.82 GHz, and 5.03-6.05 GHz. A tri-band microstrip-fed slot antenna for WLAN/WiMAX applications is proposed in [3]. A compact coplanar waveguide (CPW) fed ultra-wideband (UWB) printed monopole antenna (PMA) with triple band-notched characteristics is presented in [4]. However, some of them only have dual-band characteristics, and some cannot operate at GPS and LTE/WLAN/WiMAX bands at same time or their big sizes are not suitable for some certain applications.