In this paper, a planar quad band monopole antenna excited by the microstrip line feed is proposed for L-band, WiMAX and WLAN applications. The proposed antenna is composed of radiating element in the form of L, U and inverted L-shaped strips on the top surface of substrate and defected ground plane on the bottom surface. By adjusting the length of the strips, the resonant frequencies can be reformed individually. The overall dimension of the prototype of the proposed quad band antenna is 50x35x1.6mm³. From the measured results it is found that the proposed antenna has exhibited four distinct operating bands (return loss less than -10dB) of 170MHz (from 1.16 to 1.33GHz), 550MHz (from 1.53 to 2.08GHz), 470MHz (from 2.43 to 2.90GHz) and 3930MHz (from 3.77 to 7.70GHz). First two bands operated in L-band, third band can be used for WiMAX lower band (2.5GHz) and bandwidth of fourth band may be used for WLAN (5.2/5.8 GHz) and WiMAX (5.5GHz) applications. It is also observed that the proposed antenna has good radiation patterns and acceptable gains over the whole operating bands. The design process and parametric analyses are explained with the help of simulation software HFSS v.11
