A Broadband and Electrically Small Planar Monopole Employing Metamaterial Transmission Line

A broadband and electrically small planar monopole is presented in this letter. In order to increase the impedance bandwidth, a metal patch embedded with two epsilon-negative meander lines is used as the main radiator and the ground plane is periodically etched with cross slots. The etched ground and the patch form a metamaterial transmission line (MTL) resonance, which not only miniaturizes the antenna but also improves its bandwidth. The proposed antenna can work in the frequency band of 2.38-2.95 GHz with a fractional bandwidth as much as 21.5%. The size of the main radiator is 0.078λ0 ×0.073λ0 and the maximum gain is 3.42 dBi. The antenna can be applied to various wireless mobile communication systems such as RFID, WLAN, and WiFi.