Very simple 2.45/3.5/5.8 GHz triple-band circularly polarised printed monopole antenna with bandwidth enhancement

A very simple triple-band circularly polarised printed monopole antenna with bandwidth enhancement for 2.45/5.8 GHz wireless local area network (WLAN) and 3.5 GHz worldwide interoperability for microwave access (WiMAX) applications is presented. The circular polarisation characteristic at the WiMAX band was obtained by an inverted-U-shaped radiator rotated by 45° around the horizontal axis. To create the upper circular polarisation mode at the 5.8 GHz WLAN band, an I-shaped strip was added on the right side of the radiator. Finally, by attaching an inverted-L-shaped strip at the end of the I-shaped strip, the lower circular polarisation characteristic at the 2.45 GHz WLAN band was achieved. The proposed antenna is excited by a simple 50 Ω microstrip feed line using a transformer for impedance matching. The measured -10 dB impedance bandwidth is 450 MHz (2.35-2.8 GHz) and 4.1 GHz (3.3-7.4 GHz) and the measured 3 dB axial-ratio bandwidth reaches 12% (2.35-2.65 GHz), 10% (3.3-3.65 GHz) and 4.4% (5.6-5.85 GHz).