Penta-band circularly polarised antenna using a lumped capacitor

A very simple printed monopole antenna with penta-band circularly polarised (CP) radiation characteristics for wireless local area network (WLAN), worldwide interoperability for microwave access, and downlink of the X-band satellite communication applications is proposed for the first time. The antenna comprises a notched rectangular ground plane and a radiating patch consisting of inverted-U-shaped, I-shaped, and inverted-L-shaped radiators, and creates four CP modes operating at 2.4/3.5/5.8/7.5 GHz frequency bands. By placing a lumped capacitor of 0.5 pF in the gap between the I-shaped radiator and the inverted-L-shaped radiator, an extra CP mode at 5.2 GHz WLAN band is generated, thus completing the penta-band CP antenna. The measured -10 dB impedance bandwidth of the demonstrated antenna is 340 MHz (2.37-2.71 GHz) and 4.8 GHz (3.2-8 GHz), and the measured 3 dB axial-ratio bandwidth is 16.6, 13.5, 2.9, 2.4, and 4% in five distinct bands of 2.1-2.48, 3.1-3.55, 5.1-5.25, 5.76-5.9, and 7.45-7.75 GHz.