Bandwidth improvement of a circularly polarised printed monopole antenna using a lumped capacitor

Axial-ratio bandwidth (ARBW) improvement of a circularly polarised printed monopole antenna using a lumped capacitor is presented. To demonstrate the effectiveness of this approach, a lumped capacitor is attached in the gap of an inverted-U-shaped patch antenna having a narrow 3 dB ARBW. Simulation shows that the ARBW improves from 4.1% (5.68-5.92 GHz) to 30.7% (4.33-5.9 GHz) with the use of a 0.5 pF capacitor. The measured results show a -10 dB reflection bandwidth of 60.5% (3.75-7 GHz), and a 3 dB ARBW of 33.3% (4.25-5.95 GHz). The advantage of the proposed design is that the 3 dB ARBW of an antenna can be easily tuned and extended with the use of only one lumped capacitor.