A novel broadband omni-directional circularly polarized antenna for mobile communications

This paper presents a new broadband omni-directional circularly polarized (CP) antenna for mobile communications operating nearby 2 GHz. The new omni-directional CP antenna consists of four broadband CP rectangular loops which are bent to form a hollow cylinder. A conducting cylinder is introduced inside the hollow cylinder to improve the CP performance. A broadband balun is developed to feed the CP antenna. This antenna has a compact cylindrical configuration with a diameter of 0.4λ. The simulation shows that this antenna has a bandwidth of 30.8% (1.7 GHz-2.32 GHz) for return loss (RL) ≥10 dB and 36.1% (1.75 GHz-2.52 GHz) for average axial ratio (AR) ≤3 dB. Good agreement between simulated and measured results is achieved.