Bandwidth and F-B ratio enhancements of an electrically-small crossed-dipole antenna using an NFRP reflector

In this paper, a compact single-feed crossed-dipole antenna backed by a near-field resonant parasitic (NFRP) element is proposed to enhance the bandwidth and front-to-back (F-B) ratio of the electrically small antenna system. The NFRP element is designed to not only act as a reflector, but also to generate an extra resonance with circularly polarized (CP) radiation for the antenna system. The extra resonances are utilized to broaden the antenna bandwidth. The final design with an overall size of 35 mm × 35 mm × 13.7 mm (0.184λ
_o
× 0.184λ
_o
× 0.072λ
_o
at 1.575 GHz) has a |S
₁₁
| <; -10 dB bandwidth of 20.3% (1.485-1.820 GHz), a 3-dB axial ratio bandwidth of 9.46% (1.510-1.660 GHz), and a maximum F-B ratio of 9.8 dB. Relative to the crossed-dipole antenna without a reflector, the proposed design increases the F-B ratio from 0 to 9.8 dB and achieves approximately 150% and 400% increases in |S|
₁₁
| <; -10 dB and 3-dB AR bandwidths, respectively.