Design of a broadband circularly polarised uniplanar crossed-dipole antenna

This study presents the design of a uniplanar crossed-dipole antenna with broadband characteristics. The antenna comprises a pair of identical crossed-dipole arms printed on the same plane of a dielectric substrate. The crossed-dipole arms are corner-cut fat dipoles that are perpendicular to each other and connected with a bent stripline to generate circularly polarised (CP) radiations. A wide dipole arm was used to improve impedance matching and widen the axial ratio (AR) bandwidth. Additionally, the corner of each dipole arm was cut into a triangular shape to broaden the impedance and AR bandwidths further. The antenna in free space is excited via a wideband microstrip-to-parallel stripline tapered balun to reduce the effect of leakage current on the coaxial cable. Experiments and full-wave electromagnetic simulations were employed to design, verify, and validate the antenna design. The antenna, having an overall size of 45x45x0.508 mm(3) (0.4x0.4x0.0045 lambda(L) (3) where lambda(L) is the lowest frequency in the 3-dB AR bandwidth), demonstrates the following measured performances: an |S-11|<-10 dB impedance bandwidth of 2.53-9.14 GHz (113.3%), a 3 dB AR bandwidth of 2.65-7.75 GHz (98.1%), and peak gain of 3.7 dBic at 6.6 GHz.