Low-profile Millimeter-Wave Wideband Circularly Polarized Spiral Antenna Array

A single fed low-profile millimeter-wave mmW wideband circularly polarized (CP) spiral antenna 2x2 array is presented. By employing the regular parallel feeding network technique to excite each CP spiral element with equal amplitude and phase, the proposed array achieves the impedance bandwidth (IBW) of 6.47 GHz about 23.1% of 28 GHz. A cross slot is introduced at the bottom layer for decoupling. The bandwidth of axial ratio (AR) lower than 3 dB is 6.95 GHz (24.8% referring to 28 GHz) from 24.87 GHz to 31.82 GHz. The polarization sense at the top side and bottom side are left-hand circular polarization (LHCP) and right-hand circular polarization (RHCP), respectively. The gains of the whole desired frequency band (from 25 GHz to 31 GHz) are higher than 10 dBi with a peak gain of 11.98 dBi at 29.5 GHz.