Fully Planar Endfire Circularly Polarized Antenna of Substrate Integrated Waveguide Loaded With Planar Bending Dipole

ABSTRACT This paper proposes a fully planar endfire circularly polarized (CP) antenna on a single‐layer substrate, consisting of a substrate‐integrated waveguide (SIW) loaded with a bending dipole. The SIW horn, which can be directly integrated with RF circuits, could generate high‐gain vertically polarized (VP) radiation. The novel bending dipole is actually a traveling‐wave helical dipole radiator and could generate high‐gain horizontally polarized (HP) radiation. The bending dipole is fed by the SIW horn with a tapered parallel stripline. The mechanism and design method of the proposed antenna is presented, and its experimental prototype has been designed and measured. The measured impedance bandwidth of −10 dB covers a bandwidth of 2.4 GHz from 25.3 to 27.7 GHz, the 3‐dB axial ratio (AR) bandwidth is 2.4 GHz from 24.9 to 27.3 GHz, and the effective bandwidth is from 25.3 to 27.3 GHz. The measured CP gain is over 7.3 dBic and the peak gain is 9.1 dBic in the effective bandwidth. The high gain planar endfire CP antenna has a compact size of only 3.06 λ 0 *1.2 λ 0 *0.13 λ 0 .