Ultrawideband Low-Profile Circularly Polarized Cross-Dipole Antenna With Hybrid AMC Reflector

In this letter, an ultrawideband low-profile circularly polarized (CP) antenna with asymmetric cross-dipoles, parasitic patches, and artificial magnetic conductor (AMC) is proposed. A vacant-quarter ring connects orthogonal dipole arms to introduce the required 90° phase difference for generating CP radiation. To reduce the profile of the antenna, an AMC reflector is positioned beneath the radiator. The AMC reflector consists of hybrid metallic patterns printed on a substrate, where two different types of unit cells are arranged in the center and around the periphery separately to expand the in-phase reflection bandwidth. Additionally, metallic strips are added around the edge of the ground to improve the axial ratio and radiation pattern at lower frequencies. Measured results indicate that the impedance bandwidth and the axial ratio bandwidth of the antenna are 1.51 GHz to 5.13 GHz (109%) and 1.54 GHz to 3.57 GHz (79.5%), respectively. The antenna gains maintain 6.3 dBic to 8.3 dBic within the whole operating bandwidth. Furthermore, the antenna features a low profile of 0.13λ_L corresponding to the lowest operating frequency.