A novel tri-band circularly polarized (CP) patch antenna with multilayer and spiral-slot left-handed metamaterials (LHMs) structures is presented in this paper. The LHMs provide a novel method to realize multiband and compact CP antenna. The proposed LHMs structure enhances the series capacitance and shunt inductance by loading the metal caps and spiral-slot into the original mushroom structure. The dispersion relation of the proposed LHMs structure as well as the conventional mushroom is solved and compared, which predicts the left-handed operating frequencies and resonance modes. A tri-band CP antenna prototype is fabricated, and the length of the patch is λ _0/6.6 at the first resonant frequency. The two lower resonant frequencies belong to the left-handed frequencies, and the highest resonant frequency is the right-handed resonant frequency. Frequency ratio can be chosen by adjusting the dimensions of the central LHMs structure and the outer patch, respectively.
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