Ultralow-Profile Conformal Antenna With Large Axial Ratio Bandwidth for Flapping-Wing Insects

This letter presents an ultralow-profile flexible circularly polarized (CP) antenna that can be conformal to the wing of flapping-wing insect aircraft. The antenna is manufactured by laminating a single metal layer on a flexible polyimide substrate with a thickness of 0.125 mm (0.0025λ). Adopting an ingenious design combining asymmetric coplanar waveguide (ACPW) and a slot structure shaped like an N is used in the proposed antenna, which achieves both ultra-low profile and wide axial ratio bandwidth. ACPW is used for antenna feed, and the combination of N-like slot and ACPW can form current radiation at the slit that is orthogonal in space and time respectively, and similar in intensity. The proposed antenna realizes −10 dB impedance bandwidth of 40% (4.5–6.8 GHz) and 3 dB axis ratio bandwidth of 37% (4.6–6.7 GHz), with a gain larger than 3.5 dBi. When the antenna is bent due to wing flapping, the antenna performance remains stable.