Design of a Compact, Wideband, Bidirectional Antenna Using Index-Gradient Patches

A planar, compact, wideband, bidirectional antenna based on the index-gradient patches is proposed. In this design, a printed dipole is utilized as the launcher element, and a metasurface containing both linearly index-modulated patches and index-fixed patches is employed for both bandwidth enhancement and gain improvement. The overall dimensions are 1.35λ₀ × 0.79λ₀ × 0.01λ₀, where λ₀ corresponds to the center frequency f₀ = 3.75 GHz within the entire operation bandwidth from 1.85 to 5.65 GHz. Simulated results, verified by the measured values, show that the proposed metasurface-based antenna maintains stable bidirectional endfire radiation performance with the maximum gain of 7.32 dBi over an ultrabroad bandwidth as high as 101.3%, which would be quite suitable for the applications in the wireless coverage in long and narrow path service areas.