Enhancing Antenna Boresight Gain Using a Small Metasurface Lens Reduction in half-power beamwidth

This article presents the design of a small metasurface (MS) lens to enhance the boresight gain of antennas. The MS lens has a circular-shaped substrate with a diameter of only 1 lambda(0), where lambda(0) is the wavelength at the operating frequency of 4.5 GHz in free space, and identical patterns of unit cells having rectangular-ring shapes printed on both sides. The rectangular-ring unit cells have a constant width along the x-axis direction and varying lengths following the gradient index (GRIN) function along the y-axis direction. This results in the MS lens having a decreasing refractive index in the x-axis direction. The refractive index of the MS lens is analyzed using a computer simulation and compared with that of an ideal lens. The small MS lens is placed at a distance of lambda(0)/2 from a source antenna to form a small MS lens antenna (SMLA) for boresight gain enhancement. Two types of planar antenna, a planar slot and patch antennas, are used for studies as the source antenna using computer simulation and measurement. The simulated and measured results agree well. The results show that the small MS lens can effectively reduce the main beamwidths and, thus, enhance the boresight gain of both source antennas by more than 5 dB.