Gain Enhancement of Millimeter Wave Antenna by Ultra-thin Radial Phase Gradient Metasurface for 5G Applications

In this article, gain augmentation of a microstrip antenna (MSA) operating at 28 GHz has been enunciated in a cost-effective manner using a phase graded index lens. Different metamaterial unit cells with transmissive characteristics have been designed and placed in an array to create a radial phase graded metalens with locally varying refractive index and spatially varying surface impedance. Transformation of spherical wavefronts into planar wavefronts results in beam collimation which helps in obtaining a directive beam in the 5G frequency band. The ratio of focal length to the diameter (f/d) of the lens is 0.38. The gain of MSA is enhanced by 4.4 dB with radiation efficiency above 95% due to the focusing effect of the lens placed vertically above the antenna. The proposed planar lens is compact in size and easy to fabricate when compared with the conventional 3-D lens reported in existing works. The microstrip patch integrated lens prototype exhibits a gain of 12.4 dBi operating at 28 GHz. The performance of the lens has been analyzed theoretically and evaluated further by conducting experiments on the fabricated prototype. Measured results validate the full-wave simulation results carried out using finite element method.