Compact Modified Mikaelian GRIN Lens Antenna with Gain and Bandwidth Improvement

This letter proposes a compact Mikaelian lens antenna (LA). The proposed antenna consists of an aperture-coupled patch (ACP) antenna with a patch printed directly on a graded refractive index (GRIN) lens. By loading the ACP antenna with the dielectric lens, the antenna impedance bandwidth increases from 17.5% to 33%. In addition, the lens refractive index (RI) profile is angularly modified with the use of $cos(2\phi)$ function to improve the radiation pattern and gain of the LA to achieve the maximum theoretical aperture efficiency (AE) of 116% at 24 GHz. The proposed concept was validated in simulations and measurements of the LA operating in the 23–34.5 GHz frequency range. The fabricated LA has a volume of $2\lambda \times 2\lambda \times 1.76\lambda$ at 24 GHz. It achieves a maximum AE of 58% at 23.5 GHz for gain of 13.7 dBi, which could be improved to 96% with the use of low-loss materials.