This paper presents a very compact, wideband, and enhanced-gain antenna for 5G applications. A simple single-layer millimeter wave (mm-wave) metamaterial lens (meta-lens) is used to improve the gain, aperture efficiency, and gain bandwidth of a slotted-patch antenna over a wide range of frequencies from 25 GHz to 31 GHz. The lens exhibits a metamaterial negative refractive index behavior, which is attributed to a substantial gain enhancement of around 4-5 dBi over the whole band compared to the gain values of the slotted patch antenna alone. The lens's unit cell comprises a simple single-layer split ring resonator (SRR) whose dimensions are carefully chosen to improve transmitted power and suppress absorbed and reflected power. The meta-lens consists of <inline-formula> <tex-math notation="LaTeX">8\times 8 </tex-math></inline-formula> subwavelength SRR unit cells. Each cell has an area of <inline-formula> <tex-math notation="LaTeX">1.6\times 1.6 </tex-math></inline-formula> mm2, it is located in the near-field region closely above a slotted patch antenna to produce a total antenna size of <inline-formula> <tex-math notation="LaTeX">12.8\times 12.8\times 7.27 </tex-math></inline-formula>mm3 (<inline-formula> <tex-math notation="LaTeX">1.2~\lambda \times 1.2~\lambda \times 0.68~\lambda </tex-math></inline-formula>, where <inline-formula> <tex-math notation="LaTeX">\lambda </tex-math></inline-formula> is the free space wavelength at 28 GHz). The maximum gain of the proposed antenna is 12.7 dBi, the 1 dB gain bandwidth is 18%, the maximum aperture efficiency is 92%, and the −10 dB impedance bandwidth (10 dB B.W.) is 17%. This excellent combination of essential metrics is hard to realize at mm-wave using narrowband antenna structures (microstrip patch antennas), and the aperture efficiency is the highest thus far for such a class of antennas.