A Single Substrate Metasurface Dipole With Electrically Small Feeding Structure

Low-profile metasurface antennas are proposed for cellular base station applications. The dual-slant crossed-dipole antennas with four resonances employ both transverse magnetic (TM) and transverse electric (TE) surface wave modes. The metasurface dipole arms are capacitively coupled by an electrically small crossed-feed in a low-cost single substrate. The metasurface layer consists of <inline-formula> <tex-math notation="LaTeX">$n \times n$ </tex-math></inline-formula> element arrays. The proposed low-profile (<inline-formula> <tex-math notation="LaTeX">$0.14\lambda $ </tex-math></inline-formula>) antennas can achieve a 10-dB impedance bandwidth of 57%, 58%, and 84% for metasurface dipole arms comprising <inline-formula> <tex-math notation="LaTeX">$2\times 2$ </tex-math></inline-formula>, <inline-formula> <tex-math notation="LaTeX">$3\times 3$ </tex-math></inline-formula>, and <inline-formula> <tex-math notation="LaTeX">$4\times 4$ </tex-math></inline-formula> elements, respectively. For cellular 65° sector base station applications where 14 dB is required, a bandwidth of 51%, 52%, and 63% for <inline-formula> <tex-math notation="LaTeX">$2\times 2$ </tex-math></inline-formula>, <inline-formula> <tex-math notation="LaTeX">$3\times 3$ </tex-math></inline-formula>, and <inline-formula> <tex-math notation="LaTeX">$4\times 4$ </tex-math></inline-formula> elements, respectively, is realized. For a single dipole with a reflector, the average boresight gain is 9 dBi, 3-dB beamwidth is <inline-formula> <tex-math notation="LaTeX">$62^{\circ }~\pm ~7^{\circ }$ </tex-math></inline-formula>, front-to-back ratio is better than 25 dB, and isolation is better than 35 dB over the frequency range of 1.7–2.7 GHz. For user equipment (UE) applications, extra low-profile (<inline-formula> <tex-math notation="LaTeX">$0.11\lambda $ </tex-math></inline-formula>) antennas are also presented.