A Compact Triple-Band Antenna with a Notched Ultra-Wideband and Its MIMO Array

In this paper, a compact antenna with three operational bands, including a (notched) ultra-wideband (UWB), and its array for multiple-in multiple-out (MIMO) applications are reported. The antenna is composed of a folded patch with a shoring wall fed by a folded planar monopole with a 3-D U-slot cut. The operation of the antenna relies on the monopole-fed patch mode at low frequencies and reflector-backed monopole radiation in the middle- and high-frequency bands, which is able to cover almost all the wireless service bands in the sub-6 GHz regime, including a continuous UWB with a ratio bandwidth of 4:1. A narrow stopband can be placed within the UWB by integrating a symmetric pair of 3-D meandered slots on the folded monopole feed. A prototype of the antenna was fabricated, which has a form factor of 0.16\lambda -{L} \times 0.13\lambda -{L} \times 0.09\lambda -{L} , where \lambda -{L} is the wavelength at the lowest operating frequency, and experimentally achieves three S-{11} < -10 dB bands of 0.72-2.96, 3.25-3.59, and 5.06-6.21 GHz, with a stopband at around 1.5 GHz. It has a unidirectional radiation pattern with a wide beamwidth and a realized gain of more than 4 dBi in the majority of the operational bands. Moreover, a 2 \times 1 MIMO array of the proposed antennas is further investigated for offering both spatial and pattern diversities. The fabricated array prototype accomplishes a weak mutual coupling below -23 dB and a small envelope correlation coefficient lower than 0.001 in the targeted bands. The demonstrated antenna and its MIMO array will be highly useful for multiservice software-defined radio devices and various other wireless communication systems for numerous applications.