A Miniaturized Wideband Dual-Polarized Antenna Based on Mode-Control Principle for Base-Station Applications

In this paper, a miniaturized wideband dual-polarized antenna and its array are proposed and demonstrated for practical base-station applications. “Mode-control” principle is employed to facilitate both miniaturization and bandwidth-enhancement of the proposed antenna element. To be more specific, by inserting meander lines into a traditional crossed loop-dipole antenna, its first resonant mode can be shifted to a lower frequency without increasing the aperture size, implying that a total size reduction can be achieved. Meanwhile, by embedding a pair of crossed straight strips into the coupling region of the crossed loop-dipole antenna, its second resonant mode can be moved to a higher frequency with a good impedance matching, thereby improving the impedance bandwidth significantly. A prototype of the proposed antenna with a small radiator size of only 0.33λ x 0.33λ (λ is the wavelength at the center frequency of 2.2 GHz) is designed, fabricated and measured. Measurements show that in the target frequency band from 1.71 GHz to 2.69 GHz, i.e., 2G/3G/4G bands, a relatively good impedance matching with the VSWR of less than 1.65 and a high isolation of greater than 28 dB are obtained by the proposed antenna element. Also, a stable gain of 8.7±0.5 dBi and a stable 3-dB beamwidth of 64.8±2.7° at the
H
-plane are respectively achieved. A multiple-input-multiple-output (MIMO) antenna array consisting of two subarrays with electrical down-tilt is further developed for practical base-station applications. Each subarray is composed of ten antenna elements. The overall width of the array is only 260 mm, which is much narrower than that of typical industrial products (~305 mm). Measured results show that the antenna array has also achieved good performances such as wide impedance bandwidth, high isolations among different ports, and stable radiations over the 2G/3G/4G bands.