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This paper presents a quadruple-band indoor base station antenna for 2G/3G/4G/5G mobile communications, which covers multiple frequency bands of 0.8-0.96 GHz, 1.7-2.7 GHz, 3.3-3.8 GHz and 4.8-5.8 GHz and has a compact size with its overall dimensions of 204 × 175 × 39 mm 3. The lower frequency bands over 0.8-0.96 GHz and 1.7-2.7 GHz are achieved through the combination of an asymmetrical dipole antenna and parasitic patches. A stepped-impedance feeding structure is used to improve the impedance matching of the dipole antenna over these two frequency bands. Meanwhile, the feeding structure also introduces an extra resonant frequency band of 3.3-3.8 GHz. By adding an additional small T-shaped patch, the higher resonant frequency band at 5 GHz is obtained. The parallel surrogate model-assisted hybrid differential evolution for antenna optimization (PSADEA) is employed to optimize the overall quadruple-band performance. We have fabricated and tested the final optimized antenna whose average gain is about 5.4 dBi at 0.8-0.96 GHz, 8.1 dBi at 1.7-2.7 GHz, 8.5 dBi at 3.3-3.8 GHz and 8.1 dBi at 4.8-5.0 GHz respectively. The proposed antenna has high efficiency and is of low cost and low profile, which makes it an excellent candidate for 2G/3G/4G/5G base station antenna systems. INDEX TERMS 2G/3G/4G/5G, base station antenna, compact antennas, optimization method, quadrupleband antennas.

A dual-band dual-polarized base station antenna for the fifth-generation (5G) mobile system is presented in this paper. The proposed antenna covers the frequency bands from 3.3 to 3.8 GHz (the lower band) and from 4.8 to 5.0 GHz (the upper band) with good isolation between its ports (≥ 20 dB). It consists of two double-oval-shaped dipoles, two double-oval-shaped feeding lines and a cavity reflector. In this design, parts of the dipole antenna structure are used as the feeding lines and it is found that using one arm of the dipole to feed the whole antenna can improve impedance matching. The dual-band performance is achieved by integrating a small oval-shaped loop within the large oval-shaped loop without increasing the size of the radiating patch. The size of the radiating patch is only 0.26λ 0 × 0.26λ 0 (λ 0 is the free-space wavelength at 3.3 GHz). The cavity reflector improves the gain performance and reduces the overall size of the antenna, which is only 0.66 λ 0 × 0.66λ 0 × 0.2λ 0. The antenna has an average realized gain of 7.56 dBi in the lower band and 7.42 dBi in the higher band. Meanwhile, for both bands, the radiation pattern is stable, and the half power beamwidth is within 65 • ± 5 •. Both simulated and measured results demonstrate that the antenna is a very good candidate for 5G mobile base stations. INDEX TERMS 5G, base station antenna, coupling feeding, dual-band, dual-polarized.

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