A Miniaturized Dual-Band Dual-Polarized Base Station Antenna Loaded With Duplex Baluns

A novel miniaturized dual-band and dual-polarized base station antenna loaded with duplex baluns is proposed in this letter. The duplex balun consists of a lower-band filter structure (LFS) and an upper-band filter structure (UFS). The LFS contains a stepped-impedance filter, an open-circuited stub, and an impedance matching section. The UFS contains a high-pass filter and an impedance matching section. The proposed antenna has two independent current paths, which enables it to operate in dual bands, and the two paths are bent to achieve its small overall size. By miniaturizing the antenna and loading LFS & UFS, the operating bands of 1.71–2.17 GHz and 3.22–3.7 GHz, the compact size of 0.24 × 0.24 × 0.18
$\lambda _{LL}^3$
(
${\lambda }_{LL}$
is the wavelength at the lowest frequency of the lower band), the lower coupling coefficients (<−20 dB), the normal in-band radiation characteristics, and good out-of-band suppression characteristics (>20 dB at the lower-band ports as well as >23 dB at the upper-band ports) are obtained. It represents an excellent scheme for 5G applications.