Wideband Dual-Polarized Filtering Antennas Using Short-Circuited Coupling Structure for 4G/5G Multi-Input-Multi-Output (MIMO) Antenna Decoupling Design

A short-circuited coupling structure (SCCS) is proposed to obtain a gain-filtering response for dual-polarized antennas. A conventional dipole is designed with two intrinsic radiation nulls. By introducing an SCCS, an additional radiation null is obtained, and the impedance bandwidth of an antenna can be further improved. Based on this design principle, two dual-polarized filtering antennas are designed for 4G and 5G wireless communication devices. The impedance bandwidth of the proposed 4G filtering antenna is 1.63–2.97 GHz (|S11| < −15 dB), with four radiation nulls at 1.1 GHz, 3.25 GHz, 3.5 GHz, and 4.0 GHz. The impedance bandwidth of the proposed 5G filtering antenna is 3.23–4.21 GHz (|S33| < −15 dB), with four radiation nulls at 1.7 GHz, 2.5 GHz, 3 GHz, and 4.6 GHz. Further, the decoupling function of the SCCS on 4G/5G MIMO antenna designs is also discussed. When introducing an SCCS, the port isolation levels of two elements between the 4G and 5G antennas, as well as the adjacent 5G antennas, can be improved by 14 dB and 6 dB, respectively. The port isolation levels of five elements between the 4G and 5G antennas, as well as the adjacent 5G antennas, can be improved by 15.2 dB and 9.5 dB, respectively. This technique could also be a potential candidate for optical antenna designs in optical front-ends and other multi-wavelength fiber lasers with microstructures.