Helical Torsion Coaxial Cable for Dual-Band Shared-Aperture Antenna Array Decoupling

Direct connection between coaxial cables and antenna radiators is one of the most popular and simplest approaches for antenna excitation. In dual-band shared-aperture antenna arrays that operate in higher and lower frequency bands, feeding coaxial cables of the higher band antenna array will inevitably introduce electromagnetic coupling in the lower band antenna arrays. The cross-band coupling will further lead to radiation pattern distortion, gain decrease, and impedance mismatching in the lower band antennas. Instead of using conventional straight coaxial cable feedings, this article proposes to decouple the unwanted cross-band coupling with a novel helical torsion coaxial cable design. The helical torsion feeding (HTF) coaxial cables are investigated from equivalent circuit analysis and full-wave simulation. The analysis results demonstrate that the HTF coaxial cable possesses open-circuit characteristic in the operation band of the lower band antenna. Through this design, the cross-band coupling is effectively suppressed at 0.69 GHz. The effectiveness of the approach is then demonstrated in a dual-band shared-aperture antenna array. Both the simulated and measured results validate the proposed design. The proposed decoupling method will find applications in compact multiband 5G MIMO antenna array developments.