Bandpass Filtering Technique for Transparency in Multiband Base Station Antennas

A 0.19 λ₀ profile low-band antenna with coupled-line structures is presented, providing a bandpass response and improved electromagnetic transparency. The design employs odd- and even-mode excitations together with distributed coupling to achieve a low odd-mode characteristic impedance and enhance coupling, while suppressing high-band-induced currents through an inherent bandpass filtering mechanism. In addition, a compact 0.15 λ₀ profile high-band antenna array mitigates low-band common-mode resonance, enabling low-profile multiband antenna integration. The low-band dipole achieves 46% impedance bandwidth (0.617–0.971 GHz), whereas the high-band array attains 59% bandwidth (1.62–2.98 GHz).