Broadband Dual-Polarized Dual-Dipole Planar Antennas: Analysis, Design, and Application for Base Stations

In this article, we propose a compact ±45° dual-polarized dual-dipole (DPDD) antenna for second-, third-, and fourth-generation (2G/3G/4G) long-term evolution (LTE) base stations. The DPDD antenna consists of two perpendicularly crossed dual-dipole elements. Each dual-dipole element is directly fed by a coaxial cable. Two dual-dipole elements are printed on the same substrate, making the DPDD antenna planar and compact. Due to the coupling between two crossed dual-dipole elements, the DPDD antenna can achieve a broad bandwidth of 51% for a return loss greater than 15 dB (1.61-2.71 GHz) with a high isolation of 30 dB. The dual-polarized antenna has a gain of 9 dBi and a halfpower beamwidth (HPBW) of 65 ± 5° for ±45° polarization with a flat metallic reflector. For applications in LTE700/GSM850/900 base stations, a new artificial magnetic conductor (AMC) surface is introduced to replace the metallic reflector. It is shown that the antenna height can be significantly lowered from 105 mm (0.29λ_0.83, where λ_0.83 is the freespace wavelength at the frequency of 0.83 GHz) for a metallic reflector to 31.52 mm (0.087λ_0.83) for an AMC surface while a broad bandwidth of 52% (0.68-1.16 GHz) is still achieved. The broadband ±45° DPDD antenna is described in the "Broadband ±45° DPDD Antenna" section, and the ±45° DPDD antenna with an AMC surface is demonstrated in the "DPDD Antenna with an AMC Surface" section.