Compact Wideband Dual-Polarized Antenna With High Isolation Using Modified Direct Feeding Structure For Indoor Beamforming Array Applications

A modified direct feeding structure is proposed in this paper to realize a compact (
$45 \times 45$
mm
²
) wideband dual-polarized antenna with high isolation (33 dB) and low cross-polarization (30 dB). Compared with the conventional crossed dipole antennas, two additional pairs of dipoles are employed as coupling baluns as well as radiators. As a consequence, the proposed antenna with more symmetrical structure has the advantages of both the direct feeding (DF) and the coupling feeding (CF) structures, such as, balanced matching, high isolation, low cross-polarization, and compact size. Besides, the gap structure between adjacent dipoles is designed in elliptical shape to further improve the impedance matching. The proposed antenna realizes a wide impedance bandwidth over 51% (1.7–2.85 GHz) for VSWR <1.5. It is worth mentioning that the compact size and high isolation could greatly reduce the element spacing of beamforming antenna array. In order to investigate the performance of beamforming array, a two-element array fed by the out-of-phase power divider network is developed. The lowest operating frequency can be further extended to 1.6 GHz and the cross-polarization discrimination (XPD) is more than 10 dB within ±60° of the main lobe.