A Dual-Polarized Multi-Sector Antenna Using Dielectric Image Lines for Millimeter-Wave Indoor Base Stations

A new dual-polarized multi-sector antenna for a millimeter-wave indoor base station (27.4-27.8 GHz) is presented. The proposed antenna consists of six horizontally polarized (H-pol.) and vertically polarized (V-pol.) end-fire antennas on a ground plane. Since reflection coefficients of the ground plane are anti-phased between H- and V-pol. antennas, conventional antenna designs suffer from significant deviations of the directivity and beam tilt, resulting in a problem of unmatched coverage area. The impact is theoretically clarified, and optimally shaped dielectric image lines (DILs) with orthogonal polarization ( E₁₁^y and E₁₁^z modes) are introduced to realize the identical antenna patterns. The designed DIL antennas are then applied to the multi-sector antenna, offering a high gain of as much as 15 dBi, relatively low profile (0.46λ), polarization diversity, and matched coverage area in full azimuth angles. The measurement result confirms that the prototype has a 14.2 and 15.2 dBi directivity for H- and V-pol. antenna unit on average, and the beam tilt error is less than 1°. The proposed antenna is suitable for millimeter-wave micro base-station systems, especially for a ceiling antenna and multiple-input multiple-output applications.