A Low-Profile Dual-Polarized Omnidirectional Antenna for LTE Base Station Applications

Abstract

A novel low-profile dual-polarized omnidirectional antenna is proposed in this communication, which is designed for 1.7-2.7 GHz LTE band operation. The horizontally polarized (HP) omnidirectional radiation is realized by a circular slot array. Eight stepped-impedance slots are fed by a one to eight T junction power divider with equal amplitudes and phases. On the other hand, the vertically polarized (VP) omnidirectional radiation is realized by using the characteristics of the TM <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0n</sub> mode of the cylindrical cavity, where eight shorting copper sheets are used to excite TM <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">01</sub> and TM <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">02</sub> modes. A one to four T junction power divider is used to feed the VP unit and achieve good impedance matching. The HP antenna is used to replace the top metal disk of the VP antenna unit, and eight slots are etched on the ground of the vertical polarization unit. It substantially solves the problem of matching deterioration when the horizontal polarization antenna is placed close to the ground. Besides, a special feeding method is employed to avoid the feeding intersection, which commonly appears in dual-polarized antennas. The antenna achieves an isolation around 35 dB and it has a low profile of 0.07λ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">min</sub> , with λ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">min</sub> being the free space wavelength at the lowest operation frequency. The proposed antenna has an omnidirectional beam, which is very suitable for indoor ceiling base station applications.