Planar MIMO antenna system with polarization diversity for 2.5–2.7 GHz LTE indoor FemtoCells

This paper presents a planar MIMO antenna system designed for the 2.5-2.7 GHz LTE indoor femtocell application. The proposed antenna system consists of two orthogonally polarized arrays; each array is realized on a single PCB and is comprised by two microstrip patch antenna elements. These patch antenna elements have increased bandwidth that is achieved by using parasitic radiating patches disposed coplanar with the main patch. The proposed patch arrays use the technique of sharing one of the parasitic patches by both elements in each array. That provides a narrow radiation pattern of the antenna system in the vertical plane with more compact size of the arrays. The designed MIMO antenna system was optimized for integration with commercial LTE femtocell base station produced by Telum LLC. The measurement results confirmed the bandwidth of 2.37 - 2.79 GHz (420 MHz) for the -10 dB level of the reflection coefficient and the isolation between two MIMO input ports of > 38 dB. The gain of the designed system at the central frequency of 2.6 GHz is 8 dBi. The half-power beamwidth in the horizontal plane is 71° whereas in the vertical plane is 46°. Such antenna pattern characteristics are desirable and allow femtocell base stations located at neighboring floors of a building improving coverage area at each floor while decrease interference level between the cells.