Improving Channel Capacity in Indoor $4 \times 4$ MIMO Base Station Utilizing Small Bidirectional Antenna

Preparing toward the new-generation communication by improving the capacity in the channel can be achieved by employing a MIMO system with polarization diversity means. This paper presents a low-profile 4×4 MIMO bidirectional antenna consisting of two composite antennas mounted on a ground plane. The composite antenna is constructed by stacking a notch antenna and a loop antenna on top of each other and each antenna is fed independently. This antenna is capable of dual-polarized radiation patterns pointing in two different directions, where the notch antenna produces a horizontally polarized wave in the x-axis direction while the loop antenna gives a vertically polarized wave in the y-axis direction. The combination of two composite antennas has good isolation between the elements and is capable of improving the channel capacity for indoor MIMO base station applications. This paper includes the validation of both the fabrication of the proposed antenna design and the channel propagation measurement using the proposed antenna, confirming the excellent antenna performance for long term evolution application at a frequency of 3.5 GHz.