Compact 1 × 2 and 2 × 2 MIMO antennas with enhanced isolation for ultrawideband application

Abstract

Two small size multiple-input–multiple-out (MIMO) antennas with high isolation for ultrawideband (UWB) applications are presented. A two-element MIMO antenna, which is mounted on an FR4 substrate with a compact size of 24 mm × 33 mm, consists of two symmetric circular monopole elements and a modified ground. The protruded ground provides a way to improve isolation and impedance matching. Such a wide band from 2.75 to 11 GHz is achieved by using modified ground technology, and high isolation more than 20 dB is also accomplished. Meanwhile, moderate gain and omnidirectional radiation patterns can be obtained. Based on the circular monopole with modified ground, a four-element antenna array is also constructed and studied. The size of the four-element antenna with orthogonal arrangement is 44 mm × 44 mm. Measured results show that the antenna also exhibits good impedance matching as well as low envelope correlation coefficient over the entire UWB spectrum.