High isolation compact four-port MIMO antenna systems with built-in filters as isolation structure
In this work, we present a built-in filter method to enhance the isolation level between closely packed MIMO antennas. The built-in filter is composed of several slits etched on the ground of the antenna structure. The number and length of slits depend on both the resonance frequency and the structure of the MIMO antenna system. To illustrate its usefulness, two designs of compact planar four-port