Bandwidth analysis of low-complexity decoupling networks for multiple coupled antennas

In MIMO communication systems where coupled antennas are driven by independent amplifiers, a decoupling network is often used to eliminate power reflection from the antennas. The realization of the decoupling network is not unique, and different realizations have major differences in complexity and bandwidth. Recent designs for low-complexity networks show that a minimum of N² + N impedances are generally needed to achieve decoupling for N antennas. This paper provides a perturbation analysis of the bandwidth, and shows that a decoupling network with N² +2N impedances can often achieve a much wider bandwidth than N² +N impedances. We illustrate using a three-antenna example.