Mutual Coupling Mitigation in Broadband Multiple-Antenna Communication Systems Using Feedforward Technique

Abstract

An efficient method to mitigate the forward scattering (shadowing) effect and the near-field coupling among elements of broadband multiple-antenna communication systems is proposed. The technique is based on provision of a passive feedforward coupling among elements to cancel out the mutual couplings. Electrical current paths, with appropriate shape, location, and length, between adjacent elements are established to provide current distributions on adjacent elements that are approximately equal in magnitude and out of phase with the induced current on the same antenna due to the near-field coupling and scattering effects. As the coupling level decreases, the radiation pattern of an excited array element, in the presence of the other array elements, approaches the pattern of the antenna element in isolation. The technique is first detailed for a two-element wideband monoconical antenna array and is then extended to a uniform 12-element circular array of the same monoconical antennas where only feedforward paths are applied to circumferentially adjacent elements to reduce the coupling over a very wide bandwidth. The experimental results indicate that the application of the proposed feedforward technique to a 12-element circular array of monoconical antennas can provide a minimum of 2-dB reduction in the average gain deviation from omnidirectional radiation over an about 30% fractional bandwidth. Another important feature of the feedforward technique is removal of radiation nulls of the array elements at all frequencies and all directions.