Design of Low Mutual Coupling Dielectric Resonator Antennas Without Using Extra Decoupling Element

A simple decoupling method of using specific higher-order modes to improve the isolation of dielectric resonator antenna (DRA) elements is investigated. The higher-order modes have the feature that they can be excited by the active (source) DRA while unexcitable by means of the feeding network. As a result, the coupled fields in the passive (coupled) DRA are unable to reach the feeding port, leading to a very low mutual coupling level. When the coupled modes in the passive DRA have the same radiation characteristics with the mode that excited in the active DRA, the distortion of radiation patterns can also be avoided. This method is found effective for reducing both the E-plane and H-plane coupling. As no extra decoupling element is needed, the entire antenna system is very simple. For verification, an E-plane-coupled $1\times 2$ multiple-input-multiple-output (MIMO) DRA array has been fabricated and measured. The results show that using a proper mode, the isolation can be enhanced from about 15 to 45 dB at 5.25 GHz.