Dielectric Decouplers for Multi-antenna Systems


Student thesis: Doctoral Thesis

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Award date14 Sept 2023


Electromagnetic (EM) decoupling plays a crucial role in multi-antenna systems including multi-input-multi-output (MIMO) systems and antenna array systems. The performance of multi-antenna systems can be adversely affected by strong mutual coupling. In the past two decades, more and more decoupling techniques have been proposed to address this issue based on two basic decoupling strategies, blocking and neutralizing. This thesis investigates novel dielectric decouplers for multi-antenna systems and is divided into three parts.

First, we propose a novel decoupling method for compact multi-antenna systems based on the superposition principle. A dielectric block is employed to encompass all radiators in a compact MIMO system and acts as a dielectric decoupler when appropriately designed. It gives rise to scattered paths for EM waves. As a result, mutual couplings between any two primary radiators are superposed, combining the direct and scattered paths. Based on this insight, a dual-port decoupled antenna is then proposed for demonstration.

Second, we propose a compact tri-port antenna module with three coplanar polarizations and its high-gain hexagonal antenna array (HAA). The antenna module has three equilateral monopole radiators with high isolations for MIMO applications. The three radiators are surrounded by a cylindrical dielectric block. Establishing dielectric-air boundaries with the loaded dielectric block effectively mitigates mutual coupling. Moreover, it modifies the E-field distribution to generate three coplanar polarizations. For the HAA, dielectric-filled bow-tie-shaped slots are employed between modules to reduce the inter-module mutual coupling. Moreover, an artificial magnetic (AMC) structure is arranged on the backside to reduce the backside lobes.

Third, we propose a 3-D-printed wideband circularly polarized (CP) MIMO antenna. This antenna comprises two CP dielectric resonator antennas (DRAs) enclosed by a dielectric decoupler. Employing this decoupler, a high isolation can be obtained with the small center-to-center distance between the two DRAs.

Overall, the proposed dielectric decouplers can offer high design flexibility in terms of the number of radiators, element spacing, type of radiators and type of polarizations. Results show that this method can provide good isolation within a moderate bandwidth using a simple "dielectric decoupler" for multi-antenna systems.