Author(s): Luka Dimitrijevic, Sean Gillam
Mentor(s): Sai Radavaram
Institution UTech
A simple, cost-effective technique to minimize mutual coupling (crosstalk or interference) in linear Multiple Input Multiple Output (MIMO) antenna arrays is proposed in this project. MIMO arrays utilizes differences in both phase and voltage to steer the radiated energy or beam in the desired direction, creating constructive and destructive interference patterns that allow for the transmission of data through the beam. This ability to steer beams without any physical movement makes MIMO arrays highly versatile. In recent years, MIMO technology has seen widespread adoption in radar, satellite, and wireless communications, with advancements significantly enhancing channel capacity and efficiency. However, challenges remain, especially, the spacing between the antenna elements. Conventional MIMO systems typically space antennas at half-wavelength intervals to maximize resolution, but achieving such spacing in portable devices (e.g., smartphones) is difficult, leading to high mutual coupling that degrades bandwidth and radiation characteristics, ultimately impairing overall performance. While several techniques have been proposed to mitigate mutual coupling, many utilize complex, multi-layered structures that are expensive to fabricate and require a high form factor. To address these challenges, in here, we present a simple, single-layered, cost-effective decoupling approach aimed at improving isolation in closely spaced antenna arrays. This technique employs a novel decoupling network appended at the top and bottom edges of the antenna elements, capable of generating 180𝑜 phase shift to the signal passing through it. When combined with the existing coupling signal, this phase-reversed signal effectively cancels out the unwanted coupling. Because this decoupling structure is integrated at the edges of the antenna elements, rather than between or above them, as in previously proposed techniques, it aided in realizing a single-layered structure with small center-to-center and edge-to-edge spacing between elements of 0.26𝜆0 and 0.016𝜆0, respectively; a nearly 50% reduction compared to the conventional 0.5𝜆0 spacing. Despite this close spacing, the achieved isolation levels were over 19 dB at resonating frequency of 4.8 GHz, a 15 dB gain over the conventional case. This is especially significant considering the compact single-layered design. Additionally, this design does not utilize shorting vias. To validate the simulated results, a two-port antenna incorporating the proposed design was fabricated and tested for its impedance and radiation characteristics. The measured results agreed well with those of the simulated ones.