A Self-Decoupled Microstrip Antenna via Inhomogeneous Substrate Manipulation

In this paper, we introduce a new self‑decoupling technique that leverages an inhomogeneous dielectric substrate to significantly suppress the mutual coupling between closely spaced microstrip antennas. Unlike traditional decoupling strategies that rely on modifications of the patch or ground plane, the proposed method achieves self‑decoupling by exploring the inhomogeneous substrate manipulation, where the spatial distribution of the substrate’s permittivities is deliberately arranged, thereby enabling the mutual cancellation of several distinct coupling paths. The underlying mechanism is revealed through analytical derivation, providing a quantitative guideline for desired designs. To validate the concept, two implementation schemes of the inhomogeneous substrate are investigated. The first scheme (Type I) employs a multi‑column dielectric combination, while the second scheme (Type II) utilizes a monolithic substrate perforated with carefully designed patterns. Several examples for the 1 × 2, 1 × 4, and millimeter-wave scenarios are studied, respectively. The results confirm the superior performance of the proposed approach. To the best of our knowledge, this work constitutes the first demonstration of self‑decoupling achieved through substrate permittivity manipulation, and it showcases the potential of additive manufacturing techniques in the self-decoupling of microstrip antennas.