Exploring Hannan Limitation for 3D Antenna Array

TL;DR

This work extends Hannan Limitation from infinite 2D planar arrays to finite-size 2D arrays and studies a two-layer 3D antenna structure to enhance spatial coverage without enlarging the planar aperture. It develops a DTFT/DFT-inspired sampling framework to bound the radiation efficiency of finite 2D arrays via active reflection coefficients, and derives the fundamental efficiency and gain limits for 3D arrays, including both infinite and finite cases. The paper also analyzes the 3D feasible region under a fixed energy attenuation threshold, deriving annular planar regions and providing numerical validation that demonstrates gains in spatial coverage and the existence of an optimal interlayer spacing (≈0.75λ) for two-layer 3D arrays. These results offer practical guidance for designing 3D antenna arrays that surpass planar gain limits while managing mutual coupling and energy attenuation in real-world deployments.

Abstract

Hannan Limitation successfully links the directivity characteristics of 2D arrays with the aperture gain limit, providing the radiation efficiency upper limit for large 2D planar antenna arrays. This demonstrates the inevitable radiation efficiency degradation caused by mutual coupling effects between array elements. However, this limitation is derived based on the assumption of infinitely large 2D arrays, which means that it is not an accurate law for small-size arrays. In this paper, we extend this theory and propose an estimation formula for the radiation efficiency upper limit of finite-sized 2D arrays. Furthermore, we analyze a 3D array structure consisting of two parallel 2D arrays. Specifically, we provide evaluation formulas for the mutual coupling strengths for both infinite and finite size arrays and derive the fundamental efficiency limit of 3D arrays. Moreover, based on the established gain limit of antenna arrays with fixed aperture sizes, we derive the achievable gain limit of finite size 3D arrays. Besides the performance analyses, we also investigate the spatial radiation characteristics of the considered 3D array structure, offering a feasible region for 2D phase settings under a given energy attenuation threshold. Through simulations, we demonstrate the effectiveness of our proposed theories and gain advantages of 3D arrays for better spatial coverage under various scenarios.

Figures (16)

• Figure 1: Effect of mutual coupling on array radiation and Determination of mutual coupling.
• Figure 2: 2D array spatial radiation characteristics.
• Figure 3: Sampling points for a finite dimension 2D array.
• Figure 4: Geometry of the considered two layer 3D array.
• Figure 5: Diagram of the planar feasible region and the beamforming direction relationship for 3D arrays.

Theorems & Definitions (11)

• Theorem 1
• Remark 1
• Theorem 2
• Remark 2
• Remark 3
• Remark 4
• Corollary 1
• Remark 5
• Remark 6
• Remark 7