Abstract
This article presents a simple and effective decoupling approach based on the common mode (CM) and differential mode (DM) analysis to solve decoupling problem between two symmetrical antenna elements. Especially, the concept of the self-resonance frequencies of CM and DM is utilized in antenna decoupling analysis. It is found that when the self-resonance frequencies of CM and DM are the same, strong mutual coupling between two symmetrically and closely placed two-port antennas can be completely eliminated. The difference between self-resonance frequency and resonance frequency is discussed; and the method of obtaining the self-resonance frequencies of CM and DM is given. Since the proposed antenna decoupling judgment condition is straightforward and simple, it can effectively deal with any kind of closely placed antenna system with a plane of symmetry; and obtain good decoupling effect simply and easily. The effectiveness, feasibility and advantage of the proposed decoupling condition for the CM and DM analysis are demonstrated through several symmetrical two-port antenna examples. The decoupling approach proposed in this article can undoubtedly make the common mode and differential mode analysis for solving antenna decoupling problems more effective and practical.
Highlights
How to effectively reduce the mutual coupling in antenna array or multiple-input and multiple-output (MIMO) antenna system has always been a difficult problem, especially when the antennas are placed very close to each other
The concept of mode-cancellation analysis based on common mode (CM) and differential mode (DM) was proposed in [25,26,27], which perfectly reveals that the decoupling mechanism of two symmetrically and closely placed antennas can be elaborated by superimposing the current distributions of CM and DM
The approach is based on the coupling theory of the coupled resonant filter, and the extreme case of the coupled resonant filter is successfully applied to the antenna decoupling problem by using the CM and DM analysis
Summary
How to effectively reduce the mutual coupling in antenna array or multiple-input and multiple-output (MIMO) antenna system has always been a difficult problem, especially when the antennas are placed very close to each other. When the electric and magnetic walls are applied separately to the symmetrical plane S-S, the equivalent transformed circuit in Fig. 2 results in the following self-resonance frequencies [28, 29]: Due to the above equivalences, when the mixed coupling coefficient is equal or close to zero, the coupling mechanism in the coupled resonator system can be used to decouple the symmetrically and closely placed two-port antenna system.
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