Determination of the Equivalence of Magnetic and Electric Mode Radiation Efficiencies in Advanced Metamaterial Antennas Through Characteristic Modes Theory

This paper presents an innovative approach based on Characteristic Mode Theory (CMT) to improve radiation performance and compactness in metamaterial antennas by determining the equivalence between magnetic and electric modes for advanced applications. First, a comprehensive analytical study without excitation is conducted to evaluate the performance characteristics of Complementary Split Ring Resonator (CSRR) in terms of resonant frequencies and the radiation characteristics of electric resonant modes. Utilizing Coupled Mode Theory, we first identify the resonant modes that establish the equivalence between CSRR and Split Ring Resonator (SRR) structures. This approach simplifies the analysis by avoiding the complex task of directly determining the excitation modes of CSRR structures, which in turn significantly reduces the overall complexity. In fact, the equivalent SRR antenna, rather than its complementary counterpart, is excited with a coaxial probe feed in the dominant directional electric resonant mode to achieve exceptional radiation efficiency. The results demonstrate a strong correlation between the predictions derived from CMT and the S-parameter performance. Additionally, the proposed approach achieves a substantial 30% size reduction and improved radiation efficiency for the SRR antenna compared to conventional CSRR designs. The techniques outlined in this paper offer further potential for both size reduction and enhanced radiation performance in metamaterial-based antennas, setting the stage for more efficient and compact designs in future applications.