Duality Principle of Characteristic Modes for the Analysis and Design of Aperture Antennas

Characteristic mode analysis (CMA) is a promising method that has been used in antenna design. However, CMA of aperture antennas is cumbersome as the equivalent magnetic current is rarely available in main stream method of moments solvers. Based on the duality principle, an equivalent CMA of aperture antennas is proposed, by which the characteristic values and characteristic magnetic currents are calculated through its complementary form. A rigorous proof for such equivalence is provided. Lumped loads are very useful for the manipulation of certain modes, and in this paper, the relationship between the loads for an aperture and its complementary plate is built. The duality CMA is applied to reduce the mutual coupling between aperture antennas etched on a finite plate. Interdigital capacitors are adopted to suppress the out-of-band mutual coupling while an H-shaped aperture for the reduction of in-band one for narrow slots. Numerical and experimental results show that over 10 dB reduction of mutual coupling is achieved for both examples.