Application of Characteristic Mode Theory in HF Band Aircraft-Integrated Multiantenna System Designs

The large wavelength at high-frequency (HF) band imposes critical challenges in platform conformal HF antenna designs, especially when multiple HF antennas are required in multifunction aircraft electronic systems. This paper presents an approach for the design of the aircraft-integrated multiantenna system based on the theory of characteristic modes (CMs). By investigating the CMs of the aircraft body in the entire HF band, three types of radiation patterns are synthesized at three frequency bands centered at 8, 18, and 28 MHz, respectively. The synthesis is achieved through the linear weighting combinations of the first few dominant CMs, and a multiobjective evolutionary algorithm is implemented to seek the complex weighting coefficients in each band. Following the theoretically synthesized radiating currents, three pairs of exciters are then designed and flush mounted on optimal locations over the aircraft. Furthermore, properly designed LC matching networks are introduced in each exciter to get good impedance matching in each band. Because of the large physical size of the aircraft, scaled model of the proposed aircraft-integrated multiantenna system was fabricated and experimentally verified. Measurement results are in good agreement with simulated results and demonstrate the effectiveness of the proposed approach in the designs of HF aircraft-integrated multiantenna systems.