Aircraft-Integrated VHF Band Antenna Array Designs Using Characteristic Modes

Because of the large wavelength in very high-frequency (VHF) band, conventional design concepts for flush-mounted VHF band antenna arrays over aircraft platforms meet many challenges. This article presents an approach for the design of VHF aircraft-integrated antenna arrays with switchable beams by using the characteristic modes (CMs) of the aircraft platform. The CMs of the aircraft platform provide the modal significances, modal currents, and modal radiation fields of each mode. An in-depth investigation over the useful CMs information is performed to prove the feasibility of design VHF band antenna array using the CMs of the platform. Switchable radiation patterns with horizontal polarization are then synthesized from these CMs. The switchable beams and polarization constraint make it more challenging than CM-based fixed power pattern synthesis. The polarized switchable beam synthesis is carried out with a multiobjective evolutionary algorithm. A trade-off among the synthesized current distributions for different beam steering angles is made to determine the optimal current excitation locations for antenna array development. Meanwhile, a novel bandwidth enhanced triple-couple-line coupling element is proposed to allow aircraft platform flush-mounted designs. A scaled model of the proposed aircraft-integrated antenna array system was fabricated to experimentally verify the effectiveness of the proposed approach.