Characteristic Excitation Taper for Ultrawideband Tightly Coupled Antenna Arrays

We propose a novel technique to calculate a quasi- optimal aperture excitation for finite size, ultrawideband arrays. The approach is based on using the characteristic modes of the array´s mutual impedance matrix. Unlike standard excitation tapers, primarily used for beam shaping, the proposed characteristic mode taper provides for wideband matching of all array elements, including those at the edges of the finite array. As such, it maximizes aperture efficiency and is particularly attractive for finite size, tightly coupled antenna arrays. Our method solely relies on the N × N mutual impedance matrix of the array which is precomputed (or measured). We demonstrate this novel excitation method for an 8 × 8 array of tightly coupled dipole elements. When compared to uniform excitation, the characteristic mode excitation achieves very low VSWRs for all elements over a large bandwidth. Improvements in realized gain are also demonstrated. Due to its simplicity, this new method can be incorporated into a design process to optimize element and array geometries, leading to further performance improvements.