Spatial Power Combining of VLF Umbrella Antenna Arrays With Multi-Delay Lines

Abstract

Abstract-The output power of antennas is an important factor affecting the radiation performance of umbrella antenna arrays. Considering the power limit of very-low-frequency (VLF) umbrella arrays and the uncontrollable directivity, we propose a novel method for the spatial power-combining (SPC) of VLF umbrella arrays. Using multiple groups of feeders, the problem of phase shifting of the signals can be solved for VLF arrays. In the high frequency portion of the VLF range (25-30 kHz), this novel method can improve the efficiency of VLF arrays by 26% in the special directivity. A model of a trideco-tower umbrella antenna array is established in the FEKO simulation software. The simulation results show that compared with the in-phase feeding, the VLF transmitting antenna array forms the main beam in all directions. The array gain of the umbrella phased array in the 0 • (180 • ) beam position is larger than 1.1 dB. The front-to-back ratio of the arrays is 3.7 dB. Compared with the in-phase feed mode, the directivity of the phased array enhances and the efficiency increases markedly. The simulation results demonstrate the effectiveness of the proposed method.

Chaotic Adaptive Butterfly Mating Optimization and Its Applications in Synthesis and Structure Optimization of Antenna Arrays

“…As the optimization problems of antenna arrays become more and more complex, many nonlinear problems are ascribed to optimization models of discrete and continuous variables, such as the pattern synthesis of CCAA in reference [23]. To illustrate the practicality of the CABMO algorithm in designing antenna arrays in the real world, the proposed algorithm will be applied to optimize the structure of the VLF umbrella antenna array introduced in reference [35] by suppressing the mutual coupling. The objective is to optimize the structure of the closely spaced arrays to intensify the array gains with a mutual coupling reduction.…”

“…The input resistance of each array reflects the mutual coupling effect of the tightly coupled VLF vertical antennas with the interspacing d 12 ≈ 1/8λ. Considering the antenna arrays as a two-port network, the input resistance of each array can be obtained as follows [35]: where R 11 and R 22 is, respectively, the mutual impedance of array 1 and array 2, ψ = −kd 12 cos δ denotes the difference in the input current phase, m = I 2 /I 1 denotes the ratio of the current amplitude, h e1 and h e2 are the effective height of array 1 and array 2, respectively, and k denotes the wave number. Based on the transmission line theory, the equivalent height of the vertical antenna without the top load can be given as…”