The analog control circuit of existing RF interference cancellation system is too complex, and the convergence speed cannot be flexibly tuned. This article proposes a digital-to-analog hybrid RF interference cancellation system based on multitap structure (MDARFICS), where the analog control circuit is digitized, so it can be highly integrated and easily tuned. The analytical theory model of the MDARFICS is established for the first time, which can suppress interference with a large power dynamic range and bandwidth. The factors that affect the cancellation performance, i.e., stability, wideband interference cancellation ratio (WICR), and convergence speed, are studied. The stability criterion is obtained, that is, loop gain, sample rate, and tap delay affect the stability cooperatively, and it is found that the sample rate must be selected according to tap delay. Studies show the MDARFICS can effectively suppress wideband interference. The larger the number of taps and control step size, the smaller the bandwidth and delay difference between the tap and interference channel, and the larger the WICR. The convergence speed accelerates as the control step size and filter coefficient increase. Simulations and experiments verify the theoretical analysis. The research results are of much value to the implementation of the MDARFICS.

A novel chaotic adaptive butterfly mating optimization (CABMO) is proposed to be used in synthesizing the beam pattern. In order to improve the optimization accuracy and avoid trapping in the local optimum, the homogeneous chaotic system and adaptive movement mechanism are combined into the proposed algorithm, where the initialization and redistribution of butterflies are chaotically dispersed with an adaptive movement closely related to the ultraviolet changes. After validating the performance of CABMO through several benchmark functions with different dimensions, the improved algorithm outperforms when compared to other state-of-the-art nature-inspired metaheuristic algorithms. The proposed algorithm is then used to understand any linear array problems in terms of the sidelobe reduction. Finally, a CABMO strategy is utilized to optimize the mutual coupling model of the closely spaced VLF umbrella arrays. Results show that the optimized structure has comfortably outperformed the original structure. Full scanning of wave positions is realized from 15 to 30 kHz. The synthesis patterns are close to the theoretical optimum. The optimized results of the radiation performance and synthesized patterns demonstrate that the pattern synthesis and antenna structure optimization based on the CABMO algorithm provides a novel idea for antenna array optimization.

Under the background of spatially correlated color noise, the incidence angle of a jamming signal in a high-speed moving platform rapidly changes, which leads to the degradation of the anti-interference performance and the waveform distortion of the adaptive beamformer. In this paper, a projection-constrained null broadening beamforming algorithm based on the Toeplitz matrix structure is proposed. The algorithm first extracts the subspace of the covariance matrix of the steering vector of the pre-determined extended angle interval and constructs the constraint matrix and the projection transformation matrix. The received signal covariance matrix with a Toeplitz structure is then constructed using the correlation number between each array element and the pre-set reference array element. Finally, the constructed covariance matrix is transformed through projection, and the weight of each array element is constrained by the constraint matrix. The theoretical optimal solution of adaptive wide null beamforming in spatially correlated color noise is obtained. The simulation results show that, compared with the existing robust adaptive beamforming algorithms, the proposed algorithm can efficiently improve the distortion of adaptive anti-jamming beams, and can achieve null broadening in the jamming direction under the condition of spatially correlated color noise, which improves the output signal to the interference-plus-noise ratio (SINR) of the adaptive beamformer.

The mutual coupling between very low frequency (VLF) antenna elements is an important factor affecting the radiation performance of umbrella antenna arrays. This study evaluates the factors influencing the mutual coupling between the elements of an umbrella antenna array. We develop a mutual coupling analysis method for calculating the input impedances of a VLF antenna based on the impedance effect of mutual coupling. The radiation resistance of the VLF umbrella antenna can be obtained using numeric integral from Method of Moments (MoM) solution. Using the FEKO simulation software, a model of a trideco-tower umbrella antenna array is established. The electrical parameters of the VLF umbrella antenna array on inhomogeneous ground are calculated for both single and dual feeding modes. The impedance characteristics of the umbrella antenna arrays are also simulated for different array inter-element spacings on homogeneous ground. Representative numerical results are reported and discussed to assess the mutual coupling effect of the proposed method in comparison with full-wave simulations.