Efficient Impedance Response Modeling of Broadband Antenna Elements in Large Sparse-Regular Phased Arrays

A computationally efficient method is presented to model the scan-dependent active reflection coefficient ( $\Gamma _{act}$ ) of broadband antenna elements in sparse-regular phased arrays. The method, designed to accurately model the rapid response variations caused by the incursion of grating lobes into the visible region, constructs an adaptively sampled global surrogate model of the desired response with a presampling technique based on array factor theory. The experimental results for narrowband dipole antenna elements show that the proposed method yields a lower maximum model error than the standard space-filling techniques or pure adaptive sampling, with little or no compromise in the mean model error; similar results are attained for a broadband example with a tilted bowtie antenna element. It is also shown that for optimization procedures where the maximum $|\Gamma _{act}|$ is sought across scan angle and frequency, the proposed method consistently provides more accurate and efficient estimates than the other considered techniques.