Flexible and fast estimation method of far-field patterns for digital-coding metasurfaces

We propose a flexible and fast estimation method to calculate the far-field patterns of digital-coding metasurfaces (DCMs) by performing chirp Z-transform (CZT), called the DCM-CZT method. Because of the expression form of convolution, CZT can be accelerated by fast Fourier transform. Compared with the traditional discrete Fourier transform (DFT) method, the DCM-CZT method can accurately estimate the far-field patterns with arbitrary element periods. More importantly, the DCM-CZT method can calculate partial far-field patterns for some specific orientations, instead of the global far-field patterns like DFT does. We show that the DCM-CZT method can efficiently improve the partial space-resolution to avoid the calculation error caused by the fence effect under acceptable computing time. We present six representative examples to demonstrate the capabilities of the proposed method. Results show that the far-field patterns calculated by the DCM-CZT method have good agreements with full-wave simulations and experimental measurements. However, the results of main-lobes calculated by the DFT method have obvious deviations when the element period is about 0.2 wavelengths. We believe that the DCM-CZT method has potential applications in wireless communications and radar detections.