Cylindrical near-field measurement error models for NASA scatterometer fan-beam array antenna

The NASA scatterometer antenna is dual-pol fan beam, made up of two separate slotted waveguide-array-fed horns (one for v-pol and one for h-pol polarization), to be used in measuring the backscattered power of the sea surface. Then, the wind velocity can be extracted from these measurements. The antennas are to be calibrated to within 0.25 dB over the main beam with antenna pointing accuracy of 0.05 degrees . In order to achieve this high accuracy, a cylindrical near-field technique by which a probe samples the near field on an imaginary cylindrical surface is used in conjunction with an error analysis to reconstruct the far-field radiation patterns. An efficient and fast algorithm is developed to evaluate the cylindrical wave coefficients with 1D FFT (fast Fourier transform) and numerical integration, from which antenna patterns and directivity are obtained. The results are compared with the 2D FFT.<>