Far-Field Reconstruction of Electrically Large Antennas By Sequential Sampling Method In Cylindrical Measurement Technique

Cylindrical scanning is a well-established indirect measurement technique to characterize a wide range of antennas such as fan-beam antennas and phased array antennas with versatile radiation patterns. Cylindrical scanning technique which is based on nearfield-to-far-field transformation of cylindrical mode coefficients (CMCs), cannot predict the antenna radiation pattern with a very narrow beamwidth in azimuth plane accurately because remarkable error occurs during the calculation of the derivate of higher-order Hankel functions in CMCs extraction. We aim to address this issue and introduce a simple yet rigorous technique namely sequential sampling method (SSM) in conjunction with two-dimensional Fast Fourier technique (۲D-FFT) to efficiently calculate the far-field radiation pattern of a super directive antenna with narrow beamwidth in azimuth plane. Briefly, the SSM offers several sequences of progressive azimuth angles and the corresponding order of Hankel functions in such a way that CMCs fully span a ۳۶۰ degrees of azimuth angles ( ) in a cylindrical coordinate system in each sequence. Afterwards, by putting the far-field obtained by these sequences together, the final radiation pattern will have high angular resolution. For verifications, the far-field radiation pattern of an electrically large slot array antenna including ۸۱×۱۵ slots are calculated at ۸.۷۵ GHz by this technique and the results are compared by far-field pattern obtained from array theory. The results show that the azimuthal pattern can accurately be measured as small as ۰.۱ resolution by SSM.

Keywords:

cylindrical scanning , fast fourier technique , near-field measurement.