Near-Field Bessel-Gauss Antenna for Nonmetal Internal Defects Detection

A radial line slot array (RLSA) is proposed for Bessel-Gauss beam generation with a narrow main beamwidth and low sidelobe characteristics for nonmetallic internal defects detection. Owing to the radial attenuation factor of Gaussian function, the sidelobe level of Bessel-Gauss beam can be suppressed. By accurately adjusting the slot position and size of the RLSA, the optimum aperture field distribution can be synthesized to generate the near-field Bessel-Gauss beam based on the projection method. The simulated/measured results have shown that the maximum nondiffraction distance of 70 mm/70 mm and the null-null beam width of the Bessel-Gauss main beam of 30 mm/30 mm are achieved at the operating frequency of 12.5 GHz/12.5 GHz, while low sidelobe levels (<−18.14 dB/−18.07 dB) are generated. Compared to other antennas for microwave nondestructive testing, the proposed RLSA has merits of low sidelobes, large E-field depth and narrow main beam; therefore, it can improve the detection performance in terms of sensitivity and depth, which can be widely, used for nonmetal internal defects detection applications.