GIMA antenna design for ground penetrating radar in concrete structures NDE applications

A novel antenna, know as a Good Impedance Matching Antenna (GIMA), has been developed for use in Ground Penetrating Radar (GPR) NDE of concrete structures. The requirements of a useful GPR antenna are that it provides sufficient penetrating depth in the concrete with sufficient resolution to determine the location and magnitude of the defects, such as deterioration and delaminations. The GIMA antenna is designed to have a self-defined aperture that minimizes impedance mismatching at the aperture. This unique feature allows the antenna to be used in various frequency bands. The tested frequency range is from 500 MHz to 16 GHz. The antenna provided a high penetrating depth (more than 330 mm) and the sufficient resolution of the image that can recognize cracks up to 1 mm thick, with a radiation coefficient of about 99 %. This paper will introduce the theory behind the design, as well as present experimental results. The characteristic parameters of the antenna, such as impedance matching status represented by SWR and Smith chart, as well as the power radiated using return loss. In addition, the aperture reflection is determined via the time-domain air shot reflections. Also presented are the results of the resolution test and penetrating test using concrete slabs.