Design and Implementation of an Antipodal Vivaldi Antenna SAR-Based Imaging System for Structural Health Monitoring Applications

In synthetic aperture radar (SAR) based microwave imaging systems for non-destructive testing and evaluation (NDT&E) applications, the antenna plays a crucial role in determining the system's ability to detect defects in materials for structural health monitoring. Traditional antennas for SAR-based NDT&E often rely on narrow beam antennas such as an open-ended waveguide (OEW), which is costly and impractical for far-field inspections utilizing reflection mode. This paper proposes the design and implementation of a robust and cost-effective antipodal Vivaldi antenna (AVA) that outperforms OEW in far-field NDT&E inspections. The performance of the AVA is evaluated against OEW through simulation and experimental studies. Defective sample images were reconstructed using the autofocus range-Doppler algorithm (RDA). The results obtained demonstrated that both the OEW and AVA successfully reconstructed the defective images under test. However, at low signal-to-noise ratios (SNR) and far-field inspection, the OEW performance degraded significantly. In contrast, the AVA with its exponentially tapered slot antenna design, provided a more directive and broadband radiation pattern, featuring low side lobe levels and consistent beamwidth over a wide frequency range. Consequently, the AVA achieved a superior SNR of 2 dB, compared to OEW's -5 dB. These findings suggest that the AVA design is a more effective solution for SAR-based structural health monitoring in far-field NDT&E applications.