This work explores the application of microwave-based nondestructive testing (NDT) for detecting defects in fiber-wound hydrogen storage tanks. These tanks are valued for their lightweight, pressure-resistant properties, and high strength-to-weight ratios, making them suitable for broad applications. However, their complex manufacturing process necessitates reliable NDT methods to ensure quality and safety. Conventional NDT techniques like radiographic testing, computed tomography (CT) scanning, ultrasonic testing, and acoustic emission testing each have limitations, such as low precision and high costs. This study introduces a novel approach using a custom-designed Fermi antenna coupled with a vector network analyzer operating in the 24–25 GHz frequency range. The Fermi antenna, with its narrow beam and wide bandwidth, enhances detection sensitivity and resolution. The study tested type IV carbon fiber-wound hydrogen storage tanks with induced defects (sand inclusion, hole, and crack). Results showed significant changes in the reflection coefficient (S11) at defect sites, indicating high sensitivity and accuracy in detecting these defects. This microwave-based method proves to be a promising alternative to conventional NDT techniques, offering effective detection of both volumetric and surface defects without the need for a coupling agent.