ABSTRACT This study proposes a compact Vivaldi‐based phased array antenna (PAA) for the non‐destructive detection of internal defects in tree trunks at varying heights. The proposed PAA comprises four specially designed Vivaldi elements operating from 0.6 to 1.4 GHz, enabling deep penetration into tree trunks while maintaining high resolution. To achieve a compact design with a narrow inter‐element spacing of 0.4 and reduced mutual coupling, the outermost elements are slightly inclined, where is the wavelength at the center frequency. Additionally, a slotted metal reflector is placed behind the elements to improve impedance matching at low frequencies. The array is excited using Wilkinson power dividers to ensure stable amplitude and phase distribution. The measurement results show that the proposed PAA can steer its beam from −30° to 30° while maintaining an active voltage standing wave ratio (VSWR) below 2.5. It achieves a gain of 12–13 dBi while steering the beam. These characteristics, including a wide bandwidth, high gain, compact size, and beam‐steering capability, make the proposed PAA highly suitable for scanning tree trunks and detecting defects at different heights. The proposed PAA was further validated on a real tree trunk, confirming its effectiveness for defect detection in practical scenarios.
Cheng et al. (2026) studied this question.