Radiation Pattern Measurements of Small Antennas Using Spherical Near-field Measurement Technique

This paper presents small-antenna radiation pattern measurements using the spherical near-field measurement technique. A small radio frequency identification (RFID) tag antenna is employed in this study, where its size of 52.5$\times$ 39 mm2 at the operating frequency of 922.5 MHz. The minimum measurement range for the near-field measurement is studied in this paper. The spherical wave expansion is employed as a near-field to far-field (NF-FF) transformation algorithm, where the numerical integration is employed to evaluate associated double integration. The far-field radiation pattern of the antenna under test (AUT) is simulated by three-dimensional (3D) electromagnetic (EM) software. It is found that the simulated radiation patterns and the radiation patterns from numerical NF-FF transformation are in good agreement. Therefore, the near-field measurement can be performed inside a small and low-cost anechoic chamber room.