3–20-GHz Quad-Ridged Horn Antennas With a Partially Open Feeding Structure for Spherical Near-Field Measurement Systems

In this study, we present the design and experimental validation of a broadband quad-ridged horn antenna (QRHA) operating in the range of 3–20 GHz. A partially open feeding structure is proposed to improve the VSWR performance, particularly in the low-frequency range of 3–4 GHz. The proposed QRHA achieves a bandwidth ratio of 6.67:1, thus demonstrating its broadband characteristics. The key difference from conventional QRHAs is the implementation of an openfeeding structure in which one side of the ridge feeding section is open. Eleven QRHAs were fabricated and measured. The gain error was within 1.7 dB. The VSWR values exhibited similar trends among the antennas, remaining below 2.5. These results confirm the feasibility and reliability of the proposed design for use in spherical near-field measurement systems.