Shahid Beheshti University International Journal of Research and Technology in Electrical Industry 2821-0190 4 2 2025 02 20 A Compact Ultra-Wideband Vivaldi Antenna with Parasitic Rings for mmWave 5G Applications 106783 10.48308/ijrtei.2026.241594.1102 EN Hasan Falih Hamdan Department of Electrical Engineering, Razi University, Kermanshah, Iran Mohammad Sajjad Bayati Department of Electrical Engineering, Razi University, Kermanshah, Iran Journal Article 2025 09 18 This paper introduces a compact, ultra-wideband Vivaldi antenna with parasitic elements, designed for 5G millimeter-wave (mmWave) applications. The antenna operates across a wide frequency range from 28.57 GHz to 80 GHz, covering essential high-frequency bands for current and future communication systems. The design features innovative elements such as curved circular flares and parasitic components, which boost both gain and directivity, thereby enhancing overall performance. The antenna is implemented on a Rogers RT5880 substrate with compact overall dimensions of 23 × 20 mm². Full-wave simulations using CST software show that the antenna achieves a peak gain of 10.5 dBi throughout the operating bandwidth and a radiation efficiency of up to 96%. To ensure impedance matching and reduce surface wave effects, a stepped-feedline is incorporated, promoting stable performance across the entire frequency range. The antenna exhibits desirable radiation characteristics, including low sidelobe levels and highly directional radiation patterns. With its compact size, high gain, and efficient operation, the antenna is well-suited for mmWave 5G communication systems, radar applications, and high-speed wireless networks.