Review on Bandwidth Enhancement Techniques in Ultra-Wideband (UWB) Planar Antennas

Ultra-wideband (UWB) antennas have grown into fundamental constituents in advanced wireless applications owing to their ability to support significantly wide band frequencies demanded to achieve accelerated communication, radar, sensing, and imaging applications. However, achieving a broad and stable characteristic impedance bandwidth while keeping small-sized, tolerable gain, and stable radiation characteristics persists a considerable design challenge. To handle these challenges, the researcher has been centered on bandwidth enhancement techniques. This review paper presents an extensive survey of bandwidth improvement techniques utilized in UWB antenna designs published between 2018 and 2025. The reviewed techniques are methodically categorized into geometry-based techniques, ground-plane modification, optimized feeding methods, and the integration of electromagnetic configurations such as defected ground structures (DGS), frequency-selective surfaces (FSS), metamaterials, and fractal geometries. In addition, hybrid and optimization-assisted design techniques are explored due to their enhanced significance in achieving high-performance wideband. A comparative analysis of representative implementations is provided to demonstrate the performance, advantages, and trade-offs related to each technique. Finally, essential challenges and future research directions are determined to support the advancement of optimized UWB antennas for next-generation wireless applications.