Nisaa Yasmin bt Nor Izuddin, et al. “A Comparative Study of Four Defected Ground Structures for Ultra-Wideband Planar Antenna Application at 3.5 GHz”. ELEKTRIKA- Journal of Electrical Engineering, vol. 24, no. 2, Aug. 2025, pp. 98-103, doi:10.11113/elektrika.v24n2.556.