Fakhte, S. ., and H. . Oraizi. “Derivation of the Resonant Frequency of Rectangular Dielectric Resonator Antenna by the Perturbation Theory”. Applied Computational Electromagnetics Society Journal (ACES), vol. 31, no. 08, Aug. 2021, pp. 894-00, https://journals.riverpublishers.com/index.php/ACES/article/view/9965.