The notch antenna is constructed by slotting one side of rectangular patch placed on a substrate over the ground plane. The analysis of notch antenna is crucial owing to irregular shape. In this study, a novel resonant length expression in calculating the operating frequency is proposed for analyzing notch antennas. The expression regarding the resonant length of the antenna reflecting the impact of the slot is derived with optimization using differential evolution ( DE) algorithm. Data of 96 notch antennas including seven parameters of dimension and dielectric constant is acquired with simulations. A resonant length expression enclosing antenna parameters accompanying with optimization variables is constituted in conformity with simulation data. The variables are then optimally determined by fitting the calculated operating frequency results to the simulated results by DE algorithm. The proposed calculation is corroborated through verifying with those of simulated and measured data and validating with a prototyped notch antenna. The results demonstrate that analysis of the notch antennas concerning the operating frequency can be simply calculated by using the proposed formulation without handling sophisticated mathematics and performing simulations or measurement. (C) 2017 Wiley Periodicals, Inc.