This paper reports an electric field approximation model of the Coplanar Vivaldi antenna on the E-plane. The study is conducted in three stages, i.e., (i) evaluating the impact of various geometrical parameters to the Vivaldi's element performance at different frequencies, (ii) modeling the electric field patterns, and (iii) applying the model to evaluate the linear total array pattern. The examination of the Coplanar Vivaldi element with fractional bandwidth of 133% in the 2-10 GHz band shows the individual roles of the antenna width, the tapered slot length, the opening width and the slope of the tapered slot in determining the VSWR, resistance, reactance and E-Field performance. The Vivaldi element should be designed with element width more than 0.5λ and less than λ to reach better performance of VSWR and E-field. The longer the tapered slot (>λ) with the high value of opening rate of tapered slot, the smaller the E-field. The E-field increases with increasing opening width of the tapered slot. Knowledge of the influence of each geometry parameter is then used as a reference in developing the E-field pattern approximation model of the Vivaldi element. The derivation of the Vivaldi approximation model is started from the pattern of a horn antenna because both antennas share a similar feature, i.e., the enclosure of the E-field propagation within a tapered slot resulting in a directional radiation pattern. The result of Coplanar Vivaldi modeling is verified against the results of electromagnetic computational simulation and measurement. The Vivaldi element model is useful for total array pattern analysis to save computation time and to provide flexibility in the evaluation of array design.
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