Calculation of HF notch antenna terminal impedance for variable geometry aircraft

A mathematical modelling procedure for the prediction of near-field parameters for aircraft HF antennas is applied to the example of a variable geometry airframe. The model is constructed in such a way that it can be reconfigured as a real aircraft of this type might change its geometry and achieves this without the need to alter the discretization. This engenders some uncertainty concerning the quality of the numerical solutions obtained with the model. This is because the moveable surfaces clear the rest of the airframe by electrically very small distances. A further potential difficulty is that the excitation of the model is via a notch antenna; the area of which is of the same order as that of the wire mesh simulating the airframe. No empirically derived information is used in the construction of the model and NEC is used as the solution code. Calculations of the antenna terminal impedance throughout the band are made using this model. An assessment of the credibility of these calculations is attempted by independent theoretical means using a simple equivalent circuit model, and by semi-quantitative physical arguments