The Baum-Liu-Tesche (BLT) equation is an important calculation method for field-transmission cable coupling which is widely used in the domain of electromagnetic coupling quantitative analysis. The classical BLT equation ignores the distortion effects of the cable's insulation layer on the incident field, leading to large errors in coupling calculation under specific incident and polarization directions.

In response to this issue, a frequency domain modified BLT method is introduced into the time domain to study the calculation method of the load voltage and current response in a single cable excited by a high altitude electromagnetic pulse (HEMP). The correctness of the model is then verified through a comparison with a full wave algorithm (finite integer technique). On this foundation, the characteristics of the cable structure (height, diameter, insulation parameters, etc.) and incident field (incident direction, polarization direction, etc.) applicable to the modified method are analyzed.

Under HEMP excitation, based on the full wave simulation results, the prediction error of the classical BLT model can be more than doubled, while the accuracy of the BLT model with the insulation layer coefficient is significantly improved.

This study verifies the accuracy of the modified BLT model in analyzing the field-transmission cable coupling problem in the time domain, and puts forward the applicability criterion of the modified BLT model which helps to clarify the coupling mechanism between HEMP and actual complex cables.