An accurate analytical representation of the continuous spectrum excited on multilayer stripline structures in spectral-gap regions

In this work, an approximate asymptotic closed-form representation is derived for the continuous-spectrum current excited by a delta-gap source in a multilayer stripline. The proposed representation is accurate also very close to the source and is valid inside the low-frequency spectral-gap region of the dominant leaky mode supported by this structure, where the main contribution to the continuous-spectrum current is given by the residual-wave current. Numerical results which confirm the accuracy and numerical efficiency of the proposed approach are provided at different frequencies.