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.
Baccarelli, P., Galli, A. (2003). An accurate analytical representation of the continuous spectrum excited on multilayer stripline structures in spectral-gap regions. In IEEE MTT-S International Microwave Symposium (pp.809-812). NEW YORK : IEEE [10.1109/mwsym.2003.1212493].