Analysis of the Field-Line Coupling of the Transmission Line Above an Orthogonal Ground Plane Through Electromagnetic Reciprocity Theorem

The far-field radiation of the transmission line (TL) operating as a transmitter and the induced voltage and current at the terminals of the TL regarded as a receiver can be correlated via the electromagnetic (EM) reciprocity theorem. For a TL above an orthogonal ground plane, the far-field radiation formulas of the TL in the testing state (where the TL is deemed as a transmitter) and the electric field expressions around the TL in the receiving state (where the TL is considered as a receiver) are derived in this study. Besides, an expression for the induced voltage at the terminal of the TL is obtained for each state and the equivalence between the two expressions is proved through the EM reciprocity theorem and method of image. A voltage source is selected as the excitation in the testing state and an effective selection method is proposed. Moreover, numerical examples are provided to verify the correctness of analyzing the field line coupling problem of the TL above an orthogonal ground plane through the EM reciprocity theorem and to certify the effectiveness of the novel expression of the excitation voltage source.