Input Impedance of Nonperiodic Sources Exciting 1-D Periodic Shielded Microstrip Structures

The input impedance of nonperiodic sources that excite a periodically loaded shielded microstrip line is studied numerically with a rigorous method-of-moments approach based on the array scanning method. Both a delta-gap voltage and an impressed vertical current sheet are considered to be idealized sources exhibiting different symmetry properties. Their input impedances, calculated according to either a power-voltage or a power-current definition, are compared with the Bloch impedance of the dominant mode excited along the structure in a wide frequency range encompassing different propagation regimes of the dominant and of the first higher order mode. Numerical results, validated also through independent full-wave codes, provide physical insight and quantitative information on the mode excitation efficiency and input-impedance features of finite sources in a periodic microstrip environment.