Time domain measurement of mode characteristics in coupled microstrip lines

The even and odd mode impedances of coupled microstrip lines on a printed circuit board were calculated by a numerical method and measured by time-domain reflectometry (TDR). The capacitance matrix of the coupled lines was calculated by the method of moments. The mode impedances were obtained by utilizing a similar transformation. Measured results were found to be in good agreement with calculated data. The electromagnetic radiation characteristics of coupled lines were also observed in the time domain using a transverse electromagnetic (TEM) cell. The radiated waveform of the even mode was found to be different from that of the odd mode. The timing relationship was clearly demonstrated by the time-domain results, which provide useful information on the transient radiation characteristics of the coupled lines