Estimating the radiated emissions and received waveforms from coupled microstrip lines with unipolar signaling

This paper addresses estimating the far-field radiated emissions performance, at 10m, from three coupled microstrip lines, in which the coupling length is 5cm, and in which the risetimes of the propagating signals are 2ns. The load for each microstrip line is a 0.01pF capacitive load, and the signaling on the three lines is unipolar, with the propagating voltages switching between 0V and 3V. The nominal or isolated impedances, Z_o, of the three lines are set to about 67Ω. The edge-to-edge distances for the coupled lines are varied between 4mils and 20mils, while the width of the conductors is also varied between 8mils and 4mils. In addition, the thickness of the dielectric is varied between 8mils and 4mils. The estimated radiated emissions results that are presented in this paper are restricted to an upper frequency limit of 6GHz. For the various scenarios presented in this paper, it is shown that the maximum far-field radiated emissions levels are about 35dBμV/m, and occur at about 5.0GHz. In addition to estimating the far-field radiated emissions from the three coupled microstrip lines, the time-domain effects of the coupled lines are shown by highlighting the received eye patterns.