Crosstalk and EMI in mixed-signal / microwave multi-layer pc boards

Transmission line crosstalk and electromagnetic interference (EMI) must be carefully controlled in microwave and high-speed mixed-signal systems. Experimental results are reported from DC to 30 GHz for PC board interconnects in a low-cost 4-layer FR4 process. It is shown that stripline to coplanar waveguide (CPW) isolation can reach 100 dB at L-band and 60 dB through Ku band for 3.3cm traces separated by as little as 150mils, provided careful attention is paid to signal launch and ground-via stitching. Various line-types are compared and changes in isolation with trace separation are investigated to provide guidance useful in the early stages of PC board design. Preliminary investigations of EMI are also reported to assess the degree to which additional shielding can be avoided in systems employing multi-layer PC board technologies.