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36 DESIGN007 MAGAZINE I JUNE 2022 board be done by the PCB designer so that all the potential effects can be taken into account. You can ensure this by stipulating in the PCB specification that no copper features be added or modified without permission. PCB designers also can use these copper pours as more than just thieving patterns. By creating the copper thieving as part of the ground net, and configuring it as a solid plane, you can assist with providing a well-defined return current path. e caveat, however, is that this must be done in conjunction with the overall signal performance requirements of the design. Any additional planes must be positioned and spaced correctly, so they do not have a negative effect on the signal integ- rity of the board. e processor board (Figure 1), for instance, has what I call random copper GND pours on the outer layers. Many of these pours are totally unnecessary. Applying this concept in RF circuits, grounded metal is sometimes used as fill between the signal traces on outer layers. e grounded areas should be connected to the ground plane with vias (stitched) at less than one-quarter wavelength (Figure 2). is tech- nique changes the transmission lines from microstrip to grounded coplanar waveguide. e characteristic and differential impedance of the transmission line is lowered by using this technique because the copper pours increase the capacitance between the signal trace and ground. e coplanar waveguide (CPW) is the trans- mission medium of choice above 20GHz. CPW combines the EM fields in a more localized manner than does microstrip, thus reducing spurious coupling, radiation, and dispersion. Also, the CPW provides a precisely defined signal return path. Internal stripline configuration has an advan- tage over outer layer microstrip. Microstrip can radiate. However, with the fields confined between ground planes, stripline does not. Signals can be shielded by placing the traces on internal layers between copper planes. ese Figure 2: Dual strip coplanar waveguide grounded. (Source: iCD CPW Planner)