Minimizing radiated emissions from PCBs using grid-like ground plane impedance matching techniques

The transmission line properties of signal traces in an electronic circuit printed circuit board change considerably when multiple circuits or components are connected to a given signal trace. In low frequency circuits operating below 300 MHz, signal traces having characteristic impedance higher than the terminating impedance are being used to compensate the loading effects of circuits or components connected to the traces. In microwave and other high frequency circuits, tapered line and quarter wave transformer techniques may be used to control the signal trace impedance. This paper describes a new technique of controlling signal trace characteristic impedance by altering the properties of a grid-like ground plane. Radiated emissions measured on signal traces with grid compensated ground plane and uncompensated solid ground plane are presented and the results discussed.