Method for minimizing radio frequency emissions from plug-in adapter cards in computer systems

An improved adapter card for use in a computer system, said adapter card comprising:

• a first voltage reference plane mounted on said adapter card, said first voltage reference plane connected to a reference voltage in said computer system, said first voltage reference plane having a first length;
• a second voltage reference plane, said second voltage reference plane having a second length;
• and
• an impedance which couples said first voltage reference plane to said second voltage reference plane such that said first length and said second length are added together at a frequency of a noise signal to be suppressed to form an overall length which is greater than one-quarter of the wavelength of said noise signal.

A method of suppressing resonant noise on a circuit card in a computer system, said method comprising the steps of:

• constructing said circuit card to have a first voltage reference plane having a first length, said first length being shorter than a first resonant length for a first frequency of at least one low frequency signal present on said circuit card, said first length being approximately equal to a second resonant length of a second frequency of a higher frequency signal present on said circuit card;
• constructing a second voltage reference plane having a second length, the sum of said first length and said second length being greater than said second resonant length;
• and
• coupling said first voltage reference plane to said second voltage reference plane at said second frequency to suppress resonance of said higher frequency signal.