High-frequency noise induced to a ground system causes disturbance to electronic devices. However, there have been only a few studies into the high-frequency impedance characteristics of ground systems from the viewpoint of safe and stable functioning of electronic devices.
For the present study, the authors installed ground electrodes and measured the impedance characteristics of the ground system. This paper shows that the parallel resonance occurs at specific frequencies. The authors found that the frequency of parallel resonance depend more on the length of the ground conductor than the distance between ground electrodes or their length. This paper also shows the problems caused by the parallel resonance of ground conductors. And finally the authors propose a type of attenuator, composed of a coil and resistor connected in parallel, to suppress the impedance increase at the parallel resonance frequencies.