Improved characteristics of countermeasure method for image information leakage by electromagnetic radiation from ITE

In this paper, the results of studies on improving the frequency characteristics of masking countermeasure devices for the information leakage from information terminal equipment (ITE) is reported. When the masking technique is applied, the electric field strength of the radiated electromagnetic wave with the countermeasure device effect cannot exceed the limit value of IEC / CISPR 32. Therefore, it is important to design the frequency characteristics of the device optimally. Firstly, it is described how to set as a radiation problem from the transmission line model, an electromagnetic field where the masking signal injected from the device is radiated from the PC board. And it is explained how to design the frequency characteristics using an electromagnetic field simulator with Transmission Line Matrix (TLM) method. Secondly, the new method that uses spread spectrum modulation for the masking signal wave and uses plural different frequencies signal whose main frequencies are slightly shifted each other have been developed. It has been experimentally confirmed that the masking effect can be obtained even when the SN ratio at the peak value of the original signal and the masking signal wave is smaller than the conventional method. That is an improvement of more than 12 dB at 391.4MHz compared to the conventional method for example.