There are three general noise countermeasure methods: 1) shielding, 2) inserting a filter, and 3) reinforcing the grounding, yet there are serious problems with these methods at high frequency ranges.
Firstly, shielding is a method whereby the noise emitter is encased, making it a very effective EMI countermeasure. Yet, if there are even small gaps in the shielding, the gaps themselves act as antennas and emit noise again. In contrast, if there are no gaps at all, heat is trapped inside the shielding, and even more adverse conditions such as extraneous emission waves being reflected on the shield surface and malfunctions may occur with the shield. Next, isolation from noise frequency bands becomes more difficult with filter insulation due to rising circuit operating speeds and high signal frequencies. If the signals are forcibly filtered, the waveform becomes obtuse, resulting in malfunctions. Grounding plays a role not just as a feedback line for signal current, but incorporates noise energy that flows from the shields and bypass. Grounding must have low impedance across a wide bandwidth, as it desires no potential occurring. Yet, its high signal frequency causes the wavelength to become several cm, the ground itself acts as a distributed parameter line, resulting in a potential according to the location.
The most troublesome problem at a high frequency range is that the circuit winding itself becomes an antenna, becoming a noise emitter, making the countermeasure of changing the circuit time-consuming.