文档介绍：Optimizing EMI Shielding for Wireless Systems
EMI, or ic interference, is a familiar, though not always
understood, occurrence. EMI results from spurious signals generated by
electronic systems, (or by nature, such as lightning), that adversely affect circuits
within the same, or nearby electronics. The trend toward faster, smaller wireless
systems has engineers seeking better EMI control methods for their designs and
budgets.
Cause and effect
Unintentional EM emissions result from electric (E) and ic (H)
fields that surround current-carrying traces, wires and other conductors. The
voltage or switching frequency of the source, as well as its harmonics,
determines the EM frequencies. As operating speeds exceed 900 MHz,
wavelengths are so short that very small (<2mm) slots in an enclosure e
doorways for these troublesome emissions. They can also interact with circuit
board traces having lengths that make them act as efficient one-quarter or one-
half wavelength antennas.
Base-level treatments
Proper PCB layout offers the most cost-effective approach to dealing with
radiated EMI issues, whether preventing emissions or providing immunity.
Careful layout and separation of traces ponents on a PCB can reduce
cross talk. A number of software programs can help design engineers analyze
potential EMI problems at this level.
It is rare, however, when board layout