Würth Elektronik 2022 7
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WE-CBF SMD EMI
Suppression Ferrite
Beads
WE-CMB Common
Mode Power Line
Inductors
Conventionally, the length of the antenna is used to transform the
system to the frequency range to terminate, such as a quarter-wave
impedance transformer (since the length works at a specific narrow
banded frequency), an alternative is to use a real component that also
has high impedance in the frequency range. An antenna with a stub
traditionally starts at the stub, and the cut-off is far from the stub
(Figure 6). Similarly, an antenna with a high impedance and high-
frequency chip bead operates before the stub and has a cut-off far
from the stub. In contrast, a ferrite bead with not enough impedance
will cut off earlier near the stub, shortening the useable bandwidth.
For example, the WE-CBF HF (742862160) or (742863147) fulfill the
requirements with its high impedance peak ranging from 100MHz to
1GHz. By using a ferrite bead, not only is the same size PCB kept by
saving the space that would be occupied by the line transformation,
but the operative frequency range is also widened (Figure 7).
The advantages of using a WE-CBF HF:
■ Wider operating frequency (lower frequency region)
■ Smaller PCB size hence saves space
■ Lower cost alternative
Summary
The WE-CBF HF is a component suitable for suppressing EMI at
the higher frequencies commonly found in new and existing device
technologies. The WE-CBF is still the component of choice when
operating at lower frequencies. Due to the unique features of the
WE-CBF HF, it can also be used in a range of applications not
typically associated with chip bead ferrites. ■
Figure 6: Gain over frequency of antenna with terminating stub
(Source: Würth Elektronik)
Figure 7: PCB of an LPDA with WE-CBF HF (742862160).
(Source: Würth Elektronik)
