Electricity: electrical systems and devices – Housing or mounting assemblies with diverse electrical... – For electronic systems and devices
Reexamination Certificate
1999-11-22
2001-07-31
Gandhi, Jayprakash N. (Department: 2841)
Electricity: electrical systems and devices
Housing or mounting assemblies with diverse electrical...
For electronic systems and devices
C361S800000, C361S818000, C174S034000
Reexamination Certificate
active
06269008
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to an electromagnetic interference shield for a printed circuit board and more particularly to a multi-walled electromagnetic interference shield.
BACKGROUND OF THE INVENTION
In an electronic device operating at radio frequencies or microwave frequencies, certain circuit components may emit electromagnetic fields that amount to interference to other circuit components in the vicinity. Such unimpeded electromagnetic interference may degrade the performance of a wireless communications transmitter incorporated into a base station, for example. In some cases, if electromagnetic interaction between the circuit components is severe, an amplifier may become unstable from an electromagnetic feedback path and go into undesired oscillation. In other situations, the electromagnetic interference may degrade amplifier performance by causing inter-modulation distortion or by spreading the bandwidth of the transmit signal beyond its desired boundaries. Inter-modulation distortion refers to unwanted mixing that can occur between two signals at different frequencies within electronic circuitry.
To alleviate the foregoing problems, manufacturers have used what are commonly referred to as can shields mounted on printed circuit boards to electromagnetically isolate circuit components from one another. The prior designs of electromagnetic shields often address frequencies lower than one Gigahertz (1 GHz) because of the prevalent use of these lower frequencies in wireless communication systems over the last 20 years. However, as wireless systems are now licensed to use higher frequencies such as those greater or equal to 1.8 Gigahertz for personal communication services (PCS), some of the earlier shield designs do not provide adequate isolation between different components of a printed circuit board. Thus, a need exists for an electromagnetic shield that is applicable to printed circuit boards operating at microwave frequencies or at other frequencies.
SUMMARY OF THE INVENTION
In accordance with the invention, an electromagnetic shield includes a multi-walled cover with a peripheral gap between inner walls and outer walls. A shielding gasket may be mounted in the peripheral gap. The electromagnetic shield further includes a fence disposed within the peripheral gap and arranged for mounting on a printed circuit board. The electromagnetic shield provides a barrier to electromagnetic to signals from being radiated between an interior of the electromagnetic shield and an exterior. The electromagnetic shield is well-suited for providing electromagnetic attenuation and isolation in the lateral directions between the shield and other components on a printed circuit board by suppressing radiation at the inner walls, the fence, the shielding gasket, and the outer walls of the shield.
REFERENCES:
patent: 4218578 (1980-08-01), Oschewski et al.
patent: 4370515 (1983-01-01), Donaldson
patent: 5045971 (1991-09-01), Ono et al.
patent: 5414597 (1995-05-01), Lindland et al.
patent: 5550324 (1996-08-01), Black et al.
patent: 5844784 (1998-12-01), Moran et al.
patent: 5847938 (1998-12-01), Gammon
patent: 405206674 (1993-08-01), None
patent: 405335773 (1993-12-01), None
Gandhi Jayprakash N.
Lucent Technologies - Inc.
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