How do shielding cans and enclosures work?
Shielding reduces coupling between circuits and to the outside world. Shielding effectiveness combines reflection and absorption losses of the shield material and is usually limited by apertures and seams, not material thickness. Board-level cans soldered to ground fences isolate sections such as PAs, VCOs and LNAs; enclosures must avoid cavity resonances in the operating band.[1][2]
How do apertures limit shielding?
A slot radiates efficiently when its length approaches λ/2. A common estimate for a single slot of length L is SE ≈ 20·log10(λ/(2L)) dB (for L < λ/2), so many small holes are better than one long slot. Seams need frequent fastening or conductive gaskets.[1]
What are cavity resonances?
A metal box of dimensions a × b × d resonates at fmnp = (c/2)·√((m/a)² + (n/b)² + (p/d)²). A 50 × 30 × 5 mm can has its lowest TE110 resonance near 5.8 GHz, which can couple circuits strongly. Absorber material, internal walls or smaller compartments move or damp resonances.[3]
What are best practices for cans?
- Continuous ground via fence under the can wall.
- Separate compartments for transmit, receive and synthesizer.
- Filter signals entering the can (feedthrough capacitors or RC/LC filters).
- Check the shielded performance, since lids can detune circuits.
Frequently asked questions
Does thicker metal shield better?
At RF, absorption is usually ample; apertures dominate.
Why add absorber in a can?
To damp cavity resonances that couple circuits.
Do shields help with magnetic fields at low frequency?
High-permeability materials are needed for low-frequency magnetic shielding.
See also
References
Online sources accessed October 21, 2026; printed works cited by edition. See all sources.
- “Electromagnetic Compatibility Engineering”. H. W. Ott, Wiley. 2009.
- “Introduction to Electromagnetic Compatibility, 2nd ed.”. C. R. Paul, Wiley. 2006.
- “Microwave Engineering, 4th ed.”. D. M. Pozar, Wiley. 2012.