Would a Faraday cage block all types of radar?

[tthompson53]

Would a faraday cage block all types of radar?

 

[cragar]

It will block AM radios and other frequencies, But it will not block all radio waves.

 

[tthompson53]

Thanks cragar. Its back to the drawing board for me. Regards tthompson53

 

[sophiecentaur]

"Block" and "faraday cage" are open descriptions. You have to pay an awful lot for a screened room that will 'block' signals by more than a few tens of dB. The Electric component is easier to screen against (100dB ) but the Magnetic field, even in one of those, they don't claim better than 18dB. Microwaves tend to sneak in everywhere and you may not do better than 60dB of isolation.

A simple faraday cage, suitable for working on high voltages at AC, would behave very much like a seive to any EM waves.

 

[tthompson53]

Thanks sophiecentaur. Milliwave radar is what I am working on. Regards tthompson53

 

[sophiecentaur]

It boils down to how much money you have to spend - and how much space you have for your screened enclosure. AND, what the specification is for your requirements. How long is your piece of string? You may get by with a relatively cheap solution -like ducking behind a corrugated fence!

 

[WarVsFutility]

Say, maybe if you built a capacitor that covered a large area, it might get your desired effect, like if something were, instead of being inside of a faraday cage, inside of a hollow capacitor with a little charge. Just a thought...

 

[OJFord]

Simple but related question - can a cable running into a Faraday cage retain whatever signal it carries, without any unwanted affect on it?

 

[sophiecentaur]

You would need to describe this cable. Is it a single wire, going through a hole (big or small?) in the cage. Is is coax, a pair of wires? The answer could depend on this sort of detail.

 

[OJFord]

You would need to describe this cable. Is it a single wire, going through a hole (big or small?) in the cage. Is is coax, a pair of wires? The answer could depend on this sort of detail.

You have answered my question really - it was a hypothetical cable, I perhaps could have phrased my question. It was more "is it possible to get a wanted signal inside a cage, which is blocking all unwanted wireless signals".


Just for interest's sake, how would the answer differ - ie. what properties of the wire would change the resultant signal inside the cage?

 

[sophiecentaur]

The only sensible way to get a (signal) cable through into a Faraday cage would be to use coax. The outside of the sheath of the coax would be, effectively, just a continuation of the screen. The signal is carried between the inner skin of the sheath and the inner conductor so would not be affected. It is necessary to extend the 'screening' or filtering to all equipment which is connected to the cage because the lines in and out are potential paths for interference. RF can leak in through the most unlikely paths.
To get power and low frequency (audio) you can use separate lines or screened pairs, with series Inductances and shunt capacitors to the case, to act as a low pass filter to any unwanted hf signals.

@WarVsFutility
PS this "capacitor" idea doesn't make sense. A charge on a capacitor has no effect on AC currents. I'm not sure what you were getting at really.