RF shield ground and board ground

[mw_rookie]

Hello,

I have 4 separate grounds on my RF boards. The board overall has only one shield isolating it from another board which is the main purpose. My question is whether to connect the shield tabs to the chassis ground or to extend the input ground of the board and then use it for shield can ground. I have gone through a lot of literature and the suggestion is generally to connect the RF shield ground to chassis ground. But if that is the case, wouldn't it cause interference if there are other boards in the system connected to chassis as well? Will it be a cause of concern if I connect it to the board ground?

Any help would be greatly appreciated.

Thanks.

 

[biff44]

it is a little hard to know what you mean. Why are their 4 grounds on one rf board? For emi purposes, one RF ground is preferred!

The basic concept is, if you build a "faraday cage" with circuitry inside, those RF signals should not leak out. That is, if there is a mostly metal box surrounding the circuitry (with a ground plane being the bottom wall of that box), you have a faraday shield.

So if there are 4 separate grounds...if they are all planar you would need 4 separate metal shield boxes. If the 4 grounds are on top of one another...then you have a REAL MESS and do not have any idea where the ground return currents are actually flowing, so can not connect the box to them properly. If they are on top of one another, the only hope is for a "million" via holes connecting them all together.

 

[BigBoss]

If the ground planes are sufficiently large and good organized you connect all of them to chassis ground together.
Using seperate ground planes is to isolate the gorunds of signal,rf,digital etc.to prevent any disturbances but at last point these grounds can be connected electrically good conducting chassis ground with many screws.