how to choose a metal housing for a microwave circuit

[per_lube]

I've got a question on mounting a microwave circuit in a metal housing.

The PCB has microstrip lines and some components such as SMD transistors and diodes working @11 GHz.

I know the ground of the PCB should be connected properly & firmly to the outer metal case including .

What should be the minimum clearance between the metal surface and microstrip line?
Is there a rule-of-thumb for the minimum clearance between a transmission line and a grounded metal surface of a housing?

cheers,
per_lube

 

[BigBoss]

If you have used Microstrip Lines, there should be Ground layer.So, since you connect this GND layer to system housing by screwing,there wouldn't any problem in term of distance.

 

[biff44]

I know the ground of the PCB should be connected properly & firmly to the outer metal case including .

well, technically the board only has to make good contact where signals are going thru the housing to the pc board. Like at an sma connector..both the center pin and the ground shield of the coaxial connector have to have a good/short path to the pc board. So, it you had 2 screws to press the board to the metal housing right at the sma connector...you have achieved that. If you really want to insure good performance, nothing works like soldering or conductive epoxying the board into the housing (although you need to have the housing properly plated to do so)

As far as how far away from a side-wall and ms line has to be....I think the rule of thumb is to keep the wall at least 2 line widths away from the edge of the ms line. I would probably do more though. If the sidewall is too close...the impedance of the line will go down, which may or may not be a concern depending on the type of circuit you are using.