Parallel plate modes in stripline

[Matt]

Does anyone have a good paper on the basics of parallel plate modes in stripline transmission lines? E.g. fundamentals, design guidlines to avoid exciting them etc..

Thanks,

Matt

 

[biff44]

Secret lore from days gone-by. Look at an old directional coupler in stripline, like a narda. Notice all those metal rivets going from the top to the bottom ground plane? The width of the channel formed by those rivets had better be <<λ/2.

 

[jian]

Hi, Matt:

Parallel plate mode is easy to illustrate. Basically, if you have 2 infinite parallel plates: one at z1 and one at z2. You put a current source from z1 to z2 at (x,y)=(0,0). You will be able to excite wave propagating in the rho direction. The mode does not have any cut off.

If you have a strip line circuit, for any non-symmetry between the 2 paltes, you will be able to excite the parallel plate mode and this mode will be propagating way as loss. Therefore, in a strip line circuit, any via between traces of different layers or any hole on the ground may excite significant amount of energy for the parallel plate mode. Normally, designers use shorting vias between the 2 plates to suppress it and it is quite effective because the parallel plate mode requiers a voltage difference between the 2 plates.

Regards.

 

[Matt]

Thanks chaps.