e-FIELD between to microstrip line

I need to create virtual ground between two metal plates in such a way
that e-field of both the plates either cancels out or deflect each other. Just like even mode excitation in parallel plate coupler, as shown in attached fig. I want to create same effect at around 60GHZ. But in my case plates are not parallel instead 1st one is on top of 2nd one.
Any help, thoughts, reference will be helpful

Can you post a figure of the two plates you have?

They are coupled by the W dimension (the largest one) of the strip?

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