Electronic – Passing copper traces between two THT pins

Use a 4 layer stackup.

Calculating the trace width needed is pointless unless there is a solid ground plane under it, with a 2 layer design you may need to route traces on the other side which then pretty much ruins your impedance if they come anywhere close to your trace.

At 450Mhz you really should have solid, continuous, properly decoupled power and ground planes. This will improve noise performance, EMI issues, give you better impedance control, etc. Fabbing a 4 layer board isn't that much more to expensive than a 2 layer.

Use a 4 layer like:

>----------------Signal 1
8.3 mil
>----------------Ground
39 mil
>----------------Power
8.3 mil
>----------------Signal 2

Spacing could change a little based on your copper thickness choice.

That will give you something like 10-20mil for your 50ohm trace on Signal 1/2 depending on final dielectric and copper thickness on the Signal layers.

The short answer is that neither matter in most cases. The only good reason I have for doing such a "fence trace" is to prepare for maybe adding a shielding can later (after testing if it works okay without). The trace in itself does not help much - other than adding some distance (which you could do without the trace).

The longer answer requires you to first explain what you are trying to achieve, why you think this will work and how you think it will work.

In general: If you don't understand what you are doing - maybe don't do it :-) A lot of time is spent copying stuff we "think" is good and often creating more problems than we had in the first place.