If I lay two insulated wires side to side, or lightly twist them, then I end up with a characteristic impedance of around 100 ohms (more if the insulation is unusually thick, less if it's enamel or something).
Is there a way to start from that, and predict what happens if I add more conductors?
Specifically, start with my wires -- call them circuit A and circuit B, laid out as AB in a "ribbon". Now add one more, so that I have two wires in circuit A and one in B: ABA. Now add more yet, in a ribbon (no quotes), not twisted, so I have N/2 wires in A, and N/2 wires in B: ABAB...BAB.
Is there a way to predict -- even approximately -- what the impedance of the whole cable will be?
And no, this isn't a test question -- I have a need for an unusually low impedance transmission line (really a really low inductance way to connect point A with point B), and I'm trying to reduce the problem to the part that I really don't know. I'm also considering two parallel plates, with insulation in between -- I've found equations for that, but fabrication may be harder than "ribbon cable".