Could some electronics guru here please clarify the following:

For two tightly coupled parallel microstrips, with single, isolated mode characteristic impedance Z0, the characteristic impedance of the pair when operated in differential mode is 2.0***Z0. What would be the terminating impedances for each of this pair, Z0 OR 2.0***Z0.

Also, if a signal is propagating down ONLY one microstrip of a pair of parallel pair of microstrips, are they in odd(differential) or even mode ?

Thanks in advance for your help.