What is the definition of characteristic impedance of a lattice network?
I'm not sure what characteristic impedance means in this context.


If you "placed" an impedance on the output (on the right of the network) and looked at the impedance into the network (from the left) then the input impedance (looking in from the left) will equal the "placed" impedance when that placed impedance equals the characteristic impedance of the network.

You could go through the math and calculate the input impedance when an unknown impedance is placed on the output then equate the input impedance to that unknown impedance and it would turn out to be \$Z_0\$.

The impact of this is that you can cascade an infinite number of sections and the input impedance would remain constant.