Spectral-domain analysis of complex characteristic impedance of a leaky conductor-backed slotline

We define an "equivalent complex characteristic impedance" for a conductor-backed slotline, that can be useful for circuit modeling purposes. Standard methods for computing the characteristic impedance of non-leaky transmission lines would not apply to a conductor-backed slotline due to its non-standard leakage behavior. Two alternate methods are proposed, that are compared with each other, as well as validated by comparing with rigorous 3D simulations of a practical circuit geometry.