A full-wave analysis of a strip crossover above a conducting plane is carried out. Higher-order modes are excited in the form of evanescent waves in the vicinity of the discontinuity, while further away only the dominant (TEM) modes exist. The higher-order mode currents are modeled by triangle functions and the dominant modes by outgoing traveling waves. The method of moments is used to reduce the integral equations on the surface of each strip to matrix equations whose solution determines the currents on each strip. The impedance and scattering matrices of the four-port network and the equivalent circuit were determined. At low frequencies, the equivalent circuit agrees very well with that which was obtained previously using a quasi-static analysis. The two approaches begin to disagree when the cross-sectional dimensions of the crossover become comparable to a tenth of the wavelength. At that point the quasi-static analysis becomes inaccurate, while the full-wave analysis presented here remains valid.