The propagation of solitons in transmission lines periodically loaded with nonlinear capacitors is analyzed. It is demonstrated that the dependence of soliton amplitude on propagating velocity can be computed with a simple equation, valid for any arbitrary nonlinear capacitance. By means of an approximation to the nonlinear reactance, an analytical expression that completely describes soliton profiles is presented. This can be applied to obtain moderate to high-amplitude soliton wave forms in nonlinear transmission lines (NLTLs) loaded with heterostrucure barrier varactors, where standard approaches do not hold. This model can be of help in understanding harmonic generation in the terahertz range using monolithic NLTLs as frequency multipliers. © 2001 American Institute of Physics.