Understanding soliton wave propagation in nonlinear transmission lines for millimeter wave multiplication

It is well known that frequency multipliers based on monolithic nonlinear transmission lines (NLTLs) provide high conversion efficiency as well as broadband operation. Nonlinearity and dispersion (which is introduced by periodically charging the line with voltage variable capacitors) give rise to the possibility of soliton propagation; i.e. travelling wave pulses with permanent profile. The multiplication process in these circuits has been previously interpreted as due to the decomposition of the input signal wavecycle into a set of solitons of different amplitudes and velocities. According to it, to understand harmonic generation in NLTLs and to have design guidelines, it is important to study soliton behaviour and analyse the effects of NLTL parameters on soliton characteristics. In this work we use a very simple model to obtain soliton propagation characteristics in a NLTL with electrical parameters which are typical for actual structures. Since the origin of solitons (and hence frequency multiplication) is the periodic disposal of nonlinear capacitances in the line (usually HBVs), we present some results showing the effects of device nonlinearity variation (i.e. modifying the equilibrium capacitance of an HBV) on soliton characteristics.