Key issues in design of nonlinear transmission lines

Summary form only given: Dielectric nonlinear transmission lines (NLTLs) have demonstrated great potential in RF generation. Their main characteristic is that they do not require an electron beam to operate. However, there are some key points in their operation not clarified yet. For instance, they generate output oscillations with frequency at half the line Bragg frequency for a high number of sections (n>30); however, for smaller n (=10) this frequency appears to be near the Bragg frequency¹. In this work, it will be demonstrated that this effect has to do with the spreading of train of solitons travelling through a long line (i.e. with a high number of sections). In addition, it will be shown that for a line with higher n, the nonlinearity factor k of the dielectric can be very close to unity, which means that capacitors with more stable capacitance can be used. This effect has been observed in practice, as it is easy to produce a train of solitons with higher amplitudes for a line built with a large number of sections². Finally, the points discussed above will be checked experimentally by measuring the standard FFT of the signal along a varactor diode NLTL made with 30 sections, operating at the output frequency around 50 MHz.