Key issues in design of NLTLs

Dielectric nonlinear element 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 near half the line Bragg frequency with unmatched load less than full characteristic impedance; however, for high resistive load this frequency appears to be near the Bragg frequency. In this paper, these points are checked experimentally by measuring the standard FFT of the signal along a varactor diode NLTL made with 30 sections, whose operation frequency is in the range of 25-40 MHz depending on the load.