Comparison of Fully Distributed and Periodically Loaded Nonlinear Transmission Lines

Two different approaches to realizing nonlinear transmission lines (NLTLs) are compared in detail: those using fully-distributed and those employing periodically-loaded nonlinearities. Hetrostructure-barrier varactor measured characteristics are used as the nonlinear elements in the pulse-compression and harmonic-generation (20-60GHz tripler) simulations. We point out that the choice of simulation step size is critical in the case of fully-distributed NLTLs. It must be chosen so that no numerical Bragg cutoff frequency appears. For the frequency tripler, simulations show that with periodically loaded NLTLs, 21% efficiency at 210mW output power and 30% bandwidth can be obtained, whereas only 4.8% efficiency is possible using fully-distributed NLTLs. For pulse compression, the results are comparable but in the fully-distributed case the NLTL cannot be matched and significant reflections occur at the NLTL far end.