Phase matching using bandgap structures for efficient parametric frequency conversion

We propose a method of efficient parametric process for frequency conversion. One of the most important conditions for such nonlinear processes is phase matching. Previously, nonlinear transmission lines (NLTL) consisting of varactors have been used for harmonic generation. In this paper, we discuss the fundamental limitation, i.e. the inability to guarantee phase matching, of these conventional NLTLs. To overcome this shortcoming, a passive structure exhibiting frequency bandgap is proposed and subsequently proved that such bandgaps lead to accurate phase matching in harmonic/subharmonic frequency generation. We provide analytical treatment of the proposed structure and also report simulation results. As a proof of this concept, measurement results of a frequency doubler prototype are presented. It provides an output of 300MHz with a conversion loss of as low as 4.9dB with only five sections of the proposed structure.