How would this circuit work?
As the &quot;Graphene frequency doubler paper&quot; which you indirectly refer to states, their frequency doubler schematic uses non-linearity of a GFET's current voltage characteristic (Fig. 4) to perform harmonics generation. Effectively, the input device is supposed to square the input waveform. The series resonant RLC circuit at the output attempts to filter out all the harmonics save the second one.
Any nonlinear-device can be used to generate harmonics. The authors of Three-Gigahertz Graphene Frequency Doubler on Quartz Operating Beyond the Transit Frequency expect that the V-shaped characteristic of Fig. 4 effectively squares the input waveform, suppressing the fundamental frequency from the beginning. The paper Graphene-Based Frequency Tripler goes one step further and suggests properly biased stacked GFET's to generate a third harmonic with the help of W-shaped transfer characteristic for their &quot;graphene-based&quot; frequency tripler.
There exist devices demonstrating inherent IV characteristics with local minima; tunnel diodes, for example. The designs in which the &quot;squaring&quot; i-v characteristic is implemented with diodes and transistors are well established in microwave electronics, see the review Frequency Multipliers by Iulian Rosu on the Amateur Radio Community website.
Also, the IEEE TRANSACTIONS ON MICROWAVE THEORY AND TECHNIQUES VOL. MTT-29, NO. 3, MARCH 1981 paper Performance and Design of Microwave FET Harmonic Generators shows a schematic drawing (Fig. 1) very close to your request, only implemented with microwave stub tuners.