Analysis of oscillators synchronized by second harmonic

Synchronization of two oscillators coupled via second harmonic is analyzed. The system of two differential equations is given, and, as an example of analysis, the solution for Rayleigh oscillators is found. Identical oscillators, with second harmonic coupling, will oscillate in quadrature at the frequency of individual oscillators, and there is no frequency shift characterizing coupling via first harmonic. Yet, stability of oscillators coupled via second harmonic may be verified by the technique developed for the method of energy cycles. To show the generality of approach, an example, using multivibrators in sinusoidal regime is given, and the simulations confirm the theoretical analysis.