Most oscillators are more complicated than the Gunn diode example, since both the active device and the load may have reactance (X) as well as resistance (R). Modern negative resistance oscillators are designed by a frequency domain technique due to Kaneyuki Kurokawa. The circuit diagram is imagined to be divided by a " reference plane " (red) which separates the negative resistance part, the active device, from the positive resistance part, the resonant circuit and output load (right). The complex impedance of the negative resistance part Z N = R N ( I , ω ω ) + j X N ( I , ω ω ) depends on frequency ω but is also nonlinear, in general declining with the amplitude of the AC oscillation current I ; while the resonator part Z L = R L ( ω ω ) + j X L ( ω ω ) is linear, depending only on frequency. The circuit equation is ( Z N + Z L ) I = 0 so it will only oscillate (have nonzero I) at the frequency ω and amplitude I for which the total impedance Z N + Z L is zero. This means the magnitude of the negative and positive resistances must be equal, and the reactances must be conjugate