## 3 Simulation Results
### Finite Sum of Harmonics Current Excitation  
The periodic current \(i(t)\), consisting of three sinusoids and a dc component with period \(T=0.1\)\(\upmu\)s, is considered as the first example:  
\[i(t)=2+3\cos\left(2\pi Ft+\frac{\pi}{4}\right)+2\cos\left(4\pi Ft+\frac{\pi}{ 2}\right)+2\cos\left(6\pi Ft-\frac{\pi}{3}\right)\left[\text{mA}\right], \tag{58}\]  
where the frequency is \(F=1/T=10\) MHz. The current, \(i(t)\), voltage, \(v(t)\), and power, \(p(t)\), signals are depicted in Figure 2. They are periodic functions with the same period, \(T\). The spectra of current, \(i(t)\), and voltage, \(v(t)\), are presented in Figure 3a,b, respectively, as the weights of the Dirac delta functions representing Fourier coefficients (5) and mea  
Figure 1: Resonant circuit with feeding current source (**a**) and the frequency characteristic of its input impedance as impedance module and phase versus the excitation current frequency (**b**). Figure 2: The current, voltage and power for the case of finite sum of harmonics current. sured in [A] and [V], respectively. The colors of the circles designate the phase of each Fourier coefficient, according to the color bar, ranging from \(-\pi\) to \(\pi\). The same visualizing technique will be used for revealing the phase information in other figures. It can be seen in Figure 3b that, for the voltage spectra, the maximum in absolute value weights of the delta function are at frequencies \(\pm\)10 MHz, which correspond to the circuit resonant frequency, \(f_{r}\), and the fundamental frequency, \(F\), of considered signals. Figure 4 shows the weights of two-dimensional Dirac delta functions, forming the bifrequency spectrum, \(S_{vi}(f_{1},f_{2})\), of the current, \(i(t)\), and the voltage, \(v(t)\), in accordance with (15). These delta functions are arranged with step 10 MHz, which corresponds to the fundamental frequency, \(F\), of signals \(i(t)\), \(v(t)\) and \(p(t)\). It can be seen that the section of \(S_{vi}(f_{1},f_{2})\) at \(f_{1}=\pm\)10 MHz have maximum weights. The absolute values, in \(\upmu\)W, and phases, in radians, of the delta function weights forming the bifrequency spectrum, \(S_{vi}(f_{1},f_{2})\), are presented in Table 1, where each cell corresponds to a pair of frequencies, \(f_{1}\) and \(f_{2}\), defined in the rows and columns, respectively. Figure 4: The bifrequency spectrum for the case of finite sum of harmonics current. Figure 3: The current (**a**) and voltage (**b**) spectra for the case of finite sum of harmonics current. The alternative representation of the bifrequency spectrum is the diagram shown in Figure 5a, where each delta-function is depicted as a circle whose area is proportional to the absolute value of \(S_{vi}(f_{1},f_{2})\). This way of presenting a 3D image of \(S_{vi}(f_{1},f_{2})\), on plane, can be convenient for the visualization and rapid estimation of the relative values of \(S_{vi}(f_{1},f_{2})\) components. We preferred to use a diagrammatic representation in subsequent typical cases. The frequencies \(f_{1},f_{2}\) range from \(-30\) to \(30\) MHz. Figure 5b shows the diagram of CSCD \(S_{vi}(\alpha f)\) (21), where the weights (22) of delta functions are presented. The cyclic frequency, \(\alpha\), ranges from \(-60\) to \(60\) MHz, the frequency, \(f\), ranges from \(-30\) to \(30\) MHz. Figure 6 shows the distribution of the real and imaginary parts of average power. It can be seen that the real part contributes, in average power, more than the imaginary part. The weights of the delta function of the real part are highest at frequencies \(\pm 10\) MHz, which is the circuit resonant frequency, \(f_{r}\), and the fundamental frequency, \(F\), of considered signals.