F-frequency characteristics function is a new concept about lumped eigenvalue of the fractance approximation circuit. In order to quantitatively describe the approximation performance of F-frequency characteristics of the fractance approximation circuit, a series of concepts and corresponding mathematical functions about approximation performance analysis of F-frequency characteristics are proposed in this paper based on F-frequency characteristics function, including relative error, approximation accuracy, approximation bandwidth, approximation bandwidth exponent, K-diagram, F-index, approximation benefit, etc. And these concepts are used to analyze the Oldham fractal fractance approximation circuit to verify its effectiveness.
