In this paper,both the 1D radial mode and the equivalent circuit of a piezoceramic disk resonator were theoretically analyzed based on IEEE standards.And then,the radial resonance frequency spectra of the PZT-based (Nb/Ce co-doped Pb(Zr0.52Ti0.a8)O3,abbreviated as PZT-NC) piezoceramic circular disks were measured by an impedance analyzer.A set of resonance frequency spectra including six electrical parameters: Z,R,X,Y,G,and B,were used for making a value distinction between three possible resonance frequencies,and between three possible antiresonance frequencies.A new-form Nyquist diagram was depicted to describe the position relations of these characteristic frequencies.Such a complete resonance frequency spectrum was used to perform the accurate calculation of some material constants and electromechanical coupling parameters for the PZT-NC piezoceramics.Further,the frequency dependence of the AC conductive behavior of the specimen was characterized by the complex impedance measurement.The values of AC conductivity at resonance/antiresonance were deduced from the equivalent circuit parameters.Moreover,the Van Dyke circuit model was assigned to each element contribution and the simulated curves showed a nice fitting with the experimental results.Finally,an additional impedance analysis associated with resonance frequency calculation revealed a complicated coupled vibration mode existing in the annular disk specimen.