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A transient simulator for interconnect structures that are modeled by lossy transmission lines is outlined in this paper. Since frequency-dependent RLGC parameters must be employed to correctly model skin effects and dielectric losses for high-performance interconnects, we first study the behaviors of various lossy interconnects that are characterized by frequency-dependent line parameters (FDLPs). We then developed a frequency-domain dispersive hybrid phase-pole macromodel (DHPPM) for such lines, which consists of a constant RLGC propagation function multiplied by a residue series. The basic idea is to first extract the dominant physical phenomenology by using a propagation function in the frequency domain that is modeled by frequency-independent line parameters (FILPs). A rational function approximation is then used to account for the remaining effects of FDLP lines. By using a partial fraction expansion and analytically evaluating the required inverse Fourier transform integrals, the time-domain DHPPM can be decomposed as a sum of canonical transient responses for lines with FILP for various excitations (e.g., trapezoidal and unit step). These canonical transient responses are then expressed analytically as closed-form expressions involving incomplete Lipshitz-Hankel integrals of the first kind and Bessel functions. The closed-form expressions for these canonical responses are validated by comparing with simulation results from commercial tools like HSPICE. The DHPPM simulator can simulate transient results for various input waveforms on both single and coupled interconnect structures. Comparisons between the DHPPM results and the results produced by commercial simulation tools like HSPICE and a numerical inverse fast Fourier transform show that the DHPPM results are very accurate.