Analytical solutions for the frequency-dependent transmission line model parameters of a stranded coaxial cable, which are not trivial due to the complex geometry, are presented and discussed in this paper. A frequency-dependent effective conductor radius of a stranded wire coaxial cable is proposed to estimate the internal impedance using the Bessel function solutions of a solid wire coaxial cable. The performance of the proposed model is verified by electromagnetic field solver simulation and by experimental measurement. The results show that the proposed model successfully calculates the broadband frequency-dependent RLGC model parameters and characteristic impedance of a stranded wire coaxial cable with high accuracy.