Behavioral modeling and simulation of a PLL based integer n frequency synthesizer has been illustrated in this paper. The synthesizer generates a signal of 5.15-5.25GHz in the UNII (Unlicensed National Information Infrastructure) lower band which is used by IEEE 802.11(a). All the PLL building blocks are modeled and simulated using Simulink. The PLL performance has been evaluated using Matlab. It is verified that the PLL loop bandwidth and phase margin are 0.25MHz and 69.125 degree respectively, which satisfies the correct transfer function.