An introduction to varactor theory and applications is followed by a review of various modeling techniques with an evaluation of their accuracy and appropriate uses. The process introduced includes device measurement, impedance extraction and C–V fitting. Analytical methods and SPICE modeling simulation results are compared to advanced polynomial grading coefficient (PGC) models implemented in the Keystone ADS circuit solver, and the PGC models are validated by harmonic balance simulations. The PGC model technique presented can be more accurate and validated over wider voltage ranges for varactors compared to SPICE model techniques.