A variable Z0 impedance method (“Variable Z0”) for designing and/or optimizing antenna systems. The method provides that the value of an antenna's feed system characteristic impedance or apparatus internal impedance (Z0) changes as a true variable quantity during the antenna system design or optimization methodology. The value is allowed to be determined by the methodology, because different values of Z0 result in different antenna system performance. It is applied to any set of performance objectives on any antenna system wherein apparatus internal or transmission line characteristic impedance is an explicit or implicit parameter. Variable Z0 is applied to any design or optimization methodology. Structures include Yagi-Uda arrays, Meander Monopoles, and transmission line Multi-Stub Matching Networks, and can incorporate Central Force Optimization or Biogeography Based Optimization or other optimization algorithms.