Variable Zo applied to the optimal design of multi-stub matching network and a meander monopole

Variable Z(o), a new concept in antenna design and optimization, is applied to two optimization problems: a multi-stub matching network (MSMN) using biogeography-based optimization (BBO), and an ultra wideband meander monopole antenna (MMA) using central force optimization (CFO). BBO is a newly-proposed stochastic global search and optimization evolutionary algorithm (EA) used to determine MSMN stub lengths and locations for optimum (minimum) reflection coefficient. CFO is a deterministic EA used to optimize the MMA's impedance bandwidth (IBW) while maintaining good average gain without considering the radiation pattern in detail. Two cases are investigated for both problems: (a) fixed characteristic impedance Z(o), and (b) variable characteristic impedance. In the first case, Z(o) is a fixed user-specified parameter (the traditional methodology), whereas in the second, it is a true variable quantity whose value is determined by the optimization methodology, which is a new technology. Variable Z(o) is a fundamentally different design approach in optimization problems. BBO's fixed Z(o) results for MSMN are compared to published data computed using Nelder-Mead optimization with BBO exhibiting better performance. BBO's results are improved even more using Variable Z(o) technology. A similar performance improvement is seen for Variable Z(o) applied to the CFO-optimized MMA.