GA optimized stub-loaded monopoles with high gain performance

In general, the lengths of the stub-loaded monopoles presented in this paper are significantly longer than conventional quarter-wave monopoles. Long wires alone do not provide the desired gain and VSWR performance; the stubs connected to the long monopole are vital in realizing simultaneous high gain and low VSWR. A genetic algorithm (GA) is employed to optimize the locations and lengths of each of the stubs required to meet the design objectives. The results of this work show that over 11 dBi gain can be obtained when the stub-loaded monopoles are placed over an infinite ground plane, whereas 8 dBi is obtained for one example when sited over a finite ground plane. A prototype of an optimized stub-loaded monopole was fabricated and tested. Excellent agreement was achieved between the measured and simulated results.