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Abstract
A novel tree-shaped antenna with high directive gain and designed by the Tree Growth Competition Algorithm (TGCA) is presented. To enhance its efficiency, the TGCA is improved by defining the growth factor, growth probability and random litter threshold. The tree-shaped antenna includes a balanced transmission line and various metal strips, which are called trunk and branches respectively, and is optimized by the improved TGCA in conjunction with the full wave EM simulation for achieving a high directive gain and a good impedance match over a desired frequency band from 950 MHz to 1250 MHz. A prototype antenna is fabricated and tested. The measured results agree well with the simulated datum, and show the tree-shaped antenna achieves a broad VSWR < 2 impedance bandwidth of 41% (from 850 MHz to 1300 MHz) and a high directive gain up to 10 dBi over the most operating band.