Performance enhancement of multiband antennas through a two-stage optimization technique

This paper presents an optimization technique that aims at multiband antenna design. The proposed method is based on the framework of multi-objective evolutionary algorithms, and a two-stage mechanism that balances the degree of optimizing impedance matching and the degree of providing a wide impedance bandwidth is incorporated. Conventionally, the design optimization of multiband antennas relies on minimizing the maximum reflection coefficient or maximizing the area under the return-loss curve over targeted frequency bands. However, these widely used methods direct an optimization algorithm to improper solution sub-domains in the multiband design problem. To overcome the limitation of these conventional methods, the general rule of objective functions is thoroughly investigated in this paper. Furthermore, a two-stage optimizer is designed based on what the multiband optimization problem needs. With the use of the proposed method, two multiband antennas for mobile communication systems covering 824-960 MHz and 1710-2170 MHz are successfully developed. Simulated and measured results show that the proposed technique outperforms conventional optimization approaches significantly.