Characteristic Study Of Dual-frequency Microstrip Antenna Based On Defected Ground Structure

Since defected ground structure (DGS) was proposed by J. I. Park et al. in 1999, there has been an increasing interest in microwave and millimeter-wave applications of DGS. Similar with the photonic bandgap (PBG) structure, DGS which has etched defects in backside metallic ground plane can change the equivalent-circuit parameters, thereby changing the transformation character of a microstrip line and generating the characteristics of slow-wave and band gap. DGS can be used in restraining high order harmonics, improving the gain and bandwidth of antenna, improving efficiency and Q. Because of the advantage of DGS, such as simple structure, excellent performance, and easy to design and fabricate etc, it has been often used in fabricating low-pass filter, divider, and diplexer and so on.Microstrip antennas have been widely used in recent years because the antennas offer attractive features such as simple structure, low profile, light weight, easy and inexpensive manufacturability, and compatibility with integrated circuit technology. Now, many mobile equipments use dual-frequency microstrip antennas, because it can reduce circuit space. But its application is restricted by the problem of port isolation and high order harmonics.In this paper, two different shapes of DGS structures are simulated and there frequency characters are analyzed. On this basis, the neural networks models of these two types of DGS structures are developed. The structure dimensions of DGS and frequencies are defined as the input samples, and the parameters of transmission coefficient obtained from simulation results are sampled and defined as the output samples. Then, the neural networks models are trained with the Bayesian Regularization algorithm. At the same time, the transmission lines with DGS structures are manufactured and measured. The agreement between measured and calculated results shows that the neural networks models are very precise and effective.In the end, the dual-frequency microstrip antenna integrated with two different shapes of DGS structures is designed. Simulated and tested results show that high order harmonics are suppressed and the port isolation is enhanced successfully.