Design Of Compact Multi-Band Microstrip Antennas

In recent years, internal antennas were employed broadly in mobile terminals, and with the terminals' function diversified, it is getting more and more important for terminal antennas to have multi-band covering ability and small sizes. However, different wireless nets work on greatly different frequencies. So it becomes a challenge for internal antennas designing to make them have both multiple resonance frequencies and compact figures. Microstrip antennas are paid great attentions recently because of its small volume, low profile and low fabricating cost. This thesis focuses on the miniaturization & multi-band realizing-technology of microstrip patch antennas and printed monopole antennas.The main task of this thesis is to investigate the current flow path method on small multi-band antenna designing. Firstly, a method of notching on patch antenna or adding oscillator to monopole antenna is proposed to get multi-frequencies, this method is based on the theory that adding flow path can add resonance frequency. Then, we research into the change of resonance frequencies when the flow path is bended. The result shows that higher frequencies can be generated at the bended corner. So it is concluded that bending flow path can not only reduce antenna's size but also create new resonance frequencies. This conclusion provides a new way to achieve multi-band. At last, a compact quad-band patch antenna loaded by two non-regular slots is designed. It has a small volume(30×20×8mm~3) and covers GSM/DCS/WLAN bands well.The antennas referred to are mostly simulated by HFSS(High Frequency Structure Simulator), which is based on FEM(Finite Element Method) and supposed ideal boundary condition, so their simulation precision is credible enough for us to educe some useful rules from its results. The antennas are judged according to the parameters, such as return loss, gain, bandwidth, and radiation pattern.