Novel Application of CPW in Antenna Design for Dual-frequency Operation

In this paper, we propose a novel application of coplanar waveguide (CPW) in antenna design: by appropriate adjusting its impedance, CPW can act as both a transmission line and radiator at the same time. That is, unlike the traditional way, an extra independent frequency can be obtained without adding new component or increasing the complexity. So the new design and the original one are almost the same in geometry however completely different incapability. Through this method, antenna design could be more simple and flexible. To do this, the impedance of CPW should be carefully designed and most of all, avoid of being 50 12, otherwise the CPW will turn out to be merely transmission line (the traditional and most common usage of CPW). Here, we choose a classical single frequency planar antenna as an example to prove that by incorporating the advanced CPW, the former single frequency antenna could resonates at two different frequencies independently - the original one and the one comes from CPW. In addition, two frequencies share a very similar pattern. Since each resonant point relates to one parameter exclusively, we only need to modify one parameter at one time to place the two frequencies at the anticipate points to meet different requirements. However, impedance of CPW should be changed correspondingly to ensure sufficient gain at each frequency. In order to determine the performance of CPW's impedance as well as other two geometry parameters on frequency, parametric study is carried out using simulation software HFSS and experimental results. At last, by careful adjustment of these three parameters, we merge the two frequencies so as to acquire a wide-band operation which covers 4 GHz and more than 50% relative band-width. Simulated and measured results show excellent agreement; hence proves the validity of the new capability of CPW.