Metamaterial-based electromagnetic bandgap structures for surface-wave suppression and mutual-coupling reduction in GPS antennas

多径干扰是高精度GPS系统面临的一个严重问题。这些信号由建筑物和地球等低海拔物体的多次反射产生，模糊了实际视线(LOS)GPS数据的解释，并破坏了GPS接收器检测其位置的精度和速度。多径信号通常是通过支持传统印刷天线的金属接地板上存在的不需要的表面波来拾取的。这些表面波也是印刷天线阵列中天线元件之间发生有害耦合的原因。电磁带隙(EBG)结构是一种周期性表面，通过向其提供禁止传播的带隙，已被证明非常成功地抑制了接地面上的表面波。然而，传统的EBG具有约为lambda/2量级的周期，并且需要几个周期来充分抑制，这与滤波器非常相似。因此，采用EBG结构的天线往往大得不合理。超材料类似于EBG，但具有极小的周期，可以为这一缺点提供解决方案。尤其是传输线(TL)超材料，本质上适合与印刷电路技术集成，并以其完善的设计方法和易于实现而闻名。该项目试图表征、设计、制造和测试基于TL超材料的小型化EBG地面飞机，以抑制表面波激励，同时尝试优化GPS天线参数，如辐射方向图、轴比(AR)带宽、效率和多频段操作的容量。这将是阿什温·K·艾耶教授(艾伯塔大学埃德蒙顿分校)和GPS天线制造商NovAtel Inc.(卡尔加里分校)的研究小组合作的成果。

Multipath interference represents a serious problem for high-precision GPS systems. These signals, which are produced by multiple reflections due to low-elevation objects such as buildings and the earth, obscure the interpretation of actual line-of-sight (LOS) GPS data and corrupt the accuracy and speed with which a GPS receiver can detect its location. Multipath signals are often picked up via unwanted surface waves that exist on the metallic groundplanes that back conventional printed antennas. These surface waves are also responsible for the deleterious coupling that occurs between antenna elements in printed-antenna arrays. Electromagnetic bandgap (EBG) structures are periodic surfaces that have proven very successful in suppressing surface waves on groundplanes by presenting to them a bandgap, which forbids propagation. However, conventional EBGs have a periodicity on the order of lambda/2, and several periods are necessary for adequate suppression, much like a filter. As a result, antennas employing EBG structures are often unreasonably large. Metamaterials, which are similar to EBGs but possess extremely small periodicities, may provide a solution to this drawback. The transmission-line (TL) metamaterial, in particular, is inherently suited to integration with printed-circuit technologies and is known for its well-developed design methodology and ease of implementation. This project attempts to characterize, design, fabricate, and test, TL metamaterial-based, miniaturized EBG groundplanes to suppress surface-wave excitation, while simultaneously attempting to optimize GPS-antenna parameters such as radiation pattern, axial ratio (AR) bandwidth, efficiency, and capacity for multi-band operation. This will be a collaborative effort between the research group of Prof. Ashwin K. Iyer (University of Alberta, Edmonton, AB) and GPS-antenna manufacturer NovAtel Inc. (Calgary, AB).