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。这些信号是由于建筑物和地面等低海拔物体的多次反射而产生的，它模糊了对实际视距（LOS） GPS数据的解释，并破坏了GPS接收器探测其位置的准确性和速度。多径信号通常是通过传统印刷天线背后的金属接地面上存在的不需要的表面波来拾取的。这些表面波也是造成印刷天线阵列中天线元件之间有害耦合的原因。电磁带隙（EBG）结构是周期性表面，已被证明非常成功地抑制了地平面上的表面波，通过向它们呈现禁带隙来阻止传播。然而，传统的EBGs具有λ /2数量级的周期性，并且需要几个周期才能充分抑制，就像滤波器一样。因此，采用EBG结构的天线通常大得不合理。超材料，类似于EBGs，但具有极小的周期性，可能提供一个解决这个缺点的办法。特别是在线传输（TL）超材料，天生就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。本项目尝试表征、设计、制造和测试基于TL超材料的小型化EBG接地面，以抑制表面波激发，同时尝试优化gps天线参数，如辐射方向图、轴向比（AR）带宽、效率和多频段运行容量。这将是Ashwin K. Iyer教授（阿尔伯塔大学，埃德蒙顿，AB）和gps天线制造商NovAtel Inc.（卡尔加里，AB）的研究小组的合作成果。

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).