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

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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).