Design and characterisation of electromagnetic bandgap filters

Abstract

Most signal processing / communications applications heavily rely on filters. For adaptive spectrum filtering and for applications that switch between sets of different filter implementations, it would be beneficial to utilize just one, tuneable band-pass filter. In recent years, the study of metamaterials emerged as an area of scientific research due to the unique attributes of metamaterials. Metamaterials typically are artificial structures with properties not found in nature, for instance negative refraction indexes. Their feature sizes span a fraction of the wavelength corresponding to their frequency of operation. A sub group of metamaterials, the electromagnetic bandgap (EBG) structures, exhibit stopbands for electromagnetic waves irrespective of polarization or angle of incidence. EBG structures prominently achieved surface wave suppression to minimise cross talk between neighbouring devices and improving antenna efficiency by acting as a perfect magnetic conductor within a certain frequency range. The thesis investigates the suitability of EBG structures for filter implementations. The goal is to provide a tuneable band-pass filter for adaptive spectrum filtering and communication applications. The bandgap of an infinite array of EBG cells is numerically determined. Based on those results, an EBG band-pass filter implementation on a printed circuit board (PCB) is designed, fabricated and characterized. Different tuning methods were incorporated into the PCB design to create a tuneable EBG band-pass filter. An EBG filter was built on a fused silica wafer, in order to shift the passband to higher frequencies.