Improved RF Metamaterial Band-Pass Filter Design Using CSRR Structures on LCP Substrate

In the past decade, the emergence of man-made structures with unusual electromagnetic properties not seen in nature—commonly known as “metamaterials”—has generated much interest in designing filters, antennas, lenses, and other devices based on negative values of permittivity (ε) and permeability (μ). Manipulating negative values of these electromagnetic parameters has found applications in communication technology and cloaking research by taking advantage of interesting phenomena such as a negative index of refraction and the reverse Doppler Effect. RF and microwave filters with different frequency responses (low-pass, high-pass, band-pass, and band-stop) can be realized by varying microstrip signal line shapes at a frequency of interest due to the fact that the metamaterial frequency response is dependent on the physical dimensions of the structures. For example, the center frequency of a filter can be determined by adjusting the physical dimensions of metamaterial building blocks called split-ring resonators (SRR) or their duals, complementary split-ring resonators (CSRR). To further metamaterial applications, however, non-planar surfaces and effects of curvature on frequency response must also be considered. In this work, an RF metamaterial filter is presented to demonstrate an improvement in the band-pass frequency response from a previous design at Auburn University by enhancing the upper band behavior of the filter. This is achieved by modifying the metamaterial design on the microstrip device to incorporate new additions to the signal line to combine both high-pass and low-pass metamaterial design concepts, resulting in a band-pass response. The filter is designed using a liquid crystal polymer (LCP) slab as a substrate due in part to its dielectric properties, but also to investigate the filter's performance on a flexible structure. An exploration into the roles of different signal line and CSRR dimensions in filter design is given, and a microstrip filter designed using ANSYS HFSS is shown along with simulation results to verify band-pass filter response. LCP was selected due to its excellent RF properties, its resistance to moisture absorption, and its ability to be micromachined.