A BROADBAND NEGATIVE EPSILON FRACTAL METAMATERIAL UNIT CELL FOR COAXIAL NOTCH FILTER APPLICATIONS

Herein is presented a two-dimensional negative permittivity unit cell for coaxial notch filter applications. This novel unit cell is developed through simulation in the context of an ideal infinite parallel plate waveguide, and preliminary implementation is demonstrated through simulation and measurement in a finite parallel plate waveguide. Finally, the unit cells are incorporated as an in-line notch filter in a coaxial transmission line, and their efficacy is demonstrated through simulation and measurement. The unit cell developed for this application was formed as a broadband fractal expansion of the traditional capacitively loaded strip. A partial repetition of the basic CLS I-shape was inserted in the capacitive gap on either side of the structure. This new unit cell was developed and simulated in HFSS using an incident TEM wave excitation in a parallel plate waveguide, and was shown to have two resonant frequencies of interest. The first resonance produces a wide bandwidth of negative permittivity (29.5%) from 1.3 GHz to 1.75 GHz; the second produces a region of negative permeability from 2.05 GHz to 2.45 GHz, a bandwidth of 17.8%. The current on the structure at each of these frequencies is presented, along with the pertinent fields in the waveguide. The effects of various alterations to the basic shape of the unit cell are also presented.