Microwave Fractal Bandpass Filters Based on Modified Hilbert Curves of the First and the Second Orders

Abstract

The microwave fractal bandpass filters based on modified Hilbert shaped curves of the first and second fractal orders are experimentally and numerically analyzed. As a substrate Al₂O₃ ceramic covered by the thin silver layer with thickness of 50 μm was used. The laser patterning technique was used to design the structures of filters. The filter based on the Hilbert curve of the first order has resonance at ∼4.01 GHz, while the filter based on the second order Hilbert curve has resonances at ∼3.09 and ∼6.34 GHz. The estimated loaded Q-factor of the filter based on the first order Hilbert curve was ∼94. The electromagnetic field distribution of the filter was visualized by using the thermo-elastic optical indicator microscopy.