Electronically tunable fractal microstrip resonators and filters

A new electronically tunable fractal resonator which consists of two Hilbert fractal curves of the second order is proposed, analyzed and used for microwave filter design. The proposed resonator is characterized by an additional degree of freedom which offers more agility in the filter design. The influence of varying geometrical parameters of the resonator is first analyzed, such as the line-to-spacing ratio. By using switches placed at relevant positions in the proposed resonator, electronical tuning of the resonant frequency is obtained, while the out-of-band performances remain the same. To demonstrate advantages of the proposed approach, a two-pole electronically tunable bandpass filter is designed.