Low-Order Filter Response Enhancement in Reconfigurable Resonator Arrays

Reconfigurable resonator arrays offer the unique advantage of providing an adaptive order filter response by appropriately routing signals of interest through the desired resonators. However, this approach typically results in wasted resources since the inactive resonators of the array may occupy significant volume without actively contributing to the filter response. This paper presents the theory, design, and characterization of a new method for employing previously inactive resonators to locally enhance the array's stopband attenuation. A particular example of a six-resonator frequency-tunable array is synthesized and experimentally validated as a demonstration vehicle of the presented methodology. Two of the resonators define the passband of the filter response that tunes from 1.5 to 1.9 GHz with a 1.2% bandwidth and 2.9-2.3-dB insertion loss ( Qu=450). The four resonators that do not contribute to the passband are used to create destructive interference paths, adding tunable notches to the response that locally enhance the stopband by more than 40 dB in the 1.4-1.9-GHz frequency range. A full-wave simulation study also demonstrates the robustness of the presented approach to nonideal effects of the employed switches. Specifically, an on-state switch resistance of less than 1 Ω contributes an additional passband loss of less than 0.2 dB in the specific implementation shown. In addition, an off-state capacitance of 0.3 pF results in a spurious-free response to 3.86 GHz for a 1.5-GHz filter passband center frequency.