Reconfigurable ring filter based on single-side-access ring topology is presented. Using capacitive tuning elements, the electrical\nlength of the ring can be manipulated to shift the nominal center frequency to a desired position. A synthesis is developed to\ndetermine the values of the capacitive elements. To show the advantage of the synthesis, it is applied to the reconfigurable filter\ndesign using RF lumped capacitors. The concept is further explored by introducing varactor-diodes to continuously tune the\ncenter frequency of the ring filter. For demonstration, two prototypes of reconfigurable ring filters are realized using microstrip\ntechnology, simulated, andmeasured to validate the proposed concept.Thereconfigured filter using lumped elements is successfully\nreconfigured from 2GHz to 984.4MHz and miniaturized by 71% compared to the filter directly designed at the same reconfigured\nfrequency, while, for the filter using varactor-diodes, the frequency is chosen from 1.10GHz to 1.38GHz spreading over 280MHz\nfrequency range. Both designs are found to be compact with acceptable insertion loss and high selectivity.
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