NARROW BAND-PASS TUNED RESONATOR FILTER TOPOLOGIES HAVING HIGH SELECTIVITY, LOW INSERTION LOSS AND IMPROVED OUT-OF BAND REJECTION OVER EXTENDED FREQUENCY RANGES

摘要

A tuned resonator circuit topology is disclosed that permits implementation ofnarrow band-pass filters having high loaded Q and optimal coupling (for lowinsertion loss) using a parallel tuned resonator topology at freqencies in the1 to 2 GHz range and beyond. The topology consists of a mirror image of theparallel tuned circuit about the signal line of a conventional parallel tunedcircuit to effect a cancellation of virtually all of the induced currentsbetween the inductive elements of the resonators. This reduction in inducedcurrents reduces the magnetic coupling between the resonators, therebyoffsetting the increase in overall coupling between the resonators asfrequency increases, and thereby serves to maintain optimal coupling betweenthe resonators as the frequency of operation increases. Moreover, the mirrorimage topology increases the parallelism between the inductive elements in theresonators, thereby decreasing the inductance values and permitting anincrease in capacitance values. Increasing the capacitancevalues of theresonators effectively offsets the decrease in the loaded Q as frequency isincreased. The topology works for any number of parallel resonators. As theresolution of the manufacturing process decreases (e.g. from printed circuitboard to integrated circuit processes), the range of operating frequenciesscales with the increase in resolution.