Using parallel resonators to create improved maximally flat quarter-wavelength transformer impedance-matching networks
This paper presents a general approach for designing maximally flat quarter-wave transformer impedance-matching networks (QWT-IMN's) used in conjunction with parallel resonators. The approach used finds a maximally flat form by setting lower order terms of the general form to zero. This general form is found using ABCD matrices . The resulting maximally flat form is identical to the form for quarter-wavelength-coupled filters. Using parallel resonators improves QWT-IMN designs in three ways. First, adding parallel resonators to a QWT-IMN improves the poor stopband rejection from which QWT-IMN's suffer. Second, for a given load-to-source mismatch, a QWT-IMN has a fixed response, i.e., a fixed total Q. By using more than one parallel resonator, numerous response realizations, i.e., values of total Q, can be achieved for a given load-to-source mismatch. Third, using parallel resonators requires one less quarter-wave transformer to achieve the same order of response. © 1999 IEEE.
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