A Compact Highly-Selective Balanced-Unbalanced Filtering Power Divider Using Open-Loop Resonator

This article proposes a balanced-unbalanced power divider that employs open-loop resonators to achieve filtering characteristics with an effective suppression of common-mode signals within a single frequency band. In the center, a half-wavelength open-loop resonator is employed, which is magnetically and electrically coupled to the other two resonators. This forms a trisection filter topology. This topology inevitably produces a transmission zero in the lower half of passband thereby improving the selectivity of the filtering response. In order to design the filtering power divider, the trisection filter topology is replicated with respect to the symmetry line. A resistor is placed in between the output ports to improve the common mode response. The simulated outcomes of the proposed design exhibit a narrowband of 2% FBW at 3 GHz with three transmission zeros in differential mode response, -28dB common mode to single-ended ports suppression within the passband, port (unbalanced) matching and -35dB isolation between output ports.