A New Balanced-to-Unbalanced Filtering Power Divider With Dual Controllable Passbands and Enhanced In-Band Common-Mode Suppression

A new microstrip balanced-to-unbalanced power divider with dual bandpass filtering response is presented in this paper. The generalized mixed-mode scattering matrix for the filtering balanced-to-unbalanced power divider is derived to guide the design. Differential-mode (DM) dual-band filtering response is analyzed under the odd-mode excitation to show that the frequency ratio (k = f₂/f₁) and bandwidth of these two passbands could be flexibly controlled. For the even-mode excitation, two intrinsic transmission zeros generated by additional open-ended stub are introduced, aiming to achieve the enhancement of in-band common-mode (CM) suppression. In addition, good in-band isolation and port matching are realized by introducing a grounded resistor. To validate the design concept, two prototypes centering at 1 and 2.5 GHz (k = 2.5), as well as 0.76 and 2.75 GHz (k = 3.62) are implemented following the given design procedure. Tested results of the two fabricated circuits, well agreeing with the simulated ones, exhibit high performances in terms of DM response, in-band CM suppression, port-to-port isolation, and port matching.