Dual-Band Filtering Power Divider With Tunable First Passband Frequency and Isolator Functionality

This paper investigates a detailed design methodology for an arbitrary power division ratio (PDR) multi-functional dual-band filtering power divider (FPD) that combines tunable frequency and isolator functionality. The proposed dual-band FPD features RF isolator functionality with tunable passband frequency at first passband and reciprocal response power divider functionality at second passband. Dual-band filtering response is achieved through utilization of multi-mode time modulated resonators (MM-TMR) and admittance inverters. By using time-varying capacitors with progressive phase delay at first-mode of MM-TMR, isolator functionality (i.e. $\vert S_{21}\vert ~\ne ~\vert S_{12}\vert $ and $\vert S_{31}\vert ~\ne ~\vert S_{13}\vert $ ) is attained at first passband. Conversely, reciprocal response (i.e. $\vert S_{21}\vert = \vert S_{12}\vert $ and $\vert S_{31}\vert = \vert S_{13}\vert $ ) at second passband is achieved due to absence of time varying capacitors at second-mode of MM-TMRs. Analytical spectral scattering parameters have been derived to provide deeper understanding of non-reciprocal behavior (isolator functionality) at first passband and reciprocal behavior at second passband. By controlling the first-mode resonant frequencies of MM-TMR, tunable frequency characteristics at first passband is obtained. The design concept has been validated by fabricating and characterizing a prototype of dual-band FPD with equal PDR. In experimental results, the isolator functionality with forward transmission insertion loss of 3.92 dB and reverse attenuation higher than 20 dB are achieved while tuning first passband frequency from 1.39 GHz to 1.76 GHz (23.49%) while the second passband frequency is fixed at 2.54 GHz with reciprocal response.