Frequency-Tunable Nonreciprocal SIW Filtering Power Divider Using a Common Resonator with Mixed Static and Time-Modulated Degenerate Modes

This article presents, for the first time, a frequency reconfigurable nonreciprocal filtering power divider (FPD) based on spatio-temproal modulated (STM) substrate integrated waveguide resonators. It consists of a common square SIW cavity and four branch triangular SIW cavities. The common cavity operating in mixed static and time-modulated degenerate modes is first utilized for power distribution to reduce size. Based on the inherent out-of-phase characteristics of the TE210 mode (one of degenerate modes), the isolation resistors are crossed over the symmetry plane of the common cavity to enhance the output isolation of power divider. By tuning the time-modulated capacitors integrated on the SIW cavities, the nonreciprocal power diving responses with frequency tunability are achieved. For verification, a frequency-tunable nonreciprocal SIW FPD is designed and fabricated. Within the tuning range of 2.38-2.42 GHz, the measured 10-dB bandwidth is about 1.6% with the minimal loss of 4.8 dB. A 10-dB nonreciprocal isolation bandwidth of 21 MHz is achieved at 2.4 GHz, and the output isolation is greater than 21 dB. The lower and upper passband selectivities are 586 and 362 dB/GHz, respectively.