Compact Filtering Power Divider With Sharp Roll-Off Skirt and Deep Suppression Using Coupled Square Ring Resonator

In this article, a novel compact filtering power divider (FPD) with sharp frequency selectivity, high in-band isolation, and deep out-of-band suppression is proposed. The realization of filtering and power division functions is achieved by utilizing a U-shaped resonator coupled square ring resonator (UR-CSRR). The UR-CSRR configuration is proposed using a modified U-shaped resonator (UR) coupled with a modified square ring resonator (SRR). By loading a pair of open stubs at the ends and a stepped impedance open stub at the center of an SRR, the modified SRR with two controllable transmission zeros (TZs), which can be used to adjust the bandwidth and improve the upper stopband, is realized. The modified UR is formed by loading a single open stub and two pairs of open stubs with the ability to generate a controllable TZ at the right edge of the passband at the center and in the upper stopband at the ends of a UR, respectively. To generate the output signal, two output lines are inserted on both sides of the single open stub, which can also introduce two TZs. In addition, two resistors are introduced between the two output lines to obtain high in-band isolation. To validate this design concept, an FPD with a center frequency of 3 GHz is designed, simulated, and measured. Measurements indicate that the minimum in-band insertion loss is 1.1 dB, the 3-dB fractional bandwidth (FBW) is approximately 25%, the out-of-band suppressions of both upper and lower stopband are greater than 30 dB, and the in-band isolation is greater than 25 dB. The simulated and measured results are in good agreement, demonstrating the feasibility of the proposed design strategies.