Compact Balanced-to-Balanced Filtering Power Divider With Wide Range and High Level of Reflectionless, Isolation, Common-Mode Rejection, and Enhanced Frequency Selectivity

This paper presents a novel compact balanced-to-balanced (BTB) power divider featuring an exceptional reflectionless bandpass filtering response. A pair of three-line coupled structures (TLCSs) are utilized to provide wideband filtering response and equal power division. To enhance the frequency selectivity, an open-circuited stepped impedance stub is added to TLCSs, generating a pair of transmission zeros (TZs) on both sides of the passband. Additionally, simple absorption-isolation networks (AINs) consisting of two resistors and a half-wavelength transmission line (TL) are embedded to provide a full-band non-reflective response at the input port and achieve excellent isolation. The traditional half-wavelength TL between balanced ports is replaced by a stepped-impedance TL, improving in-band matching performance. Furthermore, a detailed theoretical analysis of the proposed design is derived, and parametric studies are presented. To verify the proposed concept, the new multifunctional BTB reflectionless filtering power divider (RFPD) operating at 1.9 GHz is fabricated and measured. The compact fabricated prototype exhibits a 10.8-dB input absorption, 21-dB common-mode (CM) suppression, and 22-dB isolation, all exceeding the bandwidth level of 263.2%. The results show good agreement between simulations and measurements.