Compact Broadband Input‐Reflectionless Filtering Power Divider With High‐Isolation and Extended Out‐Of‐Band Suppression

ABSTRACT This paper presents a filtering power divider (FPD) that integrates broadband absorptive and isolative functionalities while achieving extended out‐of‐band suppression. The proposed design employs an absorption‐isolation network (AIN), composed of microstrip lines and resistors, to ensure simultaneous reflectionless input operation and high isolation without degrading filtering performance or requiring additional absorption circuits. A cascaded coupled‐line (CL) structure facilitates broadband filtering and power division, while parallel half‐wavelength stubs enhance out‐of‐band suppression. Additionally, a π‐type defected ground structure (DGS) is incorporated to mitigate high‐frequency spurious signals, further extending out‐of‐band suppression without increasing circuit footprint. Theoretical analysis and parametric optimization are performed to establish impedance conditions for achieving reflectionless operation and optimizing circuit performance. A fabricated prototype centered at 2 GHz exhibits a 72% 3‐dB bandwidth, input reflection below −10 dB across DC‐4.5 GHz (225% absorptive bandwidth), isolation exceeding 21.1 dB over the entire band, and stopband attenuation beyond 25.2 dB up to 6.8 f 0 . Compared to existing designs, the proposed RFPD achieves broader bandwidth, stronger stopband suppression, and full‐frequency reflectionless behavior, all within a compact 0.71λ g 2 footprint and without the use of additional absorptive stubs. These results validate the proposed FPD as a compact and high‐performance solution for modern RF front‐end applications requiring spectral purity and robust isolation.