A Systematic Design of an Ultra‐Compact and Low‐Loss Broadband Filtering Power Divider Using a Novel Three‐Conductor Broadside Coupled Line in Substrate Integrated Suspended Line

ABSTRACT

Designing broadband filtering power dividers with simultaneous wide bandwidth, low insertion loss, and compact size remains a significant challenge. This paper presents a novel solution using a three‐conductor broadside coupled line (TCBCL) structure, implemented on a low‐loss multilayer substrate integrated suspended line (SISL) platform. The proposed design features an air‐gap quasi‐metallic configuration between conductors to minimize dielectric loss. Input power is coupled directly from the center conductor to two side conductors, achieving equal power division ratio with an inherent broadband bandpass response. The output ports isolation is enhanced by vertically connecting two surface mounted resistors between the top and bottom conductors. For validation, a prototype was fabricated and measured, exhibiting an ultra‐compact core circuit size of only 4.11 mm × 1.08 mm × 3.25 mm. Measured results show an insertion loss below 0.57 dB across 7.7–18.1 GHz, corresponding to a fractional bandwidth (FBW) of 80.62%. This work demonstrates an effective and miniaturized design approach for high‐performance, highly integrated RF front‐ends and passive devices.