This article introduces an ultra-compact four-way quadrature power splitter (4W-QPS) based on a novel transmission-line compression technique called double-path zigzag microstrip line (DP-ZML). Detailed design techniques with modular approach are disclosed for the state-of-the-art 5G low-band applications. The theoretical predictions are verified with experimental results through a fabricated prototype that operates from 696.55 to 876.03 MHz with >15 dB return-losses and isolations, and 90°±4° quadrature phase between adjacent outputs. The compact size of this 4W-QPS is achieved at 0.21λg×0.21λg at a center frequency of 786 MHz.