A novel multiport system, allowing for measurements of scattering parameters in over-two-octave frequency range is proposed. It is composed of two directional couplers and a standard 4 × 4 Butler matrix, and does not require any isolators. The presented system features a uniform power distribution providing the high precision of measurements, which can be further enhanced by a simple adjustment of the system's parameters. A comprehensive analysis of the proposed system configurations, a fully analytical calibration for transmission coefficient measurement, and the estimation of maximum measurement error are given. The proposed measuring system has been experimentally verified in a wide frequency range 1–5 GHz, by measurements of S-parameters of exemplary components. The measurement results are very close to the values obtained with the use of a commercial vector network analyser within the 50 dB range of measured values’ magnitude.