The invention relates to a coaxial-impedance synthesizer, comprising: a longitudinal central (0x) conductor (1); an outer conductive tube (2) arranged coaxially to the conductor (1); and at least one probe (4) mounted so as to longitudinally translate around the conductor (1), the coaxial-impedance synthesizer being characterized in that the outer tube (2) includes two separable half-tubes, such that the probe (4) is permitted to move longitudinally, relative to the central conductor (1), to a desired position when the two half-tubes are spaced apart from each other, and when the two half-tubes are near each other, the outer periphery of the probe (4) and the inner wall of the outer tube are in contact with each other.