The “Electronic structure” beamline is dedicated for realization different photoelectron spectroscopy application in the SKIF project, requires intense photon flux in the soft X-ray and VUV ranges (10 - 2000 eV). The generation of the undulator radiation in this range is very problematic for electron beams with 3 GeV energy. For keeping the opportunity to cover whole range, the special undulator design with possibility doubling of the period was proposed. The commutation of the coils groups provides change the undulator period from 10 to 20 cm with keeping the amplitude magnetic field (0.5 T). The undulator mode (5 cm period) gives a big flux for high energy edge of the range and the wiggler mode (with period 20 cm) provides the sufficient number of the photons for soft region (down to 10 eV). Some details of the undulator design are presented in the report.