Dielectric measurements of a new antiferroelectric liquid crystal series exhibiting different phase sequences have been carried out as a function of frequency from 10 Hz to 10 MHz. Structural properties of SCα* and ferrielectric SCFI* phases were discussed on the basis of the experimental results of temperature and dc bias field dependencies of the dielectric modes. Besides the soft mode observed around the SA−SCα* phase transition, a Goldstone mode was detected in the SCα* phase indicating a helicoidal structure with small pitch values. In agreement with a bilayer ordering model, the dielectric absorption in the SCFI* phase was splitted up into two contributions: one related to a Goldstone mode and the other to an azimuthal antiphase mode.