Abstract: The demand for miniaturization and high reliability of antennas in spaceborne communication systems is increasingly stringent. Traditional fixed-size quadrifilar helix antennas fail to meet the spaceborne installation requirements due to their large deployment height and excessive envelope. The helicon of the spaceborne deployable helix antenna is researched in this paper, and the design around the core goal of "no yielding in retraction and compression, and stiffness maintenance in the deployed state is carried out". First, based on the mechanical theory of helical spring structures, a parameter mapping model of "working state - free state" is established. With the constant deployed length as the constraint, the calculation methods for the mean diameter, pitch and helix angle in the free state are derived. Second, focus on the problem of reduced stability caused by the large helix ratio, a scheme of "conformal cable pre-tightening + incomplete deployment" is proposed, which balances the stiffness and yield risk through pre-tightening load. Finally, an innovative process combination of "mold forming + furnace heat treatment + heavy pressure treatment" is adopted to solve the problem of dimensional precision. Experimental verification shows that the four helicon made of beryllium bronze do not undergo yield deformation in the retracted state, the deployment repeat accuracy is less than or equal to 1 mm, and its fundamental frequency in the expanded state is greater than 1Hz, the product meets the application requirements.