The screw is of modular design and its active part consists of two identical screws that are common screw element and left-handed screw element with shallow grooves.

Impedance bandwidths of the antennas were broadened by adopting step-by-step transition feeding structure. Effects of varying the slot size on VSWR have been analyzed.

The results show that the channel region division and the ruled envelope surface generating can be solved by this approach, and the slot plunge milling of closed blisk can be achieved effectively.