I want to understand what factors determine acceptable turning radius of RF cable. are the losses high for low frequency or at high frequency if cable is turned or twisted ? the cable i am referring is an coaxial cable. i want to know how cable core conducting metal diameter, sheath metal, insulator characteristics etc in RF cable effect cable turning radius.
The problem with bending a coaxial cable too sharply is that the cross-section of the cable is crushed out of round, which would change the characteristic impedance of that section. Just as with most other defects in transmission lines, the loss will increase with frequency.
The bending radius has no direct electrical significance; it just determines how much stress there is on the materials that make up the cable, and the effect on the cable will depend on exactly what those materials are. The particular materials will also affect whether the cable is permanently damaged or it will recover when unbent.
I doubt you will find any general rule for calculating the bend radius; it's a fairly complex interaction between the material properties of the at least four different elements of the cable.