Guidelines For Phase Matching And Tracking Coaxial Cables

This article is intended as a general guideline in the selection and specification of coaxial cables for applications requiring phase matching and or phase tracking versus temperature. The match can be specified in electrical degrees as in the suggested best match curves or in nanoseconds of time delay.

The M/A-COM Antenna, Cable and Waveguide (ACW) product line has developed hundreds of various cable sizes/constructions each optimized for different applications. Most utilize solid or air-spaced PTFE dielectrics and fall into four general families that can be characterized by their Velocity of Propagation (Vp):

• 69% Velocity of Propagation
• 76% Velocity of Propagation
• 80% Velocity of Propagation
• 82% Velocity of Propagation

Cables with a solid extruded PTFE dielectric core have a nominal Vp of 69% and are generally the strongest mechanically but worst for insertion loss and phase changes as a function of temperature. Cables with a high air content and a nominal Vp of 82% are generally weaker mechanically but the best electrically with very low insertion loss and excellent phase versus temperature characteristics. Cables with intermediate values of Vp, Vp of 76% for example, are offered as a balance between mechanical and electrical parameters and have proven to be very reliable in over 40 years of service in demanding military programs.