Phase-Critical RF Cable Assemblies

Phase is a crucial parameter for detection and measurement in many RF systems such as phased array radar, anti-missile defense, electronic warfare, 5G, test equipment, and many others. These systems rely on continuous transmission and reception of RF signals with high accuracy and consistent speeds. Two primary elements can affect a coaxial cable assembly’s phase tracking characteristic: electrical length and temperature. Phased array radars are multi-elements and rely on coaxial cables with the same electrical lengths between the transmitter-receiver and antenna, which poses challenges when matching the cables.

After the initial match, the coaxial cables must also stay consistent over varying temperatures. As temperatures change, coaxial cables do not precisely track together; the phase match degrades just slightly. That small amount of degradation can adversely affect system performance. Therefore, cable assemblies must be optimized to minimize phase change over temperature.

The concept of phase starts with the fact that a microwave signal propagates in the form of a sine wave. For every sine wave cycle, 360 degrees of electrical length will accumulate.  For example, in the higher frequency range of 5G applications, millions or billions of cycles per second will accumulate. The wavelengths are very short, so maintaining phase accuracy across a cable length becomes exponentially more challenging as frequency increases.

Electronically steered antennas used in many RF applications employ an array of radiating elements to steer antenna beams rather than physically moving an antenna. Beam steering for transmission or reception is performed by adjusting the phase of the individual antenna elements in the array. The antenna array elements are each fed by high-frequency transmission lines. The accuracy of the signal phase presented to each array element depends on the phase accuracy and stability of the cable assemblies.