High power microwave cables play a critical role in transmitting radio frequency (RF) signals for countless applications across industries including military, communications, semiconductor and medical. These applications include a wide variety of directed energy weapons, such as high-power microwave and laser weapons; radar systems for detection, search and targeting; high-power communication systems; and medical imaging systems, such as MRIs.

High power microwave coaxial cables have unique requirements, as well as several potential damage mechanisms that can compromise their performance. As a result, Flexco Microwave KW- and S-series coaxial cables have been engineered to withstand damage, thereby improving performance and increasing reliability in demanding applications.

High power coaxial cable requirements

High power microwave cables are used to transmit RF signals from one point to another with low signal loss. They consist of a center conductor or core made from a single copper or copper-coated steel wire that carries the signal. A dielectric material wraps around the center conductor, which insulates it from an outer conductor. A metal shield in the form of a foil or braid wraps around the outer conductor to cancel electromagnetic interference. The coax cable assembly is then covered with an outer jacket that provides environmental protection (Figure 1).

Figure 1. Coaxial cable components. Source: Flexco Microwave

Cable damage causes and effects

High power coaxial cables may be subject to several potential mechanical, moisture and thermal damage mechanisms. Mechanical damage can occur if the cable is exposed to high stresses or large deflections that can be experienced during installation, servicing or operation with moving mechanical assemblies. This is often caused by lack of flexibility, which lead to kinks and bends that could damage the cable components, including the shielding, dielectric and jacket. Moisture damage can occur if there are poor seals at the connector or behind the connector where it is soldered or crimped to the cable, causing leaks when the cable is mated. Thermal damage can result from exposure to high heat environments or if the power transmitted through the cable exceeds the rate at which the outer layers of the cable can dissipate the heat.

Mechanical, moisture and thermal damage mechanisms can cause a variety of problems that may interrupt or incapacitate the cable, such as short circuits, signal loss or degradation, electromagnetic interference or excessive electronic noise.

Flexco high power cables

Flexco Microwave pioneered a major advance in coaxial interconnects through the development of flexible coaxial cables that maintain their electrical stability under repeated flexure. Typical power coaxial cable assemblies use a foil-wrapped and braided style outer conductor, which limits flexibility and requires a larger size to accommodate high-power applications.

Flexco’s cables provide higher average power handling capabilities than other cable assemblies of similar size by using a unique outer conductor design and extruded, homogeneous, air articulated PTFE dielectrics. The outer conductor, consisting of copper with deep convolutions, exhibit excellent thermal conductivity properties and in turn will dissipate heat more efficiently.

The Flexco high power cable design can be modified and customized to meet the unique needs of specific applications. These modifications can be applied to the cable jacket, shielding, dielectric and conductor, as described below.

• Jacket: Flexco manufactures jackets made from polyolefin, neoprene, Kynar or low-smoke zero halogen. For example, high power applications might be made of neoprene or LSZH, which can inherently withstand higher temperatures.
• Shielding: Flexco’s patented convoluted copper shielding offers added protection and durability without sacrificing flexibility. Most high-power cables are bulky and semi-rigid because they use additional foil wraps and metallic braiding, which decrease flexibility and reduce heat dissipation. Because of improved shielding, the compact cable design has the flexibility and power capability of a larger RF cable.
• Dielectric: Flexco’s patented dielectric processing methods make calculated helical cuts to air-articulate the PTFE, polyethylene and expanded PTFE tape. These cuts create a flexible air line that improves heat dissipation and cooling of the cable assembly.
• Conductors: Stranded center conductors improve performance of high-power applications where the large diameter assemblies have a tubular center conductor that allows air to pass for cooling and heat dissipation. Flexco’s outer conductors do not kink and keep the center conductor concentric.

These modifications provide high power coaxial cables with better shielding and greater ruggedness and durability, increased flexibility and higher temperature operation through a better cable cooling design.

The Flexco KW- and S-series cables provide exceptional heat dissipation and shielding without compromising flexibility. The KW-series cable (Figure 2) uses the Flexco patented convoluted outer conductor and is packaged in a larger diameter than their standard cables. This enables greater flexibility and higher power than other coaxial cables on the market.

Figure 2. Flexco KW-series cable. Source: Flexco Microwave

The S-series cable (Figure 3) differs from the KW-series cables by use of an outer conductor that uses a corrugated copper tubing with PTFE air dielectrics, which makes the S-series cable more rigid than kW-series. However, this outer conductor has excellent shielding and heat dissipation and allows the S-series cable to be offered in smaller diameters than the KW-series cables since it can handle more power with lower loss at smaller diameters.

Figure 3. Flexco S-series cable. Source: Flexco Microwave

Flexco Microwave

Flexco Microwave Inc. is a family owned and operated business in New Jersey, with more than 50 years of experience producing flexible coax cables for several industries, including military, aerospace and aeronautics. The company is compliant with and certified under several quality control programs, such as ISO 9001:2015, NIST 800:171 and J-STD-001. Our dedicated team of applications, design and manufacturing engineers can assist customers to facilitate the rapid development, qualification and manufacturing of specialized flexible cable designs for a wide variety of applications in several industries.

While Flexco has an extensive catalog containing a variety of designs for multiple applications, each cable series can be engineered to unique specifications that are needed for different user applications, environments, demands and performance. The company can supply cables to various depots for aftermarket spares, and if necessary, reverse engineer legacy cables if no supply is available. Learn more about Flexco Microwave and their solutions.