Most coaxial cables on the market have either a solid or stranded inner conductor, making the selection of a cable assembly a trade-off between lower loss (choosing the solid wire) or flexibility and phase stability (choosing the stranded wire).
A stranded wire cable assembly has higher attenuation compared to solid wire. Well known as the skin effect, the signal only flows in the outermost few microns of the inner conductor, so the signal path in the stranded conductor is longer than in the solid wire. This behavior is more pronounced with microwave signals than at low frequency. Also, the greater contact resistances between the individual strands contribute to higher loss.
On the other hand, microwave cables with solid wire have greater phase deflection with bending than cables with stranded wires, particularly for cable types with a dielectric diameter greater than 2 mm. This effect is caused by interaction among the various elements of the cable. The cable length is reduced slightly when bent, which deforms the inner conductor and results in a phase shift. To plastically deform the individual wires of a strand, a stronger bending movement is required. Alternatively, the same bending of the two cable types yields smaller changes in length and a more stable phase in the stranded microwave cable.
Two-in-one
To resolve this either/or trade-off, HUBER+SUHNER has combined the advantages of the solid and stranded wire assemblies into one product, a two-in-one cable assembly with a flexible inner conductor that is low loss and phase stable. HUBER+SUHNER has achieved this with a unique and patented rotary swaging technology, combining the advantages of solid and stranded wires in the SUCOFLEX 500 family. The latest addition to the family is the SUCOFLEX 550S, which has excellent performance to 50 GHz.
Figure 1 Inner conductor before and after swaging.
Figure 2 |S11| comparison between cable assemblies with a stranded inner conductor and a rotary swaged inner conductor.
Figure 3 The SUCOFLEX 550S is well-suited for vector network analyzer measurements to 50 GHz.
Rotary swaging is a process of mechanical deformation, guaranteeing a near-perfect round and smooth surface (see Figure 1). It is achieved through repeated blows to a conventional strand, using automated “hammers” to smooth the surface of the stranded wire. The smooth surface prevents possible discontinuities in the microwave cable, reducing return loss peaks. Conventional stranded wire has a structure susceptible to return loss peaks, caused by variations in diameter that change the impedance of the cable and reflect a portion of the microwave signal. Discontinuities occurring at a regular interval will cause a strong reflection or return loss peak at a certain frequency. The rotary swaged stranded wire eliminates this possibility, mimicking the signal path of the solid wire and improving the return loss (see Figure 2). Also, the contact resistance is lower compared to a conventional, true concentric stranded wire, which reduces insertion loss.
Developed in Switzerland, the rotary swaging technology provides the longest assembly/cable lifetime currently available on the market at an excellent price-performance ratio. Typically, cables with solid wire will break after 10,000 to 20,000 flex cycles, but all SUCOFLEX 500 assemblies will withstand more than 100,000 flexures without degrading performance. They are designed to withstand abrasion, pressure and moisture.
The SUCOFLEX 550S is well-suited for test & measurement applications, including benchtop, high throughput production testing and vector network analyzer measurements to 50 GHz (see Figure 3). For test & measurement applications, the SUCOFLEX 500 assemblies deliver the best phase and amplitude stability versus flexure, movement, temperature and tensile stress - with outstanding return loss and insertion loss to 50 GHz.
The SUCOFLEX 550 family supports customers who need affordable, customized assemblies with short delivery times. HUBER+SUHNER supplies all standard-length products within five working days and customized lengths within 10 working days, worldwide.
Other products in the HUBER+SUHNER portfolio use swaging technology, including the SUCOFLEX 100 series, flexible microwave cable assemblies with superior electrical and mechanical performance for static and dynamic applications, and the Spuma RS FR, the most flexible cable in the Spuma family, featuring a new TPU jacket material which is flame retardant without compromising flexibility.
Cable selection is no longer a trade-off. Unique in the market, the patented rotary swaging technology reflects HUBER+SUHNER’s innovative leadership in the industry.
HUBER+SUHNER AG
Herisau, Switzerland
www.hubersuhner.com