What is special about DPL?

Author: David Pike @Samtec

Samtec is constantly developing new technologies to improve its products. This information overload can confuse customers. Sometimes all they need is a clear description of a new development and an understanding of its potential for their application. With this in mind, this is the first in a regular series of blogs in which I look at some of our products in detail and explain their relevance to the everyday customer. In this first post, I take a look at NITROWAVE™ cables and ask: What's so special about the inner layer?

The inner layer refers to the dynamic power layer (DPL), which is an integral part of the NITROWAVE coaxial cable design. NITROWAVE is Samtec's range of high performance RF solutions for microwave and mmWave applications, including complete cable assemblies, cable connectors and board level interconnects.

Controlling the ratio between conductor and shield is crucial in the development of high-performance cables. The development of a shield is always a compromise between the best possible RF performance and the required flexibility of the cable. Most manufacturers achieve this by using a combination of foil tape or wrap as the inner layer and a woven braid covering the foil.

The NITROWAVE cable consists of silver-plated copper as the material for the foil and braiding. The FEP (fluoroethylene propylene) jacket in Samtec's characteristic orange color provides protection under the harshest conditions. Designed for demanding applications in the aerospace, defense, instrumentation and computer industries, the FEP jacket offers high operating temperature and abrasion resistance.

However, the DPL is one of the most interesting features of NITROWAVE. This is a thin PTFE layer between the foil and braided shield. Insignificant at first glance, the DPL is a central part of the NITROWAVE story. Its main task is to eliminate the friction between the two shielding elements so that the braid can move freely over the foil without damaging it. The DPL further improves the overall reliability. The DPL layer encases the spiral foil screen, improving its flexural strength. It forms an interface between the sensitive foil and the surrounding braided fabric, reducing the risk of conductive oxidation. The result is a cable with higher flexural fatigue strength and improved durability.

The advantages of DPL are not limited to improved mechanical performance. The improved physical properties also improve electrical performance. DPL offers better phase stability. Phase refers to the position of a wave at a specific point in time within its cycle and is important for the propagation of RF signals in cables. A phase shift is therefore a change in wave position, usually caused by external forces such as cable bending or temperature fluctuations. Higher phase stability leads to more consistent RF signals, even if the cable itself is bent.

The DPL layer also helps to reduce capacitive coupling. This is created by two separate shielding layers. In close contact, the two layers can act like the plates of a tiny capacitor. Even small electrical charges between the layers can generate unwanted noise that impairs signal integrity. Even the thin PTFE layer of the DPL is sufficient to minimize this coupling and improve the overall performance of the SI.

One of the problems with high performance products like NITROWAVE and the Samtec precision RF range is that they can alienate some customers. Just as most drivers wouldn't consider using a Rolls-Royce or Ferrari to get to work, designers wouldn't use a 110 GHz cable for their products.

However, a key feature of NITROWAVE is that it is not a single product. Rather, it is a family of cables, each optimized for different frequencies from 18 to a maximum of 110 GHz. The cables have been carefully selected after careful consideration of customer requirements, with each cable designed to provide the best possible insertion loss in its respective frequency range.

NITROWAVE is therefore a product that is not limited to the state of the art.
For a detailed insight into the features of NITROWAVE, download the Guide to Precise RF Design.