Summary

This webinar details Times’ FITS connector system and its use in Naval shipboard applications. The FITS connector system is designed to introduce new levels of flexibility and durability in the most grueling environments. Tony Fedor explains how the system meets the latest military requirements to withstand any number of changing conditions. In addition, he covers the improved shielding capabilities and the overall versatility of the FITS connector system.

Watch the video or read the session notes below.

Session Notes

This webinar provides an overview of the Field Installable Termination Systems (FITS™) connector system in Navy shipboard applications. Many of these systems are connected using MIL-DTL-17 coaxial cables, the base specification for military approved coaxial cables. MIL-DTL-17 sets forth the parameters for cable materials, whether they are low- or high-temperature, fluoropolymers, braided materials, etc. It also includes requirements for testing parameters, including mechanical, physical, and environmental testing.

Cables and assemblies that are qualified to MIL-DTL-17 specifications are listed in the Qualified Products Database (QPD) by the Defense Logistics Agency (DLA). There are about 250 “slant sheets” currently in the MIL-DTL-17 (commonly referred to as M17) spec, and they are all completely different with their own set of electrical, physical, and mechanical parameters that set forth the design. Times Microwave Systems currently maintains more than 160 QPL listings, including high-temperature, low-temperature, armored versions, and many more.

Buyers should use caution when ordering products to meet the M17 spec: some manufacturers use vague terminology such as “M17-type,” “in accordance with M17,” “similar to,” or “equivalent to,” etc., that could lead to false representation. Those designators are not accepted under the current QPL status. For example, a product that states it is “similar to an M17” may fail fluid testing or might not quite meet the electrical characteristics for a broadband test. These issues could have a degradative affect in the performance of any RF system, especially within a military system.

Evolving MIL17 Standards

Back in 1993, there was a MIL standard 454 directive that moved to eliminate the use of PVC on ships. Earlier specs such as MIL-T 24 640, and 24 643 were multiconductor power and control specs that moved to low-smoke zero-halogen parameters. Revision G added requirements for shipboard cables, and a Type 14 crosslink polyolefin jacketing material. This introduced a new series of testing requirements for weathering, abrasion resistance, fluid immersions, heat distortions and a variety of other physical and mechanical properties.

Slant 180 through 200 incorporated direct replacements to RG cables. For instance, an M17 slant 75 is an RG 214 PVC jacketed cable that transitioned into M17-slant 190, a low-smoke zero-halogen version with the Type 14 jacketing, as well as additional features.

Slant 210 through 218 included “unswept” versions that test one discrete frequency many times at 400 MHz. This provides no guarantee of broadband performance, and many are starting to be inactivated for their swept counterparts.

That leads us to the latest specs, slant 220 through slant 229. Times Microwave LLSB®—a series of low loss, highly-shielded designs that provide better overall performance for attenuation and shielding compared to an M17 standard RG cable—fit into this. These are the latest, lowest-loss designs that have been added to the MIL-DTL 17 specification.

In addition to electrical performance, LLSB cables carry the same combustion requirements and testing of the type 14 jacket. So M17 RG and MIL17 slant 220 through 229 cables all meet combustion requirements including flame performance, acid gas, halogen content, smoke and toxicity levels.

The Perfect Mate: FITS Connectors

LLSB cables are fully QPL’d under the M17-DTL or MIL-DTL-220 through 229. To add to this, Times Microwave created FITSä, a Field Installable Termination System incorporating a series of connectors and tools to fit LLSB cables.

The big advantage of FITS is the excellent and consistent RF performance of the connectors. They are truly field-installable with ruggedized performance and a superior plating thickness. We have created DLA part numbers for 16 approved FITS connectors, with new ones coming.

FITS connectors use a bi-metal tin nickel plating. Traditionally, tri-metal plating (zinc, tin, and copper) was used and by comparison, the bi-metal plating performs extremely well in terms of corrosion, including excellent performance with the MIL-STD-810 requirement, or the salt fog test.

Summary

Beyond Teflon®: RF Assemblies for Extreme Environments, is part of our Times Talks webinar series.

Teflon® coaxial cables offer excellent performance, but every material has its limits. Learn how to specify the best, hermetically sealed, custom-designed cable assemblies that fit your system. Our team has helped hundreds of customers specify and qualify the correct SiO2 cable assembly for their applications.

Watch this webinar on-demand or read the session notes below.

Session Notes

Teflon is a phenomenal dielectric for microwave cables. It’s lightweight, low loss, and very flexible. However, even an excellent product has limits. Extreme environmental conditions are one for Teflon. For example, applications such as hypersonic missile guidance will reach temperatures ranging from 200-250°C, or even as high as 600-1,000°C. Teflon will simply melt in those conditions.

Second would be any application that requires strict phase stability. As discussed in our recent webinars on phase performance, the ability to match multiple microwave cables to each other so the signal takes the exact same amount of time to travel through, as well as controlling how that phase relationship changes over temperature, are absolutely essential properties in microwave cables used in applications like phased array radar.

A third extreme environment is high radiation, found in applications such as particle accelerators, where two beams smashing together generate a significant amount of radioactivity.

To address the challenges, Times Microwave has developed a proprietary silicon dioxide dielectric (SiO2) that excels in these environments. Silicon dioxide is used throughout the micro-electronics industry for its excellent insulating properties. The construction of the silicon dioxide coaxial cable starts with a solid oxygen-free copper center conductor, a silicon dioxide insulating dielectric, and stainless-steel jacket that has copper cladding to act as the outer conductor.

Silicon dioxide provides excellent phase stability and low hysteresis and can perform at extreme temperatures ranging from just above absolute zero to 1,000°C. The metal and silicon dioxide dielectric construction makes the cable resist radiation naturally, up to 100 mega rads. The stainless-steel jacket is welded to the connectors with laser beam technology to create a hermetic seal.

When specifying electrical performance for these cables, the first thing to think about is attenuation or insertion loss, which will depend on the cable size selected. Next, in terms of electrical length, it should be determined if the cables in the system need to be phase matched.

There are several ways Times Microwave can phase match cables, including relative or absolute value. A third option is to establish a golden standard—Times Microwave builds and tests one of the assemblies, and the data for all future assemblies is matched to the golden standard to ensure everything produced is the same.

In terms of power handling capacity, silicon dioxide is excellent in high power applications due to the nature of its construction. However, there are a few things that will decrease the power handling capacity of the cable. The first is VSWR; the higher the VSWR, the lower the power handling capacity. Second is altitude. If the application is operating in a vacuum, it will lose the natural convection that takes heat away from the cable, which will in turn reduce the maximum power that can flow through the cable. Finally, the operating frequency will determine what the power handling capacity of the cable can be.

Case Study: Climate Monitoring Satellite

Following is an example of a climate monitoring satellite application that required a set of electrical performance parameters that no other cables in the world could meet. It incorporates a space-based synthetic aperture radar to find sub-millimeter sized changes in the height of an ice cap to determine how much water is present.

From an RF perspective, extreme accuracy was required—any sort of error absolutely needed to be minimized, including the transmit and receive cables. All the different antenna cables had to be phase matched so the sensors could best understand exactly what they were seeing from the radar pulses. Temperature fluctuations also had to be addressed as a space-based application will go from warm on the day side of the planet to cold at night based on its orbit.

Other mechanical elements of the silicon dioxide cable that were relevant for this application included the stainless-steel jacket with a welded connector, designed to perform very well under high vibration environments such as during launch. It is also a non-outgassing material and is compliant for radiation considerations in an orbital environment. The third feature that will impact the mechanical configuration of the cable is the connector, which is application dependent.

Case Study: Hypersonic Missile Application

In this application, it was important to focus on the temperature capabilities of the silicon dioxide cable since a hypersonic missile will go through the top of the atmosphere, generating huge amounts of heat, similar to a space shuttle during re-entry.

As previously mentioned, the silicon dioxide cable itself can readily withstand those heat loads. But beyond that, one of the important requirements was phase matching at ambient temperatures. As the cable moves from cold temperatures to very hot temperatures, the phase matching between cables needs to track.

Furthermore, there are basic assumptions that likely have applied to many other specified cable assemblies that may not fit for extreme environments. For example, a shrink-down marker band that includes data such as the part number, serial number and manufacturer is a standard component in a bill of materials. However, at high temperatures, it is very likely that those marker bands will melt and create a potential foreign object debris hazard. The cable assemblies used in this application were laser marked to ensure that the important data was still included without creating any fault in the system while in operation. Custom connectors were also designed.

Medical Ablation Medical Design Outsourcing

Microwave ablation systems provide nonsurgical methods for treating internal cancers and tumors. This application requires the right cable assemblies to achieve optimum performance.

How high-frequency interconnections affect microwave ablation systems

Radiofrequency (RF) and microwave energy carry many modern messages as part of the broadcast and wireless communications but are also potentially life-saving medical tools. Within ablation systems, radiofrequency and microwave energy can penetrate a patient’s body to heat and destroy tumors, avoiding invasive surgical procedures and long recuperation times.

These systems feature advanced software and artificial intelligence (AI) methods to treat tumors with minimal damage to surrounding tissues, but they still depend on many different types of RF/microwave components. This includes coaxial cable assemblies and often-invasive antennas formed of coaxial cables. The performance of these cables is crucial because life may depend on them.

How they work

Radiofrequency and microwave ablation systems use tiny antennas or probes projected onto a patient’s body to focus electromagnetic (EM) energy on tissues to be treated.

To reach malignant tissue with adequate EM energy, small-diameter coaxial cables are used to form finely polished antennas or probes and to transfer the EM energy from a source to the antenna. Those cables should provide performance levels that help RF and microwave ablation systems destroy the targeted malignant tissues. Shielded coaxial cables with low loss at the target frequency are typically used to preserve as much of the high-frequency source energy as possible; high loss in these interconnection cables will result in RF/microwave energy lost through heating the cables rather than heating the tumor.

How they differ

The smaller wavelengths and higher frequencies of microwave ablation systems allow deeper heating penetration and wider area heating coverage than radiofrequency ablation. Ablation systems typically operate in the ISM (industrial, scientific, medical) bands at frequencies of 915 MHz, 2.45 GHz and 5.80 GHz and at power levels of 50 W (+47 dBm) or more.

That EM energy is coupled to the antenna or probe by means of a low-loss coaxial cable assembly. Higher, millimeter-wave frequencies (through 60 and 70 GHz) have been used in ablation systems for special treatment, although the difficulty of generating EM power at these higher frequencies makes the component selection for those microwave ablation systems even more critical. That is, the energy loss of a coaxial cable increases with increasing frequency.

Cable considerations

The coaxial cables used in ablation systems and other high-frequency medical electronic systems are typically flexible cables capable of wide-band frequency coverage. They should be specified carefully according to parameters that can affect RF and microwave ablation system performance. Those parameters include loss/attenuation, phase stability, shielding, passive intermodulation (PIM) and velocity of propagation (VP).

Cable loss or attenuation is a function of its dielectric and conductive materials, diameter, length and the operating frequency. Loss increases with frequency and excessive loss can cause the temperatures of the cable and ablation antenna to rise, resulting in unwanted heating of tissues along the signal path to the antenna. In some cases, it may require some form of cooling to offset the cable temperature rise caused by handling too much power with too much loss/attenuation. Cable loss is typically characterized in dB/ft. It decreases with larger cable diameters, although they are less likely to reach a patient’s malignant tissue area.

Phase must be extremely stable along the EM power path in an RF or microwave ablation system to maintain a tightly focused energy beam on a malignant tissue. Multiple cables are used in phased arrays to create focused energy on the tumor. Phase deviations can occur with cable flexure and with temperature changes, which are usually measured and compared from cable to cable in terms of ppm/°C. Phase can also vary with impedance mismatches from a nominal 50 Ω, which are measured by variations in voltage standing wave ratio (VSWR) with frequency.

Other performance parameters include the effects of propagation delays and velocity of propagation through the cables, passive intermodulation and its impact on signal integrity, and shielding effectiveness, which describes how well a cable assembly is isolated from surrounding electrical devices and energy sources.

Shielding effectiveness is key because high energy levels could interfere with other systems using the same frequencies, such as WiFi.

RF and microwave ablation systems make huge differences in the health and lives of many patients. Coaxial cable assemblies are among the high-frequency components that make RFA and MWA systems possible. When they perform properly, they can be lifesavers.

The opinions expressed in this blog post are the author’s only and do not necessarily reflect those of Medical Design and Outsourcing or its employees.