RF Interconnect Solutions for Airframe Applications

Modern aircraft carry extensive electronic equipment on board. From supporting passenger Wi-Fi networks to ensuring seamless communications with ground control and other aircraft, communications networks aboard aircraft require durable, flexible solutions that can withstand punishing environments inside and outside the plane.

From the moment the pilot pulls away from the gate and begins receiving instructions from the control tower, they rely on a variety of cable and antenna assemblies located above, below, and inside the plane. However, for avionics equipment to function properly, durability and ease of repair are as essential as seamless communications with the ground. Key considerations for RF interconnects for challenging avionics and airframe applications are outlined below.

• Lightweight: Weight reduction is critical to increasing fuel efficiency. RF interconnects that incorporate low loss, phase stability, and high performance in a shock and vibration environment require a balancing act to reduce size with careful evaluation of materials, constructions, and maintenance. Today’s frequency band requirements are also becoming more complex as 5G, new/upgraded SATCOM systems, and more are creating the need for additional lightweight, small, high-precision RF solutions.
• High Density: In the past, it may have been common to have 20 antennas on a commercial airframe. There can now be up to 300 or more. The increasing number of antennas in aircraft environments also demands more electronic boxes and connections. Furthermore, new high-density solutions are required as frequencies increase and interconnect dimensions decrease to accommodate smaller wavelengths.
• Vibration: When a connector attached to an antenna vibrates, as it will in flight, microphonic noise can impact the connection. This can cause interference in the signal transmission and errors for the RF system. Minimizing space between the cables and connectors is necessary for the interconnect system to survive the high vibration.
• Temperature: Higher altitudes, speeds, and frequencies result in higher temperature requirements, making materials considerations more complex.
• Vapor Sealing: A key consideration in avionics applications is the coaxial cable’s dielectric and how it behaves in its environment. For example, an aircraft on the ground is fully loaded with air. But at flight altitude, a vacuum environment is created, with outgassing conditions for dielectric and other electronic materials. When the aircraft returns to the ground, the cable is fundamentally a vacuum. The dielectric will absorb any fluids or gases surrounding it, and they will recondense within it. The only way to remove contaminants is to bake it, which is not feasible inside an aircraft, so vapor sealing is critical for high-end, high-performance, high-altitude applications.
• Maintenance and Access: Antennas mounted on the aircraft’s exterior are routinely damaged, and expedited repair of those is essential to keeping airlines on schedule and passengers safe. However, antennas are often difficult to access in many avionics systems, making maintenance and replacement complicated and time-consuming.

Coaxial Cables

Innovative new RF interconnect technologies are needed to meet the wide variety of present and future safety-critical avionics application needs. We design coaxial cable assemblies for numerous commercial aviation applications supporting communications, collision avoidance, navigation, remote sensing, in-flight entertainment applications, and more.

We have been manufacturing our three most popular LMR® aviation cables for many years, spanning from the HF to the KA band, including options with a fire-retardant jacket to meet FAA flame test requirements. MaxGain® is our higher-frequency band cable; it’s an outstanding solution for KU and KA-SATCOM feeders.

Our TCA line of cables, tools and connectors has been a leading interconnect solution for the avionics industry for decades. This lightweight low-loss, high-temperature, high-flexibility cable is ideal for meeting avionics’ critical electrical and mechanical performance requirements for applications including navigation, collision avoidance, communication systems, GPS, ADS-B, SATCOM, and ATG.

The TCA product line includes unique, all-in-one prep tools for simple, safe and repeatable cable termination. Users can also save time by pre-terminating the assemblies with the cable entry and using TCA’s reusable pulling eye to “fish” the assembly through the fuselage of an aircraft. This helps cut down on tooling, debris and installation damage.

On the airframe side, our PhaseTrack® PTFE dielectric cables that tolerate high temperatures are typically used and can be combined with a higher-than-standard PTMP tape wrap that is very low loss. This type of solution can be used up to 50 gigahertz or more. At the high end of the temperature spectrum, our SiO2 silicon dioxide cables that are rated for up to 800 degrees Celsius or more can be used.

We also offer InstaBend™, a compact, phase stable, highly flexible, micro coaxial cable. Originally designed for space flight applications, this high-performance cable easily accommodates densely packed in-the-box applications inside an aircraft. InstaBend cable assemblies can be bent around tight corners and very closely behind the connector to minimize footprint, save space, and simplify cable routing in tight spaces while offering low loss and optimized performance. It also eliminates the need to protect the back of the connector and simplifies maintenance.

Connectors

The ultimate goal is to optimize avionics connectors for mechanical, environmental, and electrical performance and make them lightweight and easy to install. We have numerous options available.

The TCA flight-friendly modular connector system makes terminating the cable quick and easy while ensuring optimal electrical and mechanical performance. Modularized design enables the user to install the connectors with the configuration that best fits the final system. The TCA connectors have 2-Nickel or bi-metal plating for excellent corrosion resistance and optimized VSWR performance. No braid trimming is needed during assembly, helping to reduce foreign object debris (FOD).

TCA’s modular concept also helps improve troubleshooting and repair—the user can take off the connector fronts and change them out instead of completely removing the entire connector. Because the system uses the same intermediate heads, inventory costs and risks are reduced. They also meet IP 67 standards for moisture ingress.

Multiport, mini multiport and blind mate connectors also offer unique ways to connect the numerous antennas on an aircraft in innovative ways that address many of the challenges noted above. For example, multiport and mini-multiport connectors are ideal for high-density avionics environments, where space is at a premium, accessibility for maintenance is tricky, and performance is mission-critical. Our range of options helps to reduce space and weight while providing excellent shielding and phase stability with low VSWR and insertion loss up to 20 GHz. Multiports are available with various connectors such as M8, V8, M8E, M8M and other custom solutions.

Mini multiport connectors also offer excellent service shielding and phase stability with low VSWR and insertion loss up to 40 GHz. Our mini multiport connectors are made to survive harsh avionics environments, where high vibration, shock, temperature and humidity can cause severe cable and system performance degradation. This system is presently used on several airborne applications and has logged tens of thousands of flight hours.

Additionally, a new generation of locking miniature push-on connectors, such as our TLMP™, retains the small form factor of the SMP for highly dense environments but adds improved environmental, shielding, and power capabilities, with a frequency range from DC to 60 GHz. A positive locking feature with visible green (locked) and red (unlocked) color coding prevents de-mating under vibration and shock.

Antennas also often need to be quickly and efficiently changed out or replaced. Our blindmate antenna solutions connect the coaxial cables to a system mounted directly to the airframe and mate using a sliding or snapping action – and do not require any tools. The antenna can be easily replaced independently of the coaxial cables. Only four screws need to be removed to pull the antenna off, and the connector stays in place. Another critical reason to use blindmate antenna technology is its additional layer. It assures no path for water or moisture to enter the antenna or aircraft.

Another benefit is a blindmate antenna connection’s ability to mate and de-mate for many cycles. The blindmate antenna keeps the connector mated to the systems and transfers the mate/de-mate capability to that system. The blindmate technology also provides a spring force for better electrical performance over vibration.

Powering What’s Next: New Commercial Air Innovations

Urban Air Mobility (UAM) technology is being designed to provide a safe and efficient aviation transportation system using highly automated aircraft to transport passengers or cargo at lower altitudes. Most UAM vehicles will operate below 10,000 feet, with battery power limiting their altitude and endurance. These systems mainly depend upon antennas and high-frequency transceivers to enable the sensors to talk to each other. Hence, a low-loss, reliable, low-weight cable is critical for reliable communications.

Further developments include Advanced Air Mobility (AAM) solutions, ranging from delivery drones to electric vertical takeoff and landing (eVTOL) applications. Like electric vehicles, eVTOL controls run on onboard electric power, and batteries are heavy, so weight is a substantial consideration. As a result, these technologies require advanced solutions to meet new requirements while adhering to the size and weight principles that have governed their predecessors for decades.

Our TCA Lite and MaxGain high-performance, ultra-low-loss microwave coaxial cables are ideal for these applications.

Our long heritage of experience in developing solutions for military, commercial, and space aircraft has prepared the Times team to create cutting-edge solutions to address the challenges in traditional and emerging avionics applications. We know RF, and our team of expert engineers can craft custom solutions to meet any avionics requirement. We are not just focused on the cable, connectors or individual pieces – but on the overall system’s performance. Our experienced team of engineers understands and accommodates the complexities of how the whole system must work and how precise the assembly between the connector and the cable must be.