In this article, Dave Murray a Senior Applications Engineer at Times Microwave discusses the importance of selecting the right RF connector type for critical antenna installations on UAVs.
Unmanned aerial vehicles (UAVs) require a significant number of electronic components for data recording and transmission purposes, as well as for avionic functions. Of these components, antennas are among the most important, as they allow the vehicle to transmit and receive information from other systems, as well as communicate with those on the ground.
Just as critical as antenna performance is its connection to the coaxial cable. Both the connection and cable will influence maintenance, signal integrity, and may impact positioning, safety, and other key factors of UAVs.
This article will focus on blindmate antenna technology and specifically, details a connector technology that mates using a sliding or snapping action – and does not require any tools.
Why is this a critical consideration in building UAV systems? Because antennas can break – they get hit by rocks or other airborne objects, snap off as heavy equipment is loaded onto the UAV, or are harmed by any number of activities that can cause physical damage to the UAV.
If the antenna breaks, the UAV will lose its ability to communicate, including sending and receiving critical information such as threat locations, landscape data, and many other factors that are key for safe operation. UAVs rely on antennas and RF signals as the “eyes and ears” of the system because there is no human inside the vehicle to receive and process the information. If the UAV loses its sight or hearing, it won’t be able to accurately perform its duties.
As a result, antennas often need to be quickly and efficiently changed out or replaced. There are three primary issues involved in this: maintenance and access, environmental seal and mating life, and electrical performance over vibration.
Maintenance and Access
Maintenance is vital to the functionality and longevity of unmanned systems. Antennas need to work at all times and also be properly calibrated. In many unmanned systems and standard aircraft, antennas are often difficult to access, making maintenance and replacement very complicated and time-consuming. For example, while the C17 has many antennas, 18 of them were deemed inaccessible and therefore perfect candidates for the blindmate system. To date, these 18 antennas have never had a failure related to this system. A blindmate antenna provides a solution that connects the coaxial cables to a system mounted directly to the airframe. The antenna is also connected to this system and can be easily replaced, independently of the coaxial cables. Therefore, with the blindmate connections, only four screws need to be removed to pull the antenna off and the connector stays in place. Alternatively, with standard connectors, several elements inside the aircraft would need to be removed to access the cables that go to the antenna.
Furthermore, the more inaccessible an antenna or the cable on the back of it is, the more important it is to be able to use a blindmate on the structure. This technology also improves Mean Time to Repair (MTTR) and Mean Time Between Failures (MTBF). In the case of MTTR, the use of a blindmate antenna drastically reduces the time it takes to replace an antenna. In terms of MTBF, the time it takes for something to break or need repair, a blindmate system will not prevent failure caused by external factors, but it does create an additional layer of secure connection between the antenna and the cable, so it is more stable. This means the connection will last longer, reducing the time between failures due to antenna/cable connection issues.
Environmental Seal and Mating Life
Another key reason to use blindmate antenna technology is its environmental seal. The connection between an antenna and a cable can be a point of entrance for moisture and water leakage. In a blindmate antenna connection, an additional layer assures that there is no path for water or moisture to enter the antenna or aircraft. This further increases the MTBF.
A blindmate antenna connection’s ability to mate and de-mate for many cycles is another important consideration. For example, some helicopters and UAV designs require antennas to be mounted on doors or other compartments that are often opened and closed. These antennas will need to connect and disconnect from the coaxial cables that carry the RF signals.
The best connectors are designed to reduce loss and withstand critical environments and vibration cycles. Their mate and de-mate capabilities are often the trade-off designers need to sacrifice to achieve these key performance aspects of connector design. Because these connections are often the critical link of a system, some military and commercial specifications define the minimum number of mates and de-mates a connector must withstand—often around 500 cycles. A standard connection will seldom last longer because it simply wasn’t designed for that.
On the other hand, the blindmate antenna keeps the connector mated to the systems and transfers the mate/de-mate capability to that system. A recent test of a deployed blindmate antenna system recorded 5,000 mates with no degradation.
Electrical Performance over Vibration
Vibration is critical to consider in UAV design because when a connector attached to an antenna vibrates, as it will in flight, microphonic noise can impact the connection. If an antenna is the eyes and ears of an unmanned system, noises and interferences are the screaming toddlers, barking dogs, and bad connections of your Zoom meetings. This can cause interference in the signal transmission and errors for the RF system.
Using a blindmate, the connector is mounted to the structure of the aircraft instead to provide better electrical performance over vibration. The blindmate technology provides a spring force that counters the vibration. Similar to the way a car’s suspension provides a smoother ride, this spring force absorbs shocks and provides smoother communications. For example, visualize opening a car door at 80 miles an hour. Opening the nose door of an aircraft at over 300 miles an hour, the inside of that space becomes a hurricane. The cables shake and rattle around, creating a high vibration environment. The blindmate spring force counters that high vibration profile and keeps the cable connected to that antenna.
Blindmate antennas can also be customized to solve a range of other issues. For example, antennas need to be mounted precisely to capture the correct signals. However, the mounting surface is not always perfect. This can cause something like the threat scope in the cockpit to be off by a couple of degrees because the antenna is not pointed in the right direction. A custom design can provide the ability to boresight an antenna, enabling it to be adjusted for a perfect angle mount on an imperfect surface.
Blindmate antenna technology is an investment that can save a lot of money in UAV RF system maintenance, time and replacement. There are a variety of options in the market for blindmate antennas; look for a provider that fully understands your specific mounting challenges as well as how the signal travels. A supplier that also has experience with custom assembly and RF interconnect solutions can help you to fully understand your needs and provide the best solution. Times Microwave Systems can help you with design as well as RF questions.