Over the past four decades, the sheer amount and complexity of information transmitted through satellite communication (satcom) has substantially increased. At the same time, more mission-critical applications — such as aeronautical, maritime, and military navigation — have become increasingly reliant on these communications. As a result, the RF circuit building blocks that make up satcom technology have been through many changes to accommodate the latest advancements in the industry including miniaturization, increased reliability, and the ability to rapidly transmit even more complex data.
This article examines four RF technology trends today that are helping satcom design engineers meet the data demands of their military and aerospace clients while also making RF components that are lighter by size, weight, and power and more cost-effective to produce (SWaP-C).
1. A Shift in Active Electronically Scanned Array Construction
Chances are, you are familiar with how television display technology has evolved and dramatically reduced the depth of TVs in the past few decades. Likewise, the same type of evolution has occurred with the phased-array antenna technology powering today’s most sophisticated radar and satcom applications.
Today, satcom applications consist of active electronically scanned arrays (AESAs) that use multiple transmit/receive modules (TRMs) to electronically steer beams independently. In the past, AESAs were quite large as they used a 3D brick configuration made up of boards placed side by side and attached using multiple connectors and cables (Figure 1, left).
Instead of this bulky configuration, designs are now using 2D planar arrays that are built like a PCB using surface-mount (SM) attachment of components (Figure 1, right). A planar configuration removes the need for most connectors and cables, which not only improves SWaP-C but also increases reliability and simplifies manufacturing.
2. Operating at Increasingly High Frequencies
The whole world is moving to operate at higher frequencies and satcom applications are no exception. In response to the ever-increasing demand for communications via satellite, satcom designers are pushing through X and Ku bands to the Ka and V bands. This shift is ideal for high-throughput satellites since up to 3.5 GHz of bandwidth are available in the Ka band, which is four times more than what is available in other commonly used bands.
This increase in bandwidth is critical because, all things being equal — such as signal-to-noise ratio, encoding, and modulation schemes — a system with four times the bandwidth can help users do one of two things: send more information in a given amount of time or send the same things in a fraction of the time. Additionally, operating at higher frequencies reduces device size because higher frequencies yield smaller wavelengths. But this does not simply mean fewer components are required or devices inherently become smaller. Instead, it actually presents new challenges as more components need to fit into smaller device form factors.
Beyond making sure everything physically fits into a circuit, other considerations need to be made to ensure optimal functionality at higher frequencies. For example, in mmWave applications, whether filters are mounted close to each antenna or at some location that feeds the antenna array, considering the size of the filter relative to the rest of the front end is important. It can become physically cumbersome to mount devices close to the antenna that are appreciably different in size to the antenna, or the antenna array itself.
3. A Shift to Build Smaller, More Efficient Radio Architectures
As we’ve already hinted, satcom devices, like most communication devices, are following the general trend of performing more functions with fewer components. As a result, this is creating a shift to move from traditional heterodyne architectures to a direct RF sampling approach. By doing this, components such as mixers and local oscillators (LOs) can be eliminated since a direct sampling approach digitizes an RF signal directly without turning it into an IF signal ( Figure 2).
While removing components will inherently reduce size and cost, some level of filtering is still needed for direct sampling, which creates new challenges. These new filtering challenges are also much different at higher frequencies than at lower frequencies.
4. Improving SWaP-C Using a Surface Mount Device Assembly
As discussed, all satcom designers strive to improve SWaP-C. As a result, there is a push to move from traditional chip-and-wire or hybrid assembly approaches to a full surface mount device (SMD) assembly. One of the biggest cost-savings of SMD assembly is that it uses a single automated assembly line, dramatically reducing the cost of assembly versus a chip-and-wire or hybrid approach. Additionally, using a single-line SMD assembly can accelerate time to market.
Beyond cost and time savings, SMD implementations can help dramatically reduce the size of a circuit. For example, by using a microstrip filter, designers can minimize the space needed for the filter while maintaining high levels of performance in terms of bandwidth, rejection, and insertion loss.
But to achieve the benefits of SMD assembly, it is critical to select a supplier who is experienced in working with SMD technology at high frequencies. While SMDs have been around a while, they were not traditionally used in the Ka band, meaning many suppliers may not be familiar with the challenges of using SMDs at high frequencies.
Designing Satcom Devices for the Future
The number of devices that need to maintain mission-critical satcom connections is rapidly growing; therefore, satcom device manufacturers are looking for ways to reduce SWaP-C while also performing device innovations to take advantage of new technologies and trends today and tomorrow.
This article was written by Tim Brauner, Product Line Manager, SLC & Thin Film, at Knowles Precision Devices, Cazenovia, NY. For more information, visit here .