The pace of technological change in the New Space revolution demands innovations in the ground segment to keep up and avoid becoming the bottleneck. This is particularly important given the technological shift from the world of Geostationary Orbit (GEO) satellites to a Low-Earth Orbit (LEO) and Medium-Earth Orbit (MEO) world, where satellite’s relative motion throw up additional challenges.
A proliferation of low-cost, high-revisit smallsats capable of capturing high-resolution images of the planet has democratized space. Recent use of Ka band platforms for high data-rate missions, and developments in advanced data-processing analytics have brought the need to scale operations. This in turn requires space platforms to interact dynamically with the ground network in more collaborative, usage-based and cloud-empowered ways.
In the new multi-orbit world, says Carl Novello, CTO of NXT Communications Corp. (NXTCOMM), an Atlanta, Georgia area-based startup, the biggest challenge on the ground will be flexibility. Traditionally satellite operators have been tightly vertically integrated, with terminals designed to work with a single constellation across a relatively narrow portion of spectrum. With operators adopting a multi-orbit approach, that increasingly won’t cut it.
“The challenge is how do you move from being a product that is relatively fit for a single purpose to becoming the Swiss Army knife of antennas?” Novello asks. “One that will work in GEO use cases and LEO use cases and MEO use cases, with different requirements for frequency bands, uplink power, different regulatory requirements to meet, and so on.” In other words, concludes Novello, “How do we build a better antenna fit for this brave new world of satellite connectivity?”
Advancements in technology are shifting the ground system from purpose-built, proprietary hardware architectures to software-defined, cloud-centric, and extensible virtual platforms that support multiple satellites, payloads and orbits on demand. This is being enabled by a series of innovations in antenna technology, waveform processing and system design, quietly starting a “New Ground” revolution down on Earth, as well.
NSR, a market research and consulting firm, estimates that cumulative revenues for the entire ground segment through 2028 will total $145 billion. The market will generate $14.4 billion annually by 2028, the firm states in its recent report, Commercial Satellite Ground Segment, 4th Edition (CSGS4). The user terminal will command a substantial portion of this spend.
For broadband satellite communications applications where the platform is mobile, where the satellite is non-geostationary or both, a scanning antenna is required. The satellite communications industry, however, is dominated by dish antennas mounted on motorized gimbals for these applications. These solutions are too large, heavy, and power-consuming to offer solutions for consumer mobile applications such as the connected car or a personal satellite terminal.
Electronically steerable antennas (ESAs), often referred to as flat panels, are the critical link for next-generation constellations. Compared with their bulkier mechanical cousins, flat-panel antennas offer greater efficiency and performance while being modular and dynamically steerable—all of which are needed for the future ground segment.
A phased array antenna is a collection of antenna elements assembled together such that the power from the transmitter is fed to the antennas through devices called phase shifters, controlled by a computer system, which can alter the phase electronically, thus steering the beam of radio waves to a different direction. The result is that each antenna in the array has an independent phase and amplitude setting to form the desired radiation pattern. This phase shift will introduce interference between the signals transmitted.
The radio frequency current from the transmitter is fed to the individual antennas with the correct phase relationship so that the radio waves from the separate antennas add together to increase the radiation in a desired direction, while cancelling to suppress radiation in undesired directions. The direction of radiation can be manipulated by changing the phase of the signal fed into each antenna element.
While ESAs’ flat and conformal characteristics can have aesthetic benefits, the real benefit comes from their performance. LEO and MEO satellites require the ability to track and communicate with two or more satellites in view at the same time, and this can only be done with multiple mechanical antennas. With no moving parts, ESAs are more reliable and efficient as they can connect to multiple satellites at the same time. This gives a single ESA the ability to interoperate with multiple orbits—not just GEOs.
Many different approaches can be taken to develop next-generation flat-panel antennas. All consist of small antennas, known as radiating elements, and both receive- and transmit-side amplification. A passive antenna takes one signal from the power amplifier (PA) on the transmit side and divides this signal out to the transmit radiating elements, then combines the receive signals from the radiating elements before feeding the receive-side low-noise amplifier (LNA). An active antenna, in contrast, has a single amplifier per radiating element, for both transmit (TX) and receive (RX). In general, passive antennas are less complex, while active antennas provide greater gain performance.
Previously the cost of phased array antennas are very high, thus early applications were confined
to military and defense areas. However, this has changed in recent years. Thanks to advancements in highly reliable solid state devices and Microwave Monolithic Integrated Circuits
(MMIC) technologies, phased array antennas now become much affordable for commercial and industrial applications by increasingly matured mass production and dramatically reduced cost.
Much of the recent development has gone into the back of the antenna—how beams are formed, how one develops better RFICs, and so on. However, not much innovation capital has been invested in the front side itself, known as the radiating elements.
That’s what NXTCOMM and other satellite technology providers are working on. The company uses a technology called fragmented aperture, which tackles some of the underlying physical limitations of a conventional flat-panel or phased array satellite antenna. Fragmented aperture uses complex, pixelated structures for its radiating elements, to reduce interference and boost efficiency.
Traditional radiating-element design takes a monolithic approach—namely, a single circle of copper, a square, a trapezoidal solid, or an iron cross. These radiators are then stepped and repeated around the array to meet the required gain for the use case. One limitation is that those shapes can contribute to a reduction in gain by causing parasitic coupling. Simply put, one element close to another can interfere with its neighbor. The more elements in the array, the greater the parasitic coupling, and the lower the efficiency. This interference impacts gain in general but can also lead to undesirable grating lobes, and perhaps contribute to an undesirable antenna pattern, especially on the transmit side. These elements may also be resonant structures, limiting the antenna’s overall frequency.
Such factors negatively impact the overall efficiency of the aperture. Typical antennas using these radiating elements achieve an aperture efficiency of 60% to 70% when scaled up to a size appropriate for satellite communications.
In a fragmented aperture, the radiating element isn’t a single piece of copper. Instead, it’s pixelated, like an array within an array. Such an approach not only helps reduce the parasitic coupling between elements, but it also helps increase gain and improve sidelobe performance.
In addition, the fragmented-aperture architecture allows for significantly greater antenna bandwidth. Because the elements aren’t inherently resonant structures, they can be designed to cover very wide bandwidths. This flexibility is particularly important in the emerging LEO use case as the antenna needs to target multiple satellites simultaneously, requiring use of different ranges within the frequency band.
The fragmented-aperture approach can support bandwidths of up to 100:1 and typically 33:1. In the bands of interest for satellite communications, fragmented-aperture flat panels support the entire Ku-band (10.7 GHz to 14.75 GHz) or even the Ka-band (17.2 GHz to 30 GHz) with a single element, making it possible to use a single antenna across a wide range of satellite networks.
In terms of aperture efficiency, these antennas achieve efficiencies in the 85% to 90% range when scaled up to a size suitable for satellite communications. When compared in terms of aperture efficiency, a fragmented-aperture antenna array achieves efficiency of 80% to 90% while a traditional square-element antenna array delivers efficiency of 60% to 70%. NXTCOMM is already gearing up to start production of its new antennas. Next year, L3 Harris will start to use them in both manpack and flyaway terminals for an undisclosed U.S. Department of Defense customer.
A Paradigm Shift in Antennas
Fragmented aperture is just one new technology aiming at the dramatic performance improvements needed for the ground segment to keep up with the new multi-orbit world. Another company seeking to build a better mousetrap is Hawthorne, California-based ThinKom Solutions, whose variable inclination continuous transverse stub or VICTS phased-array technology combines the technical benefits of mechanically steered and Electronically Scanned Arrays (ESA), according to Bill Milroy, chairman and CTO. “We get the best of both worlds,” he says.
In simple terms, VICTS technology is comprised of parallel plates or discs rotating relative to each other around a single axis to steer the beam and control polarization. For space-based antennas, the plates are aluminum, and ThinKom is exploring using additive manufacturing for these. In ground-based products, the company uses metalized plastic. VICTS uses a contactless circumferential drive to move the plates like a maglev train, says Milroy. “It’s a contactless inductive drive, so if you look inside, you don’t see a motor, you don’t see gears, you don’t see pulleys, you don’t see belts.”
That gives the technology big advantages, Milroy says. The contactless drive is more reliable than either conventional mechanical movement systems like gimbals or the non-mechanical ESA antennas. He cites statistics from the company’s airborne VICTS antenna product line, that with 22 million flight hours over six years, the mean time before failure is well north of 100,000 hours. ThinKom’s parallel plate technology aims to increase scan range, reduce power requirements, improve on performance efficiency, and is lower cost. Cost savings like that are going to be an increasingly important differentiator in the new markets and verticals the multi-orbit world will open up including mass-scale use cases for consumers or even Internet of Things (IoT) applications.
“Price and price elasticity in the terminals and antenna providers is going to be key to getting into those markets,” Milroy explains, because they are potentially logarithmically larger than the current market base. “We may need to see prices reduced by an order of magnitude, which is bad for us as suppliers. But the reward is the market size, it could be orders of magnitude greater.”
Milroy says the company can force its unit costs downwards if a customer wants to buy 10,000, or 100,000 antennas. New technologies like additive manufacturing, more commonly known as 3D-printing, will also help, he says. “We think our antennas are ideally suited for additive manufacturing, which is kind of a hot topic. We’re doing some really interesting experiments in that area.”
Metamaterial Surface Antenna Technology
Phased array technology, is typically available only to government and military customers because of its expense and power consumption.
Kymeta has addressed these obstacles by developing an electronically-scanned antenna technology, based on a diffractive metamaterials concept, called Metamaterial Surface Antenna Technology (MSAT). Electronic scanning is achieved through the use of high-birefringence liquid crystals. The use of liquid crystals (LC) as a tunable dielectric at microwave frequencies permits large-angle (> 60°) beam scanning with power consumption of < 10 Watts and antenna thickness ~ 5.0 cm, with no moving parts.
Kymeta’s engineering approach, through the use of LC and optimization of the materials and design for compatibility with liquid crystal display (LCD) manufacturing processes, positions the technology for mass production by leveraging the capital infrastructure of the LCD
Conventional three-dimensional metamaterials rely on bulky structures where resonant phenomenon are used to achieve the desired effective medium properties, e.g., negative refractive index. This resonant behavior dramatically limits their bandwidth, efficiency, and ultimate utility for point-to-point communications links. In addition the tolerances required to maintain narrow resonances over physically large structures (such as the aperture sizes required for Ku- and Ka-band satellite communications) prohibits the manufacturing of such materials at consumer electronics scale and cost.
Kymeta is leveraging a metasurface concept, in conjunction with holographic beamforming principles to commercialize MSAT. Metasurfaces have a number of advantages, namely that they take up less physical space and have the potential for less-lossy structures. Metasurfaces are characterized by both the periodicity of scatterers and thickness of the surface being small relative to the wavelength of interest.
New low-profile, software-based antennas, like Kymeta’s metamaterials antennas, are a real game changer. They feature no moving parts and can be electronically steered to point to any satellite or shape beams to minimize interference. By pairing our Intelsat EpicNG High Throughput Satellites (HTS) with Kymeta’s metamaterials antennas, we’re able to accelerate and simplify access to satellite connectivity for a range of cost-effective mobility solutions. These types of advancements will let us open the door to new markets and applications that were limited by the constraints of traditional solutions.
The Navy recently live tested a new antenna that can switch between satellites in low earth orbit and geostationary orbit, fulfilling a key need for the military moving forward.
Using Intellian’s 1.5 meter antenna, the Navy was able to maintain a broadband connection while switching between Telesat’s satellites in low earth orbit and geostationary orbit. The demonstration shows how in a scenario where a satellite in geostationary orbit is attacked or denied, the antenna is able to switch to a LEO satellite to maintain a persistent broadband connection.
“Live testing over Telesat Ka-band satellites with Intellian’s 1.5m Ka convertible VSAT confirms that the antenna is an important innovation accessing space-based ‘layers’ of satellites in next-gen space architecture,” said Kurt Fiscko, technical director of PMW/A 170 at PEO C4I in a statement.
“One of the key elements that the government is looking for, particularly the military, is a path to more resilient, more flexible networking in space,” said Telestat’s Don Brown in an interview. “What Telesat is doing in this demonstration with Intellian is addressing one of the key proof points of future resiliency and flexibility … the ability to go between GEO satellite constellation and LEO constellations.”