Minimize NAVISP
References   

A new ESA-supported wide-bandwidth satnav antenna has been designed to receive both satellite and augmentation signals from anywhere in the sky, even down to just a couple of degrees above the horizon. 1)

With a growing number of satnav constellations in operation, Canada-based Tallysman Wireless’s new VeroStar antenna aims to pick up all available signals, as well as support the availability of L-band correction service signals. Its development was supported through ESA’s NAVISP (Navigation Innovation and Support Program).

The precision of GNSS fixes is routinely sharpened with correction signals from augmentation systems, such as Europe’s EGNOS and the US WAAS, which also provide ongoing integrity (or reliability) information for high-accuracy and safety-of-life uses, such as aircraft descents. However, these augmentation signals are transmitted by geostationary satellites, hanging at fixed points above the equator, meaning that they become less visible for receivers in the far north or south.

NAVISP_AutoA

Figure 1: VeroStar antenna. Tallysman's new ESA-supported wide-bandwidth satnav antenna has been designed receive both satellite and augmentation signals from anywhere in the sky, even down to just a couple of degrees above the horizon (image credit: Tallysman)

NAVISP_Auto9

Figure 2: VeroStar wideband satnav antenna. With a growing number of satnav constellations in operation, Canada-based Tallysman Wireless’s new VeroStar antenna aims to pick up all available signals, as well as support the availability of L-band correction service signals. Its development was supported through ESA’s NAVISP (image credit: Tallysman)

“If you think of a Global Navigation Satellite System (GNSS) receiver as resembling a camera, then the antenna would be the lens,” explains Allen Crawford of Tallysman. “Now, you might have an excellent top-of-the-range camera, but if it doesn’t have a clean, distortion-free, and well-focused lens, then all you’re going to get are blurred pixels that no post-processing software can fix.

“So our antenna is like a lens, except it gathers radio signals instead of light – and it is the first step in the measurement process. We want the antenna to reproduce the received satellite signals as precisely as possible, in terms of amplitude and of signal phase, on a fully representative basis, for the receiver to process.”

Available in various models and sizes, including pole-mounted, surface-mounted, and embedded versions, the VeroStar is aimed at high-performance mobile applications, such as land surveying, precision farming, maritime and autonomous vehicle navigation, typically requiring positioning accuracy down to a few centimeters.

“Different customers have differing requirements,” adds Julien Hautcouer of Tallysman. “There are plenty of GNSS antennas that work on a ‘good enough’ basis – for instance, antennas on top of cars just need to give a rough position, then the navigation receiver uses its map to estimate what street you’re on.”

“What we wanted to do, starting from scratch with this new design, for high-precision mobile users, was to be able to employ as many satellite signals from as many constellations as possible – not just GPS but also Galileo, the Russian, Chinese, Indian, and Japanese systems, plus correction service signals – and this requires good stable performance across a very wide bandwidth.”

“We want it to provide nothing but the pure right-hand circular signals, minimizing any misleading reflected ‘multipath’ signals,” notes Gyles Panther, CTO of Tallysman. “We also paid special attention to the symmetry of our antenna, so that satellite signals are treated in exactly the same way, no matter where in the sky the signals are coming from. It’s like looking through a good quality wine glass when you rotate it in front of your eyes, and your view through it stays the same.”

NAVISP_Auto7

Figure 4: Petal antenna design. Canada-based Tallysman Wireless’s new VeroStar antenna aims to pick up all available satellite navigation signals. The VeroStar design is based on eight curled ‘petals’ of printed circuit boards, inspired by the post-war Alford loop antenna, which was originally designed for simultaneous transmission of multiple FM radio signals (image credit: Tallysman)

At the same time, the modern radio spectrum is very crowded, so the design team paid particular attention to filtering out radio interference that could cause a situation where a drone might be forced down by local radio noise.

The VeroStar design is based on eight curled ‘petals’ of printed circuit boards, inspired by the post-war Alford loop antenna, which was originally designed for simultaneous transmission of multiple FM radio signals.

“The Tallysman team performed a long optimization process using electromagnetic modelling to define the final shape for manufacturing,” notes ESA navigation engineer Nicolas Girault, the project’s technical officer. “They ended up with an inexpensive, easy to repeat process, which is ideal, really.”

The design maximizes antenna efficiency and performance, adds ESA engineer Damiano Trenta: “Its rotational symmetry geometry and wideband behavior help to provide a stable phase centre over frequency and angular range. Optimization of the petals’ shape helps to improve the minimum gain at very low elevation angles, compared with the current products on the market, and keeps a very low cross-polar level for multipath mitigation. ”

Figure 5: Satnav signals. To pinpoint your location accurately, your receiver needs to receive signals from at least four navigational satellites. The receiver determines your distance from each of the satellites by measuring the time taken by the signal to travel from the satellite to your receiver antenna (image credit: ESA)

NAVISP_Auto4

Figure 7: NAVISP of ESA (image credit: ESA)

The objective of ESA's NAVISP program is to facilitate the generation of innovative propositions in partnership with Member States and industry along the entire satellite navigation value chain and strengthen the existing industrial base of the European navigation sector. 2)



NAVISP development status and PNT (Positioning, Navigation and Timing) applications

• March 14, 2022: ESA’s NAVISP programme – helping to invent the future of European navigation – is probing the science of the very small. The aim is to employ hyper-sensitive quantum technology-based sensors as supplementary navigation solutions, including tracking local variations in gravity that could be matched onto regional and global gravity maps. 3)

- But satellite navigation, whether from Galileo, GPS or other equivalent systems, possesses inherent limitations. Its signals are prone to natural or human-made interference. There are also many places where these signals simply do not reach: deep underground, under the sea, in forests or simply city centre ‘urban canyons’.

- So researchers are looking for additional positioning solutions to supplement or substitute for satnav as needed. In place of planet-hugging satellite constellations ESA’s Navigation Innovation and Support Programme (NAVISP) includes research into the opposite extreme in scale – in the shape of quantum technology.

- Isolate a sampling of atoms and they start behaving in very different ways from everyday matter, such as simultaneously existing in more than one state at once. Quantum technology utilises such exotic behaviour in various ways – including the creation of ultra-sensitive sensors.

NAVISP_Auto3

Figure 8: Cold Atom Interferometer. A commercially available ‘atom interferometer’ – exploiting clouds of ultra-cold atoms to make extremely precise measurements of variations in local gravity – on show during ESA’s inaugural Quantum Technology workshop. “We’ve been looking at applying the latest quantum technology to space,” explains ESA’s Bruno Leone. “Quantum physics is still regarded as abstract, but products based on its effects are commonplace today, such as microprocessors, solid-state imaging devices and lasers.“What we’re interested in harnessing more advanced, subtle, aspects of quantum mechanics, including superposition and entanglement, made feasible by recent advances in experimental techniques and equipment.” This desk-sized atom interferometer, produced by M Squared in the UK, is one example. Finely tuned laser beams confine clumps of atoms kept cooled close to absolute zero. Like ripples meeting on a pond, their resulting interference patterns can highlight tiny changes in the surrounding environment (image credit: ESA–G. Porter)

- Cold Atom Interferometers (CAIs) are based around a few hundred thousand atoms at a time, trapped by a combination of lasers and magnetic fields,” explains ESA navigation engineer Rok Dittrich.

- “Atoms freefalling in ‘quantum superposition’ – meaning they are existing in several separate quantum states at the same time – are then interrogated by a laser to derive their interference patterns – revealing for instance gravity or other forces acting upon them. CAIs and comparable quantum technology can operate independently from satellite navigation with extremely high performance levels – the challenge is to get them working reliably and robustly outside of lab environments.”

Figure 9: Isolating atoms using lasers for interferometry (image credit: CNRS Laboratoire Photonique, Numérique et nanosciences at the University of Bordeaux)

- Inertial navigation company iXblue is leading a NAVISP project consortium to develop a compact 3-axis CAI sensor, aimed for use aboard boats, aircraft and boats as well as at fixed sites.

NAVISP_Auto1

Figure 10: Project's prototype CAI sensor (image credit: Laboratoire Photonique, Numérique et nanosciences)

- This could be used both on a dead reckoning basis – to accurately tote up all subsequent movements relative to its starting point, without the gradually accumulated drift of classical inertial sensors – and also to fix positions, such as by matching local gravity to a detailed gravity map.

- A weakness of past quantum devices is a post-measurement ‘dead time’ when a new atom cloud needs to be cooled and isolated. The sensor avoids this by incorporating a mechanical accelerometer into its design.

- “This hybridisation of classical and quantum sensors serves to increase the dynamic range of the measurements,” comments Baptiste Battelier of CNRS Laboratoire Photonique, Numérique et nanosciences at the University of Bordeaux, participating in the project. “In addition it allows a quantum measurement of the vector acceleration along any random orientation, performed for the first time using a CAI sensor.”

NAVISP_Auto0

Figure 11: Hybrid sensor. Hybridization of fibered gyroscopes and a multi-axis atom accelerometer for navigation and onboard gravimetry (image credit: CNRS Laboratoire Photonique, Numérique et nanosciences at the University of Bordeaux)

- NAVISP’s Quantum Wayfarer project led by Teledyne with the University of Liverpool has meanwhile modelled the feasibility of gravity map matching in practice.

- Mapped globally from orbit by several spacecraft, most recently by ESA’s GOCE (Gravity field and Ocean Circulation Explorer) mission, local gravity levels are influenced by multiple variables including Earth’s rotation, surrounding topography, geology and human-made features.

- The best baseline gravity maps would deliver a current 90 m in accuracy, potentially improvable to 30 m in the near future – and might also be combined with other reference sources such as magnetic field mapping.

- The Wayfarer project also found that areas of very high gravity gradient variation – such as mountainous California – saw higher precision compared to the opposite, such as the flattish Noordwijk in the Netherlands.

- However, a more sensitive CAI gravimeter would in turn produce a higher frequency of gravity gradient measurements, producing further improvements in map matching in turn – potentially following the ‘simultaneous localisation and mapping’ SLAM approach developed for robotics navigation, where maps are created by a robot at the same time its movement is tracked.

- "These two very interesting projects were performed under the NAVISP Element 1, whose main goal is to generate innovative concepts, techniques, technologies and systems linked to the Position Navigation and Timing sector, along the entire value chain," explains Stefano Binda, NAVISP Element 1 Manager at ESA.

• February 14, 2022: Many of the experts that designed and oversaw the Galileo satnav system are now supporting cutting-edge European companies in the development of new navigation technologies and services. The result is ESA’s Navigation Innovation and Support Programme, NAVISP. 4)

- NAVISP is looking into all kinds of clever ideas about the future of navigation: ways to improve satellite navigation, alternative positioning systems and, new navigation services and applications. Working in partnership with European industry and researchers, more than 200 NAVISP projects have been initiated so far.

- NAVISP is divided into three elements, the first looking into improving and expanding satellite navigation, as well as establishing novel ‘positioning, navigation and timing’ (PNT) services. NAVISP’s second element focuses on innovation for competitiveness, developing all kinds of new PNT products and services. Its third element covers support to Member State priorities, including support for national testbeds and programmes.

Figure 12: NAVISP is divided into three elements, the first looking into improving and expanding satellite navigation, as well as establishing novel ‘positioning, navigation and timing’ (PNT) services. NAVISP’s second element focuses on innovation for competitiveness, developing all kinds of new PNT products and services. Its third element covers support to Member State priorities, including support for national testbeds and programmes (video credit: ESA)

- The current estimate is that ‘positioning, navigation and timing’ (PNT) underpins a tenth of the European economy. The transport sector is obviously reliant on PNT, but so for example is precision agriculture, along with power, communications and banking networks and the fast-growing internet of things. 5)

- Satellite navigation, with signals from space extending across the globe, represents the single biggest source of PNT information, but these signals are not available in all locations and are vulnerable to natural or human-made interference. PNT is so important that Europe needs to hone our competitiveness in this field, and be wary of relying on a single-source solution.

- NAVISP is divided into a trio of elements. NAVISP Element 1 is focused on innovation in PNT, involving novel concepts, techniques, technologies and systems along the entire value chain – often combining satnav with other solutions.

- This might involve, for instance, applying AI as well as positioning sensors to driverless cars and boats, adding wifi or 5G signals to PNT fixes, or employing high-altitude atmospheric platforms to supplement satnav coverage over regions in need.

- To compile its annual Element 1 workplan, NAVISP invites innovative PNT concepts from companies or academic entities across NAVISP Participating States. Element 1’s scope of activities ranges from initial feasibility studies and viability analyses all the way to full proof of concept for promising PNT systems and services.



1) ”Satnav antenna built for ends of the Earth,” ESA Applications / Navigation, 27 January 2021, URL: https://www.esa.int/Applications/Navigation/Satnav_antenna_built_for_ends_of_the_Earth

2) ”Navigation Programs,” ESA, URL: https://www.esa.int/About_Us/Ministerial_Council_2016/Navigation_Programmes

3) ”ESA probing navigation via the quantum realm,” ESA Applications, 14 March 2022, URL: https://www.esa.int/Applications/Navigation/ESA_probing_navigation_via_the_quantum_realm

4) ”Inventing the future of Navigation,” ESA Applications, 14 February 2022, URL: https://www.esa.int/ESA_Multimedia/Videos/2022/02/Inventing_the_future_of_Navigation

5) ”Wanted: your new ideas for navigation,” ESA Applications, Navigation, 17 February 2022, URL: https://www.esa.int/Applications/Navigation/Wanted_your_new_ideas_for_navigation


The information compiled and edited in this article was provided by Herbert J. Kramer from his documentation of: ”Observation of the Earth and Its Environment: Survey of Missions and Sensors” (Springer Verlag) as well as many other sources after the publication of the 4th edition in 2002. - Comments and corrections to this article are always welcome for further updates (herb.kramer@gmx.net).

References    Back to top