Fortem Technologies‘ new TrueView technology is being used in the U.S. Unmanned Aircraft Systems Integration Pilot Program to detect potential air-to-air collisions and enable unmanned aircraft to safely navigate beyond visual line of sight (BVLOS) day or night and in clouds, fog, smog and other challenging weather conditions.
The TrueView R20.
Fortem Technologies is working with Lead Pilot Partners to further the pilot program. The program aims to accelerate safe integration of UAS into the national airspace.
Fortem’s TrueView R20 meets critical selection criteria by putting safety and security data at the forefront to enable expanded drone operations such as BVLOS and operations at night. Using AI algorithms, TrueView provides accurate real-time situational intelligence and awareness for safe, autonomous, unmanned aircraft operations.
Fortem TrueView R20 weighs 1.5 lbs. and is a breakthrough technology because of its small form factor, weight, power requirements and low cost.
Fortem’s radar technology has been hardened over the past six years through rigorous testing with the U.S. Department of Defense.The company provides advanced radar systems and associated software systems for manned and unmanned aircraft as well as its own modern air defense system known as the Fortem DroneHunter.
In January, Fortem Technologies announced the close of a $5.5 million funding round led by Signia Venture Partners and Data Collective.
“One of the biggest challenges for the UAS industry is the ability to detect other aircraft and stay well clear from potential collisions,” said Jared Essleman, director, Utah division of aeronautics. “Achieving safe autonomous flight beyond-visual-line-of sight is going to be the next big chapter for the aviation industry. The announcement of TrueView R20 technology is an exciting development for safe autonomous operations, allowing UAS to course correct as needed to mitigate risk.”
“We are proud of our progress and ability to innovate around one of the most daunting challenges in the drone industry; namely safe BVLOS and nighttime operations,” saidTimothy Bean, CEO of Fortem Technologies. “With TrueView, we have responded to feedback from our customers to bring this needed detect-and-avoid product to a worldwide market.”
Neutron-star Interior Composition Explorer, or NICER, is an external attached payload on the International Space Station. (Image: NASA Goddard Space Flight Center)
A team of engineers at the U.S. National Aeronautics and Space Administration (NASA) has demonstrated fully autonomous X-ray navigation in space — a capability that could enable robotic spacecraft to navigate beyond the edges of the solar system.
The experiment, Station Explorer for X-ray Timing and Navigation Technology (SEXTANT), showed that millisecond pulsars could be used to accurately determine the location of an object moving at thousands of miles per hour in space, functioning in a way similar to GPS.
The system provides a new option for spacecraft to autonomously determine their locations outside Earth-based global navigation networks because pulsars are accessible in virtually every conceivable flight regime, from low-Earth to deepest space.
The SEXTANT demonstration used the 52 X-ray telescopes and silicon-drift detectors that make up NASA’s Neutron-star Interior Composition Explorer (NICER), an external attached payload on the International Space Station.
The size of a washing machine, NICER studies neutron stars, which emit radiation across the electromagnetic spectrum. Incredibly dense — one teaspoonful of neutron star matter would weigh a billion tons on Earth — these objects would collapse into black holes if compressed any further.
Pulsars. The SEXTANT experiment focuses on a particular type of neutron star: pulsars, highly magnetized, rotating neutron stars. Their electromagnetic radiation can be observed only when the beam of emission points toward Earth, thus their pulsed appearance. The short, regular rotational period produces a precise interval between pulses that ranges from milliseconds to seconds for an individual pulsar. These predictable pulsations can provide high-precision timing information similar to the atomic-clock signals supplied through GPS.
Demonstration. A demonstration in November 2017 selected four millisecond pulsar targets — J0218+4232, B1821-24, J0030+0451 and J0437-4715 — and directed NICER to orient itself so it could detect X-rays within their sweeping beams of light. These millisecond pulsars are so stable that their pulse arrival times can be predicted to accuracies of microseconds for years into the future.
During the two-day experiment, the payload generated 78 measurements to get timing data, which the SEXTANT experiment fed into its onboard algorithms to autonomously stitch together a navigational solution that revealed the location of NICER in its orbit around Earth. The team compared that solution against location data gathered by NICER’s onboard GPS receiver.
“For the onboard measurements to be meaningful, we needed to develop a model that predicted the arrival times using ground-based observations provided by our collaborators at radio telescopes around the world,” said Paul Ray, a SEXTANT co-investigator with the U.S. Naval Research Laboratory. “The difference between the measurement and the model prediction is what gives us our navigation information.”
The goal was to demonstrate that the system could locate NICER within a 10-mile radius as the space station sped around Earth at slightly more than 17,500 mph. Within eight hours of starting the experiment on Nov. 9, the system converged on a location within the targeted range of 10 miles and remained well below that threshold for the rest of the experiment. In fact, a good portion of the data showed positions that were accurate to within three miles.
GPS-level accuracy on the order of a meter or less is not necessary when navigating the far reaches of the solar system, where distances between objects measure in the millions of miles. “In deep space, we hope to reach accuracies in the hundreds of feet,” said Mitchell.
The team will now focus on updating and fine-tuning both flight and ground software in preparation for a second experiment later in 2018. The ultimate goal, which may take years to realize, is to develop detectors and other hardware to make pulsar-based navigation readily available on future spacecraft.
To advance the technology for operational use, teams will focus on reducing the size, weight and power requirements and improving the sensitivity of the instruments. The SEXTANT team now also is discussing the possible application of X-ray navigation to support human spaceflight.
If an interplanetary mission to the moons of Jupiter or Saturn were equipped with such a navigational device, for example, it would be able to calculate its location autonomously, for long periods of time without communicating with Earth.
“This successful demonstration firmly establishes the viability of X-ray pulsar navigation as a new autonomous navigation capability,” said project manager Jason Mitchell. “We have shown that a mature version of this technology could enhance deep-space exploration anywhere within the solar system and beyond.”
Averna is offering a wideband RF record and playback platform. The RP-6500 records and plays back up to 500 MHz of RF spectrum — from 9 kHz to 6 GHz — to test multi-constellation GNSS applications, the company said. The system can also capture other signals such as Wi-Fi, V2x, spectrum sharing and cellular applications.
The robust system fits into a car trunk for driving/recording applications, and syncs with both a GPS and Averna’s DriveView software for synchronized location and video capture that is time-aligned.
Preloaded with RF Studio, a state-of-the-art workflow tool, the RP-6500 Series lets users quickly set up recordings, add contextual data, visualize weak signals and analyze the collected RF environments to validate and fine-tune designs and products.
“The RP-6500 is a complete RF Record and Playback platform–it’s been designed and built from the ground up to be all-in-one,” said Alex Pelland, product line manager at Averna. “The hardware ticks all the boxes for serious users, and we’ve bundled it with RF Studio, so that all users can achieve simple configuration, file management, and visualization as well.”
Key Features and Benefits
Easy-to-use RF Studio user interface
500 MHz wide instantaneous bandwidth
Covers most common wireless protocols from 9 kHz to 6 GHz
High dynamic range (14 bits, ~ 86 dB)
Form factor allows rack mounting or car trunk portability
Time-synchronized capture of RF, signals, and messages
Making cities cleaner, providing better services and housing, and decreasing pollution are all achievements of nine cities recognized for using data to improve citizens’ lives.
In January, Bloomberg Philanthropies announced that nine cities have achieved What Works Cities certification, a first-of-its-kind national standard of excellence in city governance.
What Works Cities certification rates how well cities are managed by measuring the extent to which city leaders incorporate data and evidence in their decision-making.
Having shown leadership in data-driven government, the nine cities will receive additional expert assistance from What Works Cities to accelerate progress and deepen their leadership in using data.
Bloomberg Philanthropies launched What Works Cities in April 2015 to drive the use of data in U.S. municipal governance and to facilitate the exchange of best practices. It has reached its initial goal of bringing 100 mid-sized American city partners into the program. The nine certified cities were selected from more than 115 applications.
Los Angeles was awarded Gold Level, and eight other cities received Silver Level certification. No city has yet achieved Platinum, the highest level.
Accomplishments of each of the certified cities can be found here; below is a snapshot.
Gold Level: Los Angeles
Los Angeles has demonstrated a strong commitment and impressive track record with data-driven initiatives, according to Bloomberg Philanthropies.
Immediately upon assuming office, Mayor Eric Garcetti embraced an aggressive approach to data and analysis to better understand and map the most pressing issues in Los Angeles. Now in his second term, the mayor is using the foundation created by these efforts to develop a system-wide, evidenced-based approach to address the problems of affordable housing, crime, traffic and pollution.
Through its Data Science Federation, the city is also partnering with local universities to accelerate its use of data-driven tools at the same time that it is creating a pipeline to bring new talent into local government.
Among the major accomplishments cited:
CleanStat. In 2016, the Los Angeles Bureau of Sanitation began regularly collecting data to measure street cleanliness levels, allowing the City to more proactively and equitably clean L.A.’s streets, and place thousands of new public trash bins in areas with the greatest need. In just one year, these efforts led to an 82 percent reduction in streets previously rated as “Not Clean.”
With CleanStat, staff from the Bureau of Sanitation drive all of the more than 20,000 miles of the city’s public streets and alleys, assigning a cleanliness score from 1 to 3 — or from clean to not clean — to every block, once a quarter. Those scores are added to the Clean Streets Index, where department officials can keep track of performance and residents can hold the City accountable for its goal to eradicate red grids (ones with a score of 3) by 2018.
Home for Renters Campaign: In 2016, the City of Los Angeles identified areas where housing displacement was likely to occur, and launched a multi-faceted campaign to raise awareness of tenants’ rights under the city’s rent stabilization ordinance, with a particular focus on assisting our most vulnerable residents.
Save the Drop: In 2015, the City of Los Angeles analyzed water consumption data by ZIP code to focus conservation campaigns on regions with excessive water usage, which has helped Los Angeles reach its 20 percent water conservation goal.
Silver Level Cities
Eight cities earned the Silver Level of Certification. Here is a sample of their accomplishments.
Boston, Massachusetts (Mayor Marty Walsh): Achieving What Works Cities Certification builds on Imagine Boston 2030, Boston’s first citywide plan in 50 years. The goal of Imagine Boston 2030 is to guide growth to support the city economy and expand opportunities for residents.
The plan prioritizes inclusionary growth and puts forth a comprehensive vision to boost quality of life, equity and resilience in every neighborhood across the city. Shaped by the input of 15,000 residents who contributed their thoughts to the plan, Imagine Boston 2030 identifies five action areas to guide Boston’s growth, enhancement, and preservation, and is paired with a set of metrics that will evaluate progress and successes.
Louisville, Kentucky (Mayor Greg Fischer): Mayor Fischer signed an open data executive order that considers public information to be open by default. The new LouieStat performance management program evaluates city departments’ work and shares progress with residents.
The city’s Innovation Team is finding creative ways to involve residents in tackling tough problems, sometimes by bringing them into the data-collection process itself. In one project, placing GPS-enabled sensors on asthma inhalers is helping to pinpoint areas throughout the city where low air quality is likelier to induce asthma attacks.
In another project, built at a CDA hackathon, crowdsourcing data on internet speed is helping the City assess the extent of its digital divide and develop a digital inclusion strategy to remove the barriers that are keeping residents from better jobs and other opportunities.
San Diego, California (Mayor Kevin Faulconer), applied data insights and evidence to advance city-improvement projects. After learning that 80% of San Diegans didn’t want to make phone calls to report problems, the city bypassed the traditional 311 model and launched its Get It Done app.
Using Get It Done, residents can report and track progress on a variety of complaints directly from their mobile phones, and response crews are closing the loop by sending “after” photos to residents, who can rate their experience with a thumbs up, thumbs down, or a comment. The app is helping the city become more efficient, too.
Kansas City, Missouri (Mayor Sly James), and San Francisco, California (Interim Mayor Mark Farrell), both found new ways to give citizens a voice in public service projects and increase government transparency.
New Orleans, Louisiana (Mayor Mitch Landrieu), tackled blight and natural disaster response through data, critical in the aftermath of 2005’s Hurricane Katrina. Through the BlightStat program, the city set priorities for inspectors and researchers who identify rundown properties and determine whether to levy fines, order a demolition, force a sale, or take some other action.
New Orleans has 15,000 fewer blighted properties thanks to BlightStat, a data-driven performance management program that’s helped the City strategically address the issue. (Photo: Bloomberg)
Seattle, Washington (Mayor Jenny Durkin) made strides to improve homeless individuals’ access to housing.
Washington, D.C. (Mayor Muriel Bowser) is beginning to see its rigorous approach to data spread throughout the city’s public agencies.
What makes these cities special
What Works Cities Certification evaluates whether cities have the right people, processes and policies in place to put data and evidence at the center of decision-making.
Cities are evaluated on factors such as whether they have dedicated staff responsible for helping departments use data to track their progress; contracts are awarded based on past performance; meetings are focused on numbers; key datasets are open to the public; and whether there is transparency in both the goals set and the progress towards achieving them.
“We are proud to recognize these leading cities as the best managed nationwide, using data and evidence to drive results. All over the country local governments are jumping into this movement and dramatically improving how their cities operate,” said Simone Brody, executive director of What Works Cities at Results for America. “Our hope is that What Works Cities Certification will continue to accelerate and celebrate the progress of cities as they improve opportunities for millions of residents.”
What Works Cities Certification has been endorsed by the National League of Cities as well as many of the country’s leading urban thinkers and practitioners. It is part of Bloomberg Philanthropies’ American Cities Initiative, a suite of investments that empower cities to generate innovation and advance policy that move the nation forward.
“Congratulations to each of the nine cities that earned certification for their use of data, which is improving services for people and setting a great example for other cities,” said Michael Bloomberg, founder of Bloomberg Philanthropies and three-term mayor of New York City.
“Data allows local governments to know what’s working and citizens to hold leaders accountable for results — but the fact is, many cities aren’t capturing it and putting it to use in making decisions,” Bloomberg said. “The more cities that integrate data into their planning and operations, the more progress our country will be able to make on the common challenges we face.”
By Yongqiang Wang and Aranya Chakrabortty, Clemson University /
IEEE Power and Energy Society General Meeting, September 2017
Phasor Measurement Units (PMU) are playing an increasingly important role in wide-area monitoring and control of power systems. PMUs allow synchronous real-time measurements of voltage, phase angle and frequency from multiple remote locations in the grid, enabled by their ability to align to GPS clocks. Given that this ability is vulnerable to GPS spoofing attacks, which have been confirmed easy to launch, this paper proposes a distributed real-time wide-area oscillation estimation approach that is robust to GPS spoofing on PMUs and their associated Phasor Data Concentrators (PDCs). The approach employs the idea of checking update consistency across distributed nodes and can tolerate up to one third of compromised nodes. Numerical simulations confirmed the effectiveness of the proposed approach.
The lead author, an assistant professor of electrical and computer engineering at Clemson, leads a team that received $1 million from the National Science Foundation to fortify computers and devices against cyberattacks associated with timekeeping. “We want to provide secure timing solutions by securing the two most commonly used time distribution approaches,GPS receivers and NTP.”
While in orbit, the Deep Space Atomic Clock (DSAC) mission will use the navigation signals from GPS coupled with precise knowledge of GPS satellite orbits and clocks to confirm DSAC’s performance.
News from the Jet Propulsion Laboratory, NASA
In deep space, accurate timekeeping is vital to navigation, but many spacecraft lack precise timepieces on board. For 20 years, NASA’s Jet Propulsion Laboratory in Pasadena, California, has been perfecting a clock. It’s not a wristwatch; not something you could buy at a store. It’s the Deep Space Atomic Clock (DSAC), an instrument perfect for deep space exploration.
The atomic clock, GPS receiver and ultra-stable oscillator that make up the Deep Space Atomic Clock Payload, following integration into the middle bay of Surrey Satellite US’s Orbital Test Bed Spacecraft. (Photo: Surrey Satellite Technology)
Currently, most missions rely on ground-based antennas paired with atomic clocks for navigation. Ground antennas send narrowly focused signals to spacecraft, which, in turn, return the signal. NASA uses the difference in time between sending a signal and receiving a response to calculate the spacecraft’s location, velocity and path.
This method, though reliable, could be made much more efficient. For example, a ground station must wait for the spacecraft to return a signal, so a station can only track one spacecraft at a time. This requires spacecraft to wait for navigation commands from Earth rather than making those decisions on board and in real-time.
“Navigating in deep space requires measuring vast distances using our knowledge of how radio signals propagate in space,” said Todd Ely of JPL, DSAC’s principal investigator. “Navigating routinely requires distance measurements accurate to a meter or better. Since radio signals travel at the speed of light, that means we need to measure their time-of-flight to a precision of a few nanoseconds. Atomic clocks have done this routinely on the ground for decades. Doing this in space is what DSAC is all about.”
The Deep Space Atomic Clock in the middle bay of the General Atomics Orbital Test Bed spacecraft. (Image: NASA)
The DSAC project aims to provide accurate onboard timekeeping for future NASA missions. Spacecraft using this new technology would no longer have to rely on two-way tracking. A spacecraft could use a signal sent from Earth to calculate position without returning the signal and waiting for commands from the ground, a process that can take hours. Timely location data and onboard control allow for more efficient operations, more precise maneuvering and adjustments to unexpected situations.
This paradigm shift enables spacecraft to focus on mission objectives rather than adjusting their position to point antennas earthward to close a link for two-way tracking.
Additionally, this innovation would allow ground stations to track multiple satellites at once near crowded areas like Mars. In certain scenarios, the accuracy of that tracking data would exceed traditional methods by a factor of five.
DSAC is an advanced prototype of a small, low-mass atomic clock based on mercury-ion trap technology. The atomic clocks at ground stations in NASA’s Deep Space Network are about the size of a small refrigerator. DSAC is about the size of a four-slice toaster, and could be further miniaturized for future missions.
The DSAC test flight will take this technology from the laboratory to the space environment. While in orbit, the DSAC mission will use the navigation signals from U.S. GPS coupled with precise knowledge of GPS satellite orbits and clocks to confirm DSAC’s performance. The demonstration should confirm that DSAC can maintain time accuracy to better than two nanoseconds (.000000002 seconds) over a day, with a goal of achieving 0.3 nanosecond accuracy.
Tom Cwik, the head of JPL’s Space Technology Program (left) and Allen Farrington, JPL DSAC project manager, view the integrated atomic clock payload on Surrey Satellite US’s Orbital Test Bed Spacecraft. (Photo: Surrey Satellite Technology)
Once DSAC has proved its mettle, future missions can use its technology enhancements. The clock promises increased tracking data quantity and improved tracking data quality. Coupling DSAC with onboard radio navigation could ensure that future exploration missions have the navigation data needed to traverse the solar system.
Technologies aboard DSAC could also improve GPS clock stability and, in turn, the service GPS provides to users worldwide. Ground-based test results have shown DSAC to be upwards of 50 times more stable than the atomic clocks currently flown on GPS. DSAC promises to be the most stable navigation space clock ever flown.
“We have lofty goals for improving deep space navigation and science using DSAC,” said Ely. “It could have a real and immediate impact for everyone here on Earth if it’s used to ensure the availability and continued performance of the GPS system.”
DSAC is a partnership between NASA’s Space Technology Mission Directorate and the Space Communications and Navigation program office, a program under the Human Exploration and Operations Mission Directorate. DSAC will launch in 2018 as a hosted payload on General Atomic’s Orbital Test Bed spacecraft aboard the U.S. Air Force Space Technology Program (STP-2) mission.
More satellites, more constellations, more multi-frequency receivers — they all drive greater achievable accuracy. But they also raise the requirements on GNSS antennas because of the stronger impact that possible imperfections might have in the overall error budget for multi-frequency combinations. This analysis of antenna-induced errors in pseudorange code measurements for different antenna feed types helps identify the advantages and disadvantages of such technologies for precise positioning.
By Stefano Caizzone, Mihaela-Simona Circiu, Wahid Elmarissi, Christoph Enneking, Michael Felux and Kazeem A. Yinusa, German Aerospace Center (DLR)
The combination of signals from two frequencies and multiple constellations leads to dual-frequency multi-constellation (DFMC) capabilities, which currently appear to provide improved performance, due to the increased number of satellites available. This leads to better available satellite geometries, but also to the possibility to strongly mitigate ionosphere-related errors, thanks to dual-frequency combination of the ranging signals.
In such scenarios, the hardware-related errors (from satellite and even more from receiver side) will gain a much stronger weight in the overall error budget and should be tackled accordingly.
This article focuses mostly on the receiver antenna contribution, leaving the effects due to the satellite and to the receiver for later work. We will show that the choice of the antenna technology (mostly in terms of the number of feeding points) has a strong impact on the pattern uniformity and therefore on the differential group-delay characteristics over the aspect angle. Optimal performance is demonstrated when using more sophisticated solutions, providing a ground for cost/performance analysis to system engineers of specific applications.
GROUP DELAY PERFORMANCE
Antenna performance in GNSS application is mostly evaluated in terms of antenna gain pattern, noise figure and group delay for code measurement or phase center variation for carrier phase measurement. Gain and noise figure impact on the signal level available at the receiver, while the group delay is a measure of the delay introduced by the antenna hardware to the different spectral components of the signal. The differential group delay (DGD) is
(1)
with φ, f, Az, El being respectively the antenna phase, frequency, azimuth and elevation.
The DGD variation with respect to frequency and aspect angle (that is, elevation and azimuth) actually poses a problem in precision applications: as a matter of fact, if the group delay were constant for all frequencies and all angles of arrival of the signal, no additional error would be introduced in the position calculation, because the group delay term common to all satellites would be encapsulated at the receiver into a user clock offset.
However, group delay can change significantly with respect to aspect angle and frequency, contributing in a different manner for each satellite (due to different angles) and for different signals (due to the different spectral components of each signal), therefore finally producing errors in the pseudorange estimation.
The influence of the DGD on pseudorange measurement error has already been studied in the past and is also taken into consideration in the antenna Minimum Operational Performance Standards (MOPS) for avionic antennas. Empirical studies on the combined effect of antenna group delay and multipath effect on board commercial airplanes have been published recently. However, to our knowledge, the correlation between the antenna intrinsic characteristics (such as gain and phase patterns and smoothness) and group delay behavior has not yet been properly analyzed, leaving a gap in the full understanding of the antenna design impact on the final GNSS receiver performance.
GNSS antennas can be divided into families, according to their geometry (and the related radiation mechanisms): for instance, spiral, helix and microstrip (patch) antennas are quite common in GNSS applications.They differ in achievable bandwidth, size and ease of manufacturing.
Even antennas of the same family can provide different performance, mainly because of the number of feeding points, which are the points where the signal is fed into the antenna.
In order to analyze the relationship between the group delay performance and the antenna properties, we will take into consideration three GNSS antennas of the same family (microstrip patch), having all about half-effective-wavelength size (with the effective wavelength considering the dielectric properties of the substrate material on which the patch antenna is positioned), but with a different number of feeding points. The antennas will be denominated respectively single-feed, double-feed and four-feed antennas.
The single-feed antenna is a square patch, with truncated corners to achieve circular polarization. On the other hand, the double- and four-feed antennas are square patches, having feeds positioned along their x- and y-axis. The feeds are fed progressively: that is, with same amplitude and 0°–90° phases for the double feed and 0–90–180–270° phases for the four feed.
Single-feed antennas are representative of lower cost antennas used in mass-market applications, due to their extreme simplicity allowing for low-cost production. However, their performance exhibits strong cross polarization levels and non-uniform patterns over the azimuth. Dual- and four-feed antennas are more complicated to manufacture and need further hybrid circuits to properly distribute the signal between the different feeding points. However, an increase in the feeding points leads to more uniformity in the radiation pattern and lower-cross polarization and can therefore be expected to improve performance.
Dual-feed antennas are common in applications where a balance between precision and cost is needed, while four feeds are used in high-end applications, such as geodesy and reference stations.
The antennas under consideration here have been tuned to obtain optimal behavior at GPS L1/Galileo E1 band and have been simulated in an electromagnetic solver (Ansys HFSS), with an infinite ground plane assumption, to resemble the large metallic body frame of aircraft structures.
The gain patterns of the different antennas at GPS L1 / Galileo E1 central frequency ( f=1575 MHz) are shown in Figure 1. As discussed earlier, the pattern is not uniform over angle for the single-feed solution. On the other hand, the four-feed antenna shows improved pattern uniformity: the pattern has fewer azimuth and elevation variations, with the two-feed solution providing intermediate results.
Figure 1a. 3D RHCP patterns at f=1575 MHz for single-feed antenna. Source: Stefano Caizzone, Mihaela-Simona Circiu, Wahid Elmarissi, Christoph Enneking, Michael Felux and Kazeem A. Yinusa, German Aerospace Center (DLR)
Figure 1b. 3D RHCP patterns at f=1575 MHz for a dual-feed antenna. Source: Stefano Caizzone, Mihaela-Simona Circiu, Wahid Elmarissi, Christoph Enneking, Michael Felux and Kazeem A. Yinusa, German Aerospace Center (DLR)
Figure 1c. 3D RHCP patterns at f=1575 MHz for a four-feed antenna. Source: Stefano Caizzone, Mihaela-Simona Circiu, Wahid Elmarissi, Christoph Enneking, Michael Felux and Kazeem A. Yinusa, German Aerospace Center (DLR)
Phase patterns for the three antennas are shown in Figure 2. Here again, the one-feed solution exhibits more angular variation than the multi-feed solutions. It is interesting to notice how strong phase variations occur in the same regions where the gain pattern also varies strongly.
Figure 2a. 3D RHCP phase patterns at f=1575 MHz for a single-feed antenna. Source: Stefano Caizzone, Mihaela-Simona Circiu, Wahid Elmarissi, Christoph Enneking, Michael Felux and Kazeem A. Yinusa, German Aerospace Center (DLR)
Figure 2b. 3D RHCP phase patterns at f=1575 MHz for a dual-feed antenna. Source: Stefano Caizzone, Mihaela-Simona Circiu, Wahid Elmarissi, Christoph Enneking, Michael Felux and Kazeem A. Yinusa, German Aerospace Center (DLR)
Figure 2c. 3D RHCP phase patterns at f=1575 MHz for a our-feed antenna. Source: Stefano Caizzone, Mihaela-Simona Circiu, Wahid Elmarissi, Christoph Enneking, Michael Felux and Kazeem A. Yinusa, German Aerospace Center (DLR)
When considering the DGD, the frequency dependence of the phase pattern will have to be taken into account, according to Equation (1). To show the DGD variability with respect to the aspect angle, the standard deviation of the DGD over a 20-MHz bandwidth has been calculated (for each azimuth and elevation angle) and is shown in Figure 3, confirming the better behavior of the four-feed antenna.
Figure 3a. 3D standard deviation (calculated over frequency) of the DGD for a) single-feed antenna. Source: Stefano Caizzone, Mihaela-Simona Circiu, Wahid Elmarissi, Christoph Enneking, Michael Felux and Kazeem A. Yinusa, German Aerospace Center (DLR)
Figure 3b. 3D standard deviation (calculated over frequency) of the DGD for a dual-feed antenna. Source: Stefano Caizzone, Mihaela-Simona Circiu, Wahid Elmarissi, Christoph Enneking, Michael Felux and Kazeem A. Yinusa, German Aerospace Center (DLR)
Figure 3c. 3D standard deviation (calculated over frequency) of the DGD for a four-feed antenna. Source: Stefano Caizzone, Mihaela-Simona Circiu, Wahid Elmarissi, Christoph Enneking, Michael Felux and Kazeem A. Yinusa, German Aerospace Center (DLR)
Figure 4 shows the group delay versus frequency and elevation (with different azimuth values being represented by curves with different colors) for the three typologies of antennas: such typology of figure contains all information about DGD variation versus frequency and angle and is first introduced in this article. For comparison, in the RTCA’s 2006 MOPS document for airborne antennas, for the sake of simplicity, either DGD variation versus angle at central frequency or DGD variation over frequency at zenith were considered, hence not fully covering the complete space {Frequency, Azimuth, Elevation}.
Figure 4a. Differential group delay versus elevation angle and frequency (each color represents an azimuth value) for single-feed antenna. Source: Stefano Caizzone, Mihaela-Simona Circiu, Wahid Elmarissi, Christoph Enneking, Michael Felux and Kazeem A. Yinusa, German Aerospace Center (DLR)
Figure 4b. Differential group delay versus elevation angle and frequency (each color represents an azimuth value) for a dual-feed antenna. Source: Stefano Caizzone, Mihaela-Simona Circiu, Wahid Elmarissi, Christoph Enneking, Michael Felux and Kazeem A. Yinusa, German Aerospace Center (DLR)
Figure 4c. Differential group delay versus elevation angle and frequency (each color represents an azimuth value) for a four-feed antenna. Source: Stefano Caizzone, Mihaela-Simona Circiu, Wahid Elmarissi, Christoph Enneking, Michael Felux and Kazeem A. Yinusa, German Aerospace Center (DLR)
While the single-feed antenna in Figure 4 shows a big variation of the DGD when moving from zenith (that is, Elevation = 90°) to lower elevations, a substantial decrease in the DGD spread is recorded for the four-feed solution, with the dual-feed one having again intermediate results.
It is worthwhile noticing that the results obtained for the dual-feed solution are in agreement with the current MOPS for L1 antennas (RTCA DO-301), specifying a maximum value of 2.5 nansoseconds (ns) for the group delay spread at low elevations (normalized to boresight, El = 90°).
The results show how angular variation of the DGD can be related to non-uniformity along the aspect angle (Az or El) and frequency, hence suggesting to use multiple-feed solution for obtaining optimal performance.
A useful metric to quantify the uniformity of the group delay can be introduced as the Uniformity Indicator for Group Delay (UIGD):
( 2 )
with being the sum over frequency (Nf is the number of frequency steps considered) and DGDzenith,n being the value of the DGD at zenith for frequency n.
The UIGD expresses the maximum variation of the DGD over elevation and azimuth from a reference condition (the DGD at zenith) in the bandwidth of interest, extending de facto the MOPS requirements by considering the whole bandwidth behavior in the whole upper hemisphere.
The UIGD for the one-, two- and four-feed antennas is respectively 4.18, 1.03 and 0.05 ns, hence effectively mirroring the better pattern uniformity of the four-feed solution.
The UIGD is a comprehensive metric to describe the DGD uniformity, but needs accurate phase measurement over the entire bandwidth, which may not be always easily obtainable. As a matter of fact, phase can be challenging to measure: some indication of the areas most likely to deliver increased DGD can be found while considering gain patterns, qualitatively providing an easier metric to compare different antennas. In this case, the Uniformity Indicator for Gain (UIG)can be used:
(3)
The UIG expresses the maximum value over all elevation and azimuth angles of the standard deviation of the RHCP gain derivative over frequency (in the band of interest), therefore indicating the roughness of the antenna gain pattern in frequency and angle.
Such a metric does not relate totally with DGD behavior, but serves as an easier metric of pattern uniformity. The UIG for the one-, two- and four-feed antennas is respectively 68.5, 5.7 and 0.3%.
REAL-LIFE PERFORMANCE AND IMPACT ON ACCURACY
To evaluate the performance of actual antennas, three prototypes were measured in a Satimo Starlab anechoic chamber at the German Aerospace Center (DLR).
The antennas under test were:
A badly polarized COTS active antenna, having a behavior similar to that of a single-feed antenna;
An in-house developed passive antenna with two feeds;
An in-house developed passive four-feed antenna.
All antennas were properly tuned to obtain optimal gain and minimum reflection losses (input reflection coefficient <–10 dB) at L1 /E1 central frequency.
The measured RHCP pattern for the various antennas is shown in FiGURE 5. The UIGD for these antennas is 0.9, 0.7 and 0.2 ns respectively, while the UIG is 46.6, 38.5 and 9.0%.
Figure 5a. Measured 3D RHCP gain patterns at f=1575 MHz for a badly polarized COTS antenna. Source: Stefano Caizzone, Mihaela-Simona Circiu, Wahid Elmarissi, Christoph Enneking, Michael Felux and Kazeem A. Yinusa, German Aerospace Center (DLR)
Figure 5b. Measured 3D RHCP gain patterns at f=1575 MHz for a DLR dual-feed antenna. Source: Stefano Caizzone, Mihaela-Simona Circiu, Wahid Elmarissi, Christoph Enneking, Michael Felux and Kazeem A. Yinusa, German Aerospace Center (DLR)
Figure 5c. Measured 3D RHCP gain patterns at f=1575 MHz for a DLR four-feed antenna. Source: Stefano Caizzone, Mihaela-Simona Circiu, Wahid Elmarissi, Christoph Enneking, Michael Felux and Kazeem A. Yinusa, German Aerospace Center (DLR)
Differential group delay was calculated from the measured phase values and is shown in Figure 6.
Figure 6a. Differential group delay versus elevation angle and frequency (each color represents an azimuth value) as from measurement for a badly polarized COTS antenna. Source: Stefano Caizzone, Mihaela-Simona Circiu, Wahid Elmarissi, Christoph Enneking, Michael Felux and Kazeem A. Yinusa, German Aerospace Center (DLR)
Figure 6b. Differential group delay versus elevation angle and frequency (each color represents an azimuth value) as from measurement for a DLR dual-feed antenna. Source: Stefano Caizzone, Mihaela-Simona Circiu, Wahid Elmarissi, Christoph Enneking, Michael Felux and Kazeem A. Yinusa, German Aerospace Center (DLR)
Figure 6c. Differential group delay versus elevation angle and frequency (each color represents an azimuth value) as from measurement for a DLR four-feed antenna. Source: Stefano Caizzone, Mihaela-Simona Circiu, Wahid Elmarissi, Christoph Enneking, Michael Felux and Kazeem A. Yinusa, German Aerospace Center (DLR)
The results are similar to those obtained from simulation and clearly show the improved flatness of the DGD for the four-feed case.
Moreover, if the measured phase data are fed into an ideal GNSS receiver, able to provide the tracking biases occurring in the pseudorange code measurement for all elevations and azimuths, antenna-effects-only (as weighted by the signal characteristics) will be visible (as in this case, neither multipath nor receiver or satellite imperfections are included in the ideal receiver). The results are shown in Figure 7.
Figure 7a. Pseudorange bias versus elevation angle (each color represents an azimuth value) at L1 band for badly polarized COTS antenna. Source: Stefano Caizzone, Mihaela-Simona Circiu, Wahid Elmarissi, Christoph Enneking, Michael Felux and Kazeem A. Yinusa, German Aerospace Center (DLR)
Figure 7b. Pseudorange bias versus elevation angle (each color represents an azimuth value) at L1 band for a DLR dual-feed antenna. Source: Stefano Caizzone, Mihaela-Simona Circiu, Wahid Elmarissi, Christoph Enneking, Michael Felux and Kazeem A. Yinusa, German Aerospace Center (DLR)
Figure 7c. Pseudorange bias versus elevation angle (each color represents an azimuth value) at L1 band for a DLR four-feed antenna. Source: Stefano Caizzone, Mihaela-Simona Circiu, Wahid Elmarissi, Christoph Enneking, Michael Felux and Kazeem A. Yinusa, German Aerospace Center (DLR)
A substantial decrease in the antenna-induced error is evident as expected when the four-feed antenna is used.
The differences in performance among different antenna technologies shown here provide valuable insight in the choice of the antenna technology for a specific application, thanks to the better understanding of the impact of the antenna characteristics on the error at pseudorange level. Moreover, they can support the evaluation and definition of antenna requirements and connect them to the expected GNSS pseudorange error, such as during the process of MOPS definition as currently occurring for DFMC systems.
CONCLUSIONS
After investigating the effects of pattern uniformity on antenna-induced errors, group delay behavior over aspect angle and frequency has been shown comprehensively for different antenna feeding technologies for the first time. Minimal error in pseudorange measurements is obtained when the antenna has a smooth pattern, with no abrupt variations or nulls/sidelobes both in aspect angle and frequency. Different antenna feeding technologies currently in use for circularly polarized radiation have been evaluated, and the best performing one has been identified in the multiple-feed solution.
Both a comprehensive and an easier-to-measure metric for group delay uniformity have been identified, providing useful insight for fast comparison of the performance of multiple antennas in terms of GNSS accuracy.
STEFANO CAIZZONE received a Ph.D. in geoinformation from the University of Rome, Tor Vergata. He is is responsible for the development of innovative miniaturized antennas in the antenna group of the Institute of Communications and Navigation of the German Aerospace Center (DLR).
MIHAELA-SIMONA CIRCIU received a master’s degree in computer engineering from Technical University Gheorghe Asachi, Romania, and a master’s in navigation and related applications from Politecnico di Torino, Italy. She works on the development of the multi-frequency multi-constellation Ground Based Augmentation System for DLR.
WAHID ELMARISSI received a Dipl. Ing. in electrical engineering from the University of Applied Sciences, Kiel, Germany. He is responsible for measurement and manufacturing of antennas and antenna electronics at DLR.
CHRISTOPH ENNEKING received a MSc. degree in electrical engineering from the Munich University of Technology. He conducts research in GNSS signal design, estimation theory and GNSS intra- and inter-system interference at DLR.
MICHAEL FELUX is a research associate specializing in GBAS integrity issues for CAT -II/III operations and program manager for the research on GBAS navigation at DLR. He graduated in technical mathematics at Technische Universität München.
KAZEEM A. YINUSA received MSc. and Dr.-Ing. degrees in electrical engineering from the Technische Universität München. He is a researcher at DLR.
Esri has released a new web browser application, allowing users to create reporting dashboards that use charts, gauges, maps and other visual elements to reflect the status and performance of people, services, assets and events in real time.
Using dynamic dashboards through Operations Dashboard for ArcGIS, organizations of all types — from emergency operations centers to public utilities — can view crucial activities and key performance indicators that are vital to meeting their objectives.
“The Chicago Office of Emergency Management and Communication [OEMC] GIS team has been using Operations Dashboard to support various events with access to real-time information,” said Joe Kezon, GIS manager for the Chicago OEMC. “We are looking forward to the enhancements that will further increase our ability to ensure the safety and security of the City of Chicago.”
With an easily accessible web app, executives can monitor their organizations’ activities to assess what is working well and what needs attention.
“The Emergency Management division of the Chicago Office of Emergency Management and Communications works very closely with our public safety partners and the city’s infrastructure departments in our comprehensive approach to event and incident management,” said Thomas Sivak, deputy director, Emergency Management, Chicago OEMC. “The Operation Dashboard allows us to effectively coordinate among agencies and adjust resources to make Chicago a safe place to live, work, and play.”
Having this type of authoritative data allows decision-makers to reduce the risk of costly errors due to inaccurate or outdated information, better control the allocation of resources, maintain real-time awareness of where assets and human resources are located, monitor conditions live such as weather and traffic, and achieve real-time insight to respond to changing conditions.
“The new Operations Dashboard web app enables, at a glance, decision-making better than ever,” said Jeff Shaner, Esri product manager. “Not only can dashboards be authored online — anywhere, at any time — but the common platform allows greater collaboration among personnel.”
Operations Dashboard also provides a common interface to monitor progress and identify vulnerabilities that could compromise the success of an organization’s mission. Dashboards can be authored completely in a web browser. There is no need to download and install an app anymore.
Users can launch Operations Dashboard by using their ArcGIS organizational account. They can also browse and manage dashboards within their ArcGIS organizational content or on the dashboard home page.
The Institute of Navigation (ION) presented its Annual Awards during the ION International Technical Meeting (ITM) and Precise Time and Time Interval Systems and Applications (PTTI) meeting in Reston, Virginia, Jan. 29-Feb. 1.
The ION Annual Awards Program is sponsored by The Institute of Navigation to recognize individuals making significant contributions or demonstrating outstanding performance relating to the art and science of navigation.
Zheng Yao received the Early Achievement Award for his pioneering contributions in developing new GNSS signals and multiplexing techniques; and advancing the Chinese BeiDou Navigation Satellite Systems (BDS) signal design. The Early Achievement Award is presented in recognition of outstanding contributions made early in one’s career.
Captain Gregory DuBose received the Superior Achievement Award for sustained performance in combat operations in Afghanistan, Iraq and Syria; and assistance in the recovery of a downed B-1 crew in Montana. The Superior Achievement Award is presented to an individual demonstrating outstanding accomplishments as a practicing navigator.
William Bollwerk received the Distinguished PTTI Service Award for service to the Department of Defense and country in promoting the importance of time, and educating policymakers and mission operators to ensure understanding of time in critical operations. The Distinguished PTTI Service Award is presented to recognize outstanding contributions related to the management of PTTI systems.
Luke B. Winternitz, William A. Bamford, Samuel R. Price, J. Russell Carpenter, Anne C. Long and Mitra Farahmand received the Samuel M. Burka Award for their paper “Global Positioning System Navigation above 76,000 KM for NASA’s Magnetospheric Multiscale Mission” published in the Summer 2017 issue of NAVIGATION, Journal of The Institute of Navigation, Vol. 64, No. 2, pp. 289-300. The Samuel M. Burka Award recognizes outstanding achievement in the preparation of a paper contributing to the advancement of the art and science of positioning, navigation and timing.
Professor Allison Kealy received the Captain P. V. H. Weems Award for sustained contributions to advancing the art and science of navigation, and promoting and expanding the use of PNT among worldwide science and engineering communities. The Captain P. V. H. Weems Award is presented to individuals for continuing contributions to the art and science of navigation.
David A. Turner received the Norman P. Hays Award for his role in the formation of the International Committee on GNSS (ICG) and the development of globally recognized principles of GNSS compatibility, interoperability and transparency. The Norman P. Hays Award is given in recognition of outstanding encouragement, inspiration and support contributing to the advancement of navigation.
Yang Gao received the Thomas L. Thurlow Award for significant contributions and leadership in the development and application of Precise Point Positioning (PPP) and high-precision GNSS technology. The Thomas L. Thurlow Award recognizes outstanding contributions to the science of navigation.
New utility network management extension combines advanced system of record with location-based analytics.
Esri, the geographic information system (GIS) technology and spatial analytics company, is releasing advanced network capabilities for utilities as part of the company’s ArcGIS platform.
The ArcGIS Utility Network Management extension, which delivers the new utility network, lets users create, manage and share complete data about networks from source to demand, such as residential meters for electric, water, wastewater, gas, district heating and telecommunications companies.
These network management capabilities enhance Esri’s current utility platform for handling billions of data elements while providing access to the utility network on any device, anytime, anywhere. For the first time, workers will be able to edit and trace the path of a network from a smart device while in the field and share information securely and more easily with those who need it. Previously, each utility subnetwork — like transmission lines, substations, and distribution and low-voltage networks — had its own separate GIS database.
The utility network provides a holistic system for every component of the utility supply chain right down to the customer, as well as the ability to store unprecedented detail on each of these components, which will be very important as utilities evolve to provide higher fidelity information to operational systems.
“We are very excited about the release of our next-generation utility platform,” said Jeff Rashid, Esri global director for utilities and communications. “These advanced capabilities will help utilities and telecoms provide greater details about their networks across their organization, at a rate of speed not seen in the past.”
The ArcGIS Utility Network Management extension allows the utility network to be completely cross-platform capable, meaning it is not confined to users of desktop GIS software. Before this innovation, location data was not easily accessible for fieldworkers or executives, managers, service technicians, and accountants who needed to have accurate, real-time understanding of utility assets.
In addition, Esri partners in the utility field will be able to use this network to add greater value to their workflow, create new solutions allowing personnel to be more efficient, and to better satisfy the needs of their customers.
“We are excited about the new capabilities in Esri’s utility network management platform and look forward to evolving the ArcFM Solution XI Series to offer utilities unprecedented value,” said Jay Stinson, general manager, Schneider Electric Geospatial Business. “This next generation platform enables us to build a world class ecosystem for managing the design and construction workflow. The continued strength of the historic Esri and SE partnership will help utilities realize the full potential of their GIS investment, equipping them to address the challenges facing today’s digital utility.”
Tallysman, a manufacturer of high-performance GNSS antennas and related products, is offering a new light-weight compact GPS L1/L2 + GLONASS G1/G2 antenna, available either as an OEM (TW1829) antenna or in a housed version (TW8829).
The antenna is designed for unmanned aerial vehicle use because of its low aerodynamic profile and very light weight. The TW1829 weighs 37 grams and is 48mm (d) x 12.2mm (h). The TW8829 weighs 52 grams and is 47.3mm (d) x 18.3mm (h).
The antennas employ Tallysman’s Accutenna technology, which has proven its ability to provide high-level rejection of multipath signals, a phase linear response and tight phase centre variations (PCV).
Additionally, the antenna has pre-filters to prevent the saturation of the front end LNA by strong near frequency and harmonic signals.
The antenna is available with a choice of connectors and custom cable lengths. Additionally, Tallysman can custom tune the TW1829 for the customers’ enclosure to ensure optimal performance.
Tersus GNSS Inc. has launched the BX306Z GNSS RTK board, which has powerful flexibility and compatibility to meet the needs of original equipment manufacturers (OEMs) and system integrators, according to the company.
As a new member of the BX-series GNSS OEM boards, BX306Z is a cost-efficient GNSS real-time kinematic (RTK) board for positioning and raw measurement output.
The board is a compact, multi-GNSS (GPS L1/L2, GLONASS G1/G2, BeiDou B1/B2) RTK module with centimeter-level accurate positioning capability.
Features
The BX306Z is able to integrate with autopilots and inertial navigation units.
Log and command is compatible with major GNSS boards.
With flexible interfaces, the pin-to-pin design is compatible with Trimble BD970.
All of these features help manufacturers reduce their application cost and lead time to market.
