An Australian company that manufacturers GNSS echo sounders aided the aiders — leading a medical ship through uncharted waters in Papua New Guinea.
The CEESCOPE echo sounder enabled the ship to reach volunteers who were working to save the life of a newborn.
The ship, operated by YWAM Medical Ships Australia (YWAM MSA), visits remote villages in Papua New Guinea, giving communities access to life-saving medical and dental services. The village locations are accessed by river, and while often there is adequate tide information to help navigate, there are no available charts or bathymetry data for the passages upriver.
Without a navigable route to follow, the medical ships simply could not travel to locations where help is needed the most.
To solve this problem, YWAM decided to make its own charts, with help from CEE HydroSystems. Using a small, fast launch equipped with a CEESCOPE single-beam echo sounder and GPS hydrographic survey system, YWAM volunteer and master mariner Jeremy Schierer set out to find safe routes through vast river deltas ahead of the medical ship.
While surveying at high speed to maximize the area covered, Schierer executed reconnaissance patterns along the river while continuously updating the hydrographic survey plan based on the results seen.
Survey data gathered and processed in HYPACK acquisition software were exported to the navigation system of the ship to provide waypoints marking the safe passage route along the river. Used with available and observed tide data, the navigator of the vessel could confidently travel upriver without the risk of grounding.
The CEESCOPE is a one-box survey system that can be swapped between the two available 4.2-meter and 5.2-meter boats. It can be used without an acquisition PC on the survey launch if needed — all data recorded on the internal memory, and can run on its own battery power for an extended duration. With operation in remote areas on small boats, reliability and usability were key for YWAM.
YWAM also used the CEESCOPE with HYPACK from the wheelhouse to navigate the ship along the surveyed routes on custom electronic charts.
In the third year of YWAM’s operation in Papua New Guinea, Schierer recorded a staggering 3,400 kilometers (2,000 miles) of bathymetry to help navigate the Pacific Link. All of the rivers were uncharted before the ship traveled upstream. With incomplete tide-station coverage, determining the ship’s path was a complex calculation. Despite this, and complicated by a bore tide, YWAM was able to take its vessel 75 kilometers upstream in the Bamu River, Western Province, without published charts.
However, the most startling example of the benefit of the YWAM hydrographic survey approach took place in the second year of operation.
“Baimuru is up the Pie River from Port Romilly in the Gulf Province,” Schierer said. “The only previous known route took us about four hours through the rivers and required high tide and daylight.
“We went out with the CEESCOPE to see if we could find an alternate and more direct route to the open sea. We left the ship just before sunrise and went as far as 8 nautical miles off the coast to confirm a good passage — and we found one that was deep enough.”
Instead of leaving when scheduled, the ship received an emergency call from the medical center about 300 meters away on the shore, where there is no electricity or running water.
“A lady had just given birth, and they were requesting attendance by our doctor and midwife. Evidently the baby was born in the canoe on the way to the medical center, and for some time the baby lay in the bottom of the canoe.
“By the time we unsecured our small boat and got the medical team ashore, the baby was 35 degrees Celsius and not warming up. Our medical team was able to assist in warming the baby and reported that if we had not been there, they were quite certain that the baby would not have survived the night.
“The only reason we were still there was because we had the CEESCOPE and had been able to find another route. We’ve charted more than 1,200 kilometers with the CEESCOPE so far, and it is making a huge difference,” Schierer said.
The track of the medical ship on the previously uncharted Bamu River.
Based in Sydney, CEE HydroSystems opened an office in San Diego, California, in late 2015, to serve the United States and Canada. The company specializes in RTK GNSS-enabled precision shallow water hydrographic echo sounders. Its products are aimed at surveyors conducting shallow water bathymetric surveys.
“For inshore hydrographic surveys of water bodies such as canals, lakes, rivers or industrial water impoundments, survey firms inexperienced in hydrographic methods often have to resort to conventional and laborious processes using sounding lines, range poles or basic sonar equipment,” said Peter Garforth, CEE HydroSystems managing director. “Our CEESCOPETM survey system puts a RTK GNSS solution and precision echo sounder into a compact single package, allowing surveyors to vastly improve productivity on these surveys.”
The CEE range of echo sounders with GPS was first developed to offer surveyors a one-box solution to reduce hardware setup time and the need for interconnecting components.
Portable echo sounder
The CEESCOPE uses a built-in RTK GNSS receiver and UHF radio modem to acquire RTK-quality position and elevation that is used in hydrographic surveying software to output xyz point-cloud data files of bottom elevations in local coordinates and datums. In RTK mode, the CEESCOPE can be directly connected to the local UHF base station radio. The internal CEESCOPE GNSS receiver provides accurate position data at 1–20 Hz, and the single-beam echo sounder records soundings at up to 20Hz.
Both data streams — plus any ancillary measurements fed into the unit such as heave, pitch and roll — are precisely time-tagged using a 1PPS signal and then recorded on the CEESCOPE internal memory. Simultaneously, the data are output to an acquisition PC or tablet.
The 50th Space Wing accepted satellite control authority of the final Global Positioning System GPS IIF satellite from the GPS Directorate during a ceremony held Feb. 12 at Schriever Air Force Base, Colorado.
Following its launch from Cape Canaveral Air Force Station, Florida, Feb. 5, operators from the 50th and 310th Space Wings completed an extensive checkout of the satellite before placing it into its assigned orbital slot in the GPS constellation.
Col. Steve Whitney, Space and Missile Systems Center’s director of the GPS Directorate, responsible for the acquisition of GPS satellites, started the ceremony by transferring satellite control authority of GPS IIF-12, as Space Vehicle Number 70, to the 14th Air Force.
“The addition of the final GPS IIF satellite to the constellation is a colossal triumph, as GPS IIF capabilities are crucial to modernizing the GPS constellation. On-going modernization efforts provide the constellation with improved timing, additional civil signals and increased protection,” Whitney said. “GPS continues to be the ‘Gold Standard,’ providing precise positioning, navigation, and timing services to users around the globe.”
“This launch of the last Block IIF GPS satellite marks a significant milestone for the program, which continues unprecedented support to our military forces and the general public,” said Lt. Gen. David J. Buck, 14th Air Force commander and commander of the Joint Functional Component Command for Space, U.S. Strategic Command.
“The capabilities enabled by the position, navigation and timing signals of the GPS constellation are ingrained into the fabric of our daily lives. From paying at the gas pump, to ATM withdrawals and precision farming; international banking or international shipping, GPS enables the modern way of life,” said Buck. “It is also a critical component of delivering precise combat power in support of joint and coalition warfighter objectives, and I am pleased to make the constellation more robust and resilient than ever, ensuring we can continue to support America’s warfighters well into the future.”
Buck’s comments were echoed by those who are now entrusted with the care and operation of the satellite.
“It’s always a pleasure to transfer satellite control authority to the operators who will deliver those combat effects to the field,” said Col. DeAnna M. Burt, 50th Space Wing commander. “GPS is always a little bit different thanks to the billions of civilian users who also engage this global utility.”
Daily operation of the satellite is delegated to the 2nd Space Operations Squadron. GPS IIF satellites provide improved signal capabilities and increased user accuracy for military and civil users.
“We take great pride in commanding and controlling this constellation on a daily basis,” said Lt. Col. Todd Benson, on behalf of the 2nd and 19th Space Operations Squadrons. “This satellite is the last in a demanding schedule of IIF satellite launches; the units have teamed together to support six launches in just 18 months.”
GPS IIF-12 (SVN-70) will replace the legacy SVN-41, which will be moved to another location and provide auxiliary support to the GPS constellation. The oldest GPS satellite in the constellation, SVN-23, has been removed from the broadcast almanac to make room for GPS IIF-12. Launched Nov. 26, 1990, SVN-23 was decommissioned after 25 years of service prior to the launch of GPS IIF-12.
“GPS IIF-12 marks the 12th satellite launched in under six years, between May 2010 and Feb. 2016, and the seventh in the last 21 months,” stated Lt. Gen. Samuel Greaves, Space and Missile Systems Center commander and Air Force program executive officer for space. “This incredible track record is the result of the remarkable relationship between SMC, our operators within the 14th Air Force and our ULA/Boeing industry partners. Their continued tenacity and dedication to mission success ensures we continue to maintain a robust satellite constellation with modernized, more resilient GPS capabilities.”
Now in its 24th year, the annual GPS World Receiver Survey provides the longest running, most comprehensive database of GPS and GNSS equipment available in one place.
After choosing the most appropriate receiver for your application, you may need an antenna, too. We have collected key specifications for 320 antennas from 30 manufacturers.
A team from the National Oceanic and Atmospheric Administration (NOAA) and Raytheon has successfully demonstrated advancements of the Coyote Unmanned Aircraft System (UAS), verifying new technology that improves Coyote’s ability to collect vital weather data on hurricanes.
Coyote drops out of a P-3 weather surveillance plane, spreads its wings and flies straight at a hurricane, braving violent winds and punishing rain to gather weather data and beam it back to meteorologists.
Drew Osbrink and Eric Redweik of Sensintel and NOAA hurricane researcher Joe Cione monitor data from the Coyote as it flies into Hurricane Edouard in 2014. (Photo: NOAA)
Coyote solves a problem that has limited forecasters’ ability to tell how hard a hurricane will hit. The secret behind the storm’s punch lies in what is known as the “boundary layer” — a low-altitude area that includes the surface of the ocean. Because hurricanes are fueled by warm ocean water, information collected at the interface of atmosphere and ocean is vital to the understanding and prediction of a storm’s strength.
“That’s where the energy is extracted from the ocean to the atmosphere,” said Joe Cione, a NOAA hurricane researcher. “Unfortunately, it is too difficult for us to go with manned aircraft to fly down there.”
The Coyote can maneuver in the most violent regions of a hurricane.Traditional weather instruments parachute from a plane and grab only a snapshot of humidity, wind speed and other factors, but Coyote’s winged design enables it to linger and return to certain areas for more measurements.
“Coyote will gather data specifically in the eye wall where it can provide information for forecasters to predict intensity from a safe distance,” said John Hobday, Raytheon. “This is a significant difference for researchers: instead of providing a snapshot of data, it’s a full-length movie.”
The Coyote after a successful flight on Jan. 7. (Photo: NOAA)
Operational Upgrades
In a Jan. 7 test, the Coyote was released from NOAA’s Hurricane Hunter P-3 aircraft and flew over the Avon Park Air Force Range in Florida, to measure the transmission range of upgraded technologies. It set a new distance record for flight control and data transmission to the P-3, and provided hurricane forecasters with real-time data on atmospheric air pressure, temperature, moisture, wind speed and direction as well as surface temperature.
Data collected will help improve the accuracy of forecasts. “Here at the National Hurricane Center (NHC), we are keenly interested in obtaining measurements from the Coyote of the strongest winds near the center of the storm,” said Chris Landsea, science operations officer at NHC. “Coyote could help us paint a better picture of current storm intensity for our storm updates.”
In 2014, NOAA deployed four of the Coyote planes into Hurricane Edouard, a Category 3 storm, at controlled altitudes as low as 400 feet. Scientists on board the P-3 received meteorological data in both the eye of the storm and the eye wall.
However, the P-3 had to fly 5 to 7 miles from the Coyote to pick up its signal. So engineers at Raytheon and the NOAA Aircraft Operations Center upgraded Coyote’s sensor systems and improved its communications package to allow it to talk to the plane over longer distances. Now, Coyote can fly for 50 miles away from the launch aircraft, which will be free to continue its own mission.
Coyote also was outfitted with an upgraded instrument package that includes an infrared sensor to measure sea surface temperature, which will help scientists understand how a hurricane extracts energy from the ocean — and how it might intensify or change. The team also is working toward optimizing battery life.
The test flight verified the Coyote’s ability to transmit the data collected from its instrument package to operators aboard the P-3 as well as at the NHC, where personnel monitor storms and develop forecasts.
NOAA scientist Paul Reasor demonstrates the Coyote. (Photo: NOAA)
u-blox has launched a receiver module that brings real-time kinematic accuracy to the mass market. The NEO-M8P GNSS receiver module delivers high performance down to centimeter-level accuracy.
RTK technologies have been used for some time in low-volume niche markets, such as surveying and construction. Because of high costs and complexity, this enhanced positioning technology has been inaccessible for most other uses.
Emerging high volume markets, such as unmanned vehicles, require high-precision performance that is low cost and energy efficient. Other application areas include agriculture and robotic guidance systems, such as tractors or robotic lawnmowers. The u-blox NEO-M8P answers these demands for a small-sized, highly cost-effective, and very precise RTK-based module solution.
The RTK algorithms are pre-integrated into the module. As a result, the size and weight are significantly reduced, and power consumption is five times lower than existing solutions, cutting costs and improving usability dramatically, u-blox said.
Measuring 12.2 x 16 x 2.4 millimeters, NEO-M8P is a small, high-precision GNSS RTK module based on GPS and GLONASS satellite-based navigation systems.
The module is available in two variants. The NEO-M8P-0 has rover functionality, and the NEO-M8P-2 has rover and base-station functionality. The rover with the u-blox NEO-M8P-0 receives corrections from the u-blox base receiver NEO-M8P-2 via a communication link that uses the RTCM (Radio Technical Commission for Maritime Services) protocol, enabling centimeter-level positioning accuracy.
By using the NEO-M8P module, customers can reduce their research and development efforts, because they do not have to spend significant resources and time to develop an in-house RTK solution on a separate microprocessor system.
“NEO-M8P lowers the barriers for innovative companies looking to develop equipment that needs centimeter-level accuracy in many markets and applications, such as UAVs,” said Daniel Ammann, Executive Director Positioning and Co-Founder of u-blox. “Today, most solutions are based on board-level receiver products. NEO-M8P delivers performance that is simply a level above competitive offerings in terms of size and low-power consumption, thereby providing easy integration into customers’ existing product platforms, as well as a significant saving in their cost of goods.”
u-blox NEO-M8P is available for sampling now and will be shipping in volumes in the third quarter of 2016.
TerraGo and Eos Positioning Systems have entered a collaboration to combine the TerraGo Edge mobile GPS data-collection platform with the Eos Arrow line of sub-meter and centimeter accuracy receivers. The combination delivers a modern, cloud-based, real-time data collection capability, according to a TerraGo press release.
While the working environments and the projects are very different, customers in for water utilities, energy, survey and engineering are using TerraGo Edge and Eos Arrow receivers to replace traditional GPS handhelds for cost-savings and improved productivity.
Enmapp, a pipeline inspection company based in Canada, was able to cut hardware costs by 85 percent while capturing sub-meter data in real-time, eliminating all the costs of post-processing handheld data.
Summit Engineering, a Colorado-based engineering and land surveying firm, was able to reduce hardware costs by over 50 percent and improve productivity by more than 30 percent while surveying power lines in Minnesota for one of the country’s largest energy companies. Similar performance improvements and cost reductions are reported by joint customers in water utilities, forestry, engineering, agriculture and environmental operations, TerraGo said.
“When we talk about Eos Arrow, we’re not simply pairing their receivers via Bluetooth, there are millions of apps that do that without any meaningful integration,” said Dave Basil, VP of products and services at TerraGo. “We interoperate with their receivers at the software level to ensure our customers get the full real-time GPS data set so they can monitor, alert and capture data that meets the highest accuracy and quality standards. For customers, it’s as simple as Bluetooth pairing, but we’ve done the work to turn their phone or tablet into a survey-grade receiver.”
“TerraGo and Eos Positioning are strategic technology partners,” said Jean-Yves Lauture, chief technology officer of Eos Positioning Systems. “This means that our collaboration goes beyond simple marketing and includes sharing core technology for the benefit of our customers. For example, we have been able to share Eos software components, which TerraGo has built into the Edge app. This integration provides the full fidelity monitor and lossless capture of NMEA data from the Eos receivers, including the Arrow 200.”
Tallysman, a manufacturer of economical high-performance GNSS antennas and related products, is offering a new wideband 28-dB inline amplifier covering the full GNSS spectrum from 1 to 2 GHz.
The TW125B is a low cost, rugged, waterproof, low noise, low current/low voltage, 1 to 2 GHz band, 28dB gain in-line amplifier, specially designed to amplify all GNSS frequency signals, from GPS L5 (1164 MHz) to GLONASS G1 (1610 MHz) and beyond.
The TW125B provides for much longer cable runs from antenna to receiver, for applications such as mast-mount, large vehicle and timing systems, without degradation of system sensitivity.
Its low loading allows for both the antenna and the TW125B in-line amplifier to be powered by the GNSS receiver. The amplifier adds just 12mA of load on the circuit, well within the capabilities of most GNSS receivers on the market.
The TW125B passes DC supply to the antenna, therefore not requiring additional hardware such as bias-T, power cable and power supply.
The amplifier is available with TNC, N-Type, or SMA connectors, and is REACH and ROHS compliant.
Sokkia has introduced its new SHC500 field controller for construction and surveying applications. It is designed to provide operators a compact handheld option with numerous features and benefits, including a 4.3-inch touchscreen display and optional 5 MP camera with built-in LED flash.
The SHC500 is designed for the professional operating MAGNET Field, Site and Layout software. The data controller works with all Sokkia GNSS receivers and total stations, and meets or exceeds all field application requirements.
“With a sunlight-readable screen, even in bright conditions the controller is perfect for modern project sites,” said Ray Kerwin, director of global surveying products. “It is built rugged — waterproof up to one meter with an IP68 rating — securing the unit and optional built-in LED flash camera and 8GB flash storage.
“The SHC500’s optional internal cellular modem allows operators to send and receive data through the MAGNET suite of software solutions. Field crews can easily communicate when projects need to be changed or if important data is required back in the office,” Kerwin said.
Additional features include standard Bluetooth and Wi-Fi connectivity, 23 control buttons with numeric input, and a capacitive-touch interface.
Antenna maker Taoglas USA has opened a facility in San Diego for its North American customers.
In the midst of explosive wireless device growth in the Internet of Things (IoT) market, the company has quadrupled the original size of its local facility — now more than 16,000 square feet.
The new Taoglas IoTx Center offers a fully equipped design and test location that supports companies seeking a competitive, time-to-market advantage for machine to machine (M2M) and IoT applications.
According to Taoglas, the location offers support for customers at all stages of their product design cycle — from concept to certification readiness.
“This kind of open-door policy is rare in the antenna and wireless device testing business,” explained Dermot O’Shea, president of Taoglas USA. “We have expanded our engineering team, added more test equipment, and now have two chambers here to increase design and test capacity. As well as being able to prototype antennas and PCBs, we can test the antenna and devices in operation on site to ensure they work reliably in the real world.
“We have also now added an antenna and cable assembly operation so we can quickly produce antenna and custom RF cable orders here in San Diego,” O’Shea said. “Quite often customers require products in a few days rather than weeks and we have now facilitated that demand with this new move.”
Taoglas has dedicated the facility to support it’s North American customer base. San Diego was chosen due to the strong, experienced talent pool in the areas of antenna and hardware design.
In addition to the site’s two CTIA calibrated anechoic chambers, the campus includes a custom antenna and RF cable assembly facility, expanded development and office space as well as a well-equipped, sound-proofed customer lounge area with workspaces and other features to accommodate customers while testing and product development are in process. Taoglas will increase its San Diego staff by 50 percent this year and expects to double that in the next three years.
“Our enlarged San Diego facility reflects our growth rate last year of almost 100%,” explained O’Shea. “We’re bullish about the potential in the Internet of Things (IoT) market, which is key for us. The vendors in this space who we support not only need the off-the-shelf or custom antennas we offer, they need design services and assistance. All our services have clear explanations and fast deliverables, all available on our website. You just select your service code, or call our sales, and we will book you in for work on your device immediately. No waiting around or complicated contractual discussions.
“First time certification is also critical so wireless OEMs can avoid the hardware failures that are so common in the IoT sector. Having two anechoic testing chambers means we can work on multiple devices in real time, helping customers get successful products into the market first time and on time.”
According to International Data Corp., the IoT market will grow to $1.7 trillion by 2020, with a compound annual growth rate of 16.9 percent. “We’re currently shipping millions of antennas per month into the IoT market,” O’Shea said. “Our larger campus here will be well utilized.” Taoglas also has offices in Minneapolis, Ireland, Taiwan and Germany.
According to Rory Moore, a prominent San Diego technology company founder and investor, in addition to being CEO of Southern California startup incubator EvoNexus, “The enlarged Taoglas campus is another sign of success in the local innovation economy. San Diego already has a strong base in IoT growth and this large new Taoglas IoTx facility cements San Diego as an IoT hub in a very hot sector. I also like the fact that Taoglas has been collaborating with SDSU (San Diego State University), building useful bridges between the business and educational communities.”
Trimble has introduced version 12.81 of its Trimble GCS900 Grade Control System. The new version further expands the mix of machines supported to now include wheel loaders, demonstrating Trimble’s continued commitment to meet the contractor’s needs for construction technology across a mixed fleet and for all phases of the project life cycle.
“Trimble GCS900 version 12.81 means big productivity gains for contractors who operate wheel loaders,” said Ryan Kunisch, marketing director for Trimble’s Civil Engineering and Construction Division. “We have seen up to a 40 percent increase in productivity for material placement and grading activities and typically a 25 percent reduction in undercutting when the GCS900 system is used.”
The new configuration for wheel loaders allows contractors to realize productivity gains in both fine and rough grading applications. Operators can precisely control the amount of material being graded, improve fine grading accuracy and time, and reduce the potential for undercutting the surface during material placement or removal.
Using a wheel loader equipped with GCS900, contractors can track material weight with a Trimble LOADRITE weighing system. In addition, material placement and grade can be monitored by adding a VisionLink Project Monitoring subscription for a more accurate and complete picture of project progress.
Features of GSC900
Uses two GNSS receivers and solid state angle sensors and an inertial measurement unit (IMU) to measure the precise 3D position of the bucket
Tracks GPS, GLONASS and Galileo signals
Quickly performs complex tasks and simplify finishing slopes with accurate 3D positioning
Garmin Ltd. has entered into an agreement to acquire substantially all of the assets of DeLorme, a privately held company that designs and markets consumer-based satellite tracking devices with two-way communication and navigational capabilities.
The completion of the acquisition, which is subject to customary conditions, is expected to occur within 30 to 60 days.
One of the most compelling products in the DeLorme portfolio is its inReach series of two-way satellite communication devices. These GPS-enabled devices allow the user to send and receive satellite text messages or trigger an SOS for emergency help, anywhere in the world. In addition to inReach, DeLorme has an extensive library of digital cartography and enterprise GIS software, as well as traditional mapping.
“DeLorme is a respected brand with exciting products and technologies that are a natural fit in the Garmin portfolio,” said Cliff Pemble, Garmin’s president and CEO. “We look forward to completing the acquisition and welcoming them onto our team. We are looking forward to leveraging their expertise to further enhance the Garmin lineup of products.”
The DeLorme inReach Explorer is a two-way satellite communicator with built-in navigation.
“Our inReach technology is invaluable to hikers, hunters, boaters and pilots who often find themselves in remote areas — Garmin’s core customers. We are looking forward to completing the acquisition and are excited to help leverage our expertise into enhancing their already outstanding products,” said Michael Heffron, CEO of DeLorme. “Garmin has extensive R&D capabilities and a global distribution network that will allow us to provide this technology to customers across many markets and around the world.”
Garmin will retain most of the associates of DeLorme and will continue operations at its existing location in Yarmouth, Maine, following the completion of the acquisition. The Yarmouth facility will operate primarily as a research and development facility and will continue to develop two-way satellite communication devices and technologies. Financial terms of the purchase agreement and acquisition will not be released.
For decades, Garmin has pioneered new GPS navigation and wireless devices and applications that are designed for people who live an active lifestyle. Garmin serves five primary business units, including automotive, aviation, fitness, marine and outdoor recreation.
Assessing the performance of multi-antenna interference-rejection techniques
Several factors affect the levels of signal rejection using antenna arrays. Our authors describe experiments to assess the bounds the factors impose on its signal rejection capability.
By James T. Curran, Michele Bavaro and Joaquim Fortuny-Guasch
INNOVATION INSIGHTS with Richard Langley
IT’S ALL PHYSICS. How things work, that is. Well, maybe a little chemistry too in some cases. But I might be a little biased in my opinion given that I’m an applied physicist by training. Radio? Satellite navigation? Yes, the principles of their operation are all governed by physics. Many physicists of my generation started out as radio tinkerers. I’ve recounted in this column before that I built my first radio (from a kit) when I was 14 (not counting the crystal radio that my father helped me to put together when I was 9). Built a few more during high school, got into radio astronomy as an undergraduate, and did a Ph.D. in the application of very long baseline (radio) interferometry to geodesy.
The great American physicist Richard Feynman was also a radio tinkerer in his youth. He recounts in one of his autobiographical books how he used to fix radios. And because he would approach the task of repairing each non-functioning set by first contemplating why it wasn’t working, he got the reputation of fixing radios by thinking!
One of Feynman’s special abilities was in explaining how things worked. In fact, he has been called “The Great Explainer.” He authored what is arguably the best physics textbooks ever produced: The Feynman Lectures on Physics. The three-volume set, developed from his Caltech lectures to undergraduates between 1961 and 1964, covers mechanics, radiation, electromagnetism, matter and quantum mechanics. Many students and practicing physicists have learned or re-learned aspects of physics from the famous “red books.” Many more will now thanks to Caltech, which recently put the Lectures on line for anyone to read (feynmanlectures.caltech.edu).
In this month’s column, we are going to learn about the development of a microprocessor-controlled multi-element GNSS antenna array for interference rejection. While there are many textbooks that describe how multi-element antennas work, Feynman explains their operation in his Lectures from first principles — from the principles of physics.
The phenomenon governing the behavior of antennas with multiple elements is called interference. If we combine two electromagnetic waves, they will interfere with each other with a result that depends on the phase difference of the waves. The waves might reinforce each other leading to a larger net amplitude, called constructive interference, or partially or fully null each other out, called destructive interference. When we apply this concept to the signals received by a pair of antennas making up an array, we find that the array has directionality and we can have a null in the reception pattern in the directions parallel to the antenna baseline and will be insensitive to signals arriving from those directions. And as Feynman describes in his Lectures, by adding more antennas to the array and “some cleverness in spacing and phasing our antennas,” we can have a fairly narrow pattern null in a chosen direction. In the case of a GNSS antenna array, that direction might be that of a jamming signal and so we can null out the jammer and maintain a positioning capability.
Several factors affect the levels of signal rejection using antenna arrays. In this article, our authors describe these factors and the experiments they conducted with their microprocessor-controlled array to assess the bounds the factors impose on its signal rejection capability.
Directional antennas offer a powerful means of achieving signal selectivity when various signal sources observed by a receiver are separated spatially. In the context of GNSS, which must accommodate a mobile receiver observing many moving transmitters, adaptive antennas — or controlled radiation pattern antennas—are an attractive option. The benefits of antenna arrays have been demonstrated both for signal rejection, such as interference and multipath mitigation or anti-spoofing; and for the purposes of gain enhancement, angle-of-arrival, or attitude estimation.
A number of different factors can influence the achievable levels of signal rejection using antenna arrays. These factors include: the gain and phase stability of the analog radio-frequency (RF) and intermediate-frequency (IF) stages, the linearity of the active analog stages, and the fidelity of the signal-combining stages. Seeking to identify the bound imposed by each of these limiting factors, we have carefully examined the signal rejection capability of an antenna array in our work. The study considers a circular antenna array, consisting of seven passive dual-polarized (right-hand circularly polarized [RHCP] and left-hand circularly polarized [LHCP]) L1-L2 elements. Although signal rejection can be performed both in the analog and in the digital domain, this article focuses only on the analog combination of signals at RF, using a bank of controllable phase shifters and attenuators. We conducted broadcast experiments in a large-diameter anechoic chamber, housing a rotatable central pillar upon which the array is mounted, and two broadcast antennas mounted on movable sleds.
The results presented here include a precise three-dimensional phase and gain calibration of the antenna array using a network analyzer to explore the properties of antenna elements when placed in close proximity on a common ground plane. Further results include an investigation of the nulling depth achievable by the array via the synchronous broadcast of two GNSS-like code-division multiple access (CDMA) signals from different broadcast antennas. We then extrapolated these results to infer the relative degradation in nulling capability when the receiver’s estimate of the amplitude and phase of the signal to be rejected is poor. Finally, a comparison of analog and digital element combining is explored, with emphasis on the rejection of strong jamming signals.
This experiment sought to illustrate and quantify the unique benefits and limitations of each technique. In particular, we note that analog combining enjoys high linearity and can accommodate high interference power, but is typically restricted to the use of coarse phase and gain coefficients when combining elements. In contrast, digital combining can offer notably higher gain and phase resolution, but is limited by the dynamic range of the digitizer.
Antenna Characterization
The work reported in this article has focused on the use of a seven-element circular antenna array, consisting of dual-polarized (RHCP and LHCP), dual-frequency (L1 and L2) elements. The antenna elements are mounted on a single circular aluminum ground plane 2 millimeters thick and 50 centimeters in diameter, and placed in a hexagonal arrangement at a spacing of 12.5 centimeters, as depicted in FIGURE 1. Because the antennas are passive, and can be used both for transmission and for reception, characterization tests were performed in broadcast mode while the typical receive-mode operation of the array is performed using an in-line low-noise amplifier (LNA) after the antenna.
The experiments described here were conducted in an anechoic chamber, hemispherical in shape with a diameter of 20 meters, as depicted in FIGURE 2. The array was mounted on a surveyor’s tripod and placed at a known position on a rotatable pillar at the center of the chamber. The chamber contains two sleds, Sled A and B, which can be precisely positioned along an arc through the zenith at positions between ±115° either side of the vertical. These antennas include 1.0 to 6.0 GHz vertically and horizontally polarized standard-gain horn antennas.
FIGURE 2. Antenna array and digitizing front end in the anechoic chamber during broadcast tests.
Because the characteristics of the antenna array itself are central to the ultimate performance of beamforming or null-steering techniques, a thorough characterization of the gain and phase properties of each of the seven antenna elements was conducted.
To do so, a network analyzer was used to observe the gain and phase response of the antenna under test from a range of observation angles. The array was operated in transmit mode, broadcasting a signal sourced from Port A of the network analyzer, which was received by an antenna mounted on one of the movable sleds, and fed to Port B of the network analyzer.
The network analyzer was configured to broadcast a series of 201 equally spaced tones spanning 20 MHz centered at 1575.42 MHz at a power of -7 dBm from the antenna array.
A mechanical RF multiplexer was used to implement a time-division multiplexing of this broadcast measurement signal across each of the seven elements, such that the series of tones were transmitted once per antenna element. By performing the scan for each antenna element, for a range of positions of Sled A, and repeating this for different rotations of the central pillar, a precise frequency response could be calculated for a large set of points across the entire upper hemisphere of the antenna. The scan was computed on signals received by both the horizontal and vertical elements on Sled A, such that both the RHCP and LHCP response could be computed. The vertical cuts of this gain pattern were measured with resolution of 2°, while the horizontal cuts were measured with a resolution of 5°.
The average gain response, calculated across the 20-MHz band, for each of the seven elements is depicted in FIGURE 3. The elevation cut of the peripheral element is taken such that the -90° direction of the cut aligns with a radial line pointing away from the center of the array. The azimuth cuts are oriented such that the 0° direction aligns with a radial line extending from the center of element number 1 to the center of element number 2.
FIGURE 3. The measured gain pattern of the central element, number 1, (blue lines) and one of the peripheral elements, number 2, (red lines). The gain of the peripheral element is deflected inwards toward the center of the array because of the asymmetry of its positioning on the ground plane. (a) Elevation angle cut at an azimuth of 0°; (b) Azimuth cut at an elevation angle of 40°.
It is interesting to note that the gain pattern exhibited by each element is sensitive to its position on the ground plane and its position relative to other elements. Because of the rotational symmetry of the array, the gain patterns of all of the peripheral elements are similar, differing only in orientation, each one exhibiting a deflection of the maximum gain towards the center of the array. The central element is circularly symmetric with a single lobe in the direction of the zenith, while gain of the peripheral elements is deflected inwards, having lower gain away from the center of the array and an increased gain for high elevation angles from the center of the array. The difference in gain pattern across elements is stark and should, perhaps, influence the choice of elements to be used when forming a beam or null in a given direction. One or other of the signals should be scaled to compensate for this gain difference.
Measuring Signal Rejection
Before exploring factors that influence signal rejection, this section details the figure of merit, which might quantify the achievable performance of the array. We examined the nulling performance of the system in terms of its rejection capability: assessed as the relative received power of the signal of interest, b(t), that is to be preserved, and an unwanted signal, a(t), which is to be rejected, before and after the nulling combination. If sj(t) denotes some signal as received at antenna j, then the combination of signals received at antennas j and k can be denoted by:
(1)
where κ and ϕ, respectively, represent a unitless scaling gain and a phase rotation in radians applied in the combination. When intending to form a beam in the direction of the source of s(t), then this phase might be chosen to bring sk(t) into alignment with sj(t), and the gain may be determined as a function of the signal-to-noise ratio at each antenna, or simply set to unity. In contrast, when it is intended to reject s(t) then eiϕ must be chosen to place sk(t) in antiphase with sj(t) and must be chosen to scale the amplitude of sk(t) to be exactly equal to that of sj(t).
In this case, we consider the problem of placing a null in the direction of signal a(t) while preserving signal b(t). If the relative received power of a(t) and b(t) at antenna j is taken as a reference, then the rejection of a(t) with respect to b(t), denoted Ra,b , can be assessed by examining the change in relative power after the null has been placed:
(2)
where denotes the expected value of x. Note also that this convention implies that a value of Ra,b greater than unity corresponds to signal rejection.
Analog Null Steering at RF
This section explores some of the receiver-side factors that can limit nulling performance. The performance of an analog RF-combining circuit is examined, wherein the combining function was implemented using controllable analog attenuators and phase shifters.
The received signal from each of two antennas, j and k, was fed to a custom RF circuit board hosting a controllable phase shifter and attenuator chips. The output of two of these boards was then combined using a passive power combiner, filtered by an analog RF filter, limiting the band to the range 1530–1620 MHz, and finally fed to a power detector, which produced a signal voltage that was proportional to the total observed power. The experimental setup is depicted in FIGURE 4. The attenuators and phase shifters were controlled digitally via a microcontroller board, which also sampled the output of the power detector.
FIGURE 5. A simplified example of the steering constellation of an analog gain and phase shifter, having 3-bit phase and gain control and a gain step-size of ~1 dB.
The attenuators accept a 6-bit control, providing a dynamic range of 30 dB in steps of approximately 0.5 dB, while the phase shifters accept a 4-bit control traversing the unit circle in steps of 22.5°.
A simplified example of the finite resolution achievable using such a phase and gain shifter is shown by the steering constellation depicted in FIGURE 5, taking the case of 3-bit gain and phase control and assuming a gain step size of 1 dB. Note that the gain is displayed on a logarithmic scale. Each of the circular markers represents a possible gain and phase coefficient for a received signal, which would be used to steer one signal, a, to be approximately equal in amplitude and in anti-phase with the second signal, b.
FIGURE 4. A custom-built programmable analog phase shifter and attenuator pair used for the analog null-steering configuration.
The residual misalignment between the signals stems from the finite constellation of steering points and results in a reduced nulling performance, whereby a portion of the interference signal remains. The relative magnitude of the remaining interference signal is maximum when the true relative phase and amplitude of the signals a and b lies equidistant from the four nearest steering vectors. This is depicted in Figure 5, where the cross marker lies equidistant from the four vertices located at the corners of {0°,45°} and {7,8} dB. Note that as the gain is depicted on a logarithmic scale, the relative error is equal for points centered in any of the quadrants.
To investigate the performance of the system, we broadcast a continuous-wave interference toward the array, while the signal from one antenna was manipulated by all possible gain and phase combinations, keeping the signal from the second antenna at a fixed zero phase shift and –15 dB attenuation. For each of the 1,024 possible gain and phase combinations, the power detector was sampled and logged. A trace of the measured signal rejection as a function of the gain and phase is depicted in FIGURE 6, wherein a sharp peak is observable at approximately {–15 dB, 210°}, corresponding to the point at which the unwanted signal is most rejected — in this particular case, to a level of approximately 29 dB.
FIGURE 6. The measured interference rejection for a broadcast jamming scenario, where a brute-force search through all possible combinations of phase shift and attenuation was conducted. In this case, the maximum rejection happens to occur at an attenuation of 16.5 dB and a phase shift of 225°.
Estimating the Achievable Rejection Level. In this particular experiment, because all 1,024 possible gain and phase combinations were examined in a brute-force search, the signal rejection was not limited by inaccuracies in the estimation of the steering variables κ and ϕ. Rather, it was limited by how accurately the steering variables can be applied. A residual error exists between the phase and gain that would perfectly align and null the signal and the nearest values of phase and gain that the circuit can produce. This error is a function of the distribution of the true steering parameter and the resolution with which it is rendered. In this case, as the range and angle to the unwanted signal source is arbitrary and the distance between antenna elements is comparable to the carrier wavelength, then it is reasonable, perhaps, to assume that the residual error in the steering parameters is zero mean and uniform over the discrete control steps. To model this effect, similar to the previous section, the combining function, inclusive of these errors, can be expressed as:
(3)
where U denotes a uniform distribution, δϕ denotes the step size of the phase shifter control and δA denotes the attenuator step size. Note that as κ is in units of amplitude and δA represents the discrete steps in power gain, which corresponds to discrete steps of in amplitude, then the residual error will be distributed over a region extending in either direction. In this case, if a B-bit phase shifter is used, then:
. (4)
From this model, the minimum expected rejection level can be estimated as a function of the phase and attenuator resolution. Considering first the rejection expression given by Equation (2), we note that the variation of the power signal of interest, b(t), is a function only of the relative angles between each of a(t) and b(t) and the antenna array. When the signals are well separated, a gain of 3 dB is observed on b(t), and when a(t) and b(t) are located nearby or in exact opposite directions, then the rejection of a(t) will also reject b(t). As this power variation is a function of geometry and not of the particular nulling technique, for simplicity it is assumed that b(t) experiences no power variation. What remains is the relative power variation of a(t) with respect to and δϕ.
To find the minimum expected rejection level, we must examine the following metric:
(5)
(6)
where the two variables, eκ and eϕ, respectively represent the residual errors in amplitude and phase between the perfect steering vector, and that which can be attained by the combiner. Examining Equations (3) and (6), it is clear that the minimum rejection will be achieved when the residual phase error is equal to eϕ = 1/2δϕ and the amplitude mismatch is given by eκ = . Substituting these values yields the minimum expected rejection, as given in Equation (7):
.(7)
Determination of the average expected rejection level requires the averaging of Equation (6) over the distributions of the two error variables, eκ and eϕ. As these errors are assumed to be uniform in this particular case, this reduces to the following:
(8)
which, after some manipulation, admits the closed form expression of Equation (9):
.
(9)
Inserting the specifications of the experimental setup used here, we find that the minimum rejection that can be expected is equal to approximately 14 dB with an average value equal to 18.8 dB. Further exploring this result, it is possible to predict the minimum performance that can be achieved given some arbitrary, but finite, resolution in gain and phase rotation. A portion of the surface defined by Equation (9) is presented in FIGURE 7. One useful application of this result is that it may be used by a designer to ensure that the resolution in gain and in phase are commensurate. This can be inferred by examining the gradient of the surface, noting that optimal choices of gain and phase step size will lie along the line of steepest gradient of this surface. A flattening of the surface in one dimension indicates that the performance is limited by the other dimension. For example, it can be seen that an increase in phase resolution beyond 6 bits yields no improvement in rejection when the gain step size is greater than 0.5 dB.
FIGURE 7. Minimum achievable rejection of analog nulling-combiner as a function of phase-shifter resolution (bits) and attenuator step size (dB).
Conclusion
Early results from this study suggest that the achievable signal rejection using a controlled radiation pattern GNSS antenna, under ideal conditions, is in excess of 70 dB, and is primarily limited by the accuracy with which the angle of incidence of the interference can be estimated. Accounting for typical estimation errors, the nominal rejection levels of the order of 20 to 40 dB can be expected. However, it is observed that other aspects limit the signal rejection performance. In a practical receiver, these factors stem from component selection for the signal-combining circuitry.
For analog combining schemes, this is the resolution of the controlled attenuators and phase shifters used. The results here attempt to characterize the relationship between the minimum expected performance and the component properties. Results suggest that the choice of analog combining components should be chosen such that the phase and gain resolution are commensurate and such that resolution in one parameter is not rendered useless by a lack of resolution in the other. These results may form useful guidelines when designing analog RF null-steering antennas.
Acknowledgments
This article is based, in part, on the paper “Analog and Digital Nulling Techniques for Multi-Element Antennas in GNSS Receivers” presented at ION GNSS+ 2015, the 28th International Technical Meeting of the Satellite Division of The Institute of Navigation held in Tampa, Fla., Sept. 14–18, 2015.
Manufacturers
The equipment used in our study included an Agilent, now Keysight Technologies E8361A PNA network analyzer, Antcom Corporation 2DG1215A-MNS-4 GPS L1/L2 antennas, an Arduino LLC (www.arduino.cc) Arduino Uno microcontroller, a MACOM MAPS-010143 4-bit digital phase shifter, a Skyworks Solutions SKY12347-362LF 6-bit digital attenuator and a Tallysman Wireless TW127 in-line amplifier.
Further Reading
• Authors’ Conference Paper
“Analog and Digital Nulling Techniques for Multi-Element Antennas in GNSS receivers” by J.T. Curran, M. Bavaro and J. Fortuny in Proceedings of ION GNSS+ 2015, the 28th International Technical Meeting of the Satellite Division of The Institute of Navigation, Tampa, Fla., Sept. 14–18, 2015, pp. 3249–3261.
• Adaptive GNSS Antennas for Interference Suppression
“Advances in the Theory and Implementation of GNSS Antenna Array Receivers” by P. Arribas, C. Closas, M. Fernández-Prades, M. Cuntz, M. Meurer and A. Konovaltsev, Chapter 9 in Microwave and Millimeter Wave Circuits and Systems: Emerging Design, Technologies, and Applications, edited by A. Georgiadis, H. Rogier, L. Roselli and P. Arcioni and published by Wiley, 2012, pp. 227–273.
“Mitigation of Continuous and Pulsed Radio Interference with GNSS Antenna Arrays” by A. Konovaltsev, D.S. De Lorenzo, A. Hornbostel and P. Enge in Proceedings of ION GNSS 2008, the 21st International Technical Meeting of the Satellite Division of The Institute of Navigation, Savannah, Ga., Sept. 16–19, 2008, pp. 2786–2795.
“Navigation Accuracy and Interference Rejection for an Adaptive GPS Antenna Array” by D.S. De Lorenzo, J. Rife, P. Enge and D.M. Akos in Proceedings of ION GNSS 2006, the 19th International Technical Meeting of the Satellite Division of The Institute of Navigation, Fort Worth, Texas, Sept. 26–29, 2006, pp. 763–773.
“A Novel Interference Suppression Scheme for Global Navigation Satellite Systems Using Antenna Array” by M.G. Amin and W. Sun in IEEE Journal on Selected Areas in Communications, Vol. 23, No. 5, May 2005, pp. 999–1012, doi: 10.1109/JSAC.2005.845404.
“Wideband Cancellation of Interference in a GPS Receive Array” by R.L. Fante and J. Vaccaro in IEEE Transactions on Aerospace and Electronic Systems, Vol. 36, No. 2, April 2000, pp. 549–564, doi: 10.1109/7.845241.
JAMES T. CURRAN received a B.E. in electrical and electronic engineering in 2006 and a Ph.D. in telecommunications in 2010 from the Department of Electrical Engineering, University College Cork, Ireland. He worked as a senior research engineer with the Position, Location and Navigation group at the University of Calgary between 2011 and 2013 and is currently a grant holder at the Joint Research Center (JRC) of the European Commission (EC), Ispra, Italy. His main research interests are signal processing, information theory, cryptography and software-defined radios (SDRs) for GNSS.
MICHELE BAVARO received his master’s degree in computer science in 2003 from the University of Pisa, Italy. Shortly afterwards, he started his work on SDR technologies applied to navigation. First in Italy, then in The Netherlands and in the United Kingdom, he worked on several projects directly involved with the design, manufacture, integration, and test of GNSS equipment and supporting customers in the development of their applications. Today he is appointed as a grant holder at the EC JRC.
JOAQUIM FORTUNY-GUASCH received the engineering degree in telecommunications from the Technical University of Catalonia, Barcelona, Spain, in 1988, and the Dr.- Ing. degree in electrical engineering from the Universität Karlsruhe, Germany, in 2001. Since 1993, he has been working for the EC JRC as a senior scientific officer. He is the head of the European Microwave Signature Laboratory and leads the JRC research group on GNSS and wireless communications systems.
