The radome defending the Multi-Band Check Terminal — a big antenna on an MIT Lincoln Laboratory constructing rooftop — is proven illuminated at night time. Credit score: Glen Cooper
Reconfigurable antenna can transmit and obtain indicators over a number of radio-frequency bands related to army and industrial functions.
A 38-foot-wide dome-shaped radio antenna enclosure, or radome, sits on the rooftop of an MIT Lincoln Laboratory building. Inside the climate-controlled environment, shielded from the New England weather, a steel structure supports a 20-foot diameter, 20,000-pound satellite communications (SATCOM) antenna. Called the Multi-Band Test Terminal (MBTT), the antenna can rotate 15 degrees per second, completing a single revolution in 24 seconds. At this speed, the MBTT can detect and track satellites in medium and low Earth orbit (medium and low refer to the altitude at which the satellites orbit the Earth).
Prior to the installation of the MBTT in 2017, the laboratory relied on a variety of smaller antennas for SATCOM testing, including OTAKaTT, the Over-the-Air Ka-band Test Terminal. The MBTT is seven times more sensitive compared to the nearly eight-foot diameter OTAKaTT antenna. And unlike its predecessor, the MBTT, as its name suggests, is designed to be easily reconfigured to support multiple radio frequency (RF) bands used for military and commercial satellite SATCOM systems.
“As a much larger, more powerful, and more flexible test asset than OTAKaTT, the MBTT is a game-changer for enabling the development of advanced SATCOM technology,” says Brian Wolf. He is a technical staff member in Lincoln Laboratory’s Advanced Satcom Systems and Operations Group.
Wolf was concerned within the set up and preliminary commissioning of the MBTT in 2017. He then led the MBTT by way of a rigorous certification course of with the U.S. Military House and Missile Protection Command, accomplished in 2019, demonstrating that the transmit and obtain efficiency of the antenna was enough for it to function on the Wideband International SATCOM (WGS) system.
A constellation of 10 satellites owned and operated by the U.S. Division of Protection, WGS offers high-data-rate connectivity between numerous factors on Earth. Since 2019, Wolf has served as principal investigator on a mission that owns the MBTT, supporting the event of the U.S. House Pressure’s Protected Anti-Jam Tactical SATCOM (PATS) capabilities.
“PATS is growing the aptitude to ship protected tactical waveform, or PTW, companies over WGS, in addition to over industrial transponder satellites and new DoD satellites with devoted onboard PTW processing,” says Wolf.
The Multi-Band Check Terminal and Protected Anti-Jam Tactical satellite tv for pc communications improvement staff gathers inside a radome at MIT Lincoln Laboratory. Credit score: Glen Cooper
As Wolf explains, a waveform is the sign transmitted between two modems when they’re speaking, and PTW is a particular type of waveform designed to supply extremely safe, jamming-resistant communications. Jamming refers to when communication indicators are interfered with — both by chance by pleasant forces (who, for instance, could have misconfigured their SATCOM gear and are transmitting on the fallacious frequency) or deliberately by adversaries looking for to forestall communications. Lincoln Laboratory began growing PTW in 2011, contributing to the preliminary design and system structure. Within the years since, the laboratory has participated in prototyping and testing efforts to assist trade mature modems for processing the waveform.
“Our prototype PTW modems have been fielded to trade websites all around the nation so distributors can check in opposition to them as they develop PTW methods that will likely be deployed in the actual world,” says Wolf. The preliminary working functionality for PTW companies over WGS is anticipated for 2024.
Workers initially conceived the MBTT as a check asset for PTW. Straight beneath the MBTT is a PTW improvement lab, the place researchers can run connections on to the antenna to carry out PTW testing.
Lincoln Laboratory technician John Boughner (foreground) assists two Normal Dynamics engineers in putting in a brand new antenna feed in the course of the preliminary MBTT set up. Credit score: Glen Cooper
One of many design objectives for PTW is the flexibleness to function on a variety of RF bands related to satellite tv for pc communications. Which means researchers want a approach to check PTW on these bands. The MBTT was designed to help 4 generally used bands for SATCOM that span frequencies from 7 GHz to 46 GHz: X, Ku, Ka, and Q. Nevertheless, the MBTT may be tailored sooner or later to help different bands by way of the design of further antenna feeds, the gear connecting the antenna to the RF transmitter and receiver.
To modify between the totally different supported RF bands, the MBTT have to be reconfigured with a brand new antenna feed, which emits indicators onto and collects indicators from the antenna dish, and RF processing elements. When not in use, antenna feeds and different RF elements are saved within the MBTT command heart, positioned beneath the primary platform of the antenna. The feeds are available in a variety of sizes, with the biggest registering six ft in size and weighing practically 200 kilos.
To swap out one feed for an additional, a crane contained in the radome is used to carry up, unbolt, and take away the previous feed; a second crane then lifts the brand new feed up into place. Not solely does the feed on the entrance of the antenna should be changed, however all the RF processing elements on the again of the antenna — such because the high-power amplifier for reinforcing satellite tv for pc indicators and the downconverter for changing RF indicators to a decrease frequency extra appropriate for digital processing — additionally should be changed. A staff of expert technicians can full this course of in 4 to 6 hours. Earlier than scientists can run any checks, the technicians should calibrate the brand new feed to make sure it’s working correctly. Usually, they level the antenna onto a satellite tv for pc recognized to broadcast at a selected frequency and accumulate obtain measurements, and level the antenna straight up into free house to gather transmission measurements.
Since its set up, the MBTT has supported a variety of checks and experiments involving PTW. Through the Protected Tactical Service Subject Demonstration, a PTW modem prototyping effort from 2015 to 2020, the laboratory carried out checks over a number of satellites, together with the EchoStar 9 industrial satellite tv for pc (which provides broadband SATCOM companies, together with satellite tv for pc TV, throughout the nation) and DoD-operated WGS satellites.
In 2021, the laboratory used its PTW modem prototype because the terminal modem to conduct an over-the-air check of the Protected Tactical Enterprise Service — a ground-based PTW processing platform Boeing is growing beneath the PATS program — with the Inmarsat-5 satellite tv for pc. The laboratory once more used Inmarsat-5 to check a prototype enterprise administration and management system for enabling resilient, uninterrupted SATCOM. In these checks, the PTW modem prototype, flying onboard a 737 plane, communicated by way of Inmarsat-5 again to the MBTT.
“Inmarsat-5 offers a army Ka-band transponded service appropriate for PTW, in addition to a industrial Ka-band service known as International Xpress,” explains Wolf. “By the flight checks, we have been capable of display resilient end-to-end community connections throughout a number of SATCOM paths, together with PTW on army Ka-band and a industrial SATCOM service. This fashion, if one satellite tv for pc communications hyperlink shouldn’t be working properly — perhaps it’s congested with too many customers and bandwidth isn’t enough, or somebody is making an attempt to intervene with it — you’ll be able to change to the backup secondary hyperlink.”
In one other 2021 demonstration, the laboratory employed the MBTT as a supply of modeled interference to check PTW over O3b, a medium-Earth-orbit satellite tv for pc constellation owned by the corporate SES. As Wolf explains, SES supplied a lot of their very own terminal antenna gear, so, on this case, the MBTT was useful as a check instrument to simulate numerous forms of interference. These interferences ranged from misconfigured customers transmitting on the fallacious frequencies to simulation of superior jamming methods that could be deployed by different nation-states.
The MBTT can be supporting worldwide outreach efforts led by House Techniques Command, a part of the U.S. House Pressure, to increase the PATS functionality to worldwide companions. In 2020, the laboratory used the MBTT to display PTW at X-band over SkyNet 5C, a army communications satellite tv for pc offering companies to the British Armed Forces and coalition North Atlantic Treaty Group forces.
“Our position is available in when a world accomplice says, ‘PTW is nice, however will it work on my satellite tv for pc or on my terminal antenna?’” explains Wolf. “The SkyNet check was our first utilizing PTW over X-band.”
Related through fiber-optic hyperlinks to analysis amenities throughout Lincoln Laboratory, the MBTT has additionally supported non-PTW testing. Workers have examined new sign processing know-how to suppress or take away interference from jammers, new strategies for sign detection and geolocation, and new methods of connecting PTW customers to different Division of Protection methods.
Within the years forward, the laboratory seems ahead to performing extra testing with extra person communities within the Division of Protection. As PTW reaches operational maturity, the MBTT, as a reference terminal, may help testing of distributors’ methods. And as PTS satellites with onboard PTW processing attain orbit, the MBTT may contribute to early on-orbit checkout, measurement, and characterization.
“It’s an thrilling time to be concerned on this effort, as distributors are growing actual SATCOM methods based mostly on the ideas, prototypes, and architectures we’ve developed,” says Wolf.
