Antennas: The hard physics challenge for Space Force ‘hybrid’ SATCOM plan

By Theresa Hitchens,
Published by Breaking Defense, 15 April 2022

The Army, in particular, is looking for a “magic bullet” — one antenna that can receive SATCOM signals from constellations in LEO, MEO and GEO. But it may be disappointed due to the laws of physics, says Rick Lober, VP of defense and intelligence systems at Hughes.

WASHINGTON: As the Space Force works through how to create a “hybrid” satellite communications network that links commercial and military networks across all orbital regimes — an effort considered key to the success of the Pentagon’s high priority Joint All Domain Command and Control (JADC2) strategy — most of the stumbling blocks lie on the ground, not in orbit.

And one of the hardest nuts to crack is the question of how to reduce both the size and number of antennas required to receive satellite signals, says Rick Lober, vice president and general manager of Defense and Intelligence Systems Division at Hughes Network Systems.

“The antennas are where it gets hard,” he told Breaking Defense. “There’s a lot of things you can do with software, it’s great, and then with signal processing. But now you are coming back to physics.”

The crux of the problem is most military SATCOM terminals/receivers link to only one frequency or one type of satellite, ships and Humvees use outdated terminals that would be too expensive to replace, and sometimes new satellites end up orbiting the Earth for years without any users because the terminals to make them useful weren’t built on time.

Not to mention that most commercial SATCOM networks — whether those owned or operated by traditional providers with satellites in Geosynchronous Orbit (GEO) or newcomers rushing to populate Low and Medium Earth Orbits (LEO/MEO) with constellations for high-speed, high-volume internet traffic — use proprietary kit, said Lober.

The Army, which is the service using the most SATCOM bandwidth simply because of the size of its force, has been struggling for years to reduce the burden it bears in transporting myriad different antennas, many of which are very large, to enable myriad different SATCOM receivers to be able to ensure 24/7 communications connectivity for troops on the move.

That struggle will be complicated by the Pentagon’s plan to create an integrated multi-layer network of SATCOM constellations in LEO, MEO and GEO — the goal Space Force’s Space Warfighting Analysis Center (SWAC) is now pursuing.

“The Army in particular is kind of looking for the magic bullet right now of ‘give me one antenna that will do LEO, MEO, GEO,’” Lober said. “And there’s challenges there. It might have to be a couple of antennas.”

He explained that the difficulty is because of where and how an antenna has to focus to catch the radio frequency signals from far away satellites that, in essence, are in different positions above the Earth. So, it’s not really feasible to use one antenna for SATCOM constellations in different orbital regimes.

Since individual satellites stay visible over the horizon only for some seven to 10 minutes, Lober said current LEO SATCOM networks themselves generally rely on two parabolic antennas: one to catch the signal from the rising satellite and another to catch those of the setting satellite.

Also, different antennas as well as different signal processing software in radios/receivers are needed for the different radio frequencies used by different satellite networks.

To help solve the LEO antenna problem, he said, Hughes has prototyped a new electronically steerable, flat panel antenna based on open standards that eliminates the need for two parabolic antennas for LEO constellations.

In effect, it automatically cycles to track a LEO sat as it crosses the horizon, and as that satellites dips out of sight, it “hands off” the signal to another beam focused on the rising satellite.

According to a March 22 press release, the new antenna is “capable of seamless handoffs from one satellite beam to the next every 11 seconds and one satellite to the next every three minutes.” The company says it also has high data rates for uplink and downlink, supporting speeds during testing of 190 Mbps down and 20 Mbps up, with roundtrip latency averaging 55 milliseconds. The antenna is expected to be available in 2023.

The antenna is 14 inches by 18 inches and about 2 inches thick, Lober said, and draws only about 100 watts of power. It also has no moving parts.

A further advantage of the new design, he added, is the fact that while it was made to support the OneWeb network in LEO, it is based on open interface standards that would, for example, enable it to receive signals from SpaceX’s Starlink satellites as well. Hughes is a OneWeb partner.

Lober said that “because these proprietary waveforms and proprietary systems are not going to go away,” the trick for DoD in ensuring the success of JADC2 and the new SATCOM architecture will be focusing on network management, rather than simply looking at the receiving end. This means using artificial intelligence and software designed to route signals through and across networks in a way that maximizes efficiency of bandwidth consumption and can stay ahead of jamming or interference in any one network and/or frequency.

“Come up with a common network management technique. Use some software-defined networking to do it very cleverly,” he said. “That’s where I think the DoD should be focusing, and, you know, they may have to live with two apertures as they call them. That’s just physics. That’s tougher to change.”

See: Original Article