Meet the tiny radars that could someday sense and avoid air traffic

Honeywell technology could aid air taxis and permit drones to fly beyond visual line of sight

As I pick up a small, steel-framed radar unit at Honeywell Aerospace’s laboratory in Phoenix last month, I’m impressed that such a complex instrument could weigh so little.

And yet at 1.4 kilograms, it still has considerable heft for something the size of a paperback novel. The weight of the unit is a major focus for Honeywell’s Advanced Air Mobility business unit, I learn while visiting the laboratory in Phoenix.

The radar unit I’m holding was developed under the company’s RDR-84k program, whose name is short for radar, 8 inches by 4 inches (20 by 10 centimeters), along with “K” for K band — the frequency of the radar spectrum in which it operates. The program was begun in 2016.

The unit is light, but apparently not light enough. “Our goal is to cut that weight in half,” Larry Surace, the company’s lead architect for AAM, tells me.

The idea is to someday install multiple units on drones and air taxis to detect other aircraft. Today, heavier Honeywell radar units are installed on aircraft ranging from business jets to large military aircraft, but small electric aircraft will be constrained from carrying all but the lightest electronics due to battery power limitations.

Honeywell’s miniaturization effort reflects a global trend toward making aircraft and automobile electronics smaller and more electrically efficient, a desire driven in part by calls to move away from fossil fuels by electrifying transportation.

“Radar in aviation has traditionally been something much larger, designed to mount in the nose of a jetliner, a long-range array to detect weather out to hundreds of miles,” Surace says.

Since the rise of the consumer drone market in the early 2010s, most of the collision avoidance technology on such small aircraft has consisted of cameras, he notes.

But radar is needed for drones and other electric aircraft, such as air taxis, to fly in clouds or at night, Surace says.

“Digital processing power [of computers] has rapidly evolved, and that has allowed us to use smaller radio frequency circuits because we can process data more easily for ‘detect and avoid’ algorithms,” he says.

In other words, he says, drone software can extrapolate the trajectory of an object or aircraft in its path to calculate an avoidance maneuver, and steer around the obstacle.

This capability is crucial if drones, or remotely piloted passenger vehicles, are ever to be allowed to fly beyond visual line of sight, Taylor Alberstadt, the company’s global sales leader for the business unit, tells me during the follow-up interview.

“The difference between 3 and 6 or 8 pounds can be a payload for a last-mile delivery or an extra sensor or a camera for intelligence, surveillance and reconnaissance missions,” Alberstadt says.

Surace says the RDR-84k hardware is fixed, with no moving mechanical points, but the radar beam itself can be targeted and scan a field of view of 110 degrees azimuth [horizontal] and 30 degrees vertical.

“If we tell the beam to stay on the horizon, the beam will stay on that horizon, to an extent, even if the aircraft is climbing or turning,” he says.

Honeywell says up to six radar units can be mounted on a single aircraft and networked to provide a nearly complete view of the airspace around an aircraft. Besides seeing through clouds or darkness, the radar is designed to warn of an impending collision with a “non-cooperative” aircraft in its path, which means one that is not broadcasting its position in any way.

A flight test in 2021 on the company’s parking lot in Phoenix proved the collision avoidance ability, when a drone equipped with the RDR-84k technology dodged another drone the company had sent directly at it, Surace says. The company shows me a video of this test, which shows the radar-equipped drone swerving out of the way of an oncoming drone.

But Honeywell has stopped providing timelines for the completion of its work on downsizing the radar units. Alberstadt says only that Honeywell intends to provide the technology to drone operators initially, and he expects they will in turn seek FAA certification for their aircraft, complete with the RDR-84k technology.

“It would likely be delivery drones on a last mile trip,” Alberstadt says. “They will need to have the capability to get around a recreational or commercial drone that might be in their path.”

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Under the RDR-84K program, Honeywell aims to reduce the weight of radar units, one shown here at the company's Phoenix lab, so they could be installed on drones and electric air taxis to help detect other aircraft. Credit: Paul Brinkmann

Meet the tiny radars that could someday sense and avoid air traffic