An Origami Antenna Gives CubeSats Big Data Capabilities

CubeSats have found success across government, industry, and academia as a cost-effective way to test new technologies in orbit. But the tiny satellites suffer from a communications bottleneck: Their small antennas limit both the transmission rate at which data can be sent to another satellite, or back to Earth.

To tackle this problem, researchers at the Institute of Science Tokyo (Science Tokyo) have built on earlier origami-inspired space structures—including lightweight solar panels and antennas—to develop a foldable antenna that can be stowed in a CubeSat, and then unfolded in space to extend more than twenty-five times as large as its stored size. The innovation not only supports much higher data-rate communications, it also enables transmissions to be focused into a narrow beam to strengthen signals.

“The novelty here is that the researchers have demonstrated all elements of a working antenna system ready for space, rather than just designing one,” says Ivor Cains, a professor in space physics at the University of Sydney.

Reflectarray Antenna Boosts CubeSat Data

A primary, or feed, antenna on the CubeSat transmits linearly polarized radio waves carrying data from onboard sensors or cameras. These waves strike the new antenna, known as a reflectarray antenna, which consists of a film of precisely patterned copper elements attached to a non-conductive textile material. Beneath this film is a separate flexible copper-coated textile that acts like a mirror, reflecting the radio waves back through the array. The patterns and shapes of the copper elements vary slightly, allowing each element to shift the phase of the reflected waves by a different amount. Together, the copper elements combine the radio waves into a narrow beam directed toward Earth.

The same phase-control mechanism also enables the antenna to operate efficiently as a receiver.

“We’ve designed the shape and placement of each copper patch element so that the elements do not cross the fold lines,” says Takashi Tomura, an associate professor in the department of electrical and electronic engineering at Science Tokyo. “This prevents wrinkles from forming in the patch elements after deployment and enables high antenna gain.”

The array is also designed so that after reflection, the electric fields of the radio waves rotate to create circular polarization. “This polarization conversion is achieved by breaking the symmetry of the patch elements while still ensuring that they do not cross the fold lines,” says Tomura. In other words, the elements are intentionally made slightly uneven so that they affect different parts of the radio wave differently. This creates the rotating electric field needed to maintain reliable communications even as the satellite changes position.

The patch elements and the flexible copper-coated substrate can be bent into a U-shape. “This allows them to be folded compactly when stowed, and then to separate to a predetermined optimum distance for reflecting the radio waves efficiently,” Tomura says. “Because all parts of the antenna structure are thin, the antenna can be folded compactly while remaining lightweight.

Stowed away in the CubeSat, the antenna, which weighs just 64 grams, measures 10 by 10 by 6 centimeters in volume. When deployed, the antenna unfolds to create a 50 by 50 centimeter surface, or about 25 times as large as it is when stowed. This enables it to transmit at a frequency of 5.8 gigahertz with an antenna gain of 18 dBi, a decibel-based measure of how tightly an antenna focuses radio energy compared to an antenna that radiates equally in all directions. According to Tomura, a standard CubeSat antenna generally produces a gain of 4 or 5 dBi.

Taken together, these improvements support transmission rates of up to 20 megabits per second, whereas traditional CubeSats typically have to make do with rates measured in kilobits per second, says Tomura.

“This would dramatically increase our data download volumes in low Earth orbits,” says Cairns. “And we could place CubeSats further away, so that we have longer times over a given location for extended duration imaging, for example.”

Origami Antenna Deployment

The antenna is the result of collaboration with Hiraku Sakamoto, a professor in the department of mechanical engineering at Science Tokyo. To enable the antenna to unfold in space, Sakamoto chose a flasher origami pattern that folds into a compact circular bundle and unfolds into a large flat surface.

To maintain its deployed shape, Sakamoto constructed four hollow structural booms, or arms, made of carbon composite that can be folded along with the two-layer antenna, and which automatically expand to a preset shape “like a pop-up picture book on deployment,” he says. He further strengthened the deployment action by inserting the guts of an off-shelf stainless stell retractable tape measure in each arm.

The antenna is installed on the OrigamiSat-2 CubeSat developed by Science Tokyo and launched on 23 April. The satellite successfully deployed its antenna on 23 May.The researchers published the details of their work on 1 April in IEEE Transactions on Antennas and Propagation.

The researchers are now working on a much larger foldable antenna for Earth observation applications and intended for use on large satellites. Declining to discuss details, Sakamoto says they’ve already held talks with Japanese satellite manufacturing companies about possible applications for the technology.