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Preventing adversaries from interfering with communications is crucial to national security.

Threats in contested environments — specifically proliferated low Earth orbit (pLEO), where satellites must be as low-SWaP as possible because of the high volume of satellites present — are signal jamming and signals intelligence. Mitigating these threats through methods such as changing the shape of antenna beams in real time so that the ground user's signals can't be interfered with, and preparing for future advanced capabilities, are key to ensuring that satellites stay in communication with users on the ground.

"Looking toward the future challenges of tactical SATCOM, there is a clear need for novel approaches to radio-frequency (RF) aperture designs that are scalable and low SWaP-C without sacrificing functionality," says Michael Craton, a technical staff member in Lincoln Laboratory's Tactical Satellite Communications Group . "That is, we want to think about ways we can achieve exquisite performance using less-expensive hardware. We want to anticipate future threats and have an idea about how to deal with them before they become a problem."

One way to tackle the challenge of proliferated interference and jamming is through adaptive antenna arrays. Unlike single-element antennas, arrays are made up of multiple antennas that work together to guide and shape energy to and from the array. Adaptive arrays can change beam states quickly (a technique called adaptive beamforming) and change them in real time, depending on conditions, to prevent interference in certain directions by placing nulls, or signals that interfere with others. However, adaptive arrays have high SWaP, making them difficult to operate in SWaP-constrained environments like pLEO.

To address this problem, the team developed the Hosted Nimble Beamforming Anti-Jam Reflectarray (HoNi BAJR), a scanning reflectarray antenna prototype with a surface made up of reflective elements that can be individually controlled. When a signal hits the surface of the reflectarray, individual elements reflect energy with some phase shift to control the beam that is formed so that it blocks interference. Because the elements are very simple, the array can be scaled and controlled easily. Reflectarrays are similar to phased arrays, which consist of multiple elements that can be electronically controlled for quick beam changes, but scanning reflectarrays reflect signals toward a separate feed antenna, which eliminates much of the design complexity in conventional antenna arrays.

Unlike phased arrays that require amplifiers for each antenna element, reflectarrays do not require amplifiers because signals are collected by the feed antenna and combined in free space; this lack of amplifiers for each element in the reflectarray lowers the SWaP required and helps with scalability, as the beamforming network does not have to be redesigned each time the size of the array is changed. A reflectarray uses much less power than a typical array, dropping the power consumption by about 95 percent.