Although unmanned aerial systems (UAS) have proven increasingly useful in a variety of applications, their widespread usage within the National Airspace System is limited because of regulatory restrictions on their access to shared airspace.

The stepped-notch antenna array is a type of flared-notch antenna that uses linear steps — in this case, three different notch widths — to provide wide-bandwidth antenna matching and ease of manufacture.

A key prerequisite for routine airspace access is compliance with the Federal Aviation Administration's (FAA) requirement for aircraft to see and avoid other air traffic. For a UAS, one means of compliance is the ability to sense and avoid via onboard or ground-based sensors and algorithms. Such a sense-and-avoid system must be able to detect aircraft posing a risk to the UAS, assess that risk, and when required, maneuver the UAS to maintain the required separation between air vehicles.

Meeting the FAA's sense-and-avoid requirement in all-weather and day or night conditions naturally points to a radar solution. Also, an onboard radar sensor is the only solution for delivering a wide-area sense-and-avoid capability, which is unachievable by ground-based systems that simply provide coordination among piloted and unmanned aircraft within limited geographic regions and air spaces.

The Airborne Sense and Avoid Radar Panel during installation on a Twin Otter aircraft.

The Airborne Sense-and-Avoid (ABSAA) Radar Panel, a phased array antenna, has the potential to facilitate the introduction of UAS into the national airspace. This lightweight sensor enables an onboard sense-and-avoid system that performs quick and repeatable scanning of the search region, meets the surveillance timeline demanded of a sense-and-avoid system, and is reliable. The ABSAA panel satisfies the constrained size, weight, and power requirements for small platforms such as UAS. Additionally, the panel supports both aircraft-detecting and weather-sensing modes in a single, multifunction aperture.

The ABSAA stepped-notch antenna panel was designed for use on mid- to large-sized unmanned aircraft that would nominally carry three separate ABSAA arrays to cover a total of 220° in azimuth and 30° in elevation, with scanning rates sufficiently high to enable the sense-and-avoid system to revisit targets of interest and maneuver the UAS safely away from other airborne traffic. The ABSAA panel is also suited for many radar systems integrated on small platforms. Because the antenna can be manufactured at an order-of-magnitude reduction in cost compared to the cost of fabricating a curved antenna, the radar panel could substantially change the design of phased array panels used in many types of systems.

The ABSAA panel radiates and collects radar pulses, and processes the range and velocity of targets over a wide angular region in front of and around its host platform; for example, a UAS. Collision avoidance logic uses the radar information and knowledge of the UAS to decide if separation maneuvers are required. The ABSAA antenna is able to electronically scan a high-power narrow antenna beam over a wide field of view, allowing for fast revisit rates of targets of interest to the UAS. The panel, operating at Ku-band (13-17 GHz), enables a narrow antenna beamwidth while maintaining a small physical size.

For more information, contact Dr. Sean M. Duffy at This email address is being protected from spambots. You need JavaScript enabled to view it.; 781-981-7396.


Tech Briefs Magazine

This article first appeared in the October, 2017 issue of Tech Briefs Magazine.

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