U.S. Federal Avionics Administration (FAA) regulations limit the use of unmanned air systems (UAS) in commercial and private industry because of the potential danger that they pose to other aircraft. The development of an onboard Sense and Avoid (SAA) system is necessary for UAS to share the same airspace as other aircraft. This paper presents the design and fabrication of a radar sensor designed for use as part of a reactive path planning system. The radar is a Frequency Modulated Continuous Wave (FMCW) type with two receive channels. This enables monopulse processing to provide both range and bearing information of detected targets. Without connectors or antennas, it weighs 46 g, is 7.6 x 5 x 3.8 cm in size, and costs less than $100 when built in quantities of 100 or more. The radar has been tested using outdoor targets and is currently being integrated with a UAS autopilot and collision avoidance algorithm for airborne testing.
I. INTRODUCTIONUnmanned air systems (UAS) are currently transitioning from military to civil applications. With a potentially multibillion dollar market opening up over the next decade, radars will be exploited in commercial use for remote sensing, altimetry, bridge integrity monitoring, land surveying, collision avoidance, and numerous other applications. UAS will not be approved by the FAA for generalized commercial applications unless they can prove collision avoidance capabilities [1], [2].SAA systems are classified into cooperative and noncooperative categories. For cooperative systems, Automatic Dependent Surveillance-Broadcast (ADS-B) systems are currently a predominant choice [3], [4]. For intruder aircraft and other non-cooperative objects, radar or other optical detection systems must be used. UAS are limited in the amount of extra payload that they can carry and attributes such as size and weight are critical in the design of the radar. There is a good deal of work in the literature on compact radars, particularly for automotive collision avoidance [5].For UAS sense and avoid, design requirements are different than for other common radar applications. Size and weight are even more critical than for automotive applications, and performance of the reactive path planning algorithm is enhanced if the radar can provide bearing information. Based on these considerations, we present a design for a radar with mechanical and RF performance targeted to UAS sense and avoid applications.II. DESIGN The overall SAA system will include a radar sensor, a data processing module, and an autopilot as shown in Figure 1.