Tech Briefs

Operating at higher frequencies than other types of radar produces tighter beams and finer resolution.

An accurate view of the physical world is frequently vital. For example, rotary wing aircraft pilots must have knowledge of the terrain in order to safely fly their aircraft. Therefore, systems capable of generating images of the environment of sufficient quality to facilitate the decision process are necessary. The product of such a system is illustrated in Figure 1.

Figure 1. Terrain Map Generated From Radar Data

Radar systems are often employed to provide an accurate image; however, the performance of radar systems in a given environment is dependent upon the frequencies at which they operate. Since objects appear different when using different observation systems, development of new approaches for viewing the world would offer new information that could prove critical in situations where currently standard techniques are inadequate. One such situation occurs in Degraded Visual Environments (DVE), such as the brownout illustrated in Figure 2. In this type of situation, the observation system must be capable of overcoming the visual obscurants and providing highre-solution images of the environment in order to facilitate the decision process.

Figure 2. Brownout

Currently, lidar, a radar-like system that utilizes frequencies in the visual spectrum and millimeter wave (MMW) radar are the most common solutions to DVE. However, while lidar can produce useful images at reasonable Size, Weight, and Power (SWaP), lidar's relatively lower obscurant penetration produces problems in several types of DVE. On the other hand, MMW radars must have a high SWaP in order to produce similar quality images, resulting in degradation of image quality in order to meet the limits of the platform on which the radar will be used.

To overcome the limitations of lidar and MMW solutions, a Terahertz (THz) radar was developed as a potential solution for DVE imaging. Although the THz band is not thoroughly explored, it offers several advantages for an imaging solution. To test the potential of a THz imager, the Active Covert Terahertz Imager (ACTI) was designed and built by Mustang Technology, now a subsidiary of L3, Inc. Operating at 300 to 330 gigahertz (GHz), the ACTI is among the world's highest frequency radars (lidar excluded). By operating at higher frequencies relative to MMWs, the ACTI can employ higher gain antennas at reasonable SWaP, thereby producing tighter beams and finer resolution. The higher frequencies also offer easy utilization of higher bandwidth components, allowing for finer range resolution. The increase in frequency and corresponding decrease in wavelength also decreases the minimum size required for an object to be detectable. In addition, while the frequency is high for a true radar, the frequency is sufficiently low for the radiation to penetrate obscurants, such as dust storms.

The ACTI is a Frequency-Modulated Continuous-Wave Radar (FMCW). The beam is mechanically steered by a rotating mirror, thus providing real beam imaging and an imaging time in single-digit seconds. The beam width is 0.5 degrees (°), and the field of view is 45° horizontal by 30° vertical. With its output power of 5 milliwatts (mW) and antenna gain of 50 decibels relative to isotropic (dBi), the ACTI is safe for imaging humans even at a range as close as 1 meter.

This work was done by Henry O. Everitt, Willie D. Caraway, and Jonathan T. Richard of the Army Research, Development, and Engineering Command. ARL-0200

This Brief includes a Technical Support Package (TSP).

TERAHERTZ (THZ) RADAR: A SOLUTION FOR DEGRADED VISIBILITY ENVIRONMENTS (DVE) (reference ARL-0200) is currently available for download from the TSP library.

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