Through - Wall Imaging Radar

Knock and announce missions occur frequently on the urban battlefield. It would be advantageous to locate all of the humans inside an urban structure and obtain a "head count" prior to action. For this reason, we developed a through-wall radar sensor capable of locating moving targets through concrete-walled structures and of displaying the results (in range versus cross range) at a video frame rate of 10.8 Hz while the sensor is a safe distance from the wall. This sensor, approximately 2.25 m in length, would be mounted to a vehicle and driven near a building at a standoff range from which the user may detect the moving targets inside the building, as shown in Figure 1. The sensor uses a frequency-modulated, continuous-wave (FMCW) radar architecture operating at S-band, where some wall penetration is possible, with a center frequency of 3 GHz with a 2 GHz ultrawideband chirp. A narrowband, spatial frequency filter provides a range gate that eliminates the wall from the image, facilitating maximum receiver dynamic range to be applied to the target scene behind the wall. A time-division multiplexed (TDM), multiple-input, multiple-output (MIMO) array provides a lowest-cost, least complicated solution to a fully populated antenna aperture capable of near-field imaging. To achieve video-frame-rate imaging, a data pipeline and streamlined imaging algorithm were developed. Coherent frame-to-frame processing rejects stationary clutter, revealing the location of moving targets. In previous work, the switched-antenna-array, through-wall radar sensor was shown to be effective at imaging human targets through a 10 cm thick, solid concrete wall at a 6 m standoff range at the rate of one image The ability to locate moving targets inside a building with a sensor situated at a standoff range outside the building would greatly improve situational awareness on the urban battlefield. A radar imaging system was developed to image through walls, providing a down-range versus cross-range image of all moving targets at a video frame rate. This system uses an S-band, frequency-modulated, continuous-wave radar with a spatial frequency range gate coupled to a time-division multiplexed, multiple-input, multiple-output antenna array to rapidly acquire, process, and display radar imagery at a frame rate of 10.8 Hz. Maximum expected range through a 20 cm thick, solid concrete wall is 20 m. Measurements show that this system can locate humans (moving or standing still) behind 10 and 20 cm thick, solid concrete walls and through " cinder-block " walls.