A Through-Dielectric Radar Imaging System

Abstract

Through-lossy-slab radar imaging will be shown at stand-off ranges using a low-power, ultrawideband (UWB), frequency modulated continuous wave (FMCW) radar system. FMCW is desirable for through-slab applications because of the signal gain resulting from pulse compression of long transmit pulses (1.926-4.069 GHz chirp in 10 ms). The difficulty in utilizing FMCW radar for this application is that the air-slab boundary dominates the scattered return from the target scene and limits the upper bound of the receiver dynamic range, reducing sensitivity for targets behind the slab. A method of range-gating out the air-slab boundary by significant band-limiting of the IF stages facilitates imaging of low radar cross section (RCS) targets behind the slab. This sensor is combined with a 1D linear rail and utilized as a rail synthetic aperture radar (SAR) imaging system. A 2D model of a slab and cylinder shows that image blurring due to the slab is negligible when the SAR is located at a stand-off range of 6 m or greater, and thus, the two-way attenuation due to wave propagation through the slab is the greatest challenge at stand-off ranges when the air-slab boundary is range-gated out of the scattered return. Measurements agree with the model, and also show that this radar is capable of imaging target scenes of cylinders and rods 15.24 cm in height and 0.95 cm in diameter behind a 10 cm thick lossy dielectric slab. Further, this system is capable of imaging free-space target scenes with transmit power as low as 5 pW, providing capability for RCS measurement.

A Dual-Band Through-the-Wall Imaging Radar Receiver Using a Reconfigurable High-Pass Filter

“…When the target is located behind a wall-like obstacle, the wall-reflected wave appears at a lower frequency than the target-reflected wave. Therefore, the system requires a filter to detect the target on the other side of the wall [1,6]. Moreover, if there is insufficient isolation between the transmitting and receiving antennas, the transmitted signal directly enters the receiver and generates a large baseband signal.…”

“…In [1], a bandpass filter is used to reject unwanted signals. However, since the implemented filter has a fixed frequency response, the system operation should be adjusted to the filter specification.…”

“…However, since the implemented filter has a fixed frequency response, the system operation should be adjusted to the filter specification. The receiver system in [1] employs heterodyne architecture to adjust the intermediate frequency (IF) to the center frequency of the filter. The radar system in [6] uses a bank of bandpass filters for rejecting the unwanted signal, and an appropriate filter block is selected depending on the distance to the wall and the target.…”

“…Therefore, radar-based imaging is suited to security applications, because the system can detect a target hidden behind an obstacle. This type of radar system can be classified as through-the-wall radar [1][2][3].…”

Target-to-Clutter Ratio Enhancement of Images in Through-the-Wall Radar Using a Radiation Pattern-Based Delayed-Sum Algorithm

“…There have been many studies on TWRI. Some have focused on TWRI system architecture [1], while others have investigated signal processing issues related to TWRI [2][3][4]. To make the system more complete, however, suitable reconstruction of the radar scene is indispensable.…”