1270 IEEE TRANSACTIONS ON GEOSCIENCE AND REMOTE SENSING, VOL. 47, NO. 5, MAY 2009 Development and Implementation of a Real-Time See-Through-Wall Radar System Based on FPGA Yunqiang Yang, Member, IEEE, and Aly E. Fathy, Fellow, IEEE Abstract—This paper presents the development of a low-cost real-time ultrawideband (UWB) see-through-wall (STW) imaging radar system. The designs of the microwave front end, the UWB data acquisition, and the system integration are discussed in detail. As for the most challenging task, the UWB data acquisition, we introduce a custom low-cost module based on commercial field- programmable gate array (FPGA) boards and low-speed analog- to-digital converters. The introduced module does not require a custom implementation of high-speed wideband mixed-signal circuitry but only depends on the FPGA firmware design, which favors a rapid system prototyping. The data acquisition mod- ule accomplishes a 100-ps equivalent-time sampling resolution at 100-Msamples/s real-time rate, while the developed STW system provides a 2-D real-time view of motion with a 1.5-ms speed behind walls. The system allows for an easy reconfiguration to support multiple operating frequency ranges, pulse sampling res- olutions, and array deployments, thus providing a tremendous experimental flexibility. Our studies indicate that utilizing avail- able technologies and off-the-shelf components could produce a practical stand-alone STW system at reasonable design effort and cost, which will lead to a better understanding of the challenging problems associated with STW technology. Index Terms—Field-programmable gate arrays (FPGA), imaging, see through walls, ultrawideband (UWB) radar. I. I NTRODUCTION A N ULTRAWIDEBAND (UWB) see-through-wall (STW) imaging radar system is designed to determine the lo- cations of targets behind walls and map the contents of a building structure. It is of particular interest to the military, law enforcement, and rescue/search departments [1]. UWB STW technology has demonstrated a great potential to some extent as, currently, there are quite a few companies and research laboratories that have addressed or produced such radars, which may represent the start-of-the-art development. Involved sys- tems and organizations include the following: 1) RadarVision from Time Domain Corporation [2]; 2) Urban Eyes from Lawrence Livermore National Laboratory [3]; 3) ImpSAR from Eureka Aerospace Inc. [4]; 4) Xaver 800 from Camero Inc. [5]; and 5) Radar Scope from L3 CyTerra Corporation [6]. Their utilized bandwidth extends from 500 MHz to 3.5 GHz, and the detection ranges are from 3 to 100 m. These systems provide a 1-D range profile, a 2-D image, or a 3-D map, as claimed. Manuscript received May 14, 2008; revised September 16, 2008. First published March 24, 2009; current version published April 24, 2009. Y. Yang is with Agilent Technologies, Inc., Colorado Springs, CO 80907 USA. A. E. Fathy is with the Department of Electrical Engineering and Computer Science, The University of Tennessee, Knoxville, TN 37996 USA. Color versions of one or more of the figures in this paper are available online at http://ieeexplore.ieee.org. Digital Object Identifier 10.1109/TGRS.2008.2010251 However, numerous improvements still can be envisioned for future systems, in terms of array deployment, image formation through complex wall structures, and real-time detection, which represent only a partial list. The STW community has been aggressively involved in investigating various fundamental technology problems, such as the STW propagation mechanism and time-efficient high- resolution imaging formations, to further improve the STW technology [7]–[11]. These studies would require serious the- oretical and experimental considerations. However, due to the complexity associated with developing a custom STW system, these studies highly depend on conceptual STW systems which are composed of commercial radio-frequency/microwave in- struments, such as oscilloscopes and network analyzers [12]. A conceptual system will still provide the necessary experimental capability; however, it is a high-cost platform, particularly if one intends to acquire the real-time capability. Hence, the need has arisen for having a stand-alone, cost-effective, and real-time UWB STW platform, which may facilitate the development of various STW concepts or image-formation methods. Not only would a cost-effective UWB hardware platform be helpful for the STW development, but it can also be utilized to address other relevant UWB applications, such as medical imaging and software-defined radios. The development of a stand-alone STW system could be a challenging task by itself; however, the advance of various enabling technologies has made it more realistic to realize one with reasonable cost and design effort. Previously, we have reported our extensive work of suc- cessfully developing a conceptual STW system in [13] and references therein. We have also reported the implementation of a UWB Vivaldi linear array [14] and the preliminary consider- ation of a near-real-time UWB data acquisition module [15] for STW applications. In this paper, we leverage our previous effort on UWB hardware and software development, and introduce a real-time STW platform which is composed of both commer- cial off-the-shelf products and custom-designed components. This developed system consists of several major subsystems, namely, the microwave front end, the data acquisition mod- ule, and the system control/process module. It successfully demonstrates real-time data acquisition and motion-tracking capabilities. Generally, there are various key system implemen- tation issues facing the deployment of STW technology, and they will be addressed here, such as front-end receiver design, link-budget analysis, field-programmable gate array (FPGA) processing, and the integration of these various subsystem blocks. The specific needs and expectation of detecting targets behind walls will be discussed as well. This paper is organized as follows. Section II will address the overall design issues. 0196-2892/$25.00 © 2009 IEEE