Gregory L. Charvat

Real-time through-wall imaging using an ultrawideband multiple-input multiple-output (MIMO) phased array radar system

A real-time acquisition and processing architecture has been developed for an ultrawideband (UWB) S-band (2–4 GHz) multiple-input multiple-output (MIMO) phased array radar system that facilitates greater than 10 Hz imaging rates, providing a video-like radar image of what is behind a concrete wall. Video rate imaging enhances the interpretability of range vs. range through-wall and free-space radar imagery. Images are formed without a-priori information. Video framerate imaging is achieved by designing an electronically switched bi-static array using high-performance microwave components, a multi-threaded data pipeline, and efficient hardware-accelerated processing algorithms. Experiments successfully image low radar cross section (RCS) objects, fast moving objects in free-space, and a human behind a 10 cm-thick solid concrete wall.

An ultrawideband (UWB) switched-antenna-array radar imaging system

A low-cost ultrawideband (UWB), 1.926–4.069 GHz, phased array radar system is developed that requires only one exciter and digital receiver that is time-division-multiplexed (TDM) across 8 receive elements and 13 transmit elements, synthesizing a fully populated 2.24 m long (λ/2 element-to-element spacing) linear phased array. A 2.24 m linear phased array with a 3 GHz center frequency would require 44 antenna elements but this system requires only 21 elements and time to acquire bi-static pulses across a subset of element combinations. This radar system beamforms in the near field, where the target scene of interest is located 3–70 m down range. It utilizes digital beamforming, computed using the range migration synthetic aperture radar (SAR) algorithm. The phased array antenna is fed by transmit and receive fan-out switch matrices that are connected to a UWB LFM pulse compressed radar operating in stretch mode. The peak transmit power is 1 mW and the transmitted LFM pulses are long in time duration (2.5–10 ms), requiring the radar to transmit and receive simultaneously. It will be shown through simulation and measurement that the bi-static antenna pairs are nearly equivalent to 44 elements spaced λ/2 across a linear array. This result is due to the fact that the phase center position errors relative to a uniform λ/2 element spacing are negligible. This radar is capable of imaging free-space target scenes made up of objects as small as 15.24 cm tall rods and 3.2 cm tall metal nails at a 0.5 Hz rate. Applications for this radar system include short-range near-real-time imaging of unknown targets through a lossy dielectric slab and radar cross section (RCS) measurements.

Harmonic radar tag measurement and characterization

Conventional radar systems transmit and receive at a single, fundamental frequency. It is sometimes challenging to identify a small object against a large background with these radars due to the relatively large return from the background. In effect, the background represents a clutter environment. Harmonic radar tags can be attached to an item, such as insects, and then used to track that item against the background. To do so, the radar must transmit a signal at the fundamental frequency but receive at twice that frequency. Since the clutter return is at the fundamental frequency, the radar is able to discriminate the return from the tag. This paper describes equipment constructed at Michigan State University to conduct research on harmonic tags.

A Through-Dielectric Ultrawideband (UWB) Switched-Antenna-Array Radar Imaging System

A through-dielectric switched-antenna-array radar imaging system is shown that produces near real-time imagery of targets on the opposite side of a lossy dielectric slab. This system operates at S-band, provides a frame rate of 0.5 Hz, and operates at a stand-off range of 6 m or greater. The antenna array synthesizes 44 effective phase centers in a linear array providing

The MIT IAP radar course: Build a small radar system capable of sensing range, Doppler, and synthetic aperture (SAR) imaging

\lambda/2

Low-Cost, High Resolution X-Band Laboratory Radar System for Synthetic Aperture Radar Applications

element-to-element spacing by time division multiplexing the radars transmit and receive ports between 8 receive elements and 13 transmit elements, producing 2D (range vs. cross-range) imagery of what is behind a slab. Laboratory measurements agree with simulations, the air-slab interface is range gated out of the image, and target scenes consisting of cylinders and soda cans are imaged through the slab. A 2D model of a slab, a cylinder, and phase centers shows that blurring due to the slab and bistatic phase centers on the array is negligible when the radar sensor is located at stand-off ranges of 6 m or greater.

A Low-Power High-Sensitivity X-Band Rail SAR Imaging System [Measurement's Corner]

MIT Lincoln Laboratory sponsored a radar short course at MIT campus during the January 2011 Independent Activities Period (IAP). The objective of this course was to generate student interest in applied electromagnetics, antennas, radio frequency (RF) electronics, analog circuits, and signal processing by building a short-range radar sensor and using it in a series of field tests. Lectures on the fundamentals of radar, modular RF design, antennas, pulse compression and synthetic aperture radar (SAR) imaging were presented. Teams of three students built a radar system from a kit. This kit was developed by the authors and uses a frequency modulated continuous wave (FMCW) architecture. To save costs, empty metal coffee cans are used for antennas, components are mounted on a wood block, the system uses only six coaxial microwave parts, analog circuitry on a solderless breadboard, and runs on eight AA batteries. Analog data is acquired by the audio input port on a laptop computer. The total cost of each kit was

Time-of-Flight Microwave Camera

360 which made this radar technology accessible to students. Of the nine student groups, all succeeded in building their radar, acquiring Doppler vs. time and range vs. time plots, seven succeeded in acquiring SAR imagery, and some groups improved the radar system. By presenting these difficult topics at a high level while at the same time making a radar kit and performing field experiments, students became self motivated to explore these topics and much interest in radar design was generated.

Seeing around corners with a mobile phone?: synthetic aperture audio imaging

Entry into the field of radar cross section measurements or synthetic aperture radar (SAR) algorithm development is often difficult due to the cost of high-end precision pulsed IF or other precision radar test instruments. A low-cost entry-level alternative was developed in order to provide an intermediate step between high-end high precision radar systems and ad-hoc spare parts systems. The system developed is a frequency modulated continuous wave radar utilizing homodyne radar architecture. Transmit chirp covers 8 GHz to 10.5 GHz with 18 dBm of transmit power. Due to the fairly wide transmit bandwidth; this radar is capable of better than 12 inches of range resolution. The dynamic range of this system was measured to be 60 dB. Such a low-cost, high resolution X-band laboratory radar system could be utilized as a linear rail SAR, inverse SAR, or for motion compensation experiments

Detection algorithm implementation and measured results for a real-time, through-wall radar system using a TDM MIMO antenna array

Wideband radar imaging with range gating and high sensitivity can be achieved with the use of low-cost commercially available narrowband IF filters. Such filters reduce the effective receiver noise bandwidth of the radar system. This allows for high sensitivity, comparable to that of single-sideband radio receivers, while at the same time acquiring de-chirped wide-band received waveforms. A carefully developed radar architecture, based on the use of these IF filters, is shown in this paper. This radar architecture is then implemented in an X-band linear rail synthetic-aperture-radar (SAR) imaging system. The X- band rail SAR is a linear FM-chirped radar, which chirps from approximately 7.5 GHz to 12.5 GHz. The radar front end is mounted onto an eight-foot-long linear rail. The transmitted power is adjustable to 10dBm or less. It will be shown that objects as small as groups of pushpins in free space can be imaged using transmitted power as low as 10 nW. These results are compared to previous direct-conversion X-band FMCW rail SAR work. A high-sensitivity X-band rail SAR such as this could be useful for measuring low-radar-cross-section (RCS) targets. This radar could be used in high clutter environments that require a range gate. This low-power X-band rail SAR could be useful for operation in restricted transmission areas, where maximum radiated power is severely limited. Other applications include any that require low transmitter power, such as automotive radar.