Communications: directive radio wave systems and devices (e.g. – Presence detection only – By motion detection
Reexamination Certificate
1999-06-14
2001-04-17
Sotomayor, John B. (Department: 3662)
Communications: directive radio wave systems and devices (e.g.,
Presence detection only
By motion detection
C342S022000, C342S057000, C342S058000, C342S059000
Reexamination Certificate
active
06218979
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to radar imaging, and more particularly to high resolution radar imaging using a sparse array of time modulated ultra wideband radars.
2. Related Art
Many applications today would benefit from high resolution radar imaging. For instance, law enforcement agencies often are confronted with hostage situations where armed intruders are barricaded inside a building. Officers on the scene generally have no means for determining the number and position of persons within the building, and are thus hampered in their efforts to resolve the situation. Similarly, law enforcement personnel planning a surprise raid on an armed compound would also greatly benefit from information related to the number and position of persons within. An imaging system that could be deployed in a covert manner outside the building for imaging personnel inside the building would therefore be of great assistance to law enforcement agencies.
Various motion sensing applications would also benefit from high resolution radar data. One example would be a motion sensor that is required to detect motion in a narrow hallway from a distant point in the building, while ignoring motion in the rooms adjacent to the hallway. Another example would be a home security motion sensor designed to detect intruders entering the house but to ignore movement within. Other examples include applications which require a combination of radar imaging and motion sensing. These combined imaging/motion sensing systems could be used to distinguish moving targets from stationary targets, or to provide an image of the building structure with a superimposed image showing the location of moving objects. Even more sophisticated systems could identify various targets based on specific movements, such as vital signs.
Conventional narrowband imaging devices are unable to provide this type of functionality. The applications described above require that the system be able to resolve closely spaced objects at a distance, inside a building. In order to achieve the necessary angular resolution, the pulses of electromagnetic radiation used to image the building must either be transmitted from multiple radiators (whether multiple antennas attached to a single source, or multiple sources) spaced wide distances apart, or the frequency of the transmitted radiation must be increased.
Neither approach is adequate. The spacing between radiating elements required to achieve the necessary resolution greatly exceeds one quarter of the operating wavelength (i.e., a sparse array) and therefore suffers from off-axis ambiguities. The resolution might be increased by increasing the operating frequency, but in doing so, decreases penetration and increases scattering. Narrowband pulses having sufficiently high frequency for the required resolution would be unable to penetrate a building. As a result, conventional narrowband systems cannot provide the functionality described for the above applications.
A need therefore exists for an improved system and method for high resolution, building penetrating, radar imaging.
SUMMARY OF THE INVENTION
Briefly stated, the present invention is directed to a system and method for high resolution radar imaging using a sparse array of time modulated ultra wideband (TM-UWB) radars. TM-UWB radars emit very short RF pulses of low duty cycle approaching Gaussian monocycle pulses with a tightly controlled pulse-to-pulse interval. Two or more of these TM-UWB radars are arranged in a sparse array, i.e., they are spaced at intervals of greater than one quarter wavelength. Each TM-UWB radar transmits ultra wideband pulses that illuminate a target, and at least one receives the signal returns. The signal return data is processed according to the function being performed, such as imaging or motion detection.
An advantage of the current invention is that ultra wideband (UWB) pulses are used. As used herein, UWB refers to very short RF pulses of low duty cycle ideally approaching a Gaussian Monocycle. Typically these pulses have a relative bandwidth (i.e. signal bandwidth/center frequency) which is greater than 25%. The ultra wideband nature of these pulses improves both angle and range resolution, which results in improved performance (e.g., a clearer picture, more sensitive motion detection). The term “wavelength”, as used herein in conjunction with ultra wideband systems, refers to the wavelength corresponding to the center frequency of the ultra wideband pulse.
Another advantage of the current invention is that the TM-UWB radars are arranged in a sparse array, which results in greatly improved angular resolution. Angular resolution is a function of the width of the TM-UWB radar array, i.e., the wider the array, the greater the angular resolution. Conventional narrowband radars arranged in a sparse array suffer off-axis ambiguities, and are therefore not practical. However, the UWB pulses transmitted by the TM-UWB radars are sufficiently short in duration (with very few sidelobes) that the radars can be used in a sparse array configuration without off-axis ambiguities. Furthermore, range ambiguities are cured by time-encoding the sequence of transmitted TM-UWB pulses.
Another advantage of the current invention is that high angular resolution may be achieved at a low center frequency. Because the transmitted UWB pulses have a large relative bandwidth, and because the radar array is wide, a lower center frequency can be maintained and still achieve a high angular resolution. Operating at a lower center frequency relaxes the timing requirements of the system, which makes it easier to achieve synchronization between the radars, and results in less complex, less expensive implementations. A low center frequency also results in UWB pulses that are able to better penetrate lossy materials and withstand weather effects.
A feature of the current invention is that the TM-UWB radar array operates in several modes. In a first mode, each TM-UWB radar transmits and receives back scattering returns, and at least one TM-UWB radar receives forward scattering returns. In a second mode, each TM-UWB radar transmits but only one of the radars receives signal returns, both back and forward scattering. In a third mode, each TM-UWB radar transmits and receives back scattering signal returns, but neither receives forward scattering returns.
Another feature of the current invention is that TM-UWB radios can be used to perform other functions, such as handling communications between the radars and determining the distance separating one radar from another. Using a single TM-UWB radio to perform these functions results in a cost savings. Further, by using a single TM-UWB radar for transmitting UWB pulses and handling inter-radar communications the system achieves synchronization without additional cost.
Further features and advantages of the invention, as well as the structure and operation of various embodiments of the invention, are described in detail below with reference to the accompanying drawings. In the drawings, like reference numbers generally indicate identical, functionally similar, and/or structurally similar elements. The drawing in which an element first appears is indicated by the leftmost digit in the corresponding reference number.
REFERENCES:
patent: 4083049 (1978-04-01), Mattern et al.
patent: 4622540 (1986-11-01), Guscott et al.
patent: 4641317 (1987-02-01), Fullerton
patent: 4727593 (1988-02-01), Goldstein
patent: 4743906 (1988-05-01), Fullerton
patent: 4813057 (1989-03-01), Fullerton
patent: 4907001 (1990-03-01), Harmuth
patent: 4979186 (1990-12-01), Fullerton
patent: 5057846 (1991-10-01), Harmuth
patent: 5134408 (1992-07-01), Harmuth
patent: 5148174 (1992-09-01), Harmuth
patent: 5265121 (1993-11-01), Stewart
patent: 5361070 (1994-11-01), McEwan
patent: 5363108 (1994-11-01), Fullerton
patent: 5457394 (1995-10-01), McEwan
patent: 5465094 (1995-11-01), McEwan
patent: 5510800 (1996-04-01), McEwan
patent: 5512834 (1996-04-01), McEwan
patent: 5519400 (1996-05-01),
Barnes Mark A.
Fullerton Larry W.
Sotomayor John B.
Sterne Kessler Goldstein & Fox P.L.L.C.
Time Domain Corporation
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