Swept-step radar system and detection method using same

Details Swept-step radar system and detection method using same Swept-step radar system and detection method using same

1999-01-19

2001-05-01

Sotomayor, John B. (Department: 3662)

Communications: directive radio wave systems and devices (e.g.,

Transmission through media other than air or free space

C342S128000, C342S192000

Reexamination Certificate

active

06225941

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates generally to detection systems and methods, and, more particularly, to radar systems and detection methods.
BACKGROUND OF THE INVENTION
Various types of radar systems and target detection techniques are known. Two radar systems capable of detecting a target object at a relatively short-range include the step-frequency radar and the frequency-modulated, continuous-wave radar.
A step-frequency radar produces a carrier signal having a frequency that is stepped by predetermined interval frequencies. Return signals are processed at each of the intervals or steps from which range information is determined. Two significant limitations associated with the use of a step-frequency radar in short-range applications are its limited unambiguous ranging capability and the significant difficulty of implementing range gating for short-range applications. Range gating, in general terms, is a technique that improves the sensitivity of a short-range radar by suppressing reflections up to the point of the antenna reflection. Such undesirable reflections, if left unabated, would generally render undetectable the relatively low energy return signals received from a short-range target object.
When a step-frequency radar is operated monostatically, for example, the return signal is corrupted by reflections from the antenna feed, which significantly degrades the sensitivity of the system. Although range gating for a step-frequency radar is technically implementable, very fast switches must be employed on the transmit and receive channels to gate out undesired antenna reflections. Because switching times must be on the order of nanoseconds in typical short-range applications, a range gating implementation for a step-frequency radar which utilizes such switches is complex, costly, and is often unable to reliably provide for relatively large unambiguous step frequency ranges. It is noted that the range of the step-frequency radar is limited by the number of its frequency steps.
Several of the problems associated with the step-frequency radar may be overcome by using a frequency-modulated, continuous-wave radar system, although this approach has associated with it a number of deficiencies and limitations that negatively impact the efficacy of such radars in short-range applications. Although a frequency-modulated, continuous-wave radar approach offers the opportunity to implement range gating in a generally straightforward manner and typically provides for an unambiguous ranging capability superior to that of a step-frequency radar, the resolution of the frequency-modulated, continuous-wave radar is significantly poorer than that of a step-frequency radar.
There exists a need for a radar system and detection method that overcomes these and other limitations associated with step-frequency and frequency-modulated, continuous-wave radars. There exists a further need for such a system and method that provides for accurate target detection and range determination in short-range applications. The present invention fulfills these and other needs.
SUMMARY OF THE INVENTION
The present invention is directed to an apparatus and method for detecting an object and determining the range of the object. In accordance with the general principles of the present invention, a transmitter, coupled to an antenna, transmits a frequency-modulated probe signal at each of a number of center frequency intervals or steps. A receiver, coupled to the antenna when operating in a monostatic mode or, alternatively, to a separate receive antenna when operating in a bistatic mode, receives a return signal from a target object resulting from the probe signal. Magnitude and phase information corresponding to the object are measured and stored in a memory at each of the center frequency steps. The range to the object is determined using the magnitude and phase information stored in the memory.
The present invention provides for high-resolution probing and object detection in short-range applications. The present invention has a wide range of applications including high-resolution probing of geophysical surfaces and ground-penetration applications. The invention may also be used to measure the relative permittivity of materials.


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