Communications: directive radio wave systems and devices (e.g. – Return signal controls radar system – Transmitter
Reexamination Certificate
2002-07-12
2003-09-16
Tarcza, Thomas H. (Department: 3662)
Communications: directive radio wave systems and devices (e.g.,
Return signal controls radar system
Transmitter
C342S137000, C342S159000
Reexamination Certificate
active
06621450
ABSTRACT:
BACKGROUND
FIELD OF THE INVENTION
The present invention relates to a pulse radar system, and in particular, to a method for selecting a pulse repetition frequency of a pulse radar system to detect, track or search for a target.
BACKGROUND INFORMATION
Pulse radar systems detect a target by transmitting a signal and then receiving a return signal reflected back from the target. The target information that may be measured by a radar system includes, for example, the distance and velocity of target objects. The distance of the target is the range of the target from the radar system and the velocity of the target as the speed at which a target is moving relative to the radar system. A sequence of pulses is transmitted from pulse radar systems at a frequency referred to as a Pulse Repetition Frequency (“PRF”). A PRF for a pulse radar system can be chosen from a set of Pulse Repetition Frequencies (“PRFs”) that the pulse radar system is capable of generating. The number of PRFs or number of types (e.g., low, medium or high) of PRFs in a set are based upon the system requirements and hardware constraints of a pulse radar system.
Pulse radar systems inherently have internal clutter or interference that can obscure or prevent reception of a return signal in either or both the frequency domain and the time domain. For example, pulse radar systems transmit a stream of pulses and receive return signals in a receiving period in between the transmissions of the pulses. The return signal needs to be received in the receiving period. Otherwise, the return signal from the target will not be received and the distance of the target can not be ascertained. In addition, the return signal will also have a Doppler frequency with a spectral line that needs to be between the main carrier frequency and the PRF of the pulse radar system. Otherwise, the return signal will be obscured by the main carrier frequency or the pulse frequency of the pulse radar system. The time domain and frequency domain responses of a return signal can change because the position and velocity of the target can change.
The reception of a return signal from a target can be obscured or masked by external clutter, such as ground clutter, interference from another signal source ( e.g., signal from another radar), or a jammer. For example, if the ambiguous range of the clutter is approximately the same as the ambiguous range of the target for a given PRF, then the return signal will be obscured or masked in the time domain. Similarly, if the ambiguous Doppler frequency of the return signal is approximately the same as the ambiguous Doppler frequency of the return, then the return signal will be masked or obscured in the time domain.
SUMMARY OF THE INVENTION
A pulse radar system used to detect, track or search for a target has to dynamically change the PRF to avoid clutter that obscures reception of target features (i.e., target velocity and target distance). Different PRFs in a set of PRFs result in different relative locations within their ambiguity intervals for target and clutter signals. Therefore, a method of selecting a PRF based on cost assigned to each PRF for receiving at least one given target feature is desirable.
Exemplary embodiments of the present invention are directed to a method for selecting a pulse repetition frequency to detect or search for a target including identifying a first feature representative interval of each pulse repetition frequency within a set of pulse repetition frequencies; choosing a selected pulse repetition frequency from the set of pulse repetition frequencies based on cost assigned to each pulse repetition frequency, wherein the cost assigned to a first pulse repetition frequency is at least based on a first cost function of a first position of a first target feature in relation to a first feature assessment interval of the first pulse repetition frequency; and emitting pulsed energy from the emitter using the selected pulse repetition frequency.
Exemplary embodiments of the present invention are also directed to a method for selecting a pulse repetition frequency to detect, track or search for a target including identifying distance and velocity representative intervals of each pulse repetition frequency within a set of pulse repetition frequencies, choosing a selected pulse repetition frequency from the set of pulse repetition frequencies based on cost assigned to a each pulse repetition frequency, wherein the cost assigned to the first pulse repetition frequency is at least based on a first cost function of a first position of a target distance in relation to a distance assessment interval of the first pulse repetition frequency and a second cost function of a second position of a target velocity in relation to a velocity assessment interval of the first pulse repetition frequency, and emitting pulsed energy from the emitter using the selected pulse repetition frequency.
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Andrea Brian
Burns Doane , Swecker, Mathis LLP
Lockheed Martin Corporation
Tarcza Thomas H.
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