Communications: directive radio wave systems and devices (e.g. – Return signal controls external device – Missile or spacecraft guidance
Reexamination Certificate
1999-03-24
2001-01-23
Sotomayor, John B. (Department: 3662)
Communications: directive radio wave systems and devices (e.g.,
Return signal controls external device
Missile or spacecraft guidance
C342S089000, C342S097000, C342S195000
Reexamination Certificate
active
06177904
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of Invention
This invention relates to systems for processing receiver data. Specifically, the present invention relates to radar data processing systems adapted for use with pulsed radar systems.
2. Description of the Related Art
Radar systems are used in a variety of demanding applications including air traffic control and missile guidance. Such applications often require radar systems to effectively track a target in electrically noisy environments and receive messages from an external transmitter.
Tracking ability and message reception are particularly important in missile guidance applications where pulsed radar systems are employed. A pulsed radar system typically includes a receiver, a transmitter, and a digital signal processor such as a missile mission computer. The transmitter transmits radar signals in the direction of a target. The radar signals reflect off the target and are received by the receiver. The receiver may also receive data link messages such as steering commands from an aircraft-based missile guidance system. The digital signal processor facilitates processing of the received signals and may also provide commands to facilitate missile target tracking.
Typically, received commands or radar signals are collected and processed during predetermined time intervals called dwells. The processing of signals received during a previous dwell occurs during a subsequent dwell. An inter-dwell period exists between dwells to allow for the reconfiguration of data processing circuits and other hardware in response to the processed data of the most recent dwell. Any processing of received signals or collecting of received signals is typically halted during this inter-dwell period.
The radar system transmits or receives signals within a predetermined frequency band, i.e., channel. Radio frequency interference may corrupt the channel making it unusable. The radar system determines if the channel is corrupted with radio frequency interference (RFI) after processing received signals. If the channel is corrupted with RFI, commands are often generated to assign the radar system to the next channel upon completion of the current dwell. However, if the next channel is also corrupted with RFI, the radar system cannot make the determination until the completion of the next dwell. If several corrupted channels are assigned to the radar system in sequence, valuable time is lost. During this time, the missile cannot detect targets or update track files.
External missile guidance systems often employ data link messages to transmit data such as steering commands to an airborne missile. To receive a data link message, the missile radar system employs either a dedicated receiver or must time-share the radar receiver for synchronous data link messages. Such time-sharing detracts from radar receiver resources. Dedicated receivers increase system cost and complexity and are usually avoided if the application can tolerate the associated performance penalty.
Hence, a need exits in the art for a radar system that can efficiently handle data link messages and account for RFI without requiring the use of additional dwells. There is a further need for a system that can support asynchronous messaging to improve system flexibility and performance.
SUMMARY OF THE INVENTION
The need in the art is addressed by the efficient receiver system of the present invention. In the illustrative embodiment, the inventive system is adapted for use with a pulsed radar system and includes a circuit for converting a received radar signal (first signal) to baseband. The resulting baseband signal (first signal) is envelope detected and compared to a voltage threshold via a first circuit, the output of which is designated as the second signal. A second circuit compares the second signal to a predetermined sequence and provides a compare signal in response thereto. A third circuit stores information pertaining to the second signal in response to the compare signal. A fourth circuit generates receiver system instructions based on the stored information.
In a specific embodiment, the second signal is a digital signal and the sequence is a digital sequence. The pulsed radar system includes a circuit for receiving and collecting data during a first dwell and for processing the data during a subsequent dwell. An inter-dwell time interval exists between the first dwell and the second dwell. The first, second, third, and/or fourth circuits operate during the inter-dwell period. In the specific embodiment, information pertaining to the digital signal includes information indicating if an existing frequency channel on which the signal is received by the receiver system is corrupted with electromagnetic interference. In the event that the channel is corrupted with electromagnetic interference, the receiver instructions include instructions to set the receiver system to a new channel via an ‘avoid this channel’ re-write message.
In a more specific embodiment, the predetermined digital sequence includes all zeros or all ones to determine if radio frequency interference is present on the current channel under analysis. When checking for a data link message, the predetermined digital sequence is a tag field or synchronization pattern of a data link message. The information pertaining to the digital signal represents a section of a data link message. The receiver instructions include instructions commanding the receiver system to switch to data link reception mode.
The first circuit includes a receiver for receiving the signal. The receiver has an envelope detection circuit and a threshold circuit for comparing an envelope of the signal to one or more programmable or adjustable thresholds and providing the second signal, i.e., the digital signal in response to the comparison. The receiver includes automatic gain control circuitry to control receiver gain, which affects the magnitude of the envelope in relation to the predetermined threshold.
In an illustrative embodiment, the present invention is a system for acquiring information pertaining to an operating signal environment of a radar tracking system. The system includes a receiver system for receiving a first signal within a frequency band and providing a second signal in response thereto when the first signal exceeds a predetermined threshold. A signal sampling system selectively samples the second signal and provides information about the operating signal environment in response thereto during an inter-dwell period of the radar tracking system. A computer controls the selective sampling of the signal sampling system, establishes the predetermined threshold, and establishes the frequency band all in response to the information about the operating signal environment.
In the specific embodiment, the second signal is a digital signal and the first signal is an analog signal. The radar tracking system is a pulsed radar system. The computer is a missile mission computer that includes software for activating the data sampling system between pre-existing radar dwells of the radar system where radar system hardware settings are typically adjusted.
The signal sampling system includes a shift register that samples the digital signals at a predetermined clock rate and stores a sequence of bits corresponding to the digital signal. The data sampling system includes a system clock and a frequency controllable clock divider connected to the computer for establishing the predetermined clock rate. The signal sampling system includes a compare logic block in communication with the shift register and includes a data patterns register in communication with the compare logic block. The compare logic block compares the sequence of bits to bits pre-loaded into the data patterns register. The data patterns register is pre-loaded with bits in accordance with signal sampling system functions.
In the illustrative embodiment, the computer runs software that implements the signal sampling system functions. The sampling system functions include analyzing the sequence of
Coenen Lance G.
Goelz Candi M.
Schober Michael B.
Struthers Jeffrey R.
Collins David W.
Lenzen, Jr. Glenn H.
Raytheon Company
Rudd Andrew J.
Sotomayor John B.
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