Retrodirective RF System Using Pseudorandom Waveforms
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Solution Overview
Problem
Existing retrodirective systems face challenges in distinguishing real targets from stationary clutter, determining target range, and achieving sufficient spatial resolution, limiting their effectiveness in radar applications, especially for short-range detection of fast-moving small targets.
Innovation Solution
The implementation of a retrodirective transmit-receive apparatus using pseudorandom modulated waveforms and coherent signal processing to focus and steer a beam towards targets, enabling accurate range and bearing determination while rejecting stationary clutter, and allowing for fast target detection and acquisition without separate cuing.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Extent of automation
If traditional retrodirective systems are used, then the system can automatically transmit radiation in the same direction as the target, but the system cannot distinguish real targets from stationary clutter
Solution Approach 1:
The patent uses periodic pseudorandom code modulation in the transmit signal and corresponding correlation processing in the receiver. The transmitted signal is modulated with a pseudorandom code sequence, and the receiver correlates the received signal with the same code sequence. This periodic structure allows the system to distinguish moving targets from stationary clutter through Doppler frequency shifts, while maintaining automatic detection capability.
Solution Approach 2:
The patent changes the signal parameters by using pseudorandom code modulation instead of traditional continuous wave or simple pulse modulation. The pseudorandom code provides a unique temporal signature that, when combined with Doppler processing, enables the system to differentiate between moving targets and stationary clutter based on their different signal characteristics in the time-frequency domain.
2Productivity
If traditional retrodirective systems are used, then the system can provide basic radar functionality, but the spatial resolution is insufficient for short-range detection
Solution Approach 1:
The patent segments the transmitted signal into multiple pseudorandom code sequences with different temporal characteristics. Each code sequence provides independent measurement information, and by processing multiple segmented signals through correlation and Doppler analysis, the system achieves higher spatial resolution without sacrificing detection speed. The segmentation allows for more sophisticated signal processing that enhances target discrimination capability.
3Measurement precision
If the system uses coherent signal processing with pseudorandom waveforms, then the beam can be focused and steered accurately towards targets, but the system complexity increases
Solution Approach 1:
The patent implements self-service through the inherent properties of pseudorandom codes. The same pseudorandom code sequence used for modulation automatically serves as the correlation reference in the receiver, eliminating the need for separate reference signal generation. The code's autocorrelation properties provide automatic timing synchronization and frequency offset correction, reducing the complexity of control circuits while maintaining high beam steering accuracy.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach enables effective search-and-track radar systems to detect and acquire small targets at close range with high accuracy and speed, improving spatial resolution and distinguishing real targets from clutter, thus enhancing the functionality of retrodirective systems in radar applications.
Implementation Method 1
a transmit antenna array having a plurality of transmit elements, each configured to transmit radiation into space
Implementation Method 2
a receive antenna array having a plurality of receive elements with specific locations relative to the transmit elements
Implementation Method 3
utilizing cross correlation and linearity to create a high degree of temporal correlation in the signals between the transmit elements such that a focusing and steering of the transmitted radiation occurs on and toward the target
Data Source
AI summary
Embodiments provide radio-frequency systems that can automatically detect, focus-on, and track objects in the environment without the need for expensive electronic scanning and phase-shifting components. Some embodiments are directed to retrodirective systems including: (1) quiescently broadcast pseudorandom-modulated radiation, such as pseudorandom bit sequences, in the absence of a target, over a field-of-view comparable to the beam solid angle of a single element in the transmit array; (2) a receive antenna element or array, in a desired spatial relationship with respect to the transmit antenna array, that receives reflected pseudorandom radiation from a target; and (3) an electronic signal-processing and feedback channel between the receive and transmit arrays that carries out cross-correlation between the received radiation and the transmitted pseudorandom signals and computes complex correlation coefficients to form a re-transmitted beam. Some embodiments are useful for short-range applications involving small and fast moving targets.