Eliminating Second Time-Around Radar Returns via Phase Modulation
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Solution Overview
Problem
Conventional pulse-Doppler radar systems face performance issues due to second time-around returns, which appear as 'ghost images' and are difficult to eliminate, especially when a constant pulse repetition frequency (PRF) is required, as traditional methods to vary PRF are not applicable in all systems.
Innovation Solution
The method involves transmitting linear FM radar pulse waveform signals with alternating phase shifts to identify and eliminate second time-around ambiguous targets by demodulating received signals and identifying targets with phase shifts offset from the transmitted phase shifts, allowing for the differentiation and removal of ambiguous targets.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If pulse repetition frequency is varied to eliminate second time-around returns, then ghost images are removed, but systems requiring constant PRF cannot use this method
Solution Approach 1:
The patent applies parameter changes by modifying the phase of transmitted LFM pulses rather than varying PRF. Specifically, alternating phases (e.g., 0度和180度) are applied to consecutive pulses, allowing constant PRF systems to identify and eliminate second time-around returns through phase-based differentiation of target returns
Solution Approach 2:
The patent substitutes the mechanical approach of varying PRF with a signal processing approach using phase modulation. Instead of changing the timing frequency mechanically, the system uses phase shifts in the LFM waveforms and corresponding phase demodulation to achieve the same ghost image elimination goal in constant PRF systems
2Productivity
If second time-around returns are processed as valid targets, then detection sensitivity is maintained, but false ghost images appear in the instrumented range
Solution Approach 1:
The patent uses feedback through phase comparison. The received signals are demodulated to extract phase information, which is then compared against the known transmitted pulse phases. This feedback mechanism identifies returns with unexpected phase shifts as second time-around returns and eliminates them, while preserving valid targets within the instrumented range
Solution Approach 2:
The patent applies local quality by treating different range regions differently through phase analysis. Returns from the instrumented range exhibit consistent phase relationships with transmitted pulses, while second time-around returns show phase offsets. The system selectively processes these based on their local phase characteristics, eliminating ghost images while maintaining detection sensitivity
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 effectively identifies and eliminates second time-around ambiguous targets, preventing false detections and improving radar system performance by distinguishing between unambiguous and ambiguous targets through phase modulation, even in systems with constant PRF.
Implementation Method 1
transmitting, by a processor, a first linear FM radar ('LFM') pulse waveform signal and a second LFM pulse waveform signal to at least one target, wherein the first LFM pulse waveform signal and the second LFM pulse waveform signal have alternating phase shifts separated by a predetermined degree
Data Source
AI summary
The present invention relates to a method and system for identifying and eliminating second time-around ambiguous targets and, more particularly, to a method and system for identifying and eliminating second time-around ambiguous targets using waveform phase modulation.