Lacunar Filtering for Radar Distance-Doppler Ambiguity Rejection
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Solution Overview
Problem
Radar imaging using synthetic band waveforms is plagued by distance ambiguities, which result in 'ghost' echoes that are difficult to eliminate, especially in grazing acquisition geometries where the radar beam covers a large distance range, leading to pollution in the Distance-Doppler representation.
Innovation Solution
A filtering method that transposes the Distance-Doppler image into the frequency domain, models the parasitic energy associated with ambiguous echoes, and applies a lacunar filter with a transfer function tailored to the distribution of parasitic energy and a predefined lacunarity rate to attenuate these echoes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a synthetic band waveform is used to achieve fine distance resolution, then distance resolution is improved, but distance ambiguities cause harmful echoes that pollute the Distance-Doppler image
Solution Approach 1:
The method segments the synthetic band into multiple elementary spectra corresponding to different pulses. By analyzing the distribution of parasitic energy across these segmented spectra and applying lacunar filtering selectively, the method eliminates distance ambiguity echoes while preserving the fine distance resolution achieved through synthetic band waveform transmission.
Solution Approach 2:
The lacunar filter applies different filtering characteristics to different regions of the spectrum based on the local distribution of parasitic energy. The transfer function is designed with lacunae (gaps) positioned according to where ambiguous echoes appear, creating localized filtering that eliminates harmful echoes without affecting the overall distance resolution quality.
2Object-generated harmful factors
If conventional filtering methods are used to attenuate distance ambiguity pollution, then harmful echoes are reduced, but the method cannot systematically eliminate parasitic contributions especially in grazing acquisition geometries
Solution Approach 1:
The method uses the observed distribution of parasitic energy in the frequency domain as feedback to design the lacunar filter transfer function. By analyzing where ambiguous echoes appear across the synthetic band and incorporating this information into the filter design, the method systematically eliminates parasitic contributions regardless of acquisition geometry.
Solution Approach 2:
The method changes the filtering approach from conventional uniform attenuation to a parameterized lacunar filter where the transfer function parameters (position and width of lacunae) are determined by the parasitic energy distribution. This adaptive parameter adjustment enables systematic elimination of distance ambiguity echoes in all acquisition geometries.
Data Source
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AI summary
The method involves transposing a Doppler-distance image in a frequency domain, and modeling a distribution of noise energy associated with a presence of ambiguous echoes within a synthetic strip. Parasitizes energy is filtered using a lacunary filter, where the transfer function of the filter is developed based on the distribution of the parasitize energy and a predetermined lacunarity rate. Pixels of images are calculated for obtaining minimal value between Distance-Doppler rough images and lacunar image.