Radar Complementary Code Group Switching for Sidelobe Suppression
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Solution Overview
Problem
Conventional radar systems face challenges in accurately estimating target distance due to range sidelobes, which can lead to erroneous detection and noise in Doppler filter outputs, especially when multiple targets are present, as they struggle to suppress range sidelobes effectively and maintain high performance in measurement range and Doppler resolution.
Innovation Solution
The radar apparatus employs a pulse code generation method using complementary codes, specifically Spano codes, where a different complementary group is selected and transmitted based on a code coupling process every time the transmission count is a multiple of a code count, ensuring coherent addition of autocorrelation values to suppress range sidelobes and reduce noise.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional pulse Doppler radar performs pulse compressing process and coherent addition to improve signal-to-noise ratio, then SNR is improved, but range sidelobes are not effectively suppressed causing erroneous detection
Solution Approach 1:
The transmitted pulse train is segmented into multiple complementary groups, where each group contains pulse codes with complementary autocorrelation properties. By dividing the pulse sequence into these specialized segments and processing them separately through coherent addition, the system achieves both high SNR and effective range sidelobe suppression, resolving the contradiction between measurement precision and detection reliability
Solution Approach 2:
The patent employs composite coding schemes combining multiple complementary codes (such as Barker codes, Golay codes, or Spano codes) to form a composite pulse sequence. This composite structure leverages the mathematical properties of complementary codes where the sum of their autocorrelation functions produces a flat spectrum with minimal sidelobes, thereby simultaneously achieving high SNR through coherent addition and low sidelobe levels for accurate detection
2Measurement precision
If conventional radar uses single complementary group for pulse transmission, then coherent addition can be performed, but cyclical amplitude and phase fluctuations in range sidelobes persist causing noise after Doppler analysis
Solution Approach 1:
The patent implements periodic switching between multiple complementary groups in a systematic sequence. By cycling through different complementary groups (e.g., Group 1, Group 2, Group 3, Group 4) across successive pulse transmissions, the system creates a periodic variation in the transmitted code structure. This periodic diversity causes range sidelobes to fluctuate in position and amplitude across different groups, and when coherent addition is performed across these varied groups, the sidelobe fluctuations average out and cancel each other, significantly reducing the cyclical amplitude and phase fluctuations that would otherwise manifest as noise after Doppler analysis
Solution Approach 2:
The patent maintains continuous radar operation by seamlessly transitioning between multiple complementary groups without interrupting the pulse transmission stream. The systematic switching between groups ensures that the useful radar function (target detection and ranging) continues uninterrupted while the varying code structures continuously work to suppress sidelobes. This continuous operation with diversified coding ensures sustained performance in both SNR enhancement through coherent addition and noise reduction through sidelobe suppression across the entire measurement period
Data Source
AI summary
A radar apparatus is provided which includes a counter which counts a transmission count of pulse codes from start of measurement, a pulse code generator which selects a complementary group from among a plurality of complementary groups obtained by grouping a plurality of pulse codes generated by at least one code coupling process on at least one basic code pair as complementary codes every time the transmission count is an integral multiple of a code count in the plurality of complementary groups, and a transmitter which transmits the pulse codes belonging to the selected complementary group.