Mismatched Pulse Compression for Nonlinear FM Signal Doppler Tolerance

Solution Overview

Problem

Nonlinear frequency modulated (NLFM) waveforms in pulse compression radar systems are intolerant to Doppler shifts, leading to mainlobe widening and increased peak sidelobe levels, which limits target detection and dynamic range, especially as time-bandwidth products increase.

Innovation Solution

A signal processing method involving low-pass filtering of the reference signal before transformation and multiplication with the received NLFM waveform, followed by inverse transformation, to improve Doppler tolerance and reduce peak sidelobe levels.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Quantity of substance

If NLFM waveforms are used for pulse compression, then bandwidth and time-bandwidth product are improved, but Doppler tolerance deteriorates causing mainlobe widening and increased peak sidelobe levels

Engineering Contradiction:

ImprovebandwidthVSAvoidDoppler tolerance

Core Design Contradiction:

Quantity of substanceVSReliability

Solution Approach 1:

The patent applies preliminary action by pre-filtering the reference NLFM waveform with a low-pass filter before using it in the matched filter. This preprocessing step removes high-frequency components that cause sensitivity to Doppler shifts, while preserving the essential nonlinear frequency modulation characteristics needed for bandwidth expansion and range resolution.

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

The patent changes the frequency domain parameters of the reference waveform by applying low-pass filtering. This modifies the spectral content of the reference signal, specifically attenuating high-frequency components above a certain cutoff frequency, thereby altering the matched filter's response characteristics to improve Doppler tolerance while maintaining resolution.

Inventive Principle:

Principle #35Parameter changes

2Manufacturing precision

If NLFM waveforms are used for pulse compression, then peak sidelobe levels are reduced compared to LFM, but Doppler shifts still cause mainlobe widening and increased PSL

Engineering Contradiction:

Improvepeak sidelobe levelsVSAvoidDoppler shift tolerance

Core Design Contradiction:

Manufacturing precisionVSAdaptability or versatility

Solution Approach 1:

The patent applies preliminary action by pre-filtering the reference NLFM waveform with a low-pass filter before using it in the matched filter. This preprocessing step removes high-frequency components that cause sensitivity to Doppler shifts, while preserving the essential nonlinear frequency modulation characteristics needed for bandwidth expansion and range resolution.

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

The patent changes the frequency domain parameters of the reference waveform by applying low-pass filtering. This modifies the spectral content of the reference signal, specifically attenuating high-frequency components above a certain cutoff frequency, thereby altering the matched filter's response characteristics to improve Doppler tolerance while maintaining resolution.

Inventive Principle:

Principle #35Parameter changes

3Measurement precision

If time-bandwidth product is increased to improve resolution, then range resolution is improved, but Doppler shift effects are amplified causing greater distortion

Engineering Contradiction:

Improverange resolutionVSAvoidDoppler shift distortion

Core Design Contradiction:

Measurement precisionVSObject-affected harmful factors

Solution Approach 1:

The patent applies preliminary action by pre-filtering the reference NLFM waveform with a low-pass filter before using it in the matched filter. This preprocessing step removes high-frequency components that cause sensitivity to Doppler shifts, while preserving the essential nonlinear frequency modulation characteristics needed for bandwidth expansion and range resolution.

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

The patent changes the frequency domain parameters of the reference waveform by applying low-pass filtering. This modifies the spectral content of the reference signal, specifically attenuating high-frequency components above a certain cutoff frequency, thereby altering the matched filter's response characteristics to improve Doppler tolerance while maintaining resolution.

Inventive Principle:

Principle #35Parameter changes

Data Source

PatentUS8305262B1Mismatched pulse compression of nonlinear FM signal

Publication Date: 2012.11.06 LOCKHEED MARTIN CORP

AI summary

A signal processing method includes transforming a received NLFM waveform from a first domain to a second domain, multiplying the transform of the received NLFM waveform with a complex conjugate of a low-pass filtered and transformed reference signal, and inverse transforming a product of the multiplication from the second domain to the first domain.