Nonlinear frequency modulation chirps for active sonar

1999 ◽  
Vol 146 (6) ◽  
pp. 312 ◽  
Author(s):  
T. Collins ◽  
P. Atkins
Keyword(s):  
Frequency Modulation ◽  
Nonlinear Frequency ◽  
Active Sonar

scholarly journals Performance Analysis of NLFM Signals with Doppler Effect and Background Noise

2020 ◽  
Vol 9 (3) ◽  
pp. 737-742
Keyword(s):  
Performance Analysis ◽  
Frequency Modulation ◽  
Gaussian Noise ◽  
Doppler Effect ◽  
Background Noise ◽  
Additive White Gaussian Noise ◽  
Side Lobe ◽  
Linear Functions ◽  
Side Lobe Level ◽  
Nonlinear Frequency

This paper focuses on the study of effect of background noise and Doppler Effect on various Nonlinear Frequency Modulation (NLFM) waveforms designed using two stage piece-wise and three stage piece-wise linear and non linear functions. The background noise investigated is Additive White Gaussian Noise (AWGN). Simulations are carried out for different target speeds ranging from 100 to 5000km/hour to study Doppler Effect. The simulations are carried out using Matlab software. Among the waveforms designed, the NLFM function designed using two piece-wise Linear Frequency Modulation (LFM) is observed to be Doppler tolerant and also not affected by noise, as the SNR changes from -20 to 20 dB the peak side-lobe level (PSL) of this signal is around -34.84 dB.

An Advanced Nonlinear Frequency Modulation Waveform for Radar Imaging With Low Sidelobe

2019 ◽  
Vol 57 (8) ◽  
pp. 6155-6168 ◽  
Author(s):  
Guodong Jin ◽  
Yunkai Deng ◽  
Robert Wang ◽  
Wei Wang ◽  
Pei Wang ◽  
...  
Keyword(s):  
Frequency Modulation ◽  
Radar Imaging ◽  
Nonlinear Frequency ◽  
Low Sidelobe

Estimation of intrapulse modulation parameters of LPI radar under noisy conditions

2021 ◽  
pp. 1-18
Author(s):  
Chilukuri Raja Kumari ◽  
Hari Kishore Kakarla ◽  
K. Subbarao
Keyword(s):  
Frequency Modulation ◽  
Precise Measurement ◽  
Signal To Noise Ratio ◽  
Nonlinear Frequency ◽  
Pulse Modulation ◽  
Spectral Correlation ◽  
Electronic Warfare ◽  
Spectral Correlation Density ◽  
Low Probability ◽  
Better Than

Abstract Low probability of intercept (LPI) radars utilize specially designed waveforms for intra-pulse modulation and hence LPI radars cannot be easily intercepted by passive receivers. The waveforms include linear frequency modulation, nonlinear frequency modulation, polyphase, and polytime codes. The advantages of LPI radar are wide bandwidth, frequency variability, low power, and the ability to hide their emissions. On the other hand, the main purpose of intercept receiver is to classify and estimate the parameters of the waveforms even when the signals are contaminated with noise. Precise measurement of the parameters will provide necessary information about a threat to the radar so that the electronic attack or electronic warfare support system could take instantaneous counter action against the enemy. In this work, noisy polyphase and polytime coded waveforms are analyzed using cyclostationary (CS) algorithm. To improve the signal quality, the noisy signal is pre-processed using two types of denoising filters. The denoised signal is analyzed using CS techniques and the coefficients of spectral correlation density are computed. With this method, modulation parameters of nine types of waveforms up to −12 dB signal-to-noise ratio with an accuracy of better than 95% are extracted. When compared with literature values, it is found that the results are superior.

A φ-OTDR using Direct Digital Synthesis of Chirps and Sidelobe Suppression with Nonlinear Frequency Modulation

2021 ◽  
Author(s):  
Yonas Muanenda ◽  
Stefano Faralli ◽  
Claudio J. Oton ◽  
Philippe Velha ◽  
Fabrizio Di Pasquale
Keyword(s):  
Frequency Modulation ◽  
Nonlinear Frequency ◽  
Sidelobe Suppression ◽  
Direct Digital Synthesis ◽  
Digital Synthesis
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