Abstract The non-linear frequency modulation (NLFM) waveform is one of the existing waveforms that can be used in high range resolution radar applications. However, a sampling and consequently an expensive ADC are required. To overcome this drawback while taking advantage features NLFM waveform, we suggest approximating wideband by piecewise linear using it stepped (SF) framework. Thus, variabl...

Conventional radars commonly use a linear frequency-modulated (LFM) waveform as the transmitted signal. The LFM radar is simple system, but its impulse-response function produces −13.25 dB sidelobe, which in turn can make detection of weak targets difficult by drowning out adjacent target information with sidelobe strong target. To overcome this challenge, paper presents modeling and optimizati...

Recent research in Phase-Sensitive Optical Time Doman Reflectometry (ϕ-OTDR) has been focused, among others, on performing spatially resolved measurements with various methods including the use of frequency modulated probes. However, conventional schemes either rely phase-coded sequences, involve inflexible generation probe modulation or mostly employ simple linear (LFM) pulses which suffer fro...

Photonics-assisted microwave instantaneous frequency measurement (IFM) is considered as a promising technique for detecting an unknown radio-frequency (RF) signal, which has advantages of broad range and fast processing speed. Up to date, there no photonics-assisted IFM system that can essentially measure RF signal time-frequency information with power fluctuating seriously. Moreover, the accur...

The stochastic resonance (SR) in a bistable system driven by nonlinear frequency modulation (NLFM) signal and strong noise is studied. Combined with empirical mode decomposition (EMD) piecewise idea, an adaptive re-scaled SR method based on the optimal intrinsic function (IMF), proposed to enhance weak NLFM signal. At first, considering advantages of EMD for dealing non-stationary signals, segm...

In active sonar systems, proper selection of the transmitted waveform is critical for target detection and parameter estimation. Each signal has its own diverse characteristics. Linear FM suffers from relatively high autocorrelation (ACF) side-lobes. The ACF sidelobes could be reduced by shaping the signal; other methods include Gaussian NLFM, Rayleigh NLFM and the combination of both these pul...

Active cancellation stealth is a significant developing direction in modern stealth technology field. In this paper, according to characteristics of linear frequency modulated (LFM) signal and nonlinear frequency modulated (NLFM) signal, the cancellation signal was designed. An important parameter called cancellaty which is used to measure the effect of cancellation is proposed. The basic theor...

In order to improve the reliability of detecting debonding defects at interface thermal barrier coatings (TBC), a non-linear frequency modulated (NLFM) infrared wave detection method is proposed. A NLFM system built, and zirconia TBC specimens are prepared tested. The effects defect diameter, excitation power, initial termination on effect analyzed. Three algorithms such as principal component ...

As the useful time-frequency tool, the Fractional Fourier Transform (FRFT) and the Short Time Fourier Transform (STFT) have a great development of signal recognition. And the Reduced Fractional Fourier Transform (RFRFT) was recently proposed and has been used in the recognition and estimation of chirp signals. A new method based on STFT and RFRFT is presented for radar signals modulation recogn...

Abstract For purpose of solve the problem poor discrimination and robustness intra-pulse signal features extracted by traditional methods, this paper proposes a radar modulation type recognition algorithm based on improved residual network. Firstly, one-dimensional time-domain is converted into two-dimensional time-frequency image Smoothing Pseudo Wigner-Ville Distribution; Then preprocessed; R...