Low sidelobe robust imaging in random frequency-hopping wideband radar based on compressed sensing

High resolution range imaging with correlation processing suffers from high sidelobe pedestal in random frequency-hopping wideband radar. After the factors which affect the sidelobe pedestal being analyzed, a compressed sensing based algorithm for high resolution range imaging and a new minimized ll-norm criterion for motion compensation are proposed. The random hopping of the transmitted carrier frequency is converted to restricted isometry property of the observing matrix. Then practical problems of imaging model solution and signal parameter design are resolved. Due to the particularity of the proposed algorithm, two new indicators of range profile, i.e., average signal to sidelobe ratio and local similarity, are defined. The chamber measured data are adopted to testify the validity of the proposed algorithm, and simulations are performed to analyze the precision of velocity measurement as well as the performance of motion compensation. The simulation results show that the proposed algorithm has such advantages as high precision velocity measurement, low sidelobe and short period imaging, which ensure robust imaging for moving targets when signal-to-noise ratio is above 10 dB.

A Low-Interference Time-Domain N-Continuous OFDM Scheme

N-continuous orthogonal frequency division multiplexing(NC-OFDM) is an outstanding method to suppress sidelobe for baseband OFDM signals in future 5G wireless communications.However,the precoder of NCOFDM usually causes severe interference and high complexity.To alleviate these problems,this paper proposes an improved time-domain N-continuous OFDM(TD-NC-OFDM) by optimizing the smooth signal,which is the linear combination of rectangularly pulsed OFDM basis signals truncated by a smooth window.Furthermore,we show that the proposed scheme is with lower transceiver complexity and notable performance gain in signal-tointerference-plus-noise ratio(SINR).Lastly,simulation results show that the proposed low-interference TD-NC-OFDM can achieve similar sidelobe suppression performance,with negligible bit-error rate(BER) degradation,compared to conventional NC-OFDM.

A New Range Sidelobe Suppression Technique for Randomly Intermittent Spectra HF Radar Signal

The randomly intermittent spectra (RIS) signal is employed to combat spectrum congestion in radar and other radio services to evade the external interferences in high-frequency (HF) and ultrahigh-frequency (UHF) bands. However, the spectra discontinuity of the signal gets rise to high range sidelobes when matching the reflected echo, which is much more difficult for targets detection. So it is indispensable to investigate the technique for sidelobes suppression of the range profile when RIS signal is utilized, This paper introduced a new processing technique based on time domain filtering to lower the range sidelobes. A robust and effetive algorithm is adopted to solve the coefficients of the filter, and the restriction on the desired response of the filter is derived. The simulation results show that the peak range sidelobe can be reduced to -27 dB from -9.5 dB while the frequency band span (FBS) is 200 kHz.

A Novel 2-D Signal Processing Scheme for Quasi-Random Step Frequency Signal

Due to the heavy congestion in HF bands, HF radars are restricted to operating within narrow frequency bands. To improve the system bandwidth and avoid heavy interference bands, a quasi-random step frequency signal with discontinuous bands is presented. A novel two-dimensional signal processing scheme for this signal is proposed on the basis of delicate signal analysis. Simulation results demonstrate that the scheme could successfully realize the resolutions by decoupling the range-Doppler ambiguity, and effectively suppress the maximal sidelobe. Moreover, the scheme is simple and has good numerical stability.

ANALYSIS OF TRANSMIT BEAMFORMING PERFORMANCE ON MULTIPLE-TRANSMIT BINARY ZCZ WAVEFORMS

The Transmit BeamForming (TBF) technology, applied in a multiple-transmit radar system, is studied in this paper, where multiple elements of antenna array transmit binary Zero Correlation Zones Orthogonal Signals (ZCZ-OS) independently. For each Direction Of Arrival (DOA) with respect to the transmitting array, the analysis on the gain and sidelobe level of TBF output is presented. This paper focuses on the range sidelobes performance within the main beam (in angle domain). For the normal direction, due to the inherent phase property of ZCZ-OS, the TBF output has part zero sidelobes area, of which the distribution is discussed. For the other directions, a systematic search algorithm to optimize the transmission order of signals is proposed for an optimal relationship chart of DOA and transmission order. The range sidelobe performance within the main beam can be improved as the optimal transmission order is adopted.

STUDY OF MISMATCHED FILTERING OF PASSIVE RADAR USING TV SIGNAL

This letter delnonstrates the structure of the passive radar using TV signals. Because the TV signal is a kind of pseudoperiodic signal, the matched filtering of color TV signals would yield high sidelobes which cause the range ambiguity. To overcome this problem, the mismatched filter is proposed to suppress the correlation sidelobcs of matched filtering of TV signals. By utilizing the iteration process, this method could achieve the required peak sidclobc level. The impacts of the noise and target movement on mismatched filtering are also analysed, Simulation results are included to demonstrate the effectiveness of the proposed technique.

Performance Analysis of N-Continuous OFDM Systems with Low-Interference Signal

N-continuous orthogonal frequency division multiplexing(NC-OFDM)is a promising multicarrier transmission waveform conceived for improving sidelobe suppression performance.To reduce the severe inband interference in traditional NC-OFDM,we have proposed low-interference signal modeling for NC-OFDM.However,spectral leakage and error may be undesirably increased owing to the limited continuous differentiability of the smooth signal.In this paper,the low-interference scheme is investigated in terms of power spectrum density(PSD)and error performance,under the parameters of the highest derivative order(HDO)and the length of the smooth signal,to prove and quantify its advantages over traditional NC-OFDM.In the context of PSD,sidelobe decay is evaluated upon considering two discontinuous points due to the finite continuity of the smooth signal and its higher-order derivatives.Furthermore,it was shown that the low-interference scheme incurs small signal-to-noise ratio(SNR)loss and bit error rate(BER)for a short length of the smooth signal or a small HDO compared to traditional NC-OFDM.Meanwhile,due to the cyclostationarity loss imposed by the smooth signal,an effective solution is suggested for the time synchronization in a practical system.Based on analyses and simulation results,the trade offs between sidelobe suppression and BER are studied.

Pulse Compression Technique of Radio Fuze

The advantages of using phase-coded pulse compression technique for radio fuze systems are evaluated. With building mathematical models a matched filter has been implemented successfully. Various simulations for pulse compression waveform coding were done to evaluate the performance of fuze system under noisy environment. The results of the simulation and the data analysis show that the phase-coded pulse compression gets a good result in the signal identification of the radio fuze with matched filter. Simultaneously, a suitable sidelobe suppression filter is established by simulation, the suppressed sidelobe level is acceptable to radio fuze application.

Suppressing Autocorrelation Sidelobes of LFM Pulse Trains with Genetic Algorithm

Modulations and diversities, including the Costas-ordered stepped-frequency and nonlinear stepped-frequency waveforms are widely used in linear frequency modulation （LFM） pulse trains to reduce the relatively high autocorrelation function （ACF） sidelobes. An efficient method was developed to optimize the interpulse frequency modulation to remove most of the ACF sidelobes about the mainlobe peak, with only a small increase in the mainlobe width. The genetic algorithm is used to solve the nonlinear optimization problem to find the interpulse frequency modulation sequence. The effects on the ACF sidelobes suppression and mainlobe widening are studied. The results show that the new design is superior to the corresponding stepped-frequency LFM signal and weighted stepped-frequency LFM signal in the terms of the ACF sidelobes reduction and mainlobe spread.

A super-resolution algorithm for synthetic aperture radar based on modified spatially variant apodization

The existing spatially variant apodizations(SVAs) either cannot depress the sidelobes effectively or reduce the energy of the mainlobe.To improve this,a modified SVA(MSVA) is put forward in this paper,which expands the traditional filter from 3-taps to 5-taps and sets relevant parameters according to different sampling rates to get the excellent result that satisfies constrained optimization theory.A modified super-SVA is also presented,which compares the result after the iteration with the original signal and makes the one whose amplitude is smaller as the initial value of the next iteration.This method can eliminate the sidelobes produced by the intermediate operation,so that the following bandwidth extrapolation is more available.Super-MSVA is presented based on the modified SVA and modified super-SVA,which is suitable for any Nyquist sampling rate,can extrapolate the signal bandwidth many times through iteration with a commensurate improvement in resolution,as demonstrated by the result of the experiment.

An extended chirp scaling algorithm for spaceborne sliding spotlight synthetic aperture radar imaging

A system impulse response with low sidelobes is critical in synthetic aperture radar（SAR） images because sidelobes contribute to noise and interfere with nearby scatterers. However,the conventional tricks of sidelobe suppression are unable to be exactly applied to the case of spaceborne sliding spotlight SAR due to great azimuth shifts in both time and frequency domains. In this paper, an extended chirp scaling algorithm is presented for spaceborne sliding spotlight SAR data imaging. The proposed algorithm firstly uses the spectral analysis（SPECAN） technique to avoid the azimuth spectrum folding effect and then employs the chirp scaling（CS） algorithm to achieve data focusing, i.e., the so-called two-step approach. To suppress the sidelobe level, an efficient strategy for the azimuth spectral weighting which only involves matrix multiplications and short fast Fourier transformations（FFTs） is proposed, which is a post-process executed on the focused SAR image and particularly simple to be implemented. The SAR image processed by the proposed extended CS algorithm is very precise and perfectly phase-preserving. In the end, computer simulation results verify the analysis and confirm the validity of the proposed algorithm.

Sidelobe suppression in light-sheet fluorescence microscopy with Bessel beam plane illumination using subtractive imaging

The fluorescence from the out-of-focus region excited by the sidelobes of a Bessel beam is the major concern for light-sheet fluorescence microscopy （LSFM） with Bessel beam plane illumination. Here, we propose a method of applying the subtractive imaging to overcome the limitation of the conventional LSFM with Bessel beam plane illumination. In the proposed method, the sample is imaged twice by line scanning using the extended solid Bessel beam and the ring-like Bessel beam. By subtracting between the two images with similar out-of-focus blur, the improved image quality with the suppression of the Bessel beam sidelobes and enhanced sectioning ability with improved contrast are demonstrated.

Sidelobe suppression for coherent beam combining with laser beams placed along a Fermat spiral

We proposed an aperiodic laser beam distribution, in which the laser beams are placed along a Fermat spiral, to suppress the sidelobe power in the coherent beam combining. Owing to the changed distances between two consecutive beams, the conditions of the sidelobe suppression are naturally satisfied. The Fermat spiral array was demonstrated to achieve a better sidelobe suppression than the periodic arrays, and the effects of various factors on the sidelobe suppression were analyzed numerically. Experiments were carried out to verify the sidelobe suppression by different Fermat spiral arrays, and the results matched well with the simulations.