Stepped Frequency Modulation Research Articles

Advancing Stepped-Waveform Radar Jamming Techniques for Robust False-Target Generation against LFM-CFAR Systems.

This study investigates the utilization of a stepped wave frequency modulation jamming technique in radar systems. The objective is to enhance the effectiveness and robustness of false target jamming in the presence of linear frequency modulation (LFM) radars employing constant false alarm rate (CFAR) detection. The proposed method combines stepped frequency modulation with full pulse delay/sum repeat jamming to enhance resilience against uncertainties in target parameters. Theoretical analysis and simulation experiments are conducted to establish relationships between key jammer parameters, such as frequency slope and power compensation, and performance metrics, like false target distribution and CFAR masking. The results demonstrate that the proposed technique effectively maintains a dense distribution of false targets surrounding the protected target, even in the presence of uncertainties in position and signal-to-noise ratio. In comparison to existing methods, the utilization of stepped-waveform modulation enables improved control over target distribution and CFAR masking. Adaptive power allocation compensates for parameter errors, thereby enhancing robustness. Simulation results reveal that the proposed approach significantly reduces the probability of detecting the true target by over 95% under uncertain conditions, while previous methods experienced degradation. The integration of stepped waveforms optimizes false target jamming, thereby advancing electronic warfare capabilities in countering advanced radar threats. This study establishes design principles for resilient jamming architectures and supports enhanced survivability against radars employing pulse compression and CFAR detection. Moreover, the concepts proposed in this study have the potential for extension to emerging radar waveforms.

Synchronized Stepped Frequency Modulation for Multiplexed Ion Mobility Measurements.

Implementation of frequency-encoded multiplexing for ion mobility spectrometry (e.g., Fourier transform ion mobility spectrometry (FT-IMS)) has facilitated the direct coupling of drift tube ion mobility instrumentation with ion-trap mass analyzers despite their duty cycle mismatch. Traditionally, FT-IMS experiments have been carried out to utilize continuous linear frequency sweeps that are independent of the scan rate of the ion-trap mass analyzer, thus creating a situation where multiple frequencies are swept over two sequential mass scans. This in turn creates a degree of ambiguity in which the ion current derived from a single modulation frequency cannot be assigned to a single data point in the frequency-modulated signal. In an effort to eliminate this ambiguity, this work describes a discrete stepwise function to modulate the ion gates of the IMS while synchronization between the generated frequencies and the scan rate of the linear ion trap is achieved. While the number of individual frequencies used in the stepped frequency sweeps is less than in continuous linear modulation experiments, there is no loss in performance and high levels of precision are maintained across differing combinations of terminal frequencies and scan lengths. Furthermore, the frequency-scan synchronization enables further data-processing techniques such as linear averaging of the frequency modulated signal to drastically improve signal-to-noise ratio for both high and low intensity analytes.

FPGA based Identification of Frequency and Phase Modulated Signals by Time Domain Digital Techniques for ELINT Systems

In this paper, a decision tree algorithm based on time-domain digital technique is developed for the identification and classification of diverse radar intra-pulse modulated signals for the electronic intelligence system in real-time. This includes linear frequency modulation, non-linear frequency modulation, stepped frequency modulation and bi-phase modulation. The received signal is digitised and the instantaneous phase and high accuracy instantaneous frequency are estimated. The instantaneous amplitude is also estimated to get the start and stop of the pulse. Instantaneous parameters are estimated using a moving autocorrelation technique. The proposed algorithm is employed on the instantaneous frequency and the modulation is identified. The modulation type and modulation parameter are important for unique radar identification when similar radars are operating in a dense environment. Simulations are carried out at various SNR conditions and results are presented. The model for algorithm is developed using a system generator and implemented in FPGA. These results are compared when the proposed algorithm is used with the existing digital in-phase and quadrature-phase (DIQ) technique of instantaneous frequency and amplitude estimation.

Implementation of Stepped Frequency Modulation Pulse Compression on NI Suite

In Radars and Sonar, the pulse compression technique is used continuously to increase the range resolution, range detection and the signal-to noise ratio (SNR). This can be achieved by modulating the transmitted pulse and then correlating it to the received pulse with the transmitted signal. This transforms short pulse into long pulse and is used to increase long pulse bandwidth by some form of modulation such as linear frequency modulation (LFM), so that Range Resolution is not compromised. The proposed Stepped Frequency Modulation (SFM) is a common Pulse Compression Method, which is useful to increase the Radar Range Resolution without losing the capability of target detection. Step Frequency Continuous Wave (SFCW) is also one of the techniques used in the Pulse Compression Technique, where the return echo step is used to determine range and is used for different purposes. This type of setup is widely used in RADAR design and testing. This Paper proposes the implementation of various Modulation techniques such as LFM, SFM and SFCW for proposed Stepped frequency Modulation using NI suite hardware PXI system which has a configurable FPGA and RF front end to generate custom waveform in wide range of frequencies with bandwidth up to 1GHz design and testing.

Design of less-detectable RADAR waveforms using stepped frequency modulation and coding

Radar signal generation and processing techniques are developing with an aim of reducing interference and signal interception. Signal jamming and signal detection have become emerging areas of interest in the field of radar engineering. So there is a need for design and development of new waveforms which are less detectable by the hostile receiver and less susceptible to jamming. In the work mentioned here, Stepped Frequency Waveform (SFW) is modulated with phase modulation techniques such as Barker codes and polyphase codes to improve the complexity and to reduce the detectability of waveform thus increasing the bandwidth of waveform and limiting the transmitted power of the waveform by using pulse compression techniques. The SFW considered here is generated having varying step size. Pulse compression technique is employed here in order to generate a pulse having a range resolution of shorter pulse and transmitted power of longer pulse. The modulated waveform characteristics have been studied and analyzed using ambiguity functions of the waveform.

HRR Profiling on Integrated Radar-Communication Systems Using OFDM-PCSF Signals

In order to improve both the transmission data rate and the range resolution simultaneously in integrated radar-communication (RadCom) systems, orthogonal frequency-division multiplexing with phase-coded and stepped-frequency (OFDM-PCSF) waveform is proposed. A corresponding high resolution range (HRR) profile generation method is also presented. We first perform OFDM-PCSF waveform design by combining the intrapulse phase coding with the interpulse stepped-frequency modulation. We then give the ambiguity function (AF) based on the presented waveforms. Then, the synthetic range profile (SRP) processing to achieve HRR performance is analyzed. Theoretical analysis and simulation results show that the proposed methods can achieve HRR profiles of the targets and high data rate transmissions, while a relative low computational complexity can be achieved.

Research of FMCW for Perfect Binary Sequences Pairs

An improved FMCW auto-collision radar system is introduced. The system includes perfect binary sequences pairs theory, the method using auto-correlation functions to get target signal and measure distance, this enables itself to get constant development with theoretical progress. The new system only changes the program of signal generator a little, moreover it can be realized by DSP, which can reduce the false alert notably so as to be applied increasingly widely. Key words: stepped-frequency modulation; multi-target detection; perfect binary sequences pairs

Two-dimensional ISAR model and image reconstruction with stepped frequency-modulated signal

A two-dimensional (2-D) inverse synthetic aperture radar (ISAR) return signal model that employs stepped frequency (SF) modulation is developed. The geometry of the examined ISAR scenario is described by analytical geometrical equations. The target to be imaged is represented by a rectangular grid of point scatterers, moving along a rectilinear trajectory at constant speed, without any rotational motion. Thus, the inverse synthetic aperture results from the translational motion of the target for a short period of time. The process of ISAR signal modelling through coherent summation of the SF-modulated signals reflected from different point scatterers of the target is thoroughly described. Moreover, an efficient ISAR image reconstruction approach, including cross-correlation-based range compression and fast-Fourier-transform-based azimuth compression, is presented through analytical mathematical expressions. Numerical simulations are carried out for various SF ISAR scenarios and high-resolution ISAR images are obtained by applying the proposed ISAR image reconstruction approach. Simulation results (ISAR images and corresponding entropy values) indicate the validity of the proposed 2-D SF ISAR return signal model and the efficiency of the proposed imaging algorithms. Finally, a numerical simulation result is illustrated, which shows the comparison of the performance of the proposed ISAR image reconstruction algorithms based on SF and linear frequency modulation waveforms. It is shown that the two waveforms attain almost the same ISAR image resolution.

Digital and Analog Subcomplementary Sequences for Pulse Compression

Golay's complementary pairing has been a method to increase the utility of binary sequences, because of the temporal sidelobe suppression in the autocorrelation vector summation. Complementary sets of Tseng and Liu and of Hollis exhibit the same effect when several autocorrelations are combined. These complementary pairs and sets of sequences can be extended into long complementary chains by a simple transformation. This transformation is extended here to all pulse compression waveforms. By this method, even though analog complementary sequences cannot be formed, a new class of waveforms, called subcomplementary waveforms, can be formed. Following these rules, repetition of waveforms such as linear frequency modulation (LFM) or linear stepped frequency modulation (LSFM) in a prescribed manner is possible without creating autocorrelation grating lobes or repetitive sidelobes. This method is equally applicable to all analog or digital pulse compression waveforms.