Radar Pulse Research Articles

Reconstruction of Radar Pulse Repetition Pattern via Semantic Coding of Intercepted Pulse Trains

The timing structure of multiple successive radar pulses constructs a high-dimensional pattern for intercepted pulse trains, which is called as pulse repetition interval (PRI) pattern. By treating the radar as a machine that uses differently permuted pulses to communicate with surroundings, this pattern acts as the grammatical structure of its language. Compared with the discrete PRI set that is conventionally used for pulse train description, PRI pattern contains richer and more condensed structural information about radar pulse train, which is helpful for pulse deinterleaving and radar recognition. This article introduces the semantic coding theory to reveal and reconstruct PRI pattern from the intercepted radar pulse train. We first define the coding complexity of a pulse train, which is divided into two parts: 1) the complexity of encoding a PRI pattern dictionary with each element consisting of several successive PRIs; and 2) encoding the intercepted pulse train based on this dictionary. The coding complexity is then minimized by optimizing the components in dictionary, and the PRI timing patterns are finally obtained from the dictionary when the minimization is reached. The effectiveness of semantic coding model and PRI pattern reconstruction method is verified in the simulation part.

A novel method of deinterleaving radar pulse sequences based on a modified DBSCAN algorithm

A modified DBSCAN algorithm is presented for deinterleaving of radar pulses in modern EW environments. A main characteristic of the proposed method is that using only time of arrival of pulses, the method can sort the pulses efficiently. Other PDW information such as rise time, carrier frequency, pulse width, modulation on pulse, fall time and direction of arrival are not required. To identify the valid PRIs in a set of interleaved pulses, an innovative modification of the DBSCAN algorithm is introduced which is accurate and easy to implement. The proposed method determines valid PRIs more accurately and neglects the spurious ones more efficiently as compared to the classical histogram based algorithms such as SDIF. Furthermore, without specifying any input parameter, the proposed method can deinterleave radar pulses while up to 30% jitter is present in the associated PRI. The accuracy and efficiency of the proposed method are verified by computer simulations and real data results. Experimental simulations are based on different real and operational scenarios where the presence of missing and spurious pulses are also considered. So, the simulation results can be of practical significance.

Full-Duplex SIC Design and Power Allocation for Dual-Functional Radar-Communication Systems

To meet the requirements for simultaneous sensing and communication, full-duplex operation is essential for dual-functional radar-communication (DFRC) systems. In this letter, both the full-duplex self-interference cancellation (SIC) and the corresponding power allocation problem is studied for a pulsed DFRC system. First, a full-duplex design is provided, and the radar signal to interference-plus-noise ratio (SINR) and the communication rate are derived considering imperfect full-duplex SIC. Then, a max-min-ratio problem is formulated to maximize the radar SINR under the constraint of the communication rate. For time-invariant channels, a closed-form power allocation solution is derived for both radar and communication pulses. For time-variant channels, we provide an iterative solution by adopting quadratic transform and successive convex approximation (SCA). Simulation results are further given to verify the effectiveness of the proposed designs.

Frequency Comb-Based Ground-Penetrating Bioradar: System Implementation and Signal Processing.

Radars can be used as sensors to detect the breathing of victims trapped under layers of building materials in catastrophes like earthquakes or gas explosions. In this contribution, we present the implementation of a novel frequency comb continuous wave (FCCW) bioradar module using a commercial software-defined radio (SDR). The FCCW radar transmits multiple equally spaced frequency components simultaneously. The data acquisition of the received combs is frequency domain-based. Hence, it does not require synchronization between the transmit and receive channels, as time domain-based broadband radars, such as ultra wideband (UWB) pulse radar and frequency-modulated CW (FMCW) radar, do. Since a frequency comb has an instantaneous wide bandwidth, the effective scan rate is much higher than that of a step frequency CW (SFCW) radar. This FCCW radar is particularly suitable for small motion detection. Using inverse fast Fourier transform (IFFT), we can decompose the received frequency comb into different ranges and remove ghost signals and interference of further range intervals. The frequency comb we use in this report has a bandwidth of only 60 MHz, resulting in a range resolution of up to 2.5 m, much larger than respiration-induced chest wall motions. However, we demonstrate that in the centimeter range, motions can be detected and evaluated by processing the received comb signals. We want to integrate the bioradar into an unmanned aircraft system for fast and safe search and rescue operations. As a trade-off between ground penetrability and the size and weight of the antenna and the radar module, we use 1.3 GHz as the center frequency. Field measurements show that the proposed FCCW bioradar can detect an alive person through different nonmetallic building materials.

Synoptic Variability in Satellite Altimeter‐Derived Radar Freeboard of Arctic Sea Ice

AbstractSatellite observations of sea ice freeboard are integral to the estimation of sea ice thickness. It is commonly assumed that radar pulses from satellite‐mounted Ku‐band altimeters penetrate through the snow and reflect from the snow‐ice interface. We would therefore expect a negative correlation between snow accumulation and radar freeboard measurements, as increased snow loading weighs the ice floe down. In this study we produce daily resolution radar freeboard products from the CryoSat‐2 and Sentinel‐3 altimeters via a recently developed optimal interpolation scheme. We find statistically significant (p < 0.05) positive correlations between radar freeboard anomalies and modeled snow accumulation. This suggests that, in the period after snowfall, radar pulses are not scattering from the snow‐ice interface as commonly assumed. Our results offer satellite‐based evidence of winter Ku‐band radar scattering above the snow‐ice interface, violating a key assumption in sea ice thickness retrievals.

High-Resolution Observation of Ionospheric E-Layer Irregularities Using Multi-Frequency Range Imaging Technology

E-region field-aligned irregularities (FAIs) are a hot topic in space research, since electromagnetic signal propagation through ionospheric irregularities can undergo sporadic enhancements and fading known as ionospheric scintillation, which could severely affect communication, navigation, and radar systems. However, the range resolution of very-high-frequency (VHF) radars, which is widely used to observe E-region FAIs, is limited due to its bandwidth. As a technology that is widely used in atmosphere radars to improve the range resolution of pulsed radars by transmitting multiple frequencies, this paper employed the multifrequency radar imaging (RIM) technique in a Wuhan VHF radar. The results showed that the range resolution of E-region FAIs greatly improved when compared with the results in traditional single-frequency mode, and that finer structures of E-region FAIs can be obtained. Specifically, the imaging results in multifrequency mode show that E-region FAIs demonstrate an overall descending trend at night, and it could be related to the tides or gravity waves due to their downward phase velocities or even driven by downwind shear. In addition, typical quasi-periodic (QP) echoes with a time period of around 10 min could be clearly seen using the RIM technique, and the features of the echoes suggest that they could be modulated by gravity waves. Furthermore, the RIM technique can be used to obtain the fine structure of irregularities within a short time period, and the hierarchical structure of E-region FAIs can be easily found. Therefore, the multifrequency imaging RIM technique is suitable for observing E-region FAIs and their evolution, as well as for identifying the different layers of E-region FAIs. Combined with the RIM technique, a VHF radar provides an effective and promising way to observe the structure of E-region FAIs in more detail to study the physical mechanism behind the formation and evolution of ionospheric E-region irregularities.

Xilinx RFSoC를 사용한 레이다 펄스 신호 실시간 스펙트럼 탐색기 개발

In this paper, we present a design and implementation method for a high-speed spectrum analyzer that can detect the spectrum of a received radar pulse signal in real time. To respond to an enemy’s target search or tracking in an electronic warfare environment, it is first necessary to quickly detect the enemy radar signal. Signal search is mainly performed through spectrum analysis, and radar signals exist over a wide band of several tens of gigahertz (GHz). Therefore, signal detection is performed by dividing the entire band into several subbands and searching sequentially or in parallel. Because the search time can be reduced as the subband becomes wider, a searcher capable of processing the wideband in real time is required. In this paper, we design a digital searcher capable of detecting radar pulse signals within a 1 GHz bandwidth in real time and present a hardware implementation method. The requirements for real-time spectrum search for the hardware used are also presented. In the proposed method, the received signal is converted to digital through a high-speed analog-to-digital converter, and the spectrum of the signal can be searched in real time by performing an FFT that reflects the characteristics of the pulse signal. The spectrum analyzer was implemented on a Xilinx RFSoC board and its performance was examined.

Accurate Estimation of LPI Radar Pulse Train Parameters via Change Point Detection

Estimating the time of arrival (TOA), pulse width (PW), and pulse repetition interval (PRI) is critical for identifying the low probability of intercept (LPI) radar signals as it is common in electronic warfare (EW) to experience a pulse train being received. To determine these parameters, we need to differentiate between pulse and noise in a pulse train. However, separating the LPI radar pulse train into pulse and noise is challenging owing to its characteristics and modulation scheme. Therefore, we propose a method to accurately estimate TOA, PW, and PRI using change point detection, which can effectively classify the pulse train into pulse and noise. The main contributions of this study are as follows. First, a denoising method robust to various modulation schemes is introduced. Second, an algorithm capable of estimating the parameters without considering the threshold calculation is presented. Moreover, most prior studies have entailed parameter estimations for a single pulse. In contrast, we focus on estimating parameters when a pulse train is intercepted and generating superior results even in the signal-to-noise ratio under 0 dB. We present experiments performed on the following eight modulation schemes: linear frequency modulation, Costas, Barker, Frank, P1, P2, P3, and P4 codes. Furthermore, we compare the proposed method with the wavelet-based method, which has received much attention in EW. The results demonstrate that the proposed method outperforms the conventional approaches.

Vibrational Radar Backscatter Communications Theory and Bound

Vibrational radar backscatter communication (VRBC) utilizes millimeter-wave radar vibrometry to receive message signals from vibrating surfaces. So long as multiple transponding surfaces are separable by the system radar in angle and/or range, VRBC can simultaneously detect, isolate, and decode messages from these multiple sources. For anything-to-vehicle communications, VRBC is therefore a scalable, low-latency approach which leverages existing automotive radars to increase situational awareness without requiring any additional use of the RF spectrum. In this paper, we describe the modeling and processing of VRBC signals. We show that knowledge of surface resonances and coding constraints can be used to improve system performance by incorporating them into a Markov model. We provide insight into the rate capabilities of VRBC by providing a theoretical upper bound that incorporates the presence of intersymbol interference (ISI). Simulation results compare our upper bound to achievable communication rates using single symbol vs sequence detection maximum likelihood methods for a given symbol length, set of symbol excitations, and VRBC radar pulse repetition interval (PRI).

Radar Pulse Stream Clustering Based on MaskRCNN Instance Segmentation Network

In this paper, a clustering algorithm based on the MaskRCNN instance segmentation network is proposed to address the radar pulse stream clustering problem. Compared with traditional algorithms, the suggested algorithm successfully avoids the problem of preset parameters and algorithm structure constraints by using instance segmentation networks as clustering algorithms, and provides an end-to-end solution for the radar signal sorting issue. A PDW lattice mapping method is proposed to adapt to the input form of the instance segmentation network. The instance segmentation network based on ResNet, FPN, RPN, and RolAlign structure detects and masks the individual from the same or different radar signals. The simulation results show that the suggested algorithm performs the sorting of radar pulse stream under the condition of serious overlapping of radar parameters.

Synthetic Aperture Radar Pulse Compression with Optimized Non-linear Frequency Modulation

Synthetic Aperture Radar Pulse Compression with Optimized Non-linear Frequency Modulation

Увеличение эффективности обнаружения воздушных судов на догонных курсах в импульсно-доплеровских бортовых РЛС с малой высотой полета носителя

Problem statement. The effectiveness of solving the problem of warning about possible collisions of small aircraft or unmanned aerial vehicles intended for the development of hard-to-reach territories depends on the time of early detection of another aircraft on intersecting trajectories. As a result of the comparative analysis of radar detection methods carried out in the article, taking into account the differences in the signal-interference situation characteristic of on-board pulse−Doppler radars for targets on catch-up courses in versions "multiple input - multiple output", "with joint a posteriori processing of results" and in traditional radar with active or passive phased antenna arrays have shown that the latter have energy advantages. Therefore, for this category of pulse-Doppler radars, a method for estimating the detection range on several frames is presented, which allows you to choose the logic of operation with an increase in the detection range. Research methods. The theory of antenna arrays and the theory of radar detection for pulse-Doppler radars were actively used in the work with the specified requirements for the probabilities of correct detection, false alarm and the selected model of fluctuations of the reflected useful signal. Purpose. To substantiate the advantages of technical solutions based on a traditional technical solution with phased antenna arrays for detection on catch-up courses and to develop recommendations for finding conditions that allow to increase the detection range. Results. The simulation results are presented, showing an improvement in the conditions for radar detection in onboard pulse-Doppler radars when finding the spectrum of the reflected radar signal in the Doppler frequency range, on which the spectrum of the reflected signal from the Earth's surface is superimposed when using radar with phased antenna arrays compared with spatial processing methods in MIMO and radars with joint a posteriori processing of results. A method for calculating the detection range on several adjacent frames has been developed and it is shown that in this case a longer range is achieved compared to the case of detection on a single frame. Practical significance. The results of the work can be used in small-sized onboard pulse radars of low-altitude carriers in order to increase the time of early warning of the presence of other aircraft on the flight path. This task seems to be especially relevant when flying radar carriers in hard-to-reach, developed territories.

SSB-Based Signal Processing for Passive Radar Using a 5G Network

This paper presents an alternative processing chain for the passive radar using fifth-generation (5 G) standard technology for broadband cellular networks as illuminators of opportunity. The proposition is to use a 5 G synchronization signal block's (SSB) periodically transmitted modulated pulse in 5G-based passive coherent location (PCL) system processing. Although the SSB periodicity limits the velocity ambiguity, the paper describes a solution to tackle this problem in a single target scenario. The method is advantageous when there is a lack of transmission in the telecommunication channel, and the 5 G SSB is the only existing signal. The paper proposes a signal processing pipeline for 5G-based PCL that is inspired by passive radars using non-cooperative pulse radar as an illumination source. The method has been validated using simulated and real-life 5 G data measurements. The results presented in the paper show the possibility of detecting a moving target with a lack of data transmission in the 5 G network, using only the SSB when the classical passive radar signal processing fails. The presented results prove the possibility for a significant increase of 5 G network-based PCL utilization in short-range applications.

Экспериментальное исследование нелинейной эффективной площади рассеяния объектов в видеоимпульсном режиме

Quantitative information on the nonlinear scattering properties of probed objects at the impacts with signals close to baseband is presented, that will allow to make the requirements on transmitters and receivers of nonlinear baseband pulse radars. A prototype of a nonlinear baseband pulse radar using laboratory instruments has been developed. In the aperture of the antenna, it creates a pulsed field with an intensity of 35 W/m2 and at a front duration of 0,23 ns. The rings with a diameter of 6 сm made of copper wire with a cross section of 4 mm2 are used as sounding objects (a short-circuited ring as a linear object and a ring with the HSMS-8101 diode in its gap as a nonlinear object). The nonlinear radar cross section (NRCS) of a nonlinear object was 0,041 mm2, that fits into the typical range of NRCS for objects in a conventional (harmonic) nonlinear sounding.

Microwave Photonic Crystal Video Receiver for Radar Interception

This article introduces an approach of a crystal video receiver (CVR) based on microwave photonics (MWP) to detect pulsed radar signals. The pulsed radiofrequency (RF) envelope detection is achieved using the optical self-homodyne technique on the photodetection process. The proposed architecture uses a phase modulator (PM) to modulate the optical carrier and a fiber Bragg grating (FBG) to filter the spectrum to convert phase to intensity modulation. The self-homodyne technique eliminates the optical carrier at photodetector to reduce the shot noise and saturation on it. Moreover, the photodetection is performed at the radar pulse baseband, allowing to obtain transimpedance gain. The theoretical principle and an experimental demonstration are presented. A CVR sensitivity of 53 V/mW and a tangential signal sensitivity (TSS) equal to −40 dBm is achieved for a pulsed radar operating at 17 GHz.

Parameter Measurement Method of PD Radar Based on Non-coherent Accumulation

With the improvement in the anti-reconnaissance performance of the new system radar, the signals sent by the radar are more and more difficult to be detected, which brings new challenges to electronic reconnaissance. In order to find the enemy earlier, the receiver usually needs high sensitivity to detect weak signals. Therefore, according to the characteristics of airborne PD radar pulses, a method of PD radar parameter measurement based on non-coherent accumulation is proposed, which is of great significance to improve the receiver sensitivity. In this paper, the main peaks’ solution of PD Radar spectrum after non-coherent accumulation and the method of pulse parameter measurement are introduced in detail. Finally, the effectiveness of this method is verified by simulation experiments.

Symbol State Transition Entropy: A Novel Feature of Interpulse Radio Frequency Modulation Signal

In radar electronic warfare (EW) reconnaissance, radio frequency (RF) is an important parameter for describing the received pulse, and it is usually used in sorting and identifying radar signals. In order to achieve different detection purposes, different modulations are used in intra-pulse and interpulse radar signals. It is an important frequency modulation mode in radar signals for interpulse frequency modulation, which describes the characteristics of dynamic changes of radar pulse signals. However, it is difficult to describe these characteristics effectively by only using Pulse Description Word(PDW). In this letter, a novel feature, based on symbolization and entropy, is proposed to characterize interpulse frequency modulation characteristics of radar signals. Simulation results show that the proposed feature not only have an excellent performance of describing interpulse RF modulation radar signals, but is also insensitive to the environment with a certain rate of pulses missing and spurious pulses. Besides, in terms of time complexity, it also has a satisfactory performance.

Spectrum Sensing for a Radar Signal With Pulse Compression in Cognitive Radios

Opportunistic spectrum access to radar bands by a cognitive radio based secondary user has been recognized as an effective means to enhance the spectral utilization of the bands. A key functionality of cognitive radio is the spectrum sensing capability of detecting a primary user signal in the bands of interest. A widely used form of the primary user in radar bands is a pulse radar signal with pulse compression for achieving a higher range resolution and a longer detection range. In this letter, under the assumption that the period of a pulse radar signal is available a priori, we present GLRT based spectrum sensing schemes and provide their sensing performances in terms of the detection and false alarm probability.

Development of a fully planar logarithmic spiral antenna with integrated balun in UWB GPR systems for landmines detection

ABSTRACT In this paper, a compact cavity-backed logarithmic spiral antenna with an integrated broadband planar balun is presented. This fully planar antenna is used for detection of anti-personnel (AP) landmines in GPR systems. Unlike conventional spiral antennas, which are fed by unbalanced coaxial cable or vertical baluns, and these feed lines make them bulky and frail, in this design, a microstrip-to-parallel strip balun is integrated with the spiral antenna and makes the whole structure compact, planar, and robust. Moreover, a metal cavity is utilized at the back of the antenna to prevent backward radiation and enhance the forward penetration depth to the ground. In choosing the operational frequency bandwidth, a compromise is made between the penetration depth and detection resolution. A prototype of the antenna is fabricated and its performance in landmine detection is evaluated with measurements. The measured results show that the antenna works over the frequency range of 1.5 GHz−4.5 GHz (bandwidth = 100%) with |S11| < −10 dB, a penetration depth of 10 cm in the soil with good detection resolution, gain >8 dB and axial ratio <3 dB. These factors make the proposed antenna a suitable candidate for pulse radar applications, in which low pulse distortion and wide bandwidth are key factors.

Design of diplexer with direct synthesis method for ground penetrating radar

This paper proposes a direct synthesis method for diplexer with wide fractional bandwidth (115.4%) of the second passband and a narrow isolation bandwidth (190 MHz) between the two passbands in the frequency domain and almost no tailings of the output signals in the time domain. This diplexer is designed for pulsed ground penetrating radar (GPR), which takes both the time domain and frequency domain responses into consideration. This method is able to synthesize diplexers with low insertion loss and high rejection in the frequency domain while avoiding tailing of the output signal in the time domain. Additionally, a T-junction with alternated stepped impedance line (SIL) is proposed, this significantly reduces the length of the junction by 40% and at the same time widens the bandwidth of the second passband by 78.6%. As a design example, a diplexer operating at DC-540 MHz and 730–2720 MHz is designed and fabricated, showing IL of 0.9 dB and rejection of 24 dB, while the width of the signal in the time domain is unchanged. The measurement results are in good agreement with the simulated ones, proving the effectiveness of the design.