By partial interception and multiple forwarding of a radar transmitting signal, digital radio frequency memory-based interrupted sampling repeater jamming can yield a partial processing gain and form ...multiple false target groups in the range direction, achieving jamming effects of both suppression and deception. Various improved jamming strategies have been proposed, while jamming suppression problems have not been fully addressed. In this study, a jamming suppression method based on the idea of ‘reconstruction and cancellation’ is proposed by analysing the jamming principle. The method firstly analyses the pulse compression results with time-frequency analysis to obtain the intercepted slice number and forwarding times; then, the slice width is estimated by deconvolution processing; finally, iterative cancellation is used to suppress the jamming. Performance of the method was verified by Monte Carlo simulation. The results show that the normalised error of the slice width estimation is <5% when the jamming-to-noise ratio reaches 15 dB (after pulse compress); the cancellation method can effectively restrain the jamming by bringing an improvement of signal-to-jamming ratio >16 dB.
Main-lobe interrupted sampling repeater jamming (ISRJ) poses a serious threat to the normal use of radar. The existing anti-ISRJ target detection methods based on deep learning have problems, such as ...a large number of training samples required, complex use steps, inability to achieve ranging and speed measurement at the same time, and poor detection probability under a very low signal-to-noise ratio (SNR) environment. To solve these problems, this article proposes an end-to-end anti-ISRJ target detection method based on the range-Doppler spectrum. First, a visual object detection network based on convolutional neural networks (CNNs) is designed and trained with fewer than 9000 samples. Focal loss is introduced to train the network. It can adaptively improve the loss weight of hard samples and, therefore, improve the performance of the network under a low SNR environment. After that, the range-Doppler spectrum corresponding to the radar echo signal is input into the trained network, and then, the detection, ranging, and speed measurement of the targets under ISRJ conditions can be realized. The simulation results show that the detection probability of the proposed method under various SNRs, signal-to-jamming ratios (SJRs), and false alarm rates is better than that of the compared method. The proposed method can achieve a detection probability of more than 80% under the condition of a false alarm rate of <inline-formula> <tex-math notation="LaTeX">1e-4 </tex-math></inline-formula>, an SNR of −20 dB, and an SJR of not less than −20 dB.
As a new type of coherent jamming pattern in modern electronic warfare, Interrupted Sampling Repeater Jamming (ISRJ) has attracted increasing attention in past decades. In this paper, the joint ...optimization of transmit waveform and receive filter for wideband polarimetric radars is introduced to increase the freedom degrees of radar anti-ISRJ design. The figure of merit is formulated on the basis of the penalty function and Pareto balance framework. Different from off-the-shelf anti-jamming methods employing waveform design, the modulation of Target Impulse Response Matrix (TIRM) to the target echo is considered in the system model, for the sake of matching with a wideband illumination scenario. To solve the non-convex problem, a Majorization-Minimization (MM) based alternate iteration method is proposed. Numerical results validate the effectiveness of the proposed method, and highlight that compared to conventional single-polarization radars, a better anti-ISRJ performance can be achieved by waveform design of polarimetric radars.
The interrupted sampling repeater jamming (ISRJ) can effectively degrade the image quality and affect the subsequent target recognition by creating deceptive multiple false targets on synthetic ...aperture radar (SAR) images. A time-domain filtering method based on pulse coding to counter ISRJ is proposed in this article. First, this coding method requires the radar to transmit a full pulse signal consisting of multiple subpulse signals several times in the original pulse repetition interval (PRI), and there is a difference in the time distribution of the subpulses transmitted at different moments. Then, use the observation matrix determined by the echo conditions contained in each receiving window to filter the echo in the time domain to obtain the echo corresponding to each subpulse. Finally, the subpulse echo of the jammer sampling section is discarded and the remaining uninterfered subpulse echoes are segmented for pulse compression and subsequent imaging processing to obtain SAR images with a low jamming-to-signal ratio (JSR). Several groups of simulations show that the proposed method is effective against different kinds of ISRJ, and this time-domain filtering method can improve the effect of radar anti-ISRJ and has a high freedom of waveform design.
Repeater F-waves (Freps) were seen in patients with amyotrophic lateral sclerosis (ALS). The factors implicated for the presence and frequency of Freps were loss of the motor neurons and the changes ...in their excitability. The aim of this study was to assess the Freps in ALS patients and to compare their frequencies in thenar and hypothenar muscles.
Sixteen ALS patients and 11 healthy controls were recruited to the study. All patients had ⩾2mV CMAPs recorded from the hand muscles. Ninety F-waves were recorded from abductor digiti minimi (ADM) and abductor pollicis brevis (APB). The index of repeater neurons (RN) and Freps were calculated.
Mean index RN and index Freps values of ADM and APB muscles in ALS group (17.1 and 42.6 for ADM and 16.3 and 41.9 for APB) were significantly higher than those of healthy controls (4.7 and 13.9 for APB and 1.5 and 3.6 for ADM). ALS group had a lower persistence of F-waves for both muscles than healthy controls (56.4 and 94.6 for APB and 83.4 and 97.0 for ADM). Freps parameters were not different between thenar and hypothenar muscles, whereas persistence of F-waves was lower in the thenar (56.4%) as compared to the hypothenar (83.4%) muscles.
Similar Freps parameters in the thenar and hypothenar muscles might be caused by the inclusion criteria. Lower F-persistence in the thenar muscles was in accordance with the split-hand phenomenon.
The assessment of Freps and F persistence may be useful in understanding of the electrophysiological changes in ALS.
Basis pursuit of sparse decomposition is adopted to discriminate and identify the target echo with two kinds of mainlobe jamming named time-delay repeater jamming and smeared spectrum (SMSP) jamming, ...which can produce multiple false targets. The main idea is to extract their pulsed differences. The signal model is first transformed to an underdetermined matrix equation, the dictionary is constructed by the function form of the target echo, and then the matrix equation is solved by replacing the l0 norm problem via the l1 norm problem. The identification of time-delay repeater jamming and the target echo is by the difference of the pulse width. Identifying SMSP jamming and the target echo is by the difference of the chirp rate. The proposed algorithm is particularly relevant to the case that the signals are overlapped. Finally, simulation results demonstrate the efficacy of the proposed method and they show that the method outperforms the conventional time–frequency representation method.
This paper proposes a wireless power repeater system for long-distance and multiple-load applications with equal power load at each repeater. Each repeater performs as a power relay that not only ...receives and transmits power but also supplies power to its local load. The main contribution of this paper is to provide the design methodology of a distributed power-relay system. First, it provides the mathematical model of the power distribution among the power relays, indicating that the inductances and resistances can affect the power distribution. Second, it provides the power transfer capability of a power-relay system based on the quality factor and efficiency requirement, indicating the maximum achievable number of power relays in a system. Aiming at practical applications, this paper provides the guideline for the circuit parameter design to achieve equal power distribution. Two typical examples are proposed to realize equal power distribution. The identical M n and different R n examples are selected for implementation. The coil size is 400 mm × 400 mm, and the eight power relays achieve a transfer distance of 3.2 m with a total power of 760 W and an efficiency of 70%. Experimental results validate that equal power distribution is achieved for the multiple loads across a long distance. Each power relay dissipates about 95-W power in its local load with a power variation limited to ±2%.
We describe principles of operation of a quantum repeater, i.e., a device designed to distribute entangled states of quantum systems over long distances. A review is presented of the latest ...achievements in the field of experimental implementation of its simplest version (a first-generation quantum repeater) and in the development of its key component (quantum memory). The immediate and long-term prospects for the development of studies in this area are discussed.
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