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A large time-bandwidth product bistatic radar offers several advantages in high-resolution target detection and motion parameter estimation, but the scale factor and inner-pulse Doppler will also be introduced in the radar echoes when detecting high-speed targets. Under this condition, the conventional matched filter will cause a certain energy loss and a nonnegligible shift of the range center, which is called mismatch effect. Considering the special geometries of the bistatic radar, we first establish the precise echo signal (PES) model to describe the radar echoes for high-speed targets in a space–air-based bistatic radar system. By analyzing the mismatch effect within the pulse and the migration between pulses, we have obtained the mathematic relationship between the scale factor, inner-pulse Doppler shift, range, equivalent velocity, and acceleration. Following that, we perceive that the parameters of the matched filter are related to the target motion parameters, i.e., a priori unknown, which inspires us to propose an iterative coherent integration method to achieve the intrapulse and interpulse integration. A PES model matched filter with initial parameters is defined and a roughly motion parameter estimation is acquired by the PES model-based Keystone transform (PES-KT) and inner-pulse chirp Fourier transform (CFT). The estimated parameters are used for matched filter construction and coherent integration. This process is performed over multiple iterations to provide an accurate motion parameter result. In the end, a target detection experiment is given to show the effectiveness of the proposed method using space–air-based bistatic radar. [ABSTRACT FROM AUTHOR]

The mainlobe jamming suppression technique is one of the key techniques of radar electronic counter-countermeasure (ECCM). In the view of multistatic radar, the interference signals received with different view angles would be highly coherent, on the contrary, the target echoes would be independent due to the radar cross section (RCS) of target would randomly fluctuate as the variation of view angle. As a consequence, After the interference signals have been aligned, a steering vector can be found of interference signals, the energy of the interference signals will be concentrated in a single-rank subspace whereas the energy of the target echo signals will be scattered throughout the whole signal space of the multistatic radar. By exploiting this phenomenon, a new mainlobe interference suppression method for multistatic radar is proposed. In this method, the projection matrix is trained based on the time domain sampling data. The interference signals received by multiple node radars with different view angles can be effectively suppressed through the noise subspace projection operation. Then, a general likelihood ratio test detector used for the residual signals after projection operation is derived. The results of simulations indicate that the proposed method can effectively suppress various kinds of mainlobe jamming and improve the detection performance. Furthermore, this method is adaptive to the variation of the interference pattern and the geometric configuration of the node array. [ABSTRACT FROM AUTHOR]

As an emerging multifunctional material, Gallium-based room temperature liquid metal has attracted a lot of attention for a variety of applications due to its mobility and deformability. However, controlling the motion of a liquid metal droplet accurately still remains unrevealed, which restricts its application in many fields. In this article, we propose a hybrid framework that would control the motion of a liquid metal droplet in a one-dimensional (1-D) fluidic channel. A dynamic model of a liquid metal droplet immersed in the electrolyte when an electrical field is applied to each end of the channel is discussed first, followed by a setpoint controller designed to calculate the current input needed to drive the liquid metal droplet to its destination with vision feedback. To obtain the desired high-resolution current output, a fast and high-resolution current output power supply will be established by integrating a fast PID controller and a simple programmable dc power supply. The effectiveness of this proposed approach will be verified by controlling a liquid metal droplet so that it reaches its destination inside the polymethyl methacrylate channel. In this article, the proposed approach may lead to the development of tiny soft robots, or microfluidic systems that can be driven accurately by the liquid metal droplets. [ABSTRACT FROM AUTHOR]

As a transition platform between aircraft and satellite, hypersonic vehicle-borne (HSV) synthetic aperture radar (SAR) could offer many advantages such as strong survival ability, fast response, and wide detection range. However, due to the complex aerodynamic configuration and flight characteristics of the hypersonic platform, the HSV SAR faces new challenges including serious cross-couplings and spatial variations. In order to deal with these issues, a radius/angle algorithm (RAA) is devised, which has a similar processing flow as that of the conventional polar format algorithm (PFA). In the RAA, a novel 2-D interpolation function, similar to that of the PFA which is performed in the Cartesian coordinates, is derived in the curvilinear coordinate system. Due to the high accuracy of the multi-decomposition by using the polar radius and polar angle, the RAA has a much larger depth-of-focus than that of the PFA. Moreover, the RAA approach is insensitive to the height variations for the HSV SAR with curved trajectory flight, whereas the PFA is not because of the out-of-plane projection effect. Simulation results verify the effectiveness of the proposed approach. [ABSTRACT FROM AUTHOR]

In the traditional model of monostatic synthetic aperture radar (SAR), the flying platform should have a uniform linear trajectory. In practice, the flight path of the SAR platform, which is highly nonlinear or curvy caused by 3-D velocity and acceleration, cannot be used in the traditional model. In this paper, a geometrical model of the monostatic SAR with general configurations is graphically illustrated by vector notation. Moreover, the gradient method is utilized to point out the effects of the motion parameters, namely, velocity vector and acceleration vector, on total bandwidth and image resolution. Based on the accurate model, a general frequency-domain algorithm, with the incorporations of pre- and postprocessing, is proposed to focus the raw data. Applicability is studied through theoretical analysis and numerical experiments. All these general analyses can be applied to different realizations of monostatic SAR mode, including spotlight SAR, sliding spotlight SAR, and Terrain Observation by Progressive Scans (TOPS) SAR. [ABSTRACT FROM PUBLISHER]

Synthetic aperture radar (SAR) imaging is usually performed along a straight path. In practice, variations from the ideal caused by maneuvers with acceleration are inevitable. The main problem is the complex signal processing, particularly in the highly squinted spotlight mode. In this paper, acceleration model is analyzed in more details. Impacts are obtained how the acceleration influences the Doppler parameters and space-variant terms, including the SAR resolution and azimuth bandwidth. According to the special signal properties of the acceleration case, an approximation of the range history is made to avoid using the method of series reversion (MSR) to obtain an accurate spectrum. Based on the high-accurate spectrum, a spotlight algorithm with a modified two-step approach is given. Simulation results show the effectiveness of the modified algorithm. [ABSTRACT FROM PUBLISHER]

This letter proposes an omega-K algorithm for missile-borne synthetic aperture radar (SAR) diving with constant acceleration. The essence of the novel method is to derive a reference function multiplication from the equivalent range history. The true range history is divided into two parts: range independent and range dependent. After compensating the range-independent part with considering all the terms, we can regard the range-dependent part as an equivalent range history with a form similar to that of conventional SAR. Then, an analytical 2-D spectrum can be used for the omega-K algorithm. The proposed algorithm can handle general missile configurations with wide swaths and high squint angles. Simulation results are presented to validate the proposed method. [ABSTRACT FROM PUBLISHER]