Array Radar Research Articles

A Three-Dimensional Enhanced Imaging Method on Human Body for Ultra-Wideband Multiple-Input Multiple-Output Radar

High-resolution three-dimensional (3D) images can be acquired by the planar Multiple-Input Multiple-Output (MIMO) array radar making future work like detection and tracking easier. However, regarding portability and to save the costs of radar system, MIMO radar array adopts sparse type with limited number of antennas, so the imaging performance of a MIMO radar system is limited. In this paper, the 3D back projection imaging algorithm is verified by the experimental results of planar MIMO array for human body and an enhanced radar imaging method is proposed. The Lucy-Richardson (LR) algorithm based on deconvolution that is normally used for optical images is applied in radar images. Since the LR algorithm can amplify the noise level in a noise-contaminated system, a regularization method based on the Total Variation constraint is further incorporated in the LR algorithm to suppress the ill-posed characteristics. The proposed method shows a higher image Signal-to-Noise Ratio, a faster rate of convergence, a higher structure similarity and a smaller relative error compared to some similar methods. In the meantime, it also reduces the loss of image information after image enhancement and improves the radar image quality (get less grating lobe and clearer human limbs). The proposed method overcomes the disadvantages mentioned above and is verified by simulation experiment and real data measurement.

Differential Coincidence Imaging With Frequency Diverse Aperture

A novel coincidence imaging method using the differential of radiation patterns (DRP) generated by a frequency diverse aperture (FDA) is proposed in this letter. The proposed FDA consists of metamaterial structure cells with different resonance frequencies in double layers and a wideband patch antenna. The minimum correlation coefficient criterion of the DRP is used during the location design of metamaterial structure cells. The transmitting and receiving channels at each frequency should be separately calibrated in advance to obtain grouped and balanced DRPs. In addition, the performance of the proposed imaging method is analyzed using one-dimensional model compared with traditional imaging method with FDA and ideal random radar array. Finally, the high-resolution image is reconstructed using an optimization algorithm. The ability of the immunity against interference of the proposed method is much better compared with the traditional imaging method with FDA. The proposed imaging method and the design of the FDA are validated through experiments

Phase Fluctuation Cancellation for Uplink Radar Arrays Based on Passive Frequency Mixing

Precise time-difference detections among different radars in uplink radar arrays require ultrastable phase transfer in bidirectional analog optical fiber links. We propose and demonstrate a scheme based on passive frequency mixing to satisfy this requirement in which two continue wave (CW) radio frequency (RF) signals after passing through double-path of the transport fiber are utilized for dynamic phase fluctuation cancellation in uplink and downlink, respectively. Our scheme has the capabilities on stable phase transfers for both CW and pulsed RF signals. Experimental results show that the phase stability improvements in uplink and downlink are greater than a factor of 30 and a factor of 20 for 2.4-GHz RF signals over a 2-h measurement period along 25-km single mode fiber.

Analysis of Ten-Concentric Circular Ring Antenna Array for Radar and Wireless Applications

Analysis of Ten-Concentric Circular Ring Antenna Array for Radar and Wireless Applications

Sparse Bayesian Learning Based Three-Dimensional Imaging Algorithm for Off-Grid Air Targets in MIMO Radar Array

In recent years, the development of compressed sensing (CS) and array signal processing provides us with a broader perspective of 3D imaging. The CS-based imaging algorithms have a better performance than traditional methods. In addition, the sparse array can overcome the limitation of aperture size and number of antennas. Since the signal to be reconstructed is sparse for air targets, many CS-based imaging algorithms using a sparse array are proposed. However, most of those algorithms assume that the scatterers are exactly located at the pre-discretized grids, which will not hold in real scene. Aiming at finding an accurate solution to off-grid target imaging, we propose an off-grid 3D imaging method based on improved sparse Bayesian learning (SBL). Besides, the Bayesian Cramér-Rao Bound (BCRB) for off-grid bias estimator is provided. Different from previous algorithms, the proposed algorithm adopts a three-stage hierarchical sparse prior to introduce more degrees of freedom. Then variational expectation maximization method is applied to solve the sparse recovery problem through iteration, during each iteration joint sparsity is used to improve efficiency. Experimental results not only validate that the proposed method outperforms the existing off-grid imaging methods in terms of accuracy and resolution, but have compared the root mean square error with corresponding BCRB, proving effectiveness of the proposed method.

W-대역 영상레이다를 위한 광대역 Chirp 신호 발생장치

In this paper, we describe the designed digital waveform of a linear frequency-modulated (FM) chirp signal using field-programmable gate arrays (FPGAs) for image radar, and this signal is modulated with an I-Q modulator, and multiplied by 24 frequency multipliers to obtain a 94-GHz W-band wideband chirp generator. The developed chirp generator is an FM signal with a 94-GHz carrier frequency and a 960-MHz bandwidth, and the flatness is less than 1.0 dB at intermediate frequency (IF) (3.9 GHz), 2.0 dB in the W-band, and it has a 0.3-W output power in the W-band.

Beam Synthesis with Low-Bit Reflective Coding Metamaterial Antenna: Theoretical and Experimental Results

Coding metamaterials are the new technology where the aperture coding provides the hardware foundation for the miniaturization of the devices. As a synthetic 2-D plane, metamaterial antennas are composed of subwavelength resonant particles. It can realize real-time control of electromagnetic wave and build multifunction radar array system. We make a detailed explanation of its array structure, working principle, and hardware system. However, it is usually difficult to synthesize flexible beams because the phase value is very limited in this antenna. Two methods are proposed in this paper to demonstrate the beam synthesis based on repetitive coding and convolution, and the distribution of beam pointings is analysed on the basis of this mechanism. Experiments that measure the radiation pattern of this antenna are carried out to verify the simulated results using only 1-bit coding metasurface in a radar system, whose phase value is controlled by pin diode on the surface.

Passive Radar Array With Low-Power Satellite Illuminators Based on Fractional Fourier Transform

This paper addresses the detection of surface slow moving targets by means of an array passive radar based on low-EIRP satellite illuminators of opportunity. Particularly, the use of the receiving array of K elements is considered to provide increased detection capability for targets with limited radar cross section, together with the capability to estimate the target direction-of-arrival. A full processing scheme is proposed to exploit together both the long integration times and the multiple receiving elements. This includes a coherent space-time integration of the signal received at the K antenna elements during short frames, followed by an incoherent frame to frame integration. The proposed scheme is based on the fractional Fourier transform that is shown to map the signals into a natural rotated frequency-angle plane, where we can easily compensate the target Doppler frequency shifts available at the different antenna elements and temporal frames. Its effectiveness is shown by application to different synthetic scenarios, where the target detection is only achievable when all the possible integration gain is capitalized.

A Super-Resolution Computational Coincidence Imaging Method Based on SIMO Radar System

A super-resolution computational imaging method, called post random modulation radar imaging, based on single-input multiple-output radar detection system is proposed in this letter. In the proposed method, the target is detected in coherent mode using the multilinear frequency modulation signal. The echoes received by the radar elements of the receiving array are recorded, respectively. Then, random modulations of the directional pattern factor of the receiving radar array, which are nonlinear processes, are optimized according to the position and the size of the target that are estimated roughly using the traditional method. Finally, the super-resolution radar imaging is obtained to solve the equation group formed by the data from the nonlinear post random modulation process. The resolution of the proposed imaging method can break the diffraction limit corresponding to the aperture of the receiving radar array. The anti-interference ability of the proposed approach is improved significantly compared with the incoherent imaging method using a multiple-input single-output structure. Experiments are carried out to validate the proposed approach.

Adaptive maneuvering target tracking with 2-HFSWR multisensor surveillance system

The high frequency surface wave radar (HFSWR) with detection capability of hundreds of kilometers plays an important role in marine surveillance [1]–[8]. Nevertheless, HFSWR has low azimuth measurement accuracy, which causes great deviation of target location and tracking [9]. Meanwhile, the miniaturization of radar arrays leads to the limitation of antenna length, which further causes severe decline of azimuth accuracy. Moreover, the interference from external environment also decreases the azimuth accuracy, making the accurate tracking of vessels difficult. In recent years, the 2-HFSWR multisensor surveillance system has become a hot spot, because it only requires parameters of distance and velocity without using the azimuth measurement when tracking vessels. The 2-HFSWR multisensor surveillance system consists of two independent radars implementing the target location and tracking task by detecting the radial distance and velocity, respectively. The 2-HFSWR multisensor surveillance system can ensure the detection accuracy without azimuth measurement, which is advantageous to the miniaturization of HFSWR. However, there are still certain complicated cases to be solved for continuous tracking of vessels, for example sudden change in motion state, an inaccurate model, and unknown priori statistical properties of noise.

Low angle estimation in diffuse multipath environment by time‐reversal minimum‐norm‐like technique

This study presents a novel method for low angle estimation in diffuse multipath environment by the time-reversal (TR) minimum-norm-like (MNL) technique. In recent studies, the diffuse multipath is always regarded as the interference which is tried to be eliminated or weakened in low angle estimation for very high-frequency radar. However, it is difficult to establish the accurate model of the multipath environment. The common methods usually ignore the diffuse multipath and use the mirror reflection as the approximate model, but the ideal assumption would cause great errors. The proposed method makes the radar array working in the TR setup and the MNL technique is applied to estimate the low angle. In the proposed method, the exact model of the multipath environment does not need to be established completely but the accuracy performance of low angle estimation can be improved by making use of the multipath. Simulation results are presented to demonstrate the effectiveness of the proposed method. In addition, the performance degradation with respect to target motion is also shown in simulation results.

A Multiband, Mutipolarization Shared-Aperture Antenna: Design and evaluation

A compact, shared-aperture antenna (SAA) configuration consisting of various planar antennas embedded into a single footprint is presented in this article. An L-probefed, suspended-plate, horizontally polarized antenna operating in an 900-MHz band; an aperture-coupled, vertically polarized, microstrip antenna operating at 4.2-GHz; a 2 × 2 microstrip patch array operating at the X band; a low-side-lobe level (SLL), corporate-fed, 8 × 4 microstrip planar array for synthetic aperture radar (SAR) in the X band; and a printed, single-arm, circularly polarized, tilted-beam spiral antenna operating at the C band are integrated into a single aperture for simultaneous operation. This antenna system could find potential application in many airborne and unmanned aircraft vehicle (UAV) technologies. While the design of these antennas is not that critical, their optimal placement in a compact configuration for simultaneous operation with minimal interference poses a significant challenge to the designer. The placement optimization was arrived at based on extensive numerical fullwave optimizations.

Efficient Blind Beamforming Algorithms for Phased Array and MIMO RADAR

In this paper, we devised two new adaptive blind beamformers based on well-known constant modulus algorithm (CMA) and least square CMA (LS-CMA). First, we improved the convergence rate of CMA and then applied Hanning window to both CMA and LS-CMA to reduce side-lobe level (SLL). These new algorithms are Hanning window CMA (HW-CMA) and Hanning window LS-CMA (HW-LS-CMA),- Simulation results show the significant improvement in the convergence rate and drastic reduction in the SLL. The proposed HW-CMA converges within less than 10 iterations and the SLLs of both algorithms are reduced below −44 dB with the improvement of 33 dB as compared to classical CMA. Hence the proposed beamformers can be used in advanced communication applications.

Passive Radar Array Processing with Non-Uniform Linear Arrays for Ground Target’s Detection and Localization

The problem of ground target detection with passive radars is considered. The design of an antenna array based on commercial elements is presented, based on a non-uniform linear array optimized according to sidelobe level requirements. Array processing techniques are applied in the cross-ambiguity function domain to exploit integration gain, system resolution and the sparsity of targets in this domain. A modified two-stage detection scheme is described, which is based on a previously-published one by other authors. All of these contributions are validated in a real semiurban scenario, proving the capabilities of detection, the direction of arrival estimation and the tracking of ground targets in the presence of big buildings that generate strong clutter returns. Detection performance is validated through the probability of false alarm and the probability of detection estimation with specified estimation errors.

Multiple moving person tracking by UWB sensors: the effect of mutual shielding persons and methods reducing its impacts

Ultra-wideband (UWB) radars are sensors allowing to track people in critical environments and situations. The results reached by single UWB sensors for such applications have shown that they are able to detect and track a person very well in a single person scenario. However, in multiple moving person scenarios, the ability of a single UWB sensor to detect several persons is usually significantly reduced. This is caused by a mutual shielding among people. In this paper, we will deal with the mutual shielding effect and its impacts, as well as with the methods of improving multiple moving person tracking by UWB radars. Firstly, we will provide a comprehensive description of the mutual shielding effect. Then, based on its analyses, we will state three complementary approaches created by the authors of this paper to reduce its impacts. They include an enhancement of the low-level echo of the targets, radar antenna array positioning at a convenient height, UWB sensor network application and, finally, their mutual combinations. The properties of those approaches will be demonstrated by two experimental measurements aimed at through wall tracking of two and three people, respectively. The results obtained in the experiments will illustrate the mutual shielding effect and the potential of the methods we have proposed to reduce its impacts.

Design and Imaging of Ground-Based Multiple-Input Multiple-Output Synthetic Aperture Radar (MIMO SAR) with Non-Collinear Arrays.

Multiple-Input Multiple-Output (MIMO) radar provides much more flexibility than the traditional radar thanks to its ability to realize far more observation channels than the actual number of transmit and receive (T/R) elements. In designing the MIMO imaging radar arrays, the commonly used virtual array theory generally assumes that all elements are on the same line. However, due to the physical size of the antennas and coupling effect between T/R elements, a certain height difference between T/R arrays is essential, which will result in the defocusing of edge points of the scene. On the other hand, the virtual array theory implies far-field approximation. Therefore, with a MIMO array designed by this theory, there will exist inevitable high grating lobes in the imaging results of near-field edge points of the scene. To tackle these problems, this paper derives the relationship between target’s point spread function (PSF) and pattern of T/R arrays, by which the design criterion is presented for near-field imaging MIMO arrays. Firstly, the proper height between T/R arrays is designed to focus the near-field edge points well. Secondly, the far-field array is modified to suppress the grating lobes in the near-field area. Finally, the validity of the proposed methods is verified by two simulations and an experiment.

RF Front-End Technologies--30 Years of Applied Research and Development [Book\/Software Reviews

The author, Mike Harris was a principal research engineer, division chief, and associate director in the Electro-Optical Systems Laboratory at Georgia Technical Research Institute. He has 40 years experience in semiconductor materials and device technology. He developed semiconductor processes for gallium nitride (GaN) high-electron-mobility transistors (HEMTs) and gallium arsenide (GaAs) pseudomorphic HEMTs (pHEMTs). The second author, Rick Sturdivant, has industry experience designing products for microwave and millimeter-wave systems. He developed the world’s first array module for phased-array radar. He is currently president of Microwave Packaging Technology, Inc. This book focuses on RF application-specific integrated circuit chip set design for active electronically scanned arrays (AESAs) for radar and communication applications in both transmit and receive modules. It condenses 30 years of applied research and development of RF front-end technologies. T/R modules technology topics covered in the text include an introduction to phased arrays in radar and communication systems, T/R modules, and module components; monolithic microwave integrated circuits (MMICs); T/R module packaging; RF interconnect materials; thermal management for T/R modules, and MMICs; T/R module manufacturing and testing; module costs; and next-generation T/R modules.

Hornet biological radar for detection, tracking, direction finding, and long distance communication: Is this possible?

The late, great entomologist, Prof. Jacob S. Ishay, from the faculty of medicine in Tel-Aviv University, dedicated his life to hornet research. He found that the hornet's body produces a considerable amount of electrical energy by means of photovoltaic and piezoelectric effects. Using an electronic microscope, Prof. Ishay showed to the authors the existence of two-dimensional arrays of very short spikes on the body skin of hornets, not unlike antenna arrays for radar and wireless communication systems. Later, Prof. Ishay and his team also found that the hornet's two antennas produce electricity and include spikes. These three radiation sources enable direction finding - even at great distances - from cooperative targets by wireless communication, allowing a new hypothesis of triangulation and an inverse GPS property for hornets. In this paper, a hypothetical biological radar for hornets is presented. In particular, we present a hypothesis regarding short spikes that may act as three phased arrays with extremely short monopole antenna elements. Due to their tiny physical dimensions, the frequency range of the antennas was estimated to be beyond 250 GHz, in the THz band. A comparison with other biological radar and direction-finding wireless communication systems is also provided.

Theoretical and Experimental Investigations on Rectangular Dielectric Resonator Antenna Array for Radar and Satellite Application

ABSTRACTIn this article, the theoretical, simulation, and experimental study of high gain dual segment 4-element linear broadside rectangular dielectric resonator antenna array shaping the -field components with copper sheet on one side, has been carried out. Copper strip connected to microstripline is introduced to excite the proposed dielectric resonator antenna array to achieve the coupling for dielectric resonator material with lower dielectric constant (≤10). Proposed antenna array with copper strip excitation has been successfully fabricated and tested. The voltage standing wave ratio, gain, and radiation characteristics of the proposed array have been explored using Ansoft HFSS 15.0 simulation software. Antenna array is also investigated using the finite-difference time-domain numerical technique. Good agreement between the simulated, calculated, and measured results is obtained. High gain and appreciable bandwidth together with low cross polarization is always defiance for researchers. The gain of the proposed array has been raised by a factor of 6.05, compared with the gain of a single dielectric resonator antenna. The proposed antenna provides a high gain of 10.50 dBi with a medium bandwidth of 512 MHz (3.44–3.95 GHz) and low cross-polarization, which is definitely better than previous reported literatures. The proposed structure is a good substitute to patch antennas in array applications as it offers high gain, medium bandwidth, and nice impedance matching. However, one disadvantage compared to microstrip arrays is the added fabrication complexity involved in having to place and bond the individual elements. In the future, for mass production applications, this process could be automated using robotic pick-and-place machines.

Optimum Partitioning of a Phased-MIMO Radar Array Antenna

In a phased-multiple-input-multiple-output radar, the transmit antenna array is divided into multiple subarrays that are allowed to be overlapped. In this letter, a mathematical formula for optimum partitioning scheme is derived to determine the optimum division of an array into subarrays and number of elements in each subarray. The main concept of this new scheme is to place the transmit beam pattern nulls at the diversity beam pattern peak sidelobes and place the diversity beam pattern nulls at the transmit beam pattern peak sidelobes. This is compared to other equal and unequal schemes. It is shown that the main advantage of this optimum partitioning scheme is the improvement of the main-to-sidelobe levels without reduction in beam pattern directivity. Also, signal-to-noise ratio is improved using this optimum partitioning scheme.