Random Radiation Field Research Articles

A High-Resolution and Robust Microwave Correlation Imaging Method Based on URRF Using MC-AAMPE Algorithm

This manuscript presents a novel framework for high-resolution and robust microwave correlation imaging. In order to generate a more diverse random radiation field distribution, the unified random radiation field (URRF) model is proposed. The URRF model can accurately characterize the joint random modulation in the signals’ phase, amplitude, and frequency. Furthermore, we build a parametric imaging model based on URRF which clearly describes the relationship between the image to be reconstructed and the signals by the URRF model. By using this imaging model, the reconstruction of an image is converted into solving a multi-parameter optimization problem with multiple constraints. To solve this optimization problem with high efficiency and accuracy, the model-constrained adaptive alternating multiple parameter estimation (MC-AAMPE) algorithm is proposed. This algorithm decomposes the high-dimensional multi-parameter optimization problem into several sub-optimization problems. The renewing solutions to these sub-optimization problems make the multi-parameter optimization converge to the image of the target and the parameters of clutter and noise, which are all unknown before the solution. In comparison with the existing methods, the proposed scheme generates images with higher resolution and is more robust under noise conditions. Extensive simulation experiments confirmed the effectiveness and robustness of the proposed method.

Polarization microwave correlation imaging method based on orthogonal complement space

AbstractCurrently, microwave correlation imaging (MCI) is regarded as an important method to address the forward‐looking imaging problem in radar. The key step of this method is to form a spatio‐temporal two‐dimensional random radiation field through various means. However, the current methods do not consider the polarization domain, which is an important dimension of electromagnetic signals. The existing research mainly focuses on using polarized antenna elements, without incorporating polarization information into the imaging system. To fill this gap, this letter proposes the polarization microwave correlation imaging (PMCI) based on the orthogonal complement space, which performs instantaneous polarization measurements (IPM) while correlating imaging of the target. Through simulation analysis, this method can further improve the quality and anti‐interference ability of MCI. Moreover, under the condition of low time‐frequency product, the peak sidelobe level (PSL) and isolation of this method are approximately 3.5 dB and 12.5 dB higher than those of traditional instantaneous polarization measurement methods (TIPM).

A circular‐polarized and high‐gain microwave correlation imaging antenna based on rotating elements

In this article, a circular-polarized microwave correlation imaging antenna which is based on rotating elements is presented. The proposed reflect array consists of the circular-polarized patches, the filling substrates, and the grounded metal plates. It is known that the key to microwave correlation imaging is the construction of a two-dimensional random radiation field in space. Reflect array antennas use element rotation to achieve phase compensation, different compensation phases can be achieved through different rotation angles of elements, the rotation angle of the element is more random, and a more stray pattern for microwave correlation imaging can be obtained. In the reflector array, every single patch is randomized the rotation angle within a certain range, then a 25 × 25 unit random array is obtained by using HFSS-MATLAB co-simulation. The effective area of the feed source irradiated on the reflector is certain each time, so the use of different units to compensate for the difference in phase can make the pattern group obtained with high randomness. For verification, a sample with the overall size of 450 mm × 450 mm is designed, fabricated, and measured. When the feed source and the array move relative to each other, the correlation between the directional patterns is mainly concentrated between 0.5 and 0.8. The radiation field is sufficiently random, and the gain of the pattern can be reached 15 dB when the operating frequency is 12.5 GHz, which can effectively obtain high-quality imaging results.

Low-Cost Metamaterial Antennas: Forward-Looking Imaging Experiment and Analysis.

A phase error correction method is proposed to compensate for the phase error in super-resolution correlated imaging based on metamaterial antennas. The varying carrier frequencies of a metamaterial antenna can generate the random radiation field for super-resolution correlation imaging, but the variation of the signal carrier frequency leads to large phase errors in the imaging results. In this proposed method, the sampling matrix in the super-resolution correlated imaging algorithm is used to compensate for the phase errors. Each element of the matrix is multiplied by a compensation phase corresponding to the phase error, and the error is subtly removed from the algorithm. In the experiment, the antenna pattern at each frequency of the metamaterial antenna is measured and recorded. In addition, an external field experiment is also carried out, and the collected data are imaged with the improved algorithm. Experimental results show that this technology can effectively solve the effect of phase errors on imaging results caused by signal carrier frequency changes.

3D Imaging Method Based on Digital Coding Metasurface With Unknown Mutual Coupling

Three-dimensional (3D) imaging based on metamaterial radar system is a cutting-edge technique which elevates the hardware burden in traditional real-aperture radar and synthetic aperture radar (SAR), particularly with the enhanced systematic degree of freedom (DOF) by the emerging technique of digtal coding metasurface. This paper proposes a single-channel real-aperture 3D imaging method based on digital coding metasurface, which is simple and low-cost. The proposed system can generate random radiation field, and the target scene can be obtained by sparse reconstruction as in microwave correlation imaging (MCI) system. In this paper, we first establish the system signal model. Then, we propose the index of the DOF of the radiation field, and propose the accordingly optimization method by optimizing the digital code. And in practical applications, the coupling between metamaterial units introduces additional signal components, which affects the quality of the sparse recovery. In order to solve the coupling problem, we take the coupling coefficients into account in the priori assumptions for all the parameters in the sparse Bayesian learning, and use the maximum posterior probability method to estimate the unknown parameters. Iteratively, the MCI model can be updated with the obtained coupling information, guaranteeing a more accurate reconstruction of the target scene. The simulation results prove the effectiveness of our method.

Microwave Correlation Forward-Looking Super-Resolution Imaging Based on Compressed Sensing

Forward-looking correlated imaging plays an increasingly important role in modern radar imaging systems. It overcomes disadvantages of traditional side or squint synthetic aperture radar (SAR) which is dependent on specific relative motion between the radar and target scene. A new microwave forward-looking correlated 3-D imaging method based on random radiation field combined with sparse reconstruction is proposed in this article. Firstly, phased array radar (PAR) is adopted to form different and random antenna patterns. Then, combined with the compressed sensing (CS) theory, the target image can be recovered with very few samples which can break through Rayleigh resolution limitation. Furthermore, the proposed method can achieve resolution at least 5.5 times higher than real aperture imaging. To raise computation efficiency of sparse reconstruction, an improved quasi-Newton iteration method based on graphics processing unit (GPU) platform is developed. Meanwhile, a GPU-based (NVIDIA Tesla K40c) accelerated computing method can significantly reduce the processing time compared with the time given by a personal computer (PC). Both simulation and field experiment verify the validity of the proposed method.

Mixed Mode Radar Coincidence Imaging With Hybrid Excitation Radar Array

A novel mixed mode radar coincidence imaging (MMRCI) system, which combines the coherent radar detection and incoherent radar coincidence imaging function during the radar coincidence imaging (RCI) process, is presented in this paper. The target location function of the MMRCI system gives the target position information synchronously with imaging tests, and this makes the MMRCI work independently with low target position estimation error. In the MMRCI system, the resolution of target distance estimation is proportional to the whole bandwidth assisted by the double-frequency linear frequency modulation (DFLFM) signal when the occupied bandwidth of the DFLFM signal is less than one-tenth of the whole bandwidth. The target position estimation error caused by the target motion can be reduced effectively so that the image quality of the moving target can be guaranteed in a longer detection time. The RCI is reconstructed using the incoherent part of the transmitting signal. A general relationship between the spatial correlation of the random radiation field in the imaging plane and the deployments of linear random source is analyzed in the paper. The imaging efficiency is ensured through the grading imaging method based on the imaging requirement. The effectiveness of the MMRCI method is validated via a set of simulations and experiments, including superresolution RCI of both stationary and moving targets in various scenes using the convex optimization algorithms.

Resolution Analysis of Spatial Modulation Coincidence Imaging Based on Reflective Surface

The spatial modulation coincidence imaging (SMCI), as a novel kind of microwave coincidence imaging method, is proposed in this paper. The SMCI system provides a new way to produce the time-space independent signal instead of multitransmitter architecture with wideband randomly modulated signal in radar coincidence imaging. Due to some special features, metamaterial plate is utilized as the reflective surface to modulate the incident signal to construct random radiation field. The resolution of SMCI system is analyzed under large viewing angle with two different transmitting signals. Reflective surface is nonuniformly divided to derive the expression of resolution. The analysis results show that the resolution of SMCI system is mainly determined by the size of reflective surface and center frequency, which is similar to the traditional aperture. The SMCI system is low cost and flexible in design. Simultaneously, it can avoid the synchronization problem between subsources. Moreover, the SMCI system can achieve the resolution of space target through single transmitter–single receiver radar system. High-resolution image can be reconstructed since the tests are nonlinear. Finally, a series of simulation experiments is presented based on the nondirect-viewing scene we proposed. Using the algorithm based on a compressed sensing theory, we reconstructed the target image with high resolution.

Correlation functions for homogeneous, isotropic random classical electromagnetic radiation and the electromagnetic fields of a fluctuating classical electric dipole.

The two-point field correlation functions for homogeneous and isotropic random (Gaussian) classical electromagnetic radiation are shown to be related to the electromagnetic fields of a fluctuating electric dipole. The relationships derived between these two quantities are useful in calculations involving classical electric dipole oscillators bathed in classical electromagnetic radiation. Using these relationships, the van der Waals force is evaluated for a harmonic dipole oscillator that is a member of an arbitrary configuration of N oscillators, all of which are bathed in thermal plus zero-point classical electromagnetic radiation. Also, the expectation value of the Poynting vector is shown to be unchanged from its null value when a classical harmonic dipole oscillator is included within a classical electromagnetic isotropic and homogeneous random radiation field. A sketch is given as to how these calculations may be carried over to the case of a system of harmonic dipole oscillators uniformly accelerating through classical electromagnetic zero-point radiation. What enables these calculations to be extended to the situation of acceleration through zero-point radiation is a recent finding that the two-point field correlation functions, evaluated along trajectories described by uniform acceleration through classical electromagnetic zero-point radiation, are related to the electromagnetic fields of a uniformly accelerating electric dipole.