Shitao Zhu

Radar Coincidence Imaging With Random Microwave Source

The radar coincidence imaging (RCI), as a novel radar imaging method, is presented in this letter. Firstly, the relationship between the deployment of general random microwave array source and the resolution of RCI under second-order correlation methods (SOCM) is presented. Then, the super-resolution RCI is obtained assisted by optimization algorithms based on the matrix form of measurement data. Finally, the mirror phenomenon of RCI, which is caused by the spacing of radar elements, is presented. In experiments, we form RCI using uniform 1-D antenna array with random phase and random amplitude modulated excitation signal for each radar element. The proposed analysis is validated through numerical simulations and experiments.

Threshold Analysis of Loop-Delay Estimation Using Correlation Functions for Double-Carrier Signals in Digital Predistortion Subsystem

For wideband configuration double carrier (WCDC) signals, a novel phenomenon is analyzed in this paper, i.e., when the data rate is lower than a threshold, the integer loop-delay estimation (ILDE) accuracy sharply declines when traditional time-delay estimation methods are used in a digital predistortion subsystem. Assisted by the equivalent bandwidth of a single-carrier signal, a proposed cross-correlation model for WCDC signals is built to analyze the low data-rate threshold in the ILDE. The relationship between a low data-rate threshold, carrier spacing, carrier bandwidths, and the power difference is analyzed. The proposed method is qualified to estimate the low data-rate threshold for the ILDE methods, including the state of the art. Experiments and simulations are presented to validate the proposed method using three typical communication signals.

Ghost Imaging Based on Deep Learning

Even though ghost imaging (GI), an unconventional imaging method, has received increased attention by researchers during the last decades, imaging speed is still not satisfactory. Once the data-acquisition method and the system parameters are determined, only the processing method has the potential to accelerate image-processing significantly. However, both the basic correlation method and the compressed sensing algorithm, which are often used for ghost imaging, have their own problems. To overcome these challenges, a novel deep learning ghost imaging method is proposed in this paper. We modified the convolutional neural network that is commonly used in deep learning to fit the characteristics of ghost imaging. This modified network can be referred to as ghost imaging convolutional neural network. Our simulations and experiments confirm that, using this new method, a target image can be obtained faster and more accurate at low sampling rate compared with conventional GI method.

Robust time delay estimation based direction finding in lp-space

ABSTRACT A robust time delay estimation (TDE)-based direction-finding method for multipath signals in the presence of impulsive noise is proposed in this paper. Compared to traditional algorithms, developed for Gaussian distribution, this method performs more robust in the presence of non-Gaussian noise. The robust TDE is first obtained by utilising the matched filtering in -space which is less sensitive to outliers. Then direction-of-arrival (DOA) is estimated by ‘steering vector fitting’ approach based on the delay estimates. An iterative approach is employed to estimate each multipath component separately and improve the estimation accuracy. The method is developed in -space, which minimises the -norm of residual fitting error vector instead of the Frobenius norm. The number of antennas required can be less than that of the sources. Simulation results show that the method outperforms several outliers-resistant algorithms both in cases of impulsive noise and Gaussian distribution noise.

A high-efficiency loop delay estimator in digital predistortion subsystem

A high-efficiency time delay estimation method is presented to obtain the accurate loop delay (including integer and fractional loop delay) between the input signal and the time delayed feedback signal in digital predistortion subsystem within the same process. Compared with the conventional, a sampling position adjusting scheme for complex signals using the piecewise-parabolic filter assisted by a steady decision criterion for limited data length achieves a significant reduction in time complexity and an improvement in loop delay estimation stability and precision. Results from simulations and experiments show that the proposed method is high-efficiency and valid.

Self-Adaption Matched Filter and Bi-Directional Difference Method for Moving Target Detection

In this paper, a self-adaption matched filter (SMF) and bi-directional difference techniques are proposed to detect a small moving target in urban environments. Firstly, the SMF technique is proposed to improve the signal-to-interference-noise ratio (SINR) by using the power factor. The properties of the transmitting signal, the target echoes and the interference and noise are considered during the power factor generation. The amplitude coherent accumulation technique that extracts the coherent amplitude information of echoes after being processed by the SMF, is used to improve the SINR based on multiple measurements. Finally, the bi-directional difference technique is proposed to distinguish the target echoes and the interference/noise. Simulations and experiments are conducted to validate and demonstrate that small moving targets can be detected with high probability using the proposed method in urban environments, even with just one measurement.

Radiation Pattern Reconfigurable Waveguide Slot Array Antenna Using Liquid Crystal

In this paper, we proposed a radiation pattern reconfigurable waveguide slot array antenna using liquid crystal (LC). Together with the waveguide slot, the designed complementary electric-field-coupled resonator functions like a switch controlled by the dielectric constant of the LC, which can control the antenna element to radiate or not. Thus, the array factor and radiation pattern can be manipulated. The proposed antenna was simulated, fabricated, and measured. Its radiation direction can be reconfigured to 46° or 0° at about 15 GHz.

Cross-polarization suppression in C-shaped microstrip patch antenna employing anisotropic dielectrics

An anisotropic dielectric realized by layered ceramic structures was adopted to design a low cross-polarization C-shaped patch antenna. The anisotropic dielectric performs as a substrate and can cause additional cross-polarized fields which are able to cancel the cross-polarized fields generated by the C-shaped patch itself, and then reduce the cross-polarization level. Compared to the C-shaped patch antenna with an isotropic substrate, the cross-polarization of the proposed antenna is suppressed by more than 15dB with a little gain enhancement at 2.4GHz. The anisotropic dielectric has a little impact on the direction of the C-shaped patch antenna. The gain of the proposed C-shaped patch antenna is 6.8dB with a cross-polarization of −28dB.

Broadband Circular Polarizer Based on Plasmon Hybridizations

This paper presents a broadband circular polarizer with a ring/disk cavity structure, which is a broadband application of plasmon hybridizations. The proposed design can convert a linearly polarized wave to a circularly polarized wave from 12.66 GHz to 17.43 GHz within a bandwidth of 30%. The broadband polarization conversion characterization results from the different plasmon hybridization modes induced in the ring/disk cavity. The proposed broadband circular polarizer is demonstrated by both full-wave simulation and measurement.

Analysis of High-Efficiency Cross-Polarized Converter at Oblique Incidence

In this letter, we present a theoretical study on a cross-polarized converter based on the reflective metasurface that is composed of slanted metallic cut-lines on a perfect electrical conductor backed substrate. According to the model, although reflection and refraction laws are still applicable in the interface between the air and the substrate, the metallic cut-lines break the original boundary condition. In order to describe the broken boundary condition, the generalized Fresnels formulas are established based on the traditional Fresnels formulas and the induced radiation of the metallic cut-lines. Finally, multiple reflections and refractions are resulted from the back metallic sheet in the interface of metallic cut-lines, and the total reflected wave is obtained by summing all waves except the incident wave in air. The theoretical results agree well with the simulated and measured results at the oblique incidence. When incidence angle varies from 0° to 25°, the metasurface can convert more than 99% incident wave into its cross-polarized reflected wave within a relative bandwidth of 22%.