| Nowadays,the world is completing the leap from the Internet of everything to the smart connection of everything.Behind the smarter daily life,the transmission of massive data is indispensable,and the communication field is facing more unprecedented pressure and challenges.The ability of traditional technologies to improve the efficiency of communication systems can no longer meet the rapidly growing demand for communication capacity.In recent years,orbital angular momentum technology has provided a new idea for the application of electromagnetic waves in the field of communication and radar imaging.The electromagnetic waves carrying orbital angular momentum become vortex electromagnetic waves with a spiral phase structure,and this feature can be used to effectively improve the efficiency of communication systems and improve the performance of radar imaging.In this paper,from the principle of orbital angular momentum,combined with modern antenna and radar imaging technology,we study how to design an antenna that can radiate vortex electromagnetic waves and the use of orbital angular momentum technology to achieve high-resolution radar imaging and other aspects,which are arranged as follows.At first,this paper designs a reconfigurable vortex antenna based on RF switch for the problem that the current vortex antenna produces a single mode and cannot switch modes in real time.Based on the four-array array antenna,the phase-shifted feed network is designed to complete the equal-phase difference feed to the array elements,and the RF switch is loaded in each feed line,and the RF switch is driven by the control circuit to realize the real-time reconfiguration of the phase-shifted feed network,and the dynamic switching of the three modes is realized at 2.4GHz.The proposed antenna is simulated and processed for testing.The feasibility of the design is verified by experiments.The proposed scheme has a simple structure,is easy to design and deploy,and is of great significance for the application of vortex electromagnetic waves in the field of communication and radar imaging.Then,this paper addresses the problem that the existing ways of generating highmode vortex electromagnetic waves using parabolic antennas and array antennas require larger size and more array elements,which have many limitations in practical application in engineering,and designs six different sizes of elliptical ring microstrip patch vortex antennas from the perspective of eigenmode theory,which can generate different In the case of fixed antenna structure form,the vortex electromagnetic wave of different modes can be generated by designing different sizes.The simulation results and the actual test results in microwave darkroom show that this method can effectively generate different modes of vortex electromagnetic waves.Compared with the form of array antenna to generate vortex electromagnetic waves,the size of the antenna is greatly reduced,and it is easier to load and integrate into the communication system.In addition,this paper researches and sorts out the existing methods for generating vortex electromagnetic waves by array antennas.By analyzing the effects of different array radii and observed pitch angles on the modes,and conducting simulations and practical processing tests,it is found that the mixed stacked modes can be clearly demonstrated by the mode-weighting design and the electric field phase characteristics of the two modes inside and outside the separation can be clearly observed.By this method,the electric field plane phase of the array vortex antenna radiation can be specially designed to present one mode in the circular region near the propagation axis and another mode outside the circular region.This proposed technique is of great importance for the study of array vortex antennas applied in the field of communication and radar imaging.Finally,this paper designs a SPECAN-based EM vortex synthetic aperture twodimensional imaging method.The application of electromagnetic vortex to condensed radar to improve imaging resolution has been widely studied.In the application of vortex electromagnetic waves to synthetic aperture radar imaging,most studies have focused on single-mode electromagnetic vortex synthetic aperture radar imaging,i.e.,fixed-mode vortex electromagnetic waves are used in the imaging process,while less research has been conducted on mode-time-varying electromagnetic vortex synthetic aperture radar imaging.In this paper,we design a SPECAN-based time-varying modal electromagnetic vortex SAR imaging method to compare planar electromagnetic wave SAR imaging,compensate and further process some factor terms related to orbital angular momentum,complete the modal time-varying electromagnetic vortex SAR two-dimensional imaging,and verify the performance of electromagnetic vortex imaging azimuthal high-resolution imaging. |
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