A new method to generate ultrahigh-power microwave pulses compatible with mildly relativistic electron sources is proposed. This method involves a novel microwave compressor in the form of a metal helically corrugated waveguide, which can enhance the power of frequency-modulated nanosecond pulses up to the multigigawatt level. The results of the proof-of-principle experiments at kilowatt power levels are in good agreement with theory.

Compression of Frequency-Modulated Pulses using Helically Corrugated Waveguides and Its Potential for Generating Multigigawatt rf Radiation

The untunable bandgap is a difficult problem for Bragg structures constructed from corrugated metallic waveguides, and becomes a major barrier for applications. Based on the coupled-mode theory, this paper presents the principle as well as a corresponding theoretical model of bandgap control of two-dimensional coaxial Bragg structures under the condition of a fixed ripple shape. It is shown that such control can be achieved by varying the angular deviation between the outer and inner corrugations, which can be done by rotating one of the conductors relative to the other. The effects of the proposed method on transmission bandgap control of two example structures were investigated by theoretical analysis and electromagnetic simulation. The results confirmed the validity of the proposal, and showed that such a control method can be used to manipulate the number and location of the working bands under multiple bandgap operation. These peculiarities provide potential applications of two-dimensional coaxial Bragg structures in constructing tunable passive and active high-power microwave devices.

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Bandgap Control of Two-Dimensional Coaxial Bragg Structures With Helically Corrugated Conductors

The introduction of orthogonal frequency division multiplexing (OFDM) and multiple input multiple output (MIMO) technology enables the new generation of the Internet of Vehicles to have the ability to integrate wireless communication and target tracking. Based on the new Internet of Vehicles, a cooperative convolutional neural network with data-importance-aware (DIA) is proposed.We use wireless channel state information (CSI) to construct a micro Doppler feature data set. A distributed collaborative machine learning method of DIA is proposed to realize the target recognition of the vehicle. Experimental results show that the vehicle recognition accuracy of the proposed method is higher than 95%, and the convergence speed of the machine learning model is improved. 

CSI-based Vehicle target recognition and Collaborative CNN with Data-Importance-Aware

The introduction of orthogonal frequency division multiplexing (OFDM) and multiple input multiple output (MIMO) technology enables the new generation of the Internet of Vehicles to have the ability to integrate wireless communication and target tracking. Based on the new Internet of Vehicles, a cooperative convolutional neural network with data-importance-aware (DIA) is proposed.We use wireless channel state information (CSI) to construct a micro Doppler feature data set. A distributed collaborative machine learning method of DIA is proposed to realize the target recognition of the vehicle. Experimental results show that the vehicle recognition accuracy of the proposed method is higher than 95%, and the convergence speed of the machine learning model is improved.

Based on the mode-coupling method, comparative study is carried out for the influence of different ripple depths and different ripple angles on bandwidth and centre frequency shift characteristics operating at THz high-frequency coupling mode. The results show that the bandwidth of the working mode and the competing mode increases with the increase of the slot depth, but the centre resonance frequency almost does not shift; With the increase of the slope angle, the centre frequency of the working mode almost does not shift, while the centre frequency of the competing mode will be far away from the centre frequency of the working mode, and the farther the deviation is with the increase of the slope angle. These characteristics are conducive to better suppress the band gap overlap and construct the Bragg structure with single high-order mode at THz frequency.

The Influence of Ripple Depth and Ripple Taper on Bandwidth and Centre Frequency Shift Operating at Terahertz Frequency in a Coaxial Bragg Structure

With the continuous development of social economy, private cars have become more and more, and the traffic pressure is also increasing. To more accurately recognize vehicles violating traffic rules, the problem of recognition and optimization of license plate targets has become an urgent task with certain practical significance and guiding significance. In this paper, the license plate recognition (LPR) system is taken as the main research object, which is improved and optimized. Firstly, an improved neural network model is established by applying the improved convolutional neural network (CNN) algorithm to the license plate recognition system and based on the improved activation function, and the relevant experimental results are obtained; meanwhile compared with the traditional CNN model, the corresponding experimental results are obtained; finally, the experimental conclusions are obtained, i.e., the LPR system using improved CNN algorithm has better performance in recognizing license plate target and can more accurately recognize licence plates which are shielded. Therefore, the improved neural network model has great development potential in the application of the LPR system.

Recognition Optimization of License Plate Targets Based on Improved Neural Network Model

Making use of field expansion and the equivalent boundary, an analytical model is set up to describe the multi-mode intercoupling in two-dimensional coaxial Bragg structures with either one or both of the conductors corrugated with helical ripples. The coupled-mode equations and the explicit formulae of the coupling coefficients for all possible mode combinations are derived, and the general mode coupling rules are discussed. Based on the analytical model, the dependence of the coupling coefficients on structural parameters of the two-dimensional coaxial Bragg structures with overmoded operation is investigated by numerical calculation. The results show that the additional conductor provides more flexibility for adjustment of coupling coefficients compared with other types of two-dimensional Bragg structures with a single conductor. Taking advantage of this feature, a two-dimensional coaxial Bragg structure can provide strong reflection with high mode purity under overmoded operation by suppressing the parasitic coupling using an optimized combination of corrugated outer and inner conductors. In this way, the structure has potential applications in the design of high-Q improved Bragg resonators for high-power microwave oscillators operating in the millimeter wave or terahertz range.Making use of field expansion and the equivalent boundary, an analytical model is set up to describe the multi-mode intercoupling in two-dimensional coaxial Bragg structures with either one or both of the conductors corrugated with helical ripples. The coupled-mode equations and the explicit formulae of the coupling coefficients for all possible mode combinations are derived, and the general mode coupling rules are discussed. Based on the analytical model, the dependence of the coupling coefficients on structural parameters of the two-dimensional coaxial Bragg structures with overmoded operation is investigated by numerical calculation. The results show that the additional conductor provides more flexibility for adjustment of coupling coefficients compared with other types of two-dimensional Bragg structures with a single conductor. Taking advantage of this feature, a two-dimensional coaxial Bragg structure can provide strong reflection with high mode purity under overmoded operation by suppressing the pa...

Coupled-mode analysis for two-dimensional coaxial Bragg structures with helical ripples

The transmission characteristics of a two-dimensional coaxial Bragg structure have been investigated in this paper The dielectric layer between the outer and the inner conductors of the coaxial waveguide in the structure is helically corrugated and the grooves are loaded with a metallic strip It is found that, a dominant transmission bandgap can be obtained from the mode conversion induced by the axial and azimuthal periodicities of the hybrid filling media, and its location can be controlled by the axial period of the helical grooves These peculiarities can be employed in the applications of tunable notch filters, high-s resonators, mode converters and etc

Transmission bandgap of a two-dimensional coaxial Bragg structure with hybrid filling media

As an important member of periodic structures family, Bragg structures are widely employed in the many active and passive microwave devices, such as reflectors, couplers, filters and mode converters. In this paper, the transmission characteristics of a two dimensional coaxial Bragg structure with double frequency selective surfaces are investigated, where both of the inner and outer conductors are corrugated with helical ripples. Numerical results reveal that the transmission bandgap can be controlled by the relative angular position of the inner and outer conductors. This peculiarity may lead to potential applications of these structures in constructing tunable microwave devices.

Ying-Xin Lai

Papers

Recognition Optimization of License Plate Targets Based on Improved Neural Network Model

Coupled-mode analysis for two-dimensional coaxial Bragg structures with helical ripples

Bandgap Control of Two-Dimensional Coaxial Bragg Structures With Helically Corrugated Conductors

Transmission bandgap of a two-dimensional coaxial Bragg structure with hybrid filling media

Studies of a Two-dimensional Coaxial Bragg Structure with Double Helically Corrugated Surfaces