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Axis coincidence consideration is necessary in the design of gyrotron solenoids; besides, radial field component strongly affects the performance of gyrodevices owing to the transverse particle–wave interaction mechanism in it, especially for high-frequency operation. In this article, the theory of multiple eccentric coils is derived. It is capable of calculating the off-axis field inside the solenoid with specified displacement and tilt. Numerical calculations are validated by 3-D electromagnetic simulation methods. Based on the measured magnet field, the displacement and tilt of a three-coil magnet system are successfully predicted with a global optimization algorithm, and then, the magnet system is well calibrated using a pair of flanges. [ABSTRACT FROM AUTHOR]

This article proposes a scheme to design a broadband low-profile monopulse comparator for the dual-circularly polarized feeder. For obtaining a compact and easily integrated structure, a monopulse comparator with a ring-shaped symmetrical planner topology is proposed by using the 3 dB coupler and the phase shifter based on the groove gap waveguide (GGW). Then, in order to achieve the equal-amplitude distribution in a broad bandwidth, the asymmetrical coupling structure and the novel dispersion-matched transition are proposed to improve the directivity of a 3 dB coupler. Moreover, a ridge waveguide with periodic grooves featuring stable dispersion change is adopted to design the phase shifter, which contributes to obtain an accurate phase control in the broad frequency band. To validate experimentally the broadband performance, a dual-circularly polarized four-horn feeder with two identical monopulse comparators is designed and fabricated. The results show that the symmetrical radiation patterns with 32 dB null-depth can be obtained from 27 to 31 GHz. The monopulse comparator characterizes broad bandwidth, low loss, and a compact size, which provides a monopulse comparator with accurate amplitude/phase control for the research of the monopulse antenna. [ABSTRACT FROM AUTHOR]

Traditional waveguide Magic-T development typically explores suitable combinations of waveguide $E$ - and $H$ -plane T-junctions, which causes its inevitable bulky volume and limited integratability. Aiming at this difficulty, this letter evolves a novel hybrid Magic-T to provide a substitute option. The proposed configuration uses a universal rectangular waveguide (RW) as a sum port for input, and two microstrip probes are inserted in its $E$ -plane and distributed symmetrically along the $E$ -field-max axis to form the output ports. Then, the difference port connected by two coupling slits is placed on the opposite side of the microstrip probes. Therefore, this structure has a very compact size and the ability to integrate directly with the active chips because it avoids the use of waveguide T-junctions and employs a microstrip outputs setup. A Magic-T prototype has been fabricated and measured, and the results show great performance across the entire 26–40 GHz (Ka-band), including low loss, high isolation, and good amplitude/phase consistency. [ABSTRACT FROM AUTHOR]

In this article, a compact mode selection filter and a mode converter for the 0.22-THz sheet beam traveling-wave tube (SB-TWT) has been proposed, fabricated, and tested to realize selective absorption of high-order mode without interference on the working mode. The reasonable structure and placement is explored from theory to manufacturing method in order to minimize reflection and mode distortion by junction discontinuity. Two proof-of-concept prototypes have been fabricated and tested to analyze the error sources in terahertz device. And the corresponding error models are also constructed. Final transmission data exhibit an excellent agreement with the results of computer simulations when conductor loss is taken into consideration. Such −15-dB loss performance for high-order mode is verified allowing to cover the frequency band from 0.3 to 0.315 THz. [ABSTRACT FROM AUTHOR]

Recent hot test details and inspiring results of the W-band lossy-dielectric-loaded gyrotron traveling-wave tube (gyro-TWT) developed at the University Electronic Science and Technology of China (UESTC) are reported in this letter. Measurement of the gyro-TWT had achieved a pulse output power over 100 kW with a broad bandwidth of 8.5 GHz (92.0~100.5 GHz). For the first time as we know, the W-band gyro-TWT can stably operate with a 10% duty cycle and the average output power is over 10.3 kW in the frequency range. Excellent stability, pure spectrum and mode patterns are all verified in the hot test experiment. [ABSTRACT FROM AUTHOR]

Recently, the compression and deployment of powerful deep neural networks (DNNs) on resource-limited edge devices to provide intelligent services have become attractive tasks. Although knowledge distillation (KD) is a feasible solution for compression, its requirement on the original dataset raises privacy concerns. In addition, it is common to integrate multiple pretrained models to achieve satisfactory performance. How to compress multiple models into a tiny model is challenging, especially when the original data are unavailable. To tackle this challenge, we propose a framework termed collaborative data-free knowledge distillation via multi-level feature sharing (CDFKD-MFS), which consists of a multi-header student module, an asymmetric adversarial data-free KD module, and an attention-based aggregation module. In this framework, the student model equipped with a multi-level feature-sharing structure learns from multiple teacher models and is trained together with a generator in an asymmetric adversarial manner. When some real samples are available, the attention module adaptively aggregates predictions of the student headers, which can further improve performance. We conduct extensive experiments on three popular computer visual datasets. In particular, compared with the most competitive alternative, the accuracy of the proposed framework is 1.18% higher on the CIFAR-100 dataset, 1.67% higher on the Caltech-101 dataset, and 2.99% higher on the mini-ImageNet dataset. [ABSTRACT FROM AUTHOR]

In this article, a high-isolation power divider with ultrawideband characteristics for simultaneous operation in two adjacent bands is proposed. The power divider is developed based on a four-port coplanar Magic-T. The difference port of the Magic-T consists of a double-ridge gap waveguide (RGW) that supports quasi-TEM mode transmission, which provides the benefit of its broadband characteristics and allows for facilitated assembly. In addition, an inline microstrip line (MSL) containing a probe is inserted into the opposite side of the difference port to form the sum port. This basic configuration has actually achieved high isolation between the output arms and low return loss at each port, and however, its isolation bandwidth is limited by the narrowband matching of the sum port. To overcome this difficulty, a three-port microstrip T-junction is connected in series to the sum port of the Magic-T, resulting in a five-port 3-dB power divider with a wide isolation bandwidth. The process of considering this solution is analyzed and explained in detail in this article and the corresponding simulations and experimental verifications are performed. According to the obtained results, the proposed power divider has excellent overall performance, in particular low loss, ultrawideband, high isolation, and good amplitude/phase consistency. [ABSTRACT FROM AUTHOR]

In this paper, we present a neural network-based framework to compensate for the nonlinear distortion of high-speed continuous variable quantum key distribution (CV-QKD) systems. In practice, the nonlinear impairment of imperfect devices could bring interference to the measured quadrature values and thus compromise the parameter estimation procedure and the secure key rate. Specifically, for a high-speed CV-QKD system, the balanced homodyne detector (BHD) and the following analog-to-digital converter are the primary sources of nonlinear impairment. The nonlinear distortion effect will be more pronounced as the pulse repetition rate increases. We propose an autoencoder-based network to learn the inner patterns of distorted data and then compensate the quadrature measurements in real-time at the receiver’s side. The numerical simulation demonstrates that the excess noise induced by nonlinear impairment is reduced to the $10^{-3}$ level in the shot noise unit. Consequently, such a software approach has the ability to significantly boost the bandwidth efficiency of the BHD and the secure key bit rate. [ABSTRACT FROM AUTHOR]

High control bandwidth is usually restricted in a photoelectric tracking system (PTS) based on a Charge-Couple Device(CCD) with time delay, which hinders a good tracking performance. Generally, a model-based delay-compensation controller called Smith predictor (SP) can help increase the controller gain to promote the bandwidth by separating delay from the control loop. However, the performance promotion is insufficient because the delay still stays in the forward channel which causes errors between output and input. And the increase of the controller gain is still limited due to the effect of model mismatch on stability. In this paper, to solve the problems, a delay-compound-compensation control (DCCC) based on improved SP by trajectory prediction and velocity feedforward is proposed. The additional trajectory prediction is used to further eliminate the effect of delay existing in the forward channel. The additional velocity feedforward is used to further reform the transfer characteristics limited by the controller gain. A Kalman filter-based design method of trajectory prediction is presented and the optimal design principle of feedback and feedforward controllers is given in the face of model mismatch. Experiments demonstrate that the DCCC is valid and could greatly promote the tracking performance in the low frequency. [ABSTRACT FROM AUTHOR]

Overall design and cold test of a G-band gyrotron traveling-wave tube (gyro-TWT) amplifier are presented. This gyro-TWT aims at achieving a goal of 10-kW pulse output power in the range of 210–220 GHz. It is operated in a circular TE01 mode at the fundamental cyclotron harmonics, which is driven by a 50-kV, 3-A gyrating electron beam. Low velocity spread diode-type magnetron injection gun (MIG), multichannel TE01 mode input coupler, broadband metasurface output window, and lossy material loaded beam–wave interaction circuit are simulated and partially measured. Particle-in-cell (PIC) simulation shows that the designed gyro-TWT can achieve a saturated output power over 10 kW in the range of 210–228 GHz with a beam velocity spread of 2.29%. [ABSTRACT FROM AUTHOR]

Solving constrained multiobjective optimization problems brings great challenges to an evolutionary algorithm, since it simultaneously requires the optimization among several conflicting objective functions and the satisfaction of various constraints. Hence, how to adjust the tradeoff between objective functions and constraints is crucial. In this article, we propose a dynamic selection preference-assisted constrained multiobjective differential evolutionary (DE) algorithm. In our approach, the selection preference of each individual is suitably switching from the objective functions to constraints as the evolutionary process. To be specific, the information of objective function, without considering any constraints, is extracted based on Pareto dominance to maintain the convergence and diversity by exploring the feasible and infeasible regions; while the information of constraint is used based on constrained dominance principle to promote the feasibility. Then, the tradeoff in these two kinds of information is adjusted dynamically, by emphasizing the utilization of objective functions at the early stage and focusing on constraints at the latter stage. Furthermore, to generate the promising offspring, two DE operators with distinct characteristics are selected as components of the search algorithm. Experiments on four test suites including 56 benchmark problems indicate that the proposed method exhibits superior or at least competitive performance, in comparison with other well-established methods. [ABSTRACT FROM AUTHOR]

This article proposed an overmoded waveguide method (OWM) for more accurate measurement of dielectric properties in the subterahertz and terahertz band. Compared with the traditional standard waveguide method (SWM), the OWM is beneficial to alleviate the significant error caused by the air gap. Simulation predicts that for typical medium permittivity and loss materials, the relative errors of $\varepsilon _{r}$ and tan $\delta $ can be reduced from 10% to below 3% using the OWM with an overmoded factor of 3 when the air gap is 0.02 mm at W-band. When extending the overmoded factor over 5, the relative error can be reduced below 1.5%. The tolerance improvement was verified by measuring a polytetrafluoroethylene (PTFE) sample through SWM and OWM. Experimental results show the relative error of $\varepsilon _{r}$ is lower than 5% even when there exists a 0.24-mm air gap in the OWM. [ABSTRACT FROM AUTHOR]

Highly oversized mode converters are the critical devices for high power millimeter-wave transmission systems, characterizing high power capacity and low loss. In order to improve the conversion efficiency from TE01 to TE11 mode, the mode coupling mechanism of oversized elliptical waveguides is explored, and an optimal ellipticity interval to obtain the high conversion efficiency is deduced by analyzing the mode coupling capacity. Considering that ellipticity can affect the power capacity, breakdown thresholds of different operating modes in elliptical waveguides are studied. Based on the analyses, a synthesis method to design the elliptical mode converter integrating the mode conversion efficiency and the power capacity is proposed. A highly oversized mode converter working in $W$ -band is designed, and the simulation results demonstrate that the mode converter achieves the high conversion efficiency over 95% in a relative bandwidth of 19.6%. In order to validate the design, a prototype of the mode converter is fabricated, and the high purity of outputted TE11 mode is verified by the measurement. The oversized mode converter designed by the proposed synthesis method features high efficiency, broad bandwidth, and high power capacity, enabling its full utilization of the potential of gyrotron traveling-wave tubes (gyro-TWTs). [ABSTRACT FROM AUTHOR]

Optical access networks (OANs) with passive optical network technology have been globally deployed on a massive scale, serving as the fundamental information infrastructure of teleCommunication networks. Some telecom service providers are re-architecting their networks based on cloud central office with software-defined networking and network functions virtualization capabilities to provide service agility, intelligence, and scalability. In this article, we present a synthesized analysis of the inherent value and practical use cases of access network (AN) slicing in the context of software-defined OANs. A novel hierarchical abstraction model and a workflow of end-to-end network slicing are presented to illustrate the support of multi-service and multi-tenancy applications over a converged OAN platform by enabling automatic life cycle management of AN slicing. Two successful trials utilizing the model and the workflow are also demonstrated. [ABSTRACT FROM AUTHOR]

A diode magnetron injection gun (MIG) has been designed and analyzed for G-band gyro-traveling wave tube (Gyro-TWT). A novel curved surface emitter is proposed to enhance the beam quality. An electron beam with velocity ratio of 1.20 and transverse velocity spread of 2.11% is obtained. The beam transportation stability with geometry misalignment is also analyzed, and the assembly accuracy should be controlled under 0.1 mm. The stray electron is intercepted by the capture structure to avoid the bombardment to the interaction circuit. Then the cathode is fabricated, and the temperature distribution is measured. The experimental result matches well with the simulation. The electron beam quality considering expansion, surface roughness, and thermal emission is estimated, and the total transverse velocity spread is about 2.63%. [ABSTRACT FROM AUTHOR]

Effects of the output window reflection instability on the performance of our designed ${W}$ -band broadband gyrotron traveling wave tube (gyro-TWT) were studied by the simulation and hot test experiments. Strong oscillations and frequency self-modulation (FSM) in the after-cavity interaction (ACI) region were observed in the zero-driven state with a two-layer window and are verified with the beam-wave particle-in-cell simulation. Oscillations and FSM of 80–81.8 GHz and 91.03–94.68 GHz are, respectively, generated from the TE22 and TE02 modes in the ACI region due to the high window reflection level. By using the “sandwich” and meta-surface windows with low reflection and broad bandwidth, the parasitic ACI oscillations can be effectively suppressed. The maximum saturated output power is improved to 156.8 kW at 94 GHz and is zero-driven stable in our recent hot test experiments. [ABSTRACT FROM AUTHOR]

This article presents a modulation scheme to suppress the transient dc bias current in dual active bridge (DAB) converters. The current in the transformer at the commutating time is associated with the initial current in a switching period, so there must be a dc bias current during the transient response. To investigate the modulation scheme for suppressing the transient dc bias current, the article reviews the optimal TPS control strategy, which is derived from the zero voltage switching with the minimum current stress in the transformer. By analyzing the dc bias current, the transient dc bias current can be evaluated by the current in the transformer at the symmetry line of the primary full-bridge voltage waveform instead of the current at the commutating time. It can be concluded that the expressions of the transient dc bias current for different working modes are unified. Therefore, the modulation schemes without transient dc bias current for different working modes can be also unified. On this basis, a universal strategy can meet all the transient cases. There is no need to identify or select the working modes and power conditions in the transient dc bias current control, which simplifies the implementation of the modulation scheme in the digital signal processor. Finally, an experimental prototype has been built to verify the effectiveness of the proposed modulation scheme. [ABSTRACT FROM AUTHOR]

A circular TE0n mode content analysis technique based on the multi-mode coupler with high mode selectivity is proposed. To improve the mode selectivity, a deformed waveguide, entitled the quad-polar waveguide, which discriminates the azimuthally symmetric TE-mode on the waveguide wall, is introduced. The influence of deformation on the TE01 and TE02 modes’ field pattern, the corresponding transmission loss, and the power capacity in the quad-polar waveguide are analyzed. Based on the analysis, a dual-mode coupler of the circular TE01 and TE02 modes, consisting of an oversized deformed circular waveguide coupler and a pair of circular-to-quad-polar waveguide transitions, is designed for a high-power Ka-band gyrotron traveling-wave tube system. To verify the high mode selectivity of a quad-polar waveguide, a simple coupling with equal-radius and equal-interval holes are used. A prototype is fabricated and measured, and the results show that the coupling coefficient is −40 dB with the directivity of 27 dB for the TE01 mode, suppressing the unwanted mode TE02 mode with 53 dB. For the TE02 mode, the coupling coefficient is −40 dB with the directivity of 25 dB and suppresses the unwanted mode TE01 mode with 75 dB from 30 to 40 GHz. [ABSTRACT FROM AUTHOR]

Mode converter is one of the most important devices in the high-power microwave (HPM) applications. To conduct an in-depth research for the orthogonal mode converter, a novel 90° compact TM01-TE11 circular waveguide converter working at 9.7 GHz is proposed in this article. This design innovatively integrates the traditional mode converter with 90° bend techniques based on the mode coupling theory, which ensures a compact structure and high-power handling capacity. Calculated and simulated results illustrate that the maximum conversion efficiency of the converter at central frequency reaches 99.4% when the structure length is 535 mm, and the bandwidth reaches 680 MHz when the conversion efficiency exceeds 95%. For demonstration, a prototype is fabricated, and the corresponding experiments are investigated. According to the $S$ -parameter measurement, it has a high conversion efficiency at central frequency. Meanwhile, the high-power performance is conducted by connecting it with a relativistic backward oscillator (RBWO), and the converter works stably under a maximum output power of 4 GW. The good agreement of the theoretical analyses, simulations, and experimental results indicates the feasibility of the proposed converter. [ABSTRACT FROM AUTHOR]

This letter proposes a waveguide Magic-T operating in the $W$ -band, aiming to overcome the assembly difficulties of conventional configuration. Its primary characteristic is that it allows for the one-piece fabrication of the waveguide cavity using popular computer numerical control (CNC) technology, avoiding the assembly of extra matching elements. Second, the four ports of the Magic-T share a horizontal plane, which allows its lid to theoretically be a flat plate. This overcomes the assembly misalignment challenge, due to the presence of port in the lid of some conventional Magic-T. In addition, the use of bed-of-nails to package this Magic-T was investigated to further alleviate the difficulty of assembly. A prototype has been fabricated and measured, and the results indicated excellent overall performance over the entire 75–110-GHz range, including low loss, high isolation, and good amplitude/phase consistency. [ABSTRACT FROM AUTHOR]

This article proposes a method to excite the TM11 mode in circular waveguides. The principle of synthesizing a circular TM mode is deduced based on the electric dipole moment theory first, and the output mode and its purity are analyzed theoretically. Then, a mode conversion scheme to convert the rectangular TE10 into circular TM11 mode via a pair of out-of-phase quasi-TEM mode is proposed. In order to achieve the broadband excitation in a compact size, the ridge gap waveguide is used as a medium between the rectangular and cylindrical waveguide. Simulation results present that the proposed exciter has a propagation bandwidth up to 10 GHz in Ka-band with a mode purity over 98%. A prototype is manufactured and measured, and the presence of TM11 mode and the mode purity are confirmed by a port radiation pattern measurement. The mode exciter features high mode purity, broad bandwidth, and a compact size, which provides a low-power generator for the research of novel gyrobackward-wave devices and devices in the high-power transmission line. [ABSTRACT FROM AUTHOR]

This article explores an extremely high beam–wave interaction (BWI) efficiency technology of sheet beam traveling wave tubes (SBTWTs). An all-period phase velocity tapering optimization method is proposed to improve BWI efficiency of slow wave structure (SWS). The effects of the special electron bunching state and synchronous phase velocity change on the improvement of BWI efficiency generated by this method are analyzed. To solve the computational burden caused by dozens of parameters, self-developed 1-D nonlinear BWI code is used to calculate the BWI. For the best optimization effect, particle swarm optimization (PSO) algorithm selected from a variety of algorithms is utilized to search for the global optimal solution. The PIC simulation verification results show that by the all-period optimization method, the 80-period staggered double vane (SDV) SWS achieves a stable output power of 18 kW with 31 kV voltage 0.9-A current sheet beam at 30 GHz. The BWI efficiency of all-period phase velocity tapering SWS has reached 64.5% at center frequency, the efficiency between 28 and 35 GHz exceeds 40%. [ABSTRACT FROM AUTHOR]

This article introduces a new type of contact-less electromagnetic bandgap (EBG) structure in the form of an embedded bed of nails. Compared with the traditional bed of nails structure, the smooth upper metal plate originally used to provide the perfect electrical conductor (PEC) boundary is replaced by periodic defect grooves, and the metal pins on the base block are embedded in these grooves without any electric contact. One of the advantages of the embedded EBG structure is that it has a robust tolerance for the height of the air gap. Therefore, this structure provides a cost-effective parallel plate mode suppression solution because it allows a low-precision manufacturing process level while maintaining the stability of the bandwidth. On the other hand, the proposed EBG structure can achieve a stopband range of several octaves. This characteristic makes it indeed suitable for wideband gap waveguides (GWs) to provide horizontal open boundaries. To verify the feasibility of the proposed approach, the new ridge gap waveguide (RGW) (with an embedded bed of nails) and the classic RGW (with a traditional bed of nails) with two 90° bends are designed, fabricated, measured, and compared. The experimental and simulation results are quite consistent and indicate that the embedded RGW has prominent advantages in bandwidth and robustness. [ABSTRACT FROM AUTHOR]

This paper provides an active metamaterial (MTM) glucose sensor with programmable functionalities to sensitively detect a large scale of glucose solution concentration up to 7000 mg/dL. The active sensor consists of periodical units that can be individually actuated by PIN diodes via Micro-Control-Unit for obtaining four tunable states presented as digital coding sequences 00/01/10/11. Hence, for the MTM with ${n}$ units, it possesses as many as $4^{n}$ programable resonances, which can be taken advantage of to enhance the sensitivity and expand the detecting range of concentration. Specifically, by investigating different programmable modes for different concentration ranges, it can obtain high sensitivity of 10−3-10−2 dB/(mg/dL) for detecting concentration up to 7000 mg/dL: for concentration of 0–200 mg/dL, the programmable state 1111 is utilized with obtaining the sensitivity of $3.243\times 10^{-3}{-}1.839\times 10^{-2}$ dB/(mg/dL); for concentration of 200–3000 mg/dL, the programmable state 1011 is selected to realize the sensitivity of $2.116\times 10^{-3}{-}1.124\times 10^{-2}$ dB/(mg/dL); for more higher concentration of 3000–7000 mg/dL, another programmable state 0010 is used for obtaining sensitivity of $2.611\times 10^{-4}{-}1.149\times 10^{-3}$ dB/(mg/dL). Particularly, the programmable state 0000 is chosen as the sensing map, so that the measured S11 magnitude in the mapping state can tell the glucose concentration range of the material under test and guide the active MTM sensor go to the appropriate programmable state. This work aims to study the advantage of active sensor with programmable functionalities and motivate the use of sensors with programmable modes to identify, classify, and characterize biochemical and chemical analytes. [ABSTRACT FROM AUTHOR]

In order to enhance the power capacity of gyro-traveling wave tube (Gyro-TWT), a novel multisectorial-tunnel circuit is presented in this article. The multisectorial tunnel could extend the transverse dimension of RF circuit for higher power electron beam transportation. The azimuthal drifting and transportation distortion performance for rotated electron beam are analyzed. A multibeam magnetron injection gun (MIG) is designed. The electron beam with pitch factor of 1.09 and axial velocity spread of 3.5% is obtained. And the designed cathode was fabricated and temperature distribution was measured. It provides a possible method to enhance the power capacity of Gyro-TWT. [ABSTRACT FROM AUTHOR]

A novel fan-out wafer-level packaging (FOWLP) technology with double-sided redistribution layers (RDLs) and tall copper vertical interconnects is described. The design of a dual-polarized magnetoelectric (ME) dipole antenna based on this new packaging technology is presented. It is shown that the antenna with a size of $10\times10$ mm2 achieves good impedance matching and a stable radiation pattern over a wide bandwidth from 25 to 43 GHz, which can cover most of the millimeter-wave (mmWave) bands of the fifth-generation (5G) mobile networks in different countries. The measurement results demonstrate that the antenna is well suited for FOWLP technology and can be used for phased-array modules in 5G wireless communication systems. [ABSTRACT FROM AUTHOR]