Qianzhong Xue

In this letter, a broadband dual-circularly polarized transmitarray (dual-CP TA) with independent beam control is reported. Based on Huygens' metasurface elements, a spin-decoupled dual-CP phase design method is employed to achieve independent beam control. The transmission efficiency and phase shift range are enhanced by cascading multiple layers. Four distinct element sizes provide 180° of dynamic phase coverage, and a 90° rotation of the element enables a 180° phase reversal. A 2×2 magneto-electric (ME) dipole antenna is used as the feed, reducing the antenna profile to 4.5 λ₀. At 20 GHz, the measured gains of Left-handed CP (LHCP) wave and right-handed CP (RHCP) wave are 21.5 dBic and 21.2 dBic, with peak aperture efficiencies of 23.5% and 22%, respectively. The 2dB gain bandwidth (BW) and 2dB axial ratio (AR) BW are superior to 13.9% and 11.3%, respectively.

This article proposes a novel double-corrugated waveguide with grating (DCWG) slow wave structure (SWS) for the development of a broadband high-power terahertz (THz) back-wave oscillator (BWO). By analyzing the electromagnetic properties, it is found that this SWS is suitable for interaction with a circular electron beam, with high interaction impedance and large “cold” bandwidth. In addition, particle-in-cell (PIC) simulation results indicate that the BWO based on the DCWG SWS can generate an output power exceeding 39.5 W in the frequency range of 327.4–362.2 GHz when the electron beam voltage is between 17 and 26 kV. In particular, at a voltage of 19.5 kV, the output power of the BWO can reach 52 W at a typical operating frequency of 0.34 THz. Therefore, this device has significant potential as a broadband, high-power THz radiation source.

This letter presents an effective optimization synthesis approach for Orbital Angular Momentum (OAM) beams with low sidelobe and high mode purity through antenna array complex excitation optimization. The optimal synthesis is formulated as minimizing a linear function of the real and the imaginary parts of the array excitations on a convex set, expressed as a Convex Programming (CP) problem. Besides, two simplification methods are introduced to reduce computational complexity and enhance efficiency. Numerical experiments involving diverse array boundary configurations, element arrangements, OAM mode numbers, and complex pattern mask cases are performed, and the results validate the flexibility, effectiveness, and broad applicability of the proposed approach.

This work presents a 12-element multiple-input–multiple-output (MIMO) wideband antenna array for mobile smartphones. The antenna element is mainly composed of two parts, greatly improving the antenna array bandwidth: one is a meandering, looped radiating element and the other is a U-shaped slot. For the antenna element design, the meandering, looped radiating element measures 12.95 × 6 mm², while the U-shaped slot has a size of 15 × 3 mm². Meanwhile, the reflection coefficient indicates that the designed antenna array operates at 3.3 GHz with a bandwidth of 500 MHz; the transmission coefficient shows that the isolation between the antenna elements is better than 12 dB. In addition, more antenna array performances are presented, including nearly omnidirectional radiation characteristics, antenna efficiency ranging from approximately 17 to 60%, envelope correlation coefficients (ECCs) below 0.065, and diversity gain (DG) values of the MIMO antenna system close to 10 dB. The measurement results are highly consistent with the simulation results of the designed wideband antenna array, indicating its great potential for future practical engineering applications.

Nonperiodic perturbations are incorporated into extended interaction klystron (EIK) to broaden the bandwidth, overcoming the dilemma of effective interaction between the beam and three or more axial resonances. The theoretical exploration delves into the impact of gap position perturbations on the periodic extended interaction cavity. Furthermore, application examples demonstrating multimode operation in nonperiodic cavities are presented and validated through comprehensive full-wave simulations. Subsequently, a seven-cavity interaction circuit of a ${G}$ -band wideband EIK amplifier operating in 220 GHz is designed to further validate the nonperiodic design approach. The 3-D particle-in-cell (PIC) simulation predicts a constant 35-mW-drive bandwidth of 6.76 GHz and the corresponding maximum output power of 74 W for the designed power amplifier driven by a 20.6-kV, 0.25-A electron beam.

This letter develops a novel synthesis method for the circular aperture orbital angular momentum (OAM) antennas. The method, derived from the continuous aperture, effectively reduces the sidelobe levels (SLLs) of OAM waves and can achieve precise adjustments. Moreover, a discretization method is proposed, thus extending the applicability of the synthesis method to discrete arrays. Compared to the traditional direct sampling method, the proposed method can reduce the performance degradation of antennas in terms of SLL caused by discretizing continuous aperture distributions, especially for high-order OAM waves. Using the proposed approaches, a complex amplitude transmission metasurface is designed to generate a 2nd-order OAM wave with the desired SLLs of -25 dB. Experimental results show that the SLLs of the E-plane and H-plane are -22.87 dB and -23.02 dB, respectively. The effectiveness of the approaches for controlling SLL is demonstrated by theoretical analyses, simulations, and experiments.

In order to meet the high-power source requirement of compact submillimeter-wave systems, a high-power G-band extended interaction klystron (EIK) has been developed at the Aerospace Information Research Institute, Chinese Academy of Sciences (AIRCAS), and reported for the first time. The extended interaction circuit design based on over-synchronous voltage and high quality factor is proposed to enhance the output power and gain. In this manner, the designed EIK has achieved excellent test results compared with the same type of compact devices. Driven by a 20.3 kV, 198 mA pencil electron beam, the EIK can deliver a pulsed output power greater than 120 watts at around 0.22 THz, corresponding to a gain of 32 dB with a 5% duty cycle, and the average power and -1 dB bandwidth are 6 watts and 180 MHz respectively. Constrained by an axial magnetic field of about 1.03 T, the beam transmission is around 92% in RF operation.

A new ridge-loaded cavity structure with unequal-length slots is proposed to improve the bandwidth performance in extended interaction klystrons (EIKs). Based on the transverse-mode overlapping technology, such a structure is well suited to be driven by double sheet beams and exhibits a large efficiency bandwidth product. In contrast to the previously designed ridge-loaded structure, it operates in the longitudinal $\pi $ -mode instead of the longitudinal 2 $\pi $ -mode and has a larger characteristic impedance and smaller unloaded quality factor. It was designed as the idler cavity for a six-cavity circuit, and the simulation results predicted a maximum in-band output power of 275 W and a 3-dB bandwidth of 3.15 GHz, which expands the bandwidth by 750 MHz compared to the control circuit in the same operating conditions. The corresponding planar double sheet beams electron-optical system is also presented. The beam focusing electrode (BFE) is specifically designed with rod-shaped structure and outstretched structure to enable the two sheet beams to be compressed equally in the broadside direction, and the permanent magnet focusing structure is improved to avoid beam interception. Finally, the beams can pass through the 19-mm tunnel with 100% transmission efficiency, and the matching range of the magnet and electron gun is up to 1 mm.

It’s presented here a general pattern for quantitative evaluation of impacts imposed by uncertainties brought directly from geometrical parameters on performance parameters for traveling-wave tube (TWT) design, in a holistic perspective in terms of distribution traits. For the sake of generality and built-up of pathways, artificial neural network (ANN), rather than closed-form solution, is employed for access to the mapping between geometrical parameters with interaction parameters, involving interaction impedance, detune parameter and attenuation constant. Furthermore, with the intermediate interaction parameters derived, the geometrical variations are eventually connected with TWT performance indexes like gain, bandwidth, insertion phase and even manufacturing yield. With such an ease on the association between the two somewhat distant analysis layers in general, a Monte-Carlo analysis is carried out to reveal the ramifications brought from multi-dimensional geometrical uncertainties on performance indexes. An embodiment of the analysis approach is made with double corrugated waveguide (DWC).

An RF design of biperiodic multimode interaction circuit for $\textit{G}$ -band extended interaction klystron (EIK) is presented to overcome the bandwidth limitation of conventional EIK operating in a single mode. The $\pi $ -mode and its adjacent ladder mode are chosen as the operating modes of the input and output cavities. The effect of beam loading and the presence of the waveguide port on the cavity characteristics of the output cavity operating in the multiple modes are investigated, including the coupling coefficients, the frequencies, and the hot quality factors. The bandwidth of the gain section is broadened by the staggered tuning method. The 3-D particle-in-cell (PIC) simulation predicts a constant drive bandwidth of 4.5 GHz (exceeding 2% relative bandwidth) for the designed power amplifier around 220 GHz. Driven by a 21.4-kV, 0.25-A pencil electron beam, the amplifier can provide an output power of 195 W when the input power is 70 mW. The corresponding gain and electronic efficiency are 34.5 dB and 3.6%, respectively.