We propose a waveguide coupler based on a metamaterial slow-wave structure (SWS) and then present a dual band metamaterial Cherenkov oscillator. The high-frequency characteristics of the SWS are studied by High Frequency Structure Simulator, indicating that both n = 0 space harmonic of fundamental mode and n = -1 space harmonic of first higher order mode exhibit “backward” wave properties and high interaction impedances. Meanwhile, the transmission property of the metamaterial SWS with the waveguide couplers is investigated. The simulation results show two passbands, which are verified by the experiment. In addition, we use linear theory to predict the starting currents, which are verified by Computer Simulation Technology (CST) Particle-In-Cell (PIC) simulation. Furthermore, the performance of the dual band metamaterial Cherenkov oscillator is studied using the CST PIC solver. The results show that the electronic efficiency of the proposed oscillator reaches 52% and its tuning bandwidths are ~7 and ~30 MHz for Modes 1 and 2, respectively. The CST PIC simulation results agree well with those using the Computer-aided highly efficient electromagnetic particle-incell code. These results indicate that the proposed oscillator has small size, dual band property, and high electronic efficiency.

To develop high power and compact terahertz (THz) sheet beam traveling-wave tube (TWT), an all-metal metamaterial (MTM)-inspired slow wave structure (SWS) is proposed. This MTM-inspired SWS exhibits obvious advantages such as high interaction impedance, double beam tunnels, and compactness. The MTM-inspired SWS is devised and then simulated. The calculated average interaction impedance of the SWS for the first spatial harmonic of the fundamental mode is over $5 \Omega $ in the frequency range of 0.21–0.226 THz, which is bigger than that of the counterparts. Further, the beam-wave interaction of the MTM-inspired 0.22 THz TWT with double sheet beams is simulated. The maximum output power is predicted to be 400 W with 3-dB bandwidth of 5.4 GHz when the input power is 100 mW. Most importantly, the total length of the interaction structure of the 0.22 THz TWT is only 29.2 mm. The cross section of the proposed SWS and beam tunnels are $0.5\times0.42$ mm and $0.5\times0.37$ mm, respectively. The simulation results show that the compact THz radiation source presented here is promising for future applications such as in imaging and material analysis.

In this article, we propose a low reflection folded waveguide (LRFWG) as the slow wave structure (SWS) for the development of a terahertz (THz) traveling-wave tube (TWT). Our simulation results show that the LRFWG SWS has lower reflection and larger coupling impedance compared to the conventional folded waveguide (FWG) SWS over a wide frequency range. Using this modified SWS, we have designed, simulated, and manufactured a wide-band high-power TWT operating in the G-band. The cold test results demonstrate that the reflection parameters at the input and output ports of the TWT are less than -13.8 dB from 200 to 240 GHz, confirming the effectiveness of our proposed structure. In addition, the hot test results show that the maximum output power of the 220 GHz LRFWG TWT amplifier reaches 31.2 W at 220 GHz, with a 3 dB bandwidth exceeding 23 GHz. The power-bandwidth product of the device is greater than 717.6 W $\cdot $ GHz, providing a demonstration of a wideband high power THz source.

A coaxial coupler is proposed to develop a miniature metamaterial (MTM) backward wave oscillator (BWO). With respect to those using waveguide couplers as output structures, the MTM BWO adopting the coaxial coupler exhibits obvious miniaturized characteristics. For the MTM BWO, its high-frequency structure including the MTM slow wave structure (SWS) and the coaxial coupler has longitudinal length of $\sim 1.25\lambda $ . ( $\lambda $ is the free-space wavelength at the operating frequencies.) Importantly, the transverse size of $\sim \lambda $ /5 is only ~1/3 of those based on waveguide couplers. Furthermore, the transmission experiment is carried out. The experimental results show that the coaxial coupler with low loss property can effectively transform the TM-dominant mode in the MTM SWS to the TEM mode. The particle-in-cell simulations predict that the proposed MTM BWO yields MW-level peak output powers at frequencies from 2.85 to 2.903 GHz when the beam current is 30 A, and the beam voltage ranges from 65 to 110 kV. The simulation results confirm the feasibility of miniaturization as well as high output powers of the MTM BWO.

A dual band metamaterial (MTM)-inspired backward wave oscillator (BWO) is developed by proposing a novel dual band coaxial coupler. The MTM-inspired BWO simultaneously exhibits dual band and miniaturization properties. The dual band property is confirmed by both transmission experiments and beam-wave interaction simulations. Meanwhile, the advantage of miniaturization results from the compact high frequency structure, i.e ., its transverse and longitudinal sizes are about two-third smaller and slightly shorter than the previous BWO with the waveguide coupler, respectively. Further, the particle-in-cell results predict that the MTM-inspired BWO yields peak output powers of 114-137 kW at ~2.833 GHz and of 100-144 kW at ~4.527 GHz, respectively. Importantly, the power difference at the two frequencies is confined to ~1 dB, which is much smaller than that of the previous one with the waveguide coupler. These results confirm the feasibility of the compact dual band BWO, which might be applied to target recognition and plasma diagnostics.

To solve the problem with complex structure and low resource utilization of traditional target tracking UAV system based on visual guidance, this paper discusses an implementation method of quadrotor UAV target tracking system based on OpenMV. This system mainly includes flight control system and visual guidance system. TM4C123GH6PMI was selected as the control unit for flight control system. Six-axis motion sensor and digital magnetometer were combined into the pose measurement module. And ultrasonic sensor was selected to get the altitude information for drone. This system took OpenMV as the visual guidance system for target detection and position. For the real-time and accuracy requirements of the tracking system, the centroid-based tracking algorithm was used for calculating and resolving the target. The experiment results show that the system is stable and reliable.