A photonic radar has recently received considerable interest as a next-generation radar due to its capability to generate wideband signals beyond the technical limitations of the conventional radar. In this paper, we design and implement an X-band photonic radar for a low radar cross-section (RCS) target detection and high-resolution image acquisition in real-time. The implemented photonic radar utilizes the photonic frequency quadrupling for the transmitter and detects the dechirped signal by using a delay interferometer and a balanced photo-detector to improve the signal-to-noise ratio. The performance of the photonic radar is verified using a commercial hexacopter having a diagonal wheelbase of 1133 mm as a low-RCS target in the field experiments. We show that the implemented photonic radar can successfully detect the drone on the move even though it is 2.7 km away from the radar. In addition, a high-resolution image of the drone, which is far away 1.1 km from the radar, can be obtained in real-time.

In this paper, we propose an X-band photonic-based pulsed radar architecture with a high range resolution. The proposed architecture is operated as a pulsed radar by adding a Mach-Zehnder modulator (MZM) operating as an optical switch to a transmitter of a conventional photonic-based frequency-modulated continuous wave (FMCW) radar. In addition, a balanced photodetector (BPD) is employed to enhance the amplitude of the received signal and remove common-mode noise. A proposed photonic-based pulsed radar prototype is implemented to operate at a center frequency of 10 GHz, a bandwidth of 640 MHz, and a pulse repetition frequency (PRF) of 1 kHz considering the performances of an arbitrary waveform generator (AWG). The implemented prototype is verified through an indoor experiment. As a result, the positions of targets are detected in real-time with 1.6% error rates of a range accuracy and obtained the range resolution of 0.26 m.

The radio frequency (RF) signal generation method using an external modulator is widely used in microwave photonics applications because it has the advantage of being able to generate coherent and stable RF signals with a higher resolution performance compared to the conventional method. A Mach–Zehnder modulator is widely used as an external modulator due to its high electro-optic coefficients and low attenuation characteristics but has a critical problem in that its electrical characteristics are changed by external environments such as temperature. In this paper, we considered the stabilization configuration to overcome this problem and propose an automatic bias control technique based on the simulated annealing algorithm of a dual-parallel Mach–Zehnder modulator (DPMZM) for quadruple signal generation. The proposed technique searches for the bias voltages of the modulator in real-time through the temperature test. In addition, the output of the quadrupled signal of the DPMZM is constantly controlled throughout the temperature range. Finally, it is confirmed that signals of a 10 GHz and 22 GHz frequency are generated using the intermediate frequency signals of a 2.5 GHz and 5.5 GHz frequency with the proposed automatic bias control technique, respectively.

Manufacturing slow wave vacuum electron device (VED) components operating in a terahertz (THz) region required the use of proper techniques and detailed plans. Moreover, how to fabricate components and evaluate manufactured ones are essential in identifying defects, checking their performance, and finding what needs to be improved. This study introduces estimated conductivity based on the surface roughness and evaluations of fabricated folded waveguides (FWGs), which is one of the THz slow wave VED components, using nanoscale precision computer numerical control (nano-CNC) machining. Produced circuits operating in the G- (0.11-0.3 THz) and Y-bands (0.325-0.5 THz) were diagnosed in terms of the RF transmission loss, achievable surface roughness, tolerance, and flatness. During testing, our devices exhibited the highest reported Ra (arithmetic mean surface roughness) at less than 11.17 nm in the Y-band. The conductivities based on the measured surface roughness were estimated in the G-band and the Y-band. Through a simulation and an experiment, we analyzed the reasons for the losses caused by the reduced electrical conductivity. The main contribution of this work is the demonstration of an achievable conductivity of the THz FWGs fabricated with nano-CNC machining and an improved surface finishing capability of the fabrication technique using lubricants.

We propose a self-driving folded-waveguide traveling-wave tube (TWT) oscillator internally driven by a backward-wave oscillator (BWO). As a driving source, the initial beam energy obtained from the electrostatic field is converted to electromagnetic energy in the BWO. The TWT is designed to amplify the radio frequency signal from the spent electron beam condition as an energy-recirculating method. This paper presents a detailed design study and analysis of the individual circuits, as well as those of the combined circuit, which are conducted using the CST particle-in-cell commercial software and MAGIC code. A maximum average output power of 82.63 W at a frequency of 272 GHz is predicted under the lossless condition. Although the proposed self-driving circuit exhibits a relatively low output power, the key concept behind the novel circuit, which uses a spent electron beam as an amplification source, is validated via simulation. Furthermore, the tunable frequency of the proposed device is tested by changing the initial electron energy using CST Particle Studio, and the expected tunable frequency is 268-272GHz.

We improved the accuracy of gyrotron performance analysis using particle-in-cell (PIC) code. To accurately predict the performance of a device under development, an electron beam (e-beam) that has information that best represents realistic e-beam information should be used for a cavity simulation, and an investigation of factors that affect the e-beam information is necessary at the design stage. Thus, we conducted an intensive analysis of the association between the e-beam information changed by nonideal factors and the performance variation of the gyrotron cavity. The altered e-beam information was obtained using a fully 3-D commercial code (Computer Simulation Technology (CST) Studios), with consideration of manufacturing imperfections and misalignment. The acquired e-beam information was then directly imported and used for gyrotron cavity simulations with the CST PIC code. This allowed us to investigate the gyrotron performance degradation caused by the nonideal e-beam information. Additionally, we validated the CST results using our in-house gyrotron code (UNIST Gyrotron Design Tool, UGDT). Finally, the simulation results were compared with previously published experimental data.