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.

Digitized beam-forming metal reflectarray antennas are designed for the millimeter-wave region. The phase control of antennas has been implemented by the reconfiguration of rectangular grooves on a metal plate. The antenna has 1147 elements arranged in an aluminum metal plate. The depths of all metal grooves are manipulated for designed phase control of high-gain beam-aimed reflectors. We have demonstrated a digitized reconfigurable metal reflectarray to steer a re-radiated millimeter-wave field from the reflector in a two-dimensional scanning plane from −20${}^{\circ }$ to 20${}^{\circ }$. The far-field patterns show that the measured gain of the 2-bit reflectarray is only 1 dB lower than that of a non-digitized reflectarray antenna. The measured peak gain is higher than 31.7 dB, and the measurements show that the gain of the full 40${}^{\circ }$ scanned beam is 31.7 dB and well-defined scanned beams are obtained with a maximum scan gain loss of 0.2 dB. The proposed reconfigurable antennas can be a useful candidate for high-gain beam-aimed antennas for practical reflecting surfaces and a variety of wireless and satellite communication systems.

This paper proposes a FMCW radar transceiver with photonic elements. The proposed radar system is efficiently designed by budget analysis, and a wideband signal is generated using photonic elements. To verify the performance of the proposed radar system, field tests including changes in bandwidth are conducted. The results confirm that the resolution of ISAR images improves as the bandwidth increases as expected through the budget analysis.

Herein, an approach for mitigating disturbances in real-field inverse synthetic aperture radar (ISAR) images of drones is introduced. This is achieved through the utilization of combining UNet, atrous spatial pyramid pooling (ASPP), and residual learning, referred to as ISAR Denoising Simplified ASPP based Residual UNet (ID-SAbRUNet). Starting with raw radar data maps obtained from real-field experiments, we extract data maps of size 64 × 64 centered around the target signal. Subsequently, the target and disturbance data are separated from the signal data. Also, only-disturbance data which were also acquired from the experiments are extracted to generate training, validation and test datasets for ID-SAbRUNet. We extract feature maps of the proposed network after training to evaluate whether the training process is conducted as we expected from the design. Finally, we compare the peak signal-to-noise ratio results of ID-SAbRUNet with those of IUNet, a state-of-the-art deep learning algorithm designed for denoising ISAR data. This evaluation is conducted on the two test datasets that are divided into pretrained and nontrained datasets, to assess the performance of the proposed system. The results demonstrate that the proposed method outperforms the IUNet method on both datasets in terms of denoising and target restoration in most scenarios, regardless of the characteristics of disturbance.