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This communication presents a microstrip comb-line array antenna for the low sidelobe level (SLL) in the millimeter wave. As the width of the conventional stub-shaped radiating element becomes wider, not only the longitudinal current but also the transverse current increases; the longitudinal and transverse currents generate the co- and cross-polarized radiation, respectively. To reduce the transverse current flows on the large-width radiating element, the width of the connecting part with the feeding line in the radiating element is narrowed. In addition, the transverse current can be further reduced by adding a notch on the top of the radiating element. These two deformed radiating elements are proposed and used to design 18-element comb-line array antennas according to the array design procedure based on the radiation conductance. The array antennas were designed for the SLL of–20 dB at 79 GHz. The prototypes are fabricated and the antenna performance was measured. From the measurement results, the comb-line antenna composed only of the conventional stub-shaped elements shows the SLL of about–16.58 dB, whereas the array antenna using the proposed elements has the SLL of–19.4 dB. This communication demonstrates the feasibility of the proposed elements for low SLL, through analysis and measurement. [ABSTRACT FROM AUTHOR]

For an automatic recognition system, a huge number of micro-Doppler signature images is required to train a classifier. However, in general, measurements are only possible for hovering drones, so the dynamic radar cross section (RCS) of a drone with various motions is estimated through EM simulation and converted into a micro-Doppler signature image. In this work, we use far-field approximation and mesh-element rotation in the method of moments to quickly estimate the dynamic RCS of a drone in various motions. First, 3-D meshes and the impedance matrix of a single propeller are generated only once. Instead of rotating the propeller, the position information of the mesh elements is rotated without recreating 3-D meshes or the impedance matrix. Next, using the mirror-image symmetric characteristics of drone propellers and the far-field approximation, the dynamic RCS of multiple propellers is synthesized from that of a single propeller. Finally, the dynamic RCS was estimated at 3 and 9 GHz and converted to micro-Doppler signatures, spectrogram, and cadence-velocity diagram (CVD). As a result, it was more accurate to estimate the dynamic RCS at 9 GHz, and it was easier to obtain the rotation frequency at 3 GHz in the CVD. [ABSTRACT FROM AUTHOR]

The image-domain ray-tube integration formula (IRIF) is an efficient way to build a large database for synthetic-aperture radar automatic target recognition (SAR-ATR) because the IRIF can rapidly generate an inverse SAR (ISAR) image of a computer-aided design (CAD) model. Additionally, calculation of the IRIF can be accelerated by a nonuniformly sampled impulse train and the nonuniform fast Fourier transform (NUFFT). In a numerical implementation, upsampled ISAR images are required and the IRIF can calculate the upsampled ISAR images directly in image-domain. However, image-domain upsampling increases the computation time because the NUFFT calculates a matrix whose size is increased by the upsampling factor. In this letter, we propose a method to minimize the increase in computation time caused by image-domain upsampling. We derive a formula to approximately predict the scattered far-field under the small-angle condition and accelerate the formula by utilizing the nonuniformly sampled impulse train and the NUFFT. The NUFFT is used to calculate a far-field matrix without upsampling. Then, zero-padding in the field-domain and the FFT are utilized to generate an upsampled ISAR image. To validate the proposed method, ISAR images of a tank and a helicopter CAD models were simulated and were compared with those of the previous methods. [ABSTRACT FROM AUTHOR]

Vehicle-to-Everything (V2X) creates many new opportunities in the area of wireless communications, while its feasibility on enabling vehicular positioning (VP) has not been fully explored despite its importance for autonomous driving. This article aims at investigating whether V2X can help VP from different perspectives. We first explain V2X's critical advantages over other technologies (e.g., GPS, RADAR, LIDAR, and camera) and suggest new scenarios of V2X-based VP. Then, we review the state-of-the-art positioning techniques discussed in different standardizations and point out their limitations. Lastly, some promising research directions for V2X-based VP are presented, which contribute to realizing fully autonomous driving by overcoming the current obstacles. [ABSTRACT FROM AUTHOR]

Conventional two-coil wireless power transfer (WPT) systems achieve the maximum output power at the optimal distance. In the over-coupled state, in which the distance between coils is shorter than the optimal distance, the input impedance is significantly higher than that with the optimal distance. As a result, the output power at the load is dramatically decreased. In this letter, we propose a method to improve the maximum output power by applying a negative-impedance converter (NIC) to an additional coil. The proposed system can drastically improve the output power at a load even in the over-coupled state because the negative coil eliminates the impedance reflected by mutual coupling between coils. To validate the proposed method, the NIC was implemented with an operational amplifier and four identical coils. In the experiment, the proposed system transferred enhanced power, which was three times higher than the maximum output power of the conventional system. [ABSTRACT FROM AUTHOR]

This letter proposes a novel capacitively coupled microstrip comb-line (CCMCA) array antenna for millimeter-wave band applications. The proposed antenna has the advantages of low profile, low cost, and ease of fabrication for the millimeter-wave band. By adjusting the gaps between the radiating strips and feeding line, an antenna with low sidelobe level can easily be designed. To verify the suitability of the proposed antenna for millimeter-wave applications, two arrays (1 × 18 and 4 × 18) were designed and developed at the design frequency of 79 GHz. The measured results show good agreement with the simulated ones in terms of reflection characteristics and radiation patterns. In addition, the CCMCA antenna has stable beam direction even with frequency change, compared to a conventional series-fed microstrip rectangular patch array antenna. [ABSTRACT FROM AUTHOR]

In the wireless power transfer systems, a coupling coefficient is one of the measures of performance. In particular, the coupling coefficient at critical coupling does not ensure maximum system energy efficiency but guarantee maximum output power to the load. As the coupling coefficient goes beyond the critical-coupled state, output power begins to decline. In this letter, we propose a method to maximize output power even in an overcoupled state as in the critical-coupled state by adjusting the capacitance of the resonator. Our proposal is verified by comparing the calculations and simulations with measurements, and they are in good agreement. [ABSTRACT FROM AUTHOR]

In this letter, we compare two operating frequency tuning methods—the zero phase angle (ZPA) and the minimum reflection coefficient magnitude (MRCM) frequency tuning methods—to enhance the power transfer efficiency and output power in the wireless power transfer (WPT) system. For the MRCM frequency tuning method which has been introduced recently, the WPT system can be analyzed by considering the system as a matching network connected to a generator and a load. Through experiments, in the over-coupled region, the MRCM frequency tuning method has higher output power and efficiency than the ZPA frequency tuning method. Above all, the MRCM frequency tuning method does not need the information on the coupling coefficient as well as the primary and secondary resonators. [ABSTRACT FROM PUBLISHER]