Yeong-Hoon Noh

Digital light processing (DLP), a high-resolution 3D printing technique known for its smooth surface finish and fast printing speed, has recently been explored for fabricating patterned dielectric substrates for phase shifters in antenna systems. However, integrating metal inks to produce conductive circuits often results in poor conductivity due to porosity and incomplete sintering, requiring precise control of sintering temperature and process. In this study, a phase shifter was fabricated using DLP-based 3D printing with a photocurable resin. Recessed circuit patterns formed within the dielectric substrate and filled with Ag nanoparticle (NP) ink via a squeegee technique. A low-temperature thermal-pressing method applied to enhance electrode conductivity without exceeding the polymer substrate thermal limitations. Microstructural analyses under varying pressing conditions revealed improved interparticle connectivity and densification of the Ag NP network, significantly reducing resistivity. The fabricated phase shifter exhibited 6.8 dB insertion loss and a full 360° phase tuning range at the target frequency of 3.1 GHz under bias voltage control, closely matching RF simulation results. The results of this study suggest that the combination of DLP 3D printing and thermal pressing offers a promising avenue for developing and manufacturing miniature, high-performance RF devices and components, such as phase shifters with complex circuit structures, transmission lines, filters, antennas and arrays essential for 5 G, satellite communications, and other emerging wireless systems.

This paper validates the accuracy of radar cross section (RCS) measurements conducted in an environment that significantly reduces the three main costs associated with RCS measurements: spatial costs, target under test (TUT) production costs, and the costs of constructing and maintaining an anechoic chamber. Measurement results for simple shapes that satisfy far-field conditions, such as metal spheres and metal plates, are presented. Additionally, results are provided for a geometrically complex 1/15 aircraft scale model that does not satisfy far-field conditions. The noise equivalent RCS (NERCS) of the proposed non-anechoic chamber setup is determined by measuring various sizes of metal spheres, and the RCS error over time is evaluated by measuring a metal plate continuously for 12 h in a non-temperature and humidity-controlled environment. The NERCS is found to be -43.2 dBsm. The mean RCS error for the metal plate, measured immediately after background measurement and again after 12 h, is found to be 0.005 dB and 0.220 dB, respectively. For RCS measurements of the 1/15 scale model, an image-based near-field to far-field transformation (NFFFT) algorithm is employed. The NFFFT results, including image filtering, show a mean RCS error of 5.6 dB. This error is 1.9 dB higher than previously reported results obtained in an anechoic chamber environment using an amplifier to enhance the signal-to-noise ratio (SNR). These findings can serve as guidelines for considering measurement results in a highly simplified RCS measurement setup, offering rapid feedback crucial for stealth platform design.

We developed a new technique for generating three-dimensional monostatic inverse synthetic aperture radar (ISAR) images using various types of polarimetric information on targets. To remove clutter around a target, we adopted the CLEAN method, in which only the main signals were reconstructed using an iterative algorithm. We conducted a simulation as follows: electric field data that were subjected to polarimetric scattering were obtained for the target using a full-wave electromagnetic analysis simulator. The linear polarization data of a 2 × 2 matrix were compressed into the linear to circular polarization data of a 2 × 1 matrix using the Jones vector based on circular polarization. On the grounds of the post-processed data, inverse Fourier transform was carried out to map scattering points to the spatial domain, after which the CLEAN method was used to retain only the primary scattering points.

This paper addresses the issue of electromagnetic interference (EMI) in electric vehicle supply equipment (EVSE) charging cables, which can disrupt the communication signal for the real-time monitoring of the charging status, leading to the termination of charging. We propose a dedicated measurement jig for the Combined Charging System Combo Type 1 (CCS-CT1) cable structure and models its electrical characteristics of the jig using the impedance peeling technique for de-embedding. The obtained pure S-parameters of CCS-CT1 are then used to conduct a simulation of the signal integrity problem caused by Gaussian noise, which is the worst-case scenario that can occur in a typical charging system. This paper suggests that the root cause of this problem may be related to the high-power AC/DC conversion device included in the EVSE, which uses a switch-mode power conversion (SMPC) method that involves nonlinear operation and can result in increased harmonic noise and a more complex signal protocol for precise control. Finally, this study provides insights into the challenges of implementing high-speed charging systems and offers a solution for obtaining the accurate electromagnetic characteristics of charging cables.

This communication presents a novel technique for obtaining bistatic radar cross sections (RCSs) extracted from a monostatic scattering field dataset using a discrete scattering center model and basis pursuit denoising (BPDN) algorithm, which is compressive sensing (CS) technique. With the high-frequency assumption, a complex vector of independent point sources is formulated in a monostatic configuration for a geometrical relationship among the transmitter, receiver, and equivalent scatterers. A matrix equation for the scattering problem of an underdetermined form is effectively calculated by an iterative BPDN solver. Then, compensating the phase difference in the bistatic condition can derive the bistatic RCS at specific frequency points and observation angles. The accuracy of the proposed method for extracting bistatic results is verified using two numerical examples, and the performance of the method in terms of measurement efficiency and data resolution in frequency and angle domains is compared with that of conventional method.

In this paper, a numerical algorithm for the electromagnetic scattering analysis of singly curved dielectric structures, which can be applied to a canopy of fighter aircraft, is presented with experimental verification. At first, the Poggio–Miller–Chang–Harrington–Wu–Tsai (PMCHWT) method is used as a MoM-based solution for the electromagnetic scattering of a dielectric material. Its formulation was generated with the EFIE formulation in a multi-region condition. The PMCHWT algorithm is implemented with C++ code, and the accuracy is verified by calculating the bistatic RCS of some canonical structures with conductive or dielectric materials. RCS measurement under quasi-anechoic condition is presented with its procedure and calibration method. The monostatic RCS results of a specially modeled singly curved dielectric structures are obtained analytically with the PMCHWT, as well as experimentally, revealing excellent agreement.

한국전자파학회논문지 (The Journal of Korean Institute of Electromagnetic Engineering and Science)

To measure the electromagnetic properties of steel fiber-reinforced concrete (SFRC) in the X-band, 1-port measurements were performed using a lens horn antenna in a free-space measurement system. Free-space 1-port calibration with translations of the position of the reflector regarding the characteristics of the focused beam lens horn antenna was applied. The intrinsic impedance and complex permittivity of the SFRC were obtained from the measured reflection characteristics. The steel fiber content increased and the electromagnetic properties of the SFRC gradually changed from a dielectric to a conductor, even in very low frequencies compared to the plasma frequencies of general metal, which are optical frequencies. This is considered to be the plasmon effect of the metallic structure formed by the steel fiber. This result is applicable for analyses of the electromagnetic phenomenon of large structures with fiber content.