In-June Hwang

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

This letter proposes an inverse design method for radome frequency selective surface (FSS) based on conditional generative adversarial network (cGAN). Wasserstein loss with gradient penalty (GP) is applied to enhance the optimization of the generative network. FSS design typically requires the integration of high-permittivity radomes, which complicates achieving multifunctional characteristics and leads to significant increases in computation time. The trained network facilitates the real-time generation of novel designs that closely approximate the target frequency responses, even in the absence of corresponding data in the existing dataset. The proposed network was validated through simulations and experimental measurements of the fabricated prototype. One of the generated structures achieved dual pass band with fractional bandwidths at the -2.5 dB transmission level of 5.13% in the K-band and 6.08% in the Ka-band, demonstrating high frequency selectivity.

We propose a pixel-based metasurface design with asymmetry parameters with a large number of pixels used to construct the unit cell. Each square-shaped pixel has only two states, either metal or dielectric. Typically, the unit cell is designed to have a rotational symmetry. However, in this work, we introduce a set of additional parameters that can break the symmetry of the unit cell, closely associated with the physics of bound states in the continuum. These asymmetry parameters, defined by the scale of pixels in two dimensions, induce Fano resonances with high quality-factors in the transmission spectra and allow for the design of frequency-selective metasurfaces that are more specific to the general frequency-response characteristics.

In this letter, we propose multifunctional radome-based frequency selective surface (FSS) composites for stealth applications. The proposed composite simultaneously implements band stop characteristics in the X-band and band pass characteristics in the K- and Ka-bands. The composite consists of a sandwich structure, where two FSS layers are separated by a constant spacing. Thick dielectric materials with higher permittivity and loss tangent than air degrade the filtering performance. We thus performed conformational space annealing (CSA)-based optimization on both the FSS shape and dimension, resulting in a miniaturized pixelated FSS. This approach effectively addresses the downward shift in the resonance frequency by employing an FSS that is 22% smaller than a standalone FSS. We validated the proposed composite through simulations and measurements under varying polarizations and incident angles. The proposed composite achieved insertion losses greater than 20 dB across the entire X-band at a 45° oblique incidence in transverse electric (TE) mode. Under transverse magnetic (TM) mode at a 30° oblique incidence, the composite allowed transmission in the dual K-band and Ka-band while maintaining insertion losses below -18 dB within the stop-band.

In this study, a millimeter-wave far-field range antenna measurement system is proposed for W-band monopulse antenna measurements. Since the W-band monopulse antenna installed in radar systems has many input/output ports, multiple calculations are required to measure all the ports. We propose a system structure capable of the simultaneous measurement of multiple channels to quickly and accurately measure the performance of a monopulse antenna. The proposed measurement system includes a multi-channel rotary joint, a pair of diplexers, and multiple vector network analyzer extenders. In addition, an RF sub-system is implemented to reliably measure the phase of the W-band radiation pattern. It utilizes a shared local oscillator source and external power amplifiers for the transmit and receive paths. Employing the proposed multi-channel antenna measurement system, the sum/difference channels of a monopulse antenna were simultaneously measured according to the azimuth angle. In addition, a comparison of the far-field measurements provided by the proposed system and the near-field measurements was conducted.

In this letter, we propose a multifunctional frequency selective surface (FSS) designed for wide incident angles, optimized for X-band reflection and K-/Ka-band transmission. To verify its applicability, we analyzed the performance variations of the FSS with respect to polarizations and incidence angles. The proposed FSS facilitates space communication in the K/Ka-band, while simultaneously minimizing electromagnetic interference for X-band defense applications. The pixelated structures of the FSS are optimized to realize fine frequency selectivity in the target frequency bands. The proposed FSS is implemented in a double-layer to provide higher-order characteristics. To validate its performance, measurements are conducted in a free-space measurement system with spot-focusing lens horn antennas. The proposed structure demonstrates a -1.5 dB bandwidth from 17.41 to 20.97 GHz in the pass band of the K-band and 30.09 to 33.24 GHz in the pass band of the Ka-band, with fractional bandwidths of 18.6% and 9.9%, respectively. Additionally, it satisfies -15 dB blocking performance across the entire X-band.

The infinitesimal dipole modeling (IDM) technique represents the current density of the antenna under test as an array of infinitesimal dipole moments. Using the IDM concept, complicated structures of antennas and scatterers can be replaced with compact infinitesimal dipoles. With the rapid progress of antenna technology, antenna coupling analysis applicable to both near-field and far-field has become essential. The coupling phenomenon can be easily analyzed with IDM. Existing studies required additional mutual admittance calculations, and verification at the measurement level needed to be improved. In this paper, we propose an equation that directly calculates S21 from the extracted infinitesimal dipoles of the transmitter and receiver using IDM. The proposed method is demonstrated through comparison with both the numerical simulation results and measurements.

An integrated electro-optic (EO) sensor and its dedicated control system for intense electromagnetic pulse measurements are designed and implemented. The sensor performance, specifically the sensitivity, dynamic range, linearity, and bandwidth, is evaluated. For optimal measurements of intense electromagnetic pulses representing an electronic threat, a technique to optimize the sensitivity of the integrated EO sensors is presented. The sensors measure pulses with rise time of 2–3 ns and duration of 23–26 ns, and electric field strength up to 50 kV/m, thus meeting the requirement of MIL-STD-461G RS105 radiated susceptibility test for transient electromagnetic field such as nuclear electromagnetic pulses.

The fare payment system for public transportation has developed from coins, paper tickets, magnetic strips, and pre-paid cards to new technologies such as Radio-Frequency Identification (RFID) and Near Field Communication (NFC). Most fare payment systems are a fusion of NFC and mobile payment. As the latest fare payment system, the studies on gate-free technology without tag action are in progress. The gate-free system has several advantages, such as improving user convenience, eliminating congestion, and preventing the spread of infectious diseases. We introduce a gate-free system using Bluetooth Low Energy (BLE) technology as the next-generation fare payment system for public transportation. We propose a smart block structure for a gate-free system and analyze the antenna for this structure. A directional antenna is required for location detection of multiple mobile terminals in the gate-free zone, and an antenna to satisfy the requirements is analyzed. A stacked air-gap patch array that satisfies BLE performance and has high directivity has been proposed within the limited smart block size. To compensate for the low bandwidth of the patch antenna, an air gap is added between the patch radiator and the ground, and the antenna gain is increased by applying a stacked patch on the patch radiator. Based on the proposed antenna and smart block, a gate-free system testbed is installed, and the testing results are presented.