Hong Soo Park

When electronic systems within enclosures are exposed to high-power electromagnetic fields, functional disruption or damage may occur, highlighting the need for predictive models that assess the likelihood of such effects in advance. In enclosure-based scenarios, where the geometry is complex and large relative to the wavelength, electromagnetic field coupling exhibits significant variability. In addition, the susceptibility of electronic devices is uncertain, making deterministic prediction difficult and motivating the need for a stochastic modeling approach. This article presents a framework that combines random coupling model-based statistical predictions of coupled power at the target port with a threshold distribution obtained through direct-injection measurements, where the limited data are fitted using a Weibull model. The proposed method is validated through experimental measurements in a wave-chaotic cavity, with comparisons based on Monte Carlo simulation, bootstrap resampling, and two-sided p-value analysis. The close agreement between the predicted and measured outcomes confirms the capability of the framework to reliably estimate target effect probabilities in complex electromagnetic environments.

A 90° hybrid coupler is one of the essential components widely used in various RF applications. The arms of the conventional branch line 90° hybrid coupler typically require a $\lambda $ /4 length. In applications operating at low frequencies in the megahertz range or those demanding extremely small form factors, miniaturization becomes even more critical. In this letter, we present a 90° hybrid coupler using a hybrid approach to achieve miniaturization by combining meander lines and discontinuity lines. The proposed 90° hybrid coupler is validated via simulation and measurement, where the results show that the size of the proposed coupler is less than $0.1\lambda $ in both the width and length, indicating a size reduction of 95.1%.

For the detection of buried targets in a dielectric medium, the decomposition of time-reversal operator (DORT) using multistatic system has been effective in separating multiple targets and imaging their locations. Recently, nonlinear (harmonic) radar-based DORT has been introduced to detect nonlinear targets with small radar cross sections (RCS). However, faulty antennas (i.e., elements unable to transmit or receive signals) can distort the received multistatic response matrix, significantly degrading detection performance and accuracy, necessitating an extension of DORT to address such scenarios. This paper presents double scan-DORT (DS-DORT), an extended DORT approach that ensures effective buried nonlinear target detection even in the presence of faulty antennas. Unlike conventional DORT, DS-DORT employs two arrays, each performing both transmission and reception, generating two multistatic responses that compensate for distortions caused by faulty antennas. By simultaneously retransmitting two sets of back-propagation signals derived from these responses, DS-DORT minimizes inaccuracies, maintaining robust target detection. Furthermore, DS-DORT offers practical advantages in real-world scenarios such as hazardous/inaccessible environments, or when antenna failures occur unpredictably, without requiring additional hardware or complex algorithms. Beyond its capability to mitigate faulty antenna effects, DS-DORT also enables the reconstruction of three-dimensional (3-D) target locations by leveraging a two-dimensional (2-D) antenna array configuration when all antennas function correctly. The proposed approach is validated through numerical simulations and measurements, demonstrating superior detection performance compared to conventional DORT in scenarios involving single or multiple faulty antennas. The results confirm that DS-DORT enables accurate detection of buried nonlinear targets even under faulty antenna conditions.

There has been growing interest in the field of wireless power transfer (WPT), especially for a high-power (Watt-level) applications. Rectifiers are essential components for WPT, as they convert incoming RF into DC power. However, conventional Schottky diodes used in WPT exhibit their highest efficiency at low power levels typically less than few Watts. To address this limitation, we introduce a power dividing rectenna system that can handle beyond several Watts of input RF power. The proposed rectenna consists of a single patch antenna integrated with a radial power divider, whose output ports are connected to rectifiers. In this way, incident RF power can be distributed into lower levels at which Schottky diode-based-rectifier can accommodate. Via simulation and measurement, we demonstrate that the input power (about 10 W) received through the proposed structure can be uniformly distributed to each output port of the divider to be rectified at lower power levels, which are then combined at DC to provide several Watts of DC power. The proposed rectenna can be utilized in WPT applications requiring beyond several Watts. Furthermore, by configuring the proposed structure into an array, even higher power handling can be achieved for applications that require hundreds of Watts.

Forover-the-air (OTA) testing of base station (BS) antenna systems, a plane wave generator (PWG) offers the advantages of a low-cost and compact setup. To suppress radiation energy outside the quiet zone (QZ), PWG designs adopting optimization with specific conditions have recently been proposed. In this letter, we present a PWG approach that provides effective plane wave synthesis based on reference field shaping without imposing any conditions, which can reduce computational complexity. Here, we use a super-Gaussian distribution as the reference field to calculate the optimal excitation coefficients, and the effectiveness of the proposed approach is verified via simulation and measurement. The overall results demonstrate that by inherently taking advantage of super-Gaussian distribution, stable QZ performance can be achieved while simply avoiding unwanted field intensity outside the QZ.

For the prediction of electromagnetic (EM) coupling in a complex (wave-chaotic) enclosure, the random coupling model (RCM) has proven useful. The applicability of RCM has been demonstrated using various complex enclosures, but their reported validations are mostly with the input and output ports placed within the enclosure. However, since many practical scenarios consist of EM coupling through an aperture of the enclosure from external sources, an extension of the RCM to accommodate such scenarios would be of interest. In this article, we present an extended RCM approach that provides an effective statistical prediction of EM coupling in a complex enclosure for an aperture excitation scenario. Here, we treat the entire wave propagation paths as a cascaded system of two-port networks with an analysis of the aperture using the transmission line theory. This allows us to accurately extract the cavity-specific loss parameter which is required for the RCM prediction of EM coupling, even for an aperture excitation scenario. The overall experimental results suggest that the statistics of the voltages induced on the target port inside the cavity are accurately predictable even in the case of aperture excitation.

We introduce an encryption device based on a compact wave-chaotic cavity to enhance the physical security of wireless communication. The proposed encryption device is composed of a compact quasi-2D disordered cavity, where transmit signals pass through to be distorted in time before transmission. On the receiving end, the signals can only be decrypted when they pass through an identical cavity. In the absence of a proper decryption device, the signals cannot be properly decrypted. If a cavity with a different shape is used on the receiving end, vastly different wave propagation paths will prevent the signals from being decrypted, causing them to appear as noise. We experimentally demonstrate the proposed concept in an apparatus representing a wireless link.