This article presents a fan-beam lens antenna design for impulse radio ultrawideband (IR-UWB) through-the-wall human detection radar applications operating in the 1–8 GHz. The proposed fan-beam lens antenna integrates a dielectric lens, designed by adjusting the lengths of dielectric slabs and air layers, with a Vivaldi antenna to achieve a fan-beam pattern characterized by a narrow beamwidth in the E-plane while maintaining a wide beamwidth in the H-plane. The antenna demonstrates excellent time-domain characteristics with a high fidelity factor exceeding 0.93, low reflection signal ringing, and maintained narrow beamwidth in the E-plane for far-field pulse radiation patterns. Through experimental validation, the antenna achieved SNR improvement due to concentrated signal propagation, enabling stable human detection at distances beyond 5 m through walls. The wide H-plane beamwidth allows effective detection of subjects in various postures, including lying positions. The proposed antenna design shows promising potential for various applications including disaster site search and rescue, building surveillance, fall detection in care facilities, noncontact vital sign monitoring, and smart home occupancy detection systems.

This article proposes a heatable dual-band frequency selective surface (FSS) designed to operate in the Ku and Ka bands commonly used in satellite communications. This design effectively solves the problems arising from the integration of heating elements while maintaining the desired electromagnetic performance. The structural evolution process of a general dual-band FSS for heating element separation is described. To analyze the performance of the FSS, an equivalent circuit model is developed to provide insight into the effect of each design element. The proposed FSS was manufactured, and its electromagnetic and heat generation characteristics were measured using free space measurement, a thermal imaging camera, and a thermocouple. The FSS has a small change between heated and unheated states, with transmittances of over -0.32 dB and -0.88 dB at 15.3 GHz and 27.3 GHz, respectively. Heating performance has also been proven, with the FSS reaching a surface temperature of up to 127°C when heated at 30V for over 3 minutes. The thermal-electromagnetic analysis reveals that the FSS maintains stable performance even under heating conditions, with minimal changes in the reflection and transmission coefficients. This study successfully integrates heating functionality into an FSS designed for radome de-icing in satellite applications, providing valuable insight into the development of similar multifunctional structures.

This paper presents a novel frequency selective surface (FSS) with embedded heating elements for radome applications, addressing the critical challenge of maintaining electromagnetic performance while providing effective de-icing capabilities. The proposed structure uniquely separates heating elements from radio wave transmission components, enabling independent control of thermal and electromagnetic characteristics. A bottom-up fabrication approach utilizing particle alignment technology was developed, achieving precise control of heating wire dimensions with minimum line widths of 1 µm and surface roughness below Rz 0.3 µm. The fabricated FSS demonstrated excellent transmission characteristics at 32 GHz with -0.298 dB (93.4%) for TE polarization and -0.283 dB (93.7%) for TM polarization, maintaining broad -1 dB transmission bandwidths. Thermal performance tests showed temperature increases exceeding 50 °C within 3 minutes under 12 VDC bias, while mechanical reliability tests confirmed durability through 5000 bending cycles at various curvature radii. The structure's equivalent circuit model was developed and validated, explaining the polarization-dependent characteristics. This approach effectively resolves the traditional trade-off between heating and electromagnetic performance, offering a promising solution for high-performance radome applications requiring both thermal management and radio wave transmission capabilities.

We propose a hybrid modeling technique for human signal detection through the walls using distributed radar. The high resolution and excellent penetration performance of the impulse radio ultrawideband (IR-UWB) radar systems can be used in important applications such as survivor detection in disaster scenarios. The radar channel transfer function between the transmitting and receiving radars obtained from the electromagnetic (EM) simulator is used for signal processing on MATLAB, followed by coherent synthesis. We perform a hybrid simulation of human detection through the walls using a single radar and verify it through experiments. In addition, we model vital signs behind the walls in various scenarios using the distributed radar and present the coherent synthesis results. The proposed hybrid modeling technique allows us to analyze various distributed radar scenarios in advance. This can reduce the time-consuming and resource-intensive real experiments. It is expected to contribute to radar system design optimization, signal processing algorithm development, and the identification of potential errors before practical implementation. The proposed method is expected to play an important role in various applications of IR-UWB radar technology, including disaster relief operations, noncontact biosignal monitoring, security, and surveillance systems.

This article presents a fan-beam lens antenna design for impulse radio ultrawideband (IR-UWB) through-the-wall human detection radar applications operating in the 1–8 GHz. The proposed fan-beam lens antenna integrates a dielectric lens, designed by adjusting the lengths of dielectric slabs and air layers, with a Vivaldi antenna to achieve a fan-beam pattern characterized by a narrow beamwidth in the E-plane while maintaining a wide beamwidth in the H-plane. The antenna demonstrates excellent time-domain characteristics with a high fidelity factor exceeding 0.93, low reflection signal ringing, and maintained narrow beamwidth in the E-plane for far-field pulse radiation patterns. Through experimental validation, the antenna achieved SNR improvement due to concentrated signal propagation, enabling stable human detection at distances beyond 5 m through walls. The wide H-plane beamwidth allows effective detection of subjects in various postures, including lying positions. The proposed antenna design shows promising potential for various applications including disaster site search and rescue, building surveillance, fall detection in care facilities, noncontact vital sign monitoring, and smart home occupancy detection systems.

This article proposes a heatable dual-band frequency selective surface (FSS) designed to operate in the Ku and Ka bands commonly used in satellite communications. This design effectively solves the problems arising from the integration of heating elements while maintaining the desired electromagnetic performance. The structural evolution process of a general dual-band FSS for heating element separation is described. To analyze the performance of the FSS, an equivalent circuit model is developed to provide insight into the effect of each design element. The proposed FSS was manufactured, and its electromagnetic and heat generation characteristics were measured using free space measurement, a thermal imaging camera, and a thermocouple. The FSS has a small change between heated and unheated states, with transmittances of over -0.32 dB and -0.88 dB at 15.3 GHz and 27.3 GHz, respectively. Heating performance has also been proven, with the FSS reaching a surface temperature of up to 127°C when heated at 30V for over 3 minutes. The thermal-electromagnetic analysis reveals that the FSS maintains stable performance even under heating conditions, with minimal changes in the reflection and transmission coefficients. This study successfully integrates heating functionality into an FSS designed for radome de-icing in satellite applications, providing valuable insight into the development of similar multifunctional structures.

This paper presents a novel frequency selective surface (FSS) with embedded heating elements for radome applications, addressing the critical challenge of maintaining electromagnetic performance while providing effective de-icing capabilities. The proposed structure uniquely separates heating elements from radio wave transmission components, enabling independent control of thermal and electromagnetic characteristics. A bottom-up fabrication approach utilizing particle alignment technology was developed, achieving precise control of heating wire dimensions with minimum line widths of 1 µm and surface roughness below Rz 0.3 µm. The fabricated FSS demonstrated excellent transmission characteristics at 32 GHz with -0.298 dB (93.4%) for TE polarization and -0.283 dB (93.7%) for TM polarization, maintaining broad -1 dB transmission bandwidths. Thermal performance tests showed temperature increases exceeding 50 °C within 3 minutes under 12 VDC bias, while mechanical reliability tests confirmed durability through 5000 bending cycles at various curvature radii. The structure's equivalent circuit model was developed and validated, explaining the polarization-dependent characteristics. This approach effectively resolves the traditional trade-off between heating and electromagnetic performance, offering a promising solution for high-performance radome applications requiring both thermal management and radio wave transmission capabilities.

We propose a hybrid modeling technique for human signal detection through the walls using distributed radar. The high resolution and excellent penetration performance of the impulse radio ultrawideband (IR-UWB) radar systems can be used in important applications such as survivor detection in disaster scenarios. The radar channel transfer function between the transmitting and receiving radars obtained from the electromagnetic (EM) simulator is used for signal processing on MATLAB, followed by coherent synthesis. We perform a hybrid simulation of human detection through the walls using a single radar and verify it through experiments. In addition, we model vital signs behind the walls in various scenarios using the distributed radar and present the coherent synthesis results. The proposed hybrid modeling technique allows us to analyze various distributed radar scenarios in advance. This can reduce the time-consuming and resource-intensive real experiments. It is expected to contribute to radar system design optimization, signal processing algorithm development, and the identification of potential errors before practical implementation. The proposed method is expected to play an important role in various applications of IR-UWB radar technology, including disaster relief operations, noncontact biosignal monitoring, security, and surveillance systems.

We propose a novel design procedure for a 2-D array of tapered dielectric structures for broadband and wide-incident-angle transmission. We exploit a stereolithography apparatus (SLA)-type 3-D printer to fabricate tapered dielectric samples. This technology eliminates the costly and complicated processes (e.g., perforation and etching) that are required in the fabrication of tapered dielectric structures. Specifically, we adopt the rigorous coupled wave analysis (RCWA) technique to extract the effective permittivity (EP) of a tapered dielectric unit structure. An optimization algorithm is employed to determine the ultimate optimal design parameters for the maximum transmittance. The free-space measurement is performed to evaluate the electromagnetic (EM) performance of designed samples. We demonstrate that a 2-D array of optimized tapered dielectric unit structures can exhibit enhanced transmission property in comparison to a half-wavelength dielectric layer and tapered dielectric structure without optimization, viz. above 60% transmittance over the entire Ka-band up to 60° of the incidence angle for both transverse electric (TE) and magnetic polarizations.

This study proposed an improved atmospheric refractivity interpolation method using mountain weather station data. To overcome the limitations of conventional IDW interpolation techniques that used only upper-air meteorological station data, that inadequately reflected complex terrain effects and local meteorological phenomena in mountainous regions, surface meteorological data from mountain weather stations in Gangwon Province were additionally incorporated. The proposed method developed a novel interpolation technique that propagated surface-level refractivity from mountain stations to the upper layers through an exponential weighting distribution and considered it together with upper-air meteorological data. The performance evaluation through leave-one-out cross-validation demonstrated significant improvements in accuracy compared with conventional methods. The proposed method is expected to significantly contribute to the performance prediction and operational optimization of radar and communication systems operating in mountainous regions.

This study proposes an improved shooting and bouncing rays (SBR) technique for accurate radar cross-section (RCS) analysis of curved cavity structures. Conventional flat-mesh-based SBR methods suffer from reflection direction errors because of discontinuous normal vectors and cannot track wavefront changes owing to the absence of curvature information. We employ surface fitting to estimate the local curvature, calculate continuous normal vectors, and apply a virtual divergence factor to compensate for energy convergence and divergence effects. Numerical experiments demonstrate that the proposed method achieves an NRMSE improvement of over 20 % compared to commercial software. The proposed technique can be effectively utilized for the RCS analysis of curved cavity structures.

Existing low-Earth-orbit (LEO) communication link analyses face two main challenges: (1) limited accuracy of 3D atmospheric refractivity reconstructed from sparsely sampled radiosonde data, and (2) numerical instability in previous nonuniform plane-wave ray-tracing algorithm [1] (i.e., underflow under standard double precision), where non-uniform plane waves inevitably arise at complex-valued dielectric interfaces, is caused by extremely small atmospheric loss terms. To address these issues, we reconstruct a high-resolution 3D complex-valued refractivity model using numerical weather prediction data, and develop a fast and numerically stable non-uniform planewave ray tracer. The method remains stable in double precision and delivers a 24-fold speedup over high-precision benchmarks. Comparisons show that boresight-error deviations and pathloss differences between the rigorous method and the uniformplane- wave approximation remain negligible, even under heavy precipitation. Although rays in a lossy atmosphere experience different phase and attenuation direction vectors-forming nonuniform plane waves-the resulting effective attenuation along the path is nearly identical to that predicted by the uniformplane- wave model. These findings justify the continued use of uniform plane wave ray-tracing in practical LEO link analyses.

In this study, an artificial intelligence (AI)-based ionospheric electron density model specialized for the Korean Peninsula was developed and used to analyze the Faraday rotation, a propagation characteristic of radio waves passing through the ionosphere. The Faraday rotation values calculated using the developed AI model, ionosonde observation data, and global empirical model IRI-2016 data were compared to analyze the differences among the electron density models. In addition, the errors between the simplified Faraday rotation calculation method and a more accurate approach based on ray tracing and the Appleton-Hartree equation were evaluated. The results of this study can contribute to improving the accuracy of predicting radio wave propagation characteristics in the ionosphere over the Korean Peninsula.