Search

This paper investigates various array beam shapes for high-power electronic warfare applications using an actual broadband array antenna. For use in a limited mounting space, a compact printed log periodic dipole array (LPDA) operating over a wide bandwidth is designed. The LPDA is then extended to an 8 × 1 array, with active element patterns (AEPs) obtained through simulation and measurement. Beam synthesis is performed by the superposition of several array patterns, which involves adjusting the weight of each AEP. To derive a synthesized array beam shape that is similar to the guided mask, the Taylor window weighting method is applied to each array pattern. Finally, beam synthesis for the flat-top beam, cosecant-squared beam, and iso-flux beam is performed using Taylor window-weighted AEPs, and the results are compared with those of beam shapes using ideal isotropic patterns. The results demonstrate that various beam shapes can be achieved for high-power electronic warfare applications using the AEPs of an actual array antenna.

In this paper, we propose a dual-band shared-aperture antenna composed of array elements with high electromagnetic (EM) transparency. To increase EM transparency, the antenna consists of an optimized substrate with low effective permittivity by combining thin dielectric sheets and air-gap layers. To further improve the EM transparency, thin dual-loop radiators with optimized widths and lengths are adopted for the S-band element, and an E-shaped patch antenna is employed for an X-band element. This configuration minimize the pattern distortion in the X-band elements while enhancing antenna bandwidths. In addition, a calibration layer comprising four monopole probes and microstrip transmission lines is included for monitoring the phase and amplitude errors of each element. To verify the feasibility, the proposed antenna is fabricated to measure antenna characteristics, such as reflection coefficients, beam steering performance, and mutual coupling in a full anechoic chamber. The fractional bandwidths of the antenna in the S- and X-bands are 16.4% and 26.8%, respectively. The array gains at the bore-sight are 16.0 dBi in the S-band and 24.0 dBi in the X-band.

This paper proposes a compact ultra-wideband (UWB) direction-finding antenna with a single-radiator multiple-port (SRMP) design. The proposed antenna consists of a single-radiator, self-decoupling feed structure (SDFS), and via walls considering the limited mounting space for mobile applications. The SDFS is optimized to improve isolation characteristics between adjacent ports. To verify the feasibility, the proposed SRMP antenna is fabricated, and antenna performance such as reflection coefficients, mutual couplings, and radiation patterns are measured in a full anechoic chamber. The SRMP antenna achieves a broadband of 2.1 GHz (from 6.3 GHz to 8.4 GHz) and a low mutual coupling of −21.22 dB at 8 GHz. In addition, a bore-sight gain of 0.78 dBi is measured at the target frequency of 8 GHz. To investigate the direction of arrival (DoA) estimation of the SRMP antenna, we utilize the Qorvo test board with the DW3000 chip, generally used in commercial UWB direction-finding systems. At distances of 1 m and 2 m, average estimated errors of 2.35° and 2.13° are obtained, respectively. These results demonstrate that the proposed compact SRMP antenna is suitable for UWB direction-finding systems of smart devices.

In this paper, we propose an S/X-band shared-aperture array antenna with a mutual complementary design to improve the electromagnetic (EM) transparent characteristics. A unit-cell of the proposed antenna includes one dual-loop element for the S-band and $3\times 3$ dual-loop elements for the X-band. To configure the shared-aperture structure in a limited space, the S-band element is stacked on top of the X-band elements. To solve the practical engineering problems of the shared-aperture antennas, novel design techniques such as using a mutual complementary structure, a coupling compensation array, an interface layer, and an antenna modularization are employed. To verify the antenna feasibility, the fabricated unit-cell extends into a $4\times 4$ unit-cell array. The fractional bandwidth of the reflection coefficients for the proposed array are 14.7% and 15% in the S- and X-bands, respectively. In the S-band, as the steering direction of the main beam increases from 0° to 45°, the maximum gain decreases from 14.6 dBi to 11.8 dBi. In the X-band under the same conditions, the maximum gain varies from 26.6 dBi to 25.3 dBi.

This paper proposes a novel feed array antenna to achieve a uniform electric field distribution in the near-field region for feeding a large-aperture antenna. The feed antenna has a 4 × 4 rectangular array configuration to obtain uniform near-field distribution on a virtual target surface. Each element of the array consists of a Vivaldi radiator and parasitic rings, and these two components have different radiating modes. In particular, the near-field pattern of the parasitic rings can be varied by adjusting their radii. Thus, the required near-field distribution on the virtual target surface can be achieved by optimizing the radii of the parasitic rings. To further enhance the uniformity of the electric field, the input phase of each Vivaldi radiator is adjusted by applying different transmission line lengths to the Vivaldi radiators depending on their positions in the array. To verify the feasibility of the proposed antenna, the electric field distributions are measured in an electromagnetic anechoic chamber. The results demonstrate that the proposed feed array antenna can achieve uniform near-field distribution with an average of 1.7 dB and a deviation of 6.8 dB on the virtual target surface placed within half a wavelength from the antenna aperture.

In this paper, we propose an all-metal Vivaldi antenna with pyramidal-shaped conductive wings for use in satellite signal intelligence applications. The inner metal Vivaldi antenna consists of radiating flares and a transition part between the feeder and the flares. The curvature of the inner flares is optimized, while the outer edges of the radiating flares are connected to the pyramidal-shaped wings to obtain a higher antenna gain over the entire operating frequency band. To verify the antenna’s feasibility, performance aspects such as the reflection coefficient, the radiation patterns, and the boresight gain are measured in a full anechoic chamber. The fractional bandwidth of the proposed antenna is 54%, while the boresight gain is greater than 7.3 dBi in the frequency range from 8 GHz to 12 GHz. To examine array performance aspects such as the total gain and beam steering, the proposed Vivaldi antenna is extended to a 4 × 1 linear array configuration. When the main beam is steered from 0° to 15°, the maximum gain is varied from 14.5 dBi to 13.7 dBi, while the side lobe level is decreased from 11.2 dB to 6.3 dB.

This paper presents a Kriging interpolation method for constructing a database of atmospheric refractivity in Korea. To collect as much data as possible for the interpolation, meteorological data from 120 regions of Korea, including both land and sea areas, are examined. Then, the normalized atmospheric refractivity Nn is calculated for an altitude of 0 m, because the refractivity tends to vary depending on the altitude of the observation site. In addition, the optimal variogram model to obtain the spatial correlation required for the Kriging method is investigated. The estimation accuracy of the Kriging interpolation is compared with that of the inverse distance weighting (IDW) and the bi-linear methods. The average and maximum estimation errors when using the Kriging method are 0.24 and 1.32, respectively. The result demonstrates that the Kriging method is more suitable for the interpolation of atmospheric refractivity in Korea than the conventional methods.

In this paper, we propose a metal 3D printed double-ridged horn antenna with a truncated cone feeding structure, curve-shaped cavity, and mode suppressor for a feeder of a reflector antenna. The truncated cone feeding structure is employed to obtain symmetrical patterns, and the curve-shaped cavity is implemented to obtain broadband characteristics. The mode suppressor is then applied to maintain a stable bore-sight gain. To simplify the manufacturing and assembly process, the proposed antenna is designed with only two parts and is fabricated using metal 3D printing technology. To verify the performance of the antenna, the voltage standing wave ratio (VSWR), bore-sight gains, and radiation patterns are measured in a full anechoic chamber. The measured VSWR shows a maximum of 3.0 and an average of 1.9 from 2 GHz to 18 GHz. At 2 GHz, the measured bore-sight gains in the radiation pattern are 5.37 dBi for co-polarization and −20.7 dBi for cross-polarization. The measured radiation patterns are in good agreement with the simulated results.

This paper proposes a single radiator multiple patterns (SRMP) antenna that utilizes a single circular disc radiator to provide multiple radiation patterns that are suitable for ultra-wideband (UWB) direction-finding. The antenna design includes a circular disc and a ground structure for broadband characteristics and a slot structure to reduce mutual coupling. In addition, we simplify the UWB direction-finding system by employing a monopulse method that uses only sum and difference patterns rather than the sensitive phase difference of arrival (PDoA) method. The coordinates for conventional monopulse systems are converted into $\alpha $ -, $\beta $ -, and $y$ -axes that are more suitable for the proposed SRMP antenna. Then, the monopulse ratios on each of the three axes, obtained using sum and difference patterns, are then compared to the simulation and ideal results. To verify the feasibility, the proposed SRMP antenna is fabricated, and antenna characteristics, such as reflection coefficients, mutual couplings, and radiation patterns are measured in a full anechoic chamber. To examine the direction of arrival (DoA) estimation using the proposed antenna, we use the monopulse ratios calculated based on the measured data in the $z\alpha $ -, $z\beta $ -, and zy-planes. The maximum RMS error is reduced to 0.105 using the three-axis monopulse system within the angle range from −15° to 15°. The results confirm that the proposed SRMP antenna is suitable for the UWB three-axis monopulse direction finding.

This paper proposes a circularly polarized (CP) high-gain low-profile patch antenna using a higher-order mode with a heterogeneous layer for global positioning system (GPS) applications. To obtain theoretical insights, we analyze a CP patch using the cavity model, which has two feeding points. Radiated electric fields (E-fields) are derived from the sum of the $\textrm {TM}_{030}^{x}$ and $\textrm {TM}_{003}^{x}$ modes with a 90° phase difference at each port using a hybrid chip coupler. To verify the performance of the proposed antenna, it is fabricated and measured in a full anechoic chamber to obtain the antenna characteristics. The measured and simulated reflection coefficients of the proposed antenna are −33.1 dB and −28.3 dB at 1.575 GHz, respectively. The measured and simulated maximum gains are 9.1 dBic and 9.4 dBic at 1.575 GHz, respectively.

This paper proposes a single circular radiator with a multi-port (SRMP) antenna that can estimate the direction-of-arrival (DoA) in the azimuth and elevation directions. The proposed SRMP antenna is designed to minimize the size of the ultra-wideband system by using only one patch radiator. To verify the feasibility, the proposed antenna is fabricated, and the reflection coefficient and boresight gain are measured (−13.3 dB and 3.4 dBi at 8 GHz). Then, to observe the direction-finding performance, the DoA estimation results using the Bartlett beamformer are compared with the typical array. At all incident angles, a root-mean-square error of less than 1° is observed when the signal-to-noise ratio is higher than 6 dB.

This paper proposes an all-metal Vivaldi array antenna with a wide-angle impedance matching (WAIM) layer for high-power jamming systems. To reduce fabrication complexity and time, the proposed array antenna is manufactured using a metal 3D printing method. The Vivaldi unit cell, composed of a radiating flare part and an inner cavity, is extended into an $8\times $ 8 array with a ±45° slant configuration. To further enhance the beam steering angle, the WAIM layer is placed on top of the proposed array antenna. The performances of the proposed array antenna, such as its active reflection coefficients (ARCs), gains, and array radiation patterns, are investigated in a full anechoic chamber. At a steering angle of ( $\theta _{0} =45^{\circ }$ , $\phi _{0} = 25^{\circ }$ ), the measured and simulated average ARCs of the center element (Port 36) with the WAIM layer are −13.2 dB and −18.5 dB, respectively. At 4 GHz, the measured and simulated boresight gains of the proposed array antenna are 19 dBi and 20.6 dBi, respectively. In addition, the measured and simulated boresight gains for the ( $\theta _{0} =45^{\circ }$ , $\phi _{0}$ = 0°) steering angle in the zx -plane are 18 dBi and 21 dBi, respectively. In the zy -plane, boresight gains for the ( $\theta _{0} =45^{\circ }$ , $\phi _{0} = 0^{\circ }$ ) steering angle are 19.3 dBi by measurement and 19.1 dBi by simulation. These results demonstrate that the proposed array antenna is suitable for high-power jamming systems because stable boresight gains are observed even at wide steering angles without unwanted grating lobes.

This paper proposes a wideband printed patch dipole antenna with a simple on-board feeding network. The proposed antenna is composed of two dipole radiators, a transmission line, and an on-board feeding network with a chip balun. The dipole radiators are printed on a substrate, and the edges of the radiators are truncated to create a hexagonal shape with wide impedance-matching characteristics. The chip balun is embedded in an RO4003C printed circuit board (PCB) to excite differential feeding to each radiator with a 180° phase difference. The proposed antenna is optimized using a CST Studio full electromagnetic software tool, and it is fabricated and measured in an anechoic chamber. The measured fractional bandwidth for the reflection coefficient below −10 dB is 79.5%, and the proposed antenna has a measured gain of 7.1 dBi at 3.5 GHz.

This paper presents a method for predicting atmospheric duct conditions from a clutter power spectrum using deep learning. To accurately predict the duct conditions, deep learning with a binary classification is applied to the proposed refractivity from the clutter (RFC) method. The input data set is the artificial clutter data that are generated via the Advanced Refractive Prediction System (AREPS) simulation software Ver. 3.6 in conjunction with random atmospheric refractive indices. The output of the RFC method is then predicted via binary classification, indicating whether the atmospheric conditions are duct or non-duct. For the cross-validation, the clutter power spectrum data are generated based on real atmospheric refractivity data. The results show that the DNN trained with 5600 pieces of data (validation accuracy of 95.99%) exhibits a binary classification accuracy of 98.36%. The deep neural network (DNN) trained with 28,000 pieces of data (validation accuracy of 98.20%) achieves a binary classification accuracy of 99.06% with an F1-score of 0.9921.

In this paper, we propose a stacked dual-patch antenna with 3D printed thick quasi-air substrates and a cavity wall for wideband applications. To achieve the theoretical maximum bandwidth of the patch antenna, the quality factor of the system needs to be minimized. To achieve this, the area of the conductive radiator should be enlarged, while the permittivity of the substrate within the patch must be reduced close to 1. To realize a patch antenna with this maximum bandwidth, the stacked dual-patch configuration is employed to obtain an extended conductive radiator area. In addition, square-pipe resin frames manufactured using a 3D printing method are applied to the proposed antenna to implement a quasi-air substrate structure that has a low permittivity value close to 1. The proposed stacked dual-patch antenna with a quasi-air substrate has a broad bandwidth of 20.7%. The results demonstrate that by using the proposed antenna structure, broadband characteristics close to the fundamental bandwidth limit of the patch antenna can be achieved.

This paper analyzes low-Earth-orbit (LEO) satellite downlinks when an airborne interference source moves parallel to the satellite trajectory by considering the relative angle differences between the satellites and the interference sources. To make the experimental interference situations more like actual environments, the LEO trajectories are obtained from two-line element set (TLE) data. Airborne interference sources with various altitudes move parallel to the LEO trajectories, and a jamming to signal (J/S) ratio is calculated based on the relative angle differences between the ground station, the LEO satellite, and the interference source. To accurately calculate the J/S ratio, we should apply the sidelobe gain from which the interference signal enters to the ground station antenna. In order to calculate the relative angle difference ψ, the coordinates of the satellite and the interference source are converted from the World Geodetic System 1984 (WGS84) to the ground station-centered east–north-up (ENU) system. The resulting J/S ratio demonstrates that the distance and the relative angle difference ψ between the ground stations, LEO satellite, and airborne interference source appear to be important factors causing changes in the J/S ratio. Among them, the relative angle difference ψ, which determines the sidelobe gain of the ground station antenna, is the most significant factor affecting the J/S ratio variation.

In this paper, we propose a deployable broadband mesh reflector antenna for use in signals intelligence (SIGINT) satellite systems, considering performance degradation due to shape deformation. To maximize gain by increasing the diameter of the reflector while reducing the weight of the antenna, the reflector of the antenna is designed using lightweight silver-coated Teflon mesh. The mesh reflectors are typically expanded by tension to maintain their parabolic structure; thus, shape deformation cannot be avoided. This shape deformation results in shape differences between the surface of the mesh reflector and the ideal parabolic reflector, thus resulting in the degradation of the performance of the mesh reflector antenna. To observe this degradation, we analyze antenna performance according to the number of arms, the number of joints, the feed distance, and the distance from the reflector center to each joint. The performance of the mesh reflector antenna is examined using an effective lossy conducting surface (ELCS) that has the same reflectivity as the silver-coated Teflon mesh to reduce simulation time and computing resources. The designed silver-coated Teflon mesh reflector and the double-ridged feed antenna are fabricated, and the bore-sight gain is measured using the three-antenna method. The measured bore-sight gain of the proposed antenna is 31.6 dBi at 10 GHz, and the measured and simulated results show an average difference of 3.28 dB from 2 GHz to 18 GHz. The proposed deployable mesh reflector antenna can be used in a variety of applications where small stowed volume is required for mobility, such as mobile high-gain antennas as well as satellite antenna systems. Through this study, we demonstrate that shape deformation of the mesh reflector surface significantly affects the performance of reflector antennas.

This article proposes the S/X band dual-loop shared-aperture 2 × 2 array antenna, which is constructed using a unit-cell having one S-band element stacked on 3 × 3 X-band elements. The unit-cell employs a coupled-fed dual-loop structure with a direct-feed pin on the upper loop to obtain the broadband matching characteristics and low manufacturing error. This radar configuration has the advantages of easy installation and low cost. In addition, the thin loop structure of the upper layer S-band element is optimized so that the S-band element has electromagnetic (EM) transparent characteristics in the X-band. The extended via cavity wall is also applied outside the nine X-band elements to block the mutual coupling effect among the X-band elements. To confirm the feasibility of the proposed array antenna, the beamforming performance and active reflection coefficient (ARC) characteristics of the fabricated array are examined in the S/X band.

As UWB technology develops and devices become smaller, miniaturization techniques for an array antenna system are required. In addition, more in-depth research is needed for UWB direction-finding techniques using channel impulse response (CIR) data. This paper proposes an ultra-wideband (UWB) antenna using a single-radiator multiple-port (SRMP) design for the direction-finding systems of smart devices. The proposed SRMP antenna was designed using a single tripod-shaped patch that can replace the array system. The tripod-shaped radiator was optimized using the edge shape design function to improve its broadband and mutual coupling characteristics. For performance verification, the proposed antenna was fabricated, and the reflection coefficient, mutual coupling, and radiation patterns were measured in a fully anechoic chamber. The proposed antenna has an operating frequency band of 6.1 GHz (from 5.8 GHz to 11.9 GHz) for port 1 and a measured mutual coupling of −14.8 dB at 8 GHz. The SRMP antenna has measured maximum gains of 3.5 dBi for port 1 and 2.9 dBi for port 2. To examine the direction-finding performance, the fabricated antenna was connected to a circuit module with a DW3000 chip, which is widely employed in commercial mobile UWB systems. The direction of arrival (DoA) results using the measured CIR data show root-mean-square (RMS) errors of 1.57° and 4.58° at distances of 30 cm and 60 cm.

This paper proposes the design of a gain enhanced single circular patch radiator (SCPR) with a cavity-backed structure using multiple substrate integrated waveguide (SIW) feeders for monopulse systems. We derive the equations of a radiation pattern for the multi-feed SCPR and compare it with the full EM simulation results. Based on the theoretical results, the proposed SCPR with multiple feeds is designed by adding the cavity-backed structure to obtain high gain characteristics. In the feeding network, four SIW structures are designed and circularly arranged, which can reduce loss and mutual coupling. Each pair of the SIW feeders can provide sum ( $\Sigma$ ) and difference ( $\Delta$ ) patterns to achieve the monopulse direction finding (DF) properties in both elevation and azimuth directions. To verify the feasibility, the proposed antenna is fabricated, and the antenna characteristics are measured. The measured reflection coefficient is −14.5 dB at 5.8 GHz, and the maximum gains are 4.9 dBi and 4.8 dBi in zy-plane. To observe the monopulse DF, the estimated direction of arrival (DOA) results are examined in both elevation and azimuth directions. In the whole estimated angle range, the estimation error is lower than 0.49, and the average error is 0.26.

This paper proposes an S/X-band single-layer shared-aperture array antenna for the multifunction radars of military ships. A unit cell of the proposed antenna consists of one S-band element and four X-band elements. The S- and X-band elements are printed on the same layer to prevent a blockage effect by upper elements in the stacked shared-aperture antenna. Herein, the S-band element has a mutual complementary configuration for the X-band elements. In addition, the unit cell of the proposed antenna is designed in a symmetrical structure, which can be flexibly extended to a full array configuration. To verify the antenna feasibility, antenna performances are measured in a full anechoic chamber. The fractional bandwidths of the S- and X-band elements are 13.6% and 13.4%, respectively. Moreover, in the 2 × 2 array configuration, the S-band array gain in the bore-sight direction varies from 5.4 dBi to 3.5 dBi when the main beam is steered from 0° to 45°. Under the same conditions, the measured X-band array gain in the bore-sight direction decreases from 13.4 dBi to 11.6 dBi.

This paper investigates a low-Earth orbit (LEO) satellite downlink for high-speed data communication in interference situations. A choke ring horn type antenna is used as the data transmitting antenna with an isoflux pattern in the LEO satellite, which has a beam coverage of ±51.6° and a bore-sight gain of 4.4 dBi at 8 GHz. The receiving antenna on the ground station is a parabolic type antenna with a diameter of 11.3 m, and it has a half-power beam width (HPBW) of 0.2° with a maximum gain of 59 dBi at 8 GHz. The jamming-to-signal ratio (J/S) is calculated assuming that the LEO satellite transmits signals to the ground station, and an elevation angle of the interference source varies from 0° to 90° at an altitude of 10 km. Applying antenna characteristics, such as HPBWs and side lobes, to the calculated space wave path loss makes it possible to predict the J/S results according to the location of the interference source and the satellite. The results show that it is necessary to consider the space environment to accurately analyze the LEO satellite downlink, especially at the low elevation angle of the satellite.

This paper proposes an electrically small and frequency selective loop (FSL) antenna for shielding effectiveness (SE) measurement in low frequency (10 kHz – 30 MHz) magnetic fields. The proposed antenna consists of an outer loop and an inner loop. A low-pass filter is placed between outer and inner loop to improve the antenna factor (AF) in the upper frequency band as the number of loop turns increases. The size of the designed antenna is 220 mm $\times220$ mm, which achieves 46 % reduction of the antenna area compared to conventional 300 mm loop antennas and the proposed antenna preserves the AF characteristic over the entire frequency range (10 kHz – 30 MHz). In addition, the loop of the designed antenna is printed using microstrip techniques, which reduces the cost and complexity of the antenna fabrication. The results demonstrate that the proposed antenna is suitable for SE measurements of small enclosures (all dimensions between 0.75 m and 2 m).

In this paper, we propose a design for an on-glass 5G monopole antenna for a vehicle window glass. The proposed antenna consists of a monopole resonator, an inductive line, and a co-planar waveguide (CPW), which can adjust the phase so that the current in each resonator is close to in phase. Therefore, although the vehicle window glass has a high dielectric loss, the proposed monopole with an inductive line can obtain an antenna gain that is suitable for applying to vehicle 5G communications. To verify the antenna characteristics, the reflection coefficients and the radiation patterns are measured in a full anechoic chamber. The results demonstrate that the proposed on-glass antenna is suitable for applying in vehicle 5G communications.

This article investigates the scattering characteristics inside the cabinet of a nuclear power plant by the mode-matching technique (MMT) when arbitrary wireless devices are assumed to be applied in the plant. The modal decomposition, multiregion problem, and power conservations of the MMT are introduced to confirm the scattered field inside the cabinet. It is found that stronger scattered fields are usually found when the center of the gap in the rear door of the cabinet is located $1.5\lambda _{0}$ away from the side wall. Therefore, when determining the geometry of the cabinet and digital modules, the scattered field inside the cabinet is systematically analyzed in advance, and appropriate design guidelines for the cabinet can be suggested.

This study investigates non-uniform array configurations to maximize the beamforming performance of passive coherent location (PCL) systems. The proposed array consists of eight dipole elements that are divided into two groups with different distances from the array center. This double-layered non-uniform configuration is designed considering the array antenna characteristics (peak-to-side lobe ratio, first null bandwidth, null width, and null depth). The resulting antenna array can provide more appropriate patterns for PCL systems than a conventional uniform circular array. The target detection performance of the proposed array in PCL systems is tested in a certain scenario. The results demonstrate that the proposed antenna in PCL systems can detect the target with Doppler and range errors of 1 Hz and 1.2 km, respectively, in a given situation.

This paper proposes a novel miniaturized loop antenna consisting of a multi-turn printed strip and a ring-shaped ferrite core. The lateral surface of the ferrite core is tightly wrapped by the circular multi-turn strip, which is printed on a thin, ring-shaped Styrofoam. To verify the feasibility, the proposed antenna is fabricated, and the antenna factor (AF) levels are measured using the three-antenna method from the VLF to HF band. The AF levels by measurement, theory, and simulation are 36.14 dB, 34.01 dB, and 33.6 dB at 30 kHz, respectively. In the VLF band, the antenna has a diameter of 114 mm, which is miniaturized to less than 60% compared to previous research. In addition, the proposed antenna is employed in the shielding effectiveness (SE) measurement of a small commercial cabinet to observe its suitability for SE measurement of small shielding enclosures. The SE values averaged over the frequency range from 10 kHz to 3 MHz are 5.19 dB and 14.14 dB in the horizontal and vertical polarizations.

This paper presents an analytical interpretation of electromagnetic interference between solid-bottom type open cable trays in a nuclear power plant under the assumption that an electric-line current is undesirably generated from a damaged cable in an open cable tray. Based on the superposition principle and Helmholtz's equation in conjunction with the separation of variables, we employ a mode-matching method to obtain analytical solutions to the postulated electromagnetic interference problem. Before conducting a mode-matching analysis, we investigate the radiating principle of the electric field interfering with a victim cable tray by deriving the array factor in consideration of an imaginary electric-line current. In addition, we characterize the electric fields with a propagating mode at an observation point in the victim cable tray using the derived expression of the electric field. Based on this, we validate the formulation and computation of our mode-matching method and then computationally investigate the strength and distribution of interfering electric fields in terms of the separation distances provided in regulatory guidance on the electrical independence of a nuclear power plant. Finally, we compute the strength and distribution of the interfering electric field at the observation point when the location of an electric-line current is modified. The results of the study provide us with the useful information to alleviate the electromagnetic interference between open cable trays in a nuclear power plant.

We propose a novel method to calculate the propagation from a geostationary orbit (GEO) satellite to a ground station considering dispersive and inhomogeneous atmospheric environments with an actual satellite parabolic reflector antenna. The proposed simulation method is based on the hybrid numerical techniques including physical optics (PO), the 3-dimensional (3-D) ray tracing technique, and geometrical optics (GO). The electromagnetic propagation from an actual GEO satellite parabolic reflector antenna to a ground station at Seoul, Korea is calculated using PO. Reflections and refractions at the boundaries of the stratified refractive index model for the atmosphere are then calculated by the ray tracing approach and GO to take into account inhomogeneous atmospheric environments. Our method is verified by comparing with the results with the prediction method of rain attenuation given in ITU-R P.618-13 and the unified model. The comparison generally shows a good agreement. Atmospheric attenuation and boresight errors from a GEO satellite to a ground station are calculated and discussed. As a result of the calculations, when the rainfall rate is 26.19 mm/h, the atmospheric attenuation from a GEO satellite (COMS-1) to a ground station at Seoul, Korea is 12.1621 dB and the boresight error is 0.0336 degrees.

This paper proposes a design of a small array antenna with an extended cavity structure for wireless power transmission. The proposed array element consists of a square radiating loop, which is designed to resonate at 5.8 GHz, and an extended cavity structure to reduce the mutual coupling between adjacent elements. We derive the optimal element number in a limited space by considering the input power for each element, fabrication cost, and aperture efficiency of the system. To verify the suitability of the proposed a small array with an extended cavity structure, a 2 × 2 downscaled array antenna is fabricated and measured in a full anechoic chamber. The results confirm that the proposed antenna element with an extended cavity structure is suitable for wireless power transmission systems; the proposed array has a transmission efficiency of about 1% at a distance of 2 m when the array is applied to both transmitting and receiving antennas.

This paper proposes a multi-band array antenna that shares a common aperture with heterogenous array elements. The multi-band array antenna includes one printed dipole antenna for the S-band and 3 × 3 array E-shaped patch antennas for the X-band. The current directions of the printed dipole and E-shaped antenna are orthogonal to each other, which properly diminishes the mutual coupling interference. To decrease the mutual coupling interference among the X-band components, we placed cavities using multiple vias surrounding the X-band components. To check the validity of the proposed design, the unit-cell was expanded to a 12 × 12 X-band array configuration, and then the beam steering properties were examined. The proposed antenna’s average gains are 5.2 dBi in the S-band and 5.2 dBi in the X-band. The bore-sight gain of the extended array configuration on the ship mast is 35.6 dBi. The results confirm that the proposed design is suitable for MFR applications even in a shared aperture.

This article proposes the design of a coupled-fed printed dipole antenna for direction finding (DF) systems. The antenna consists of a radiating 50° angled expanded-arm printed dipole as well as a fan-shaped feeder that is located on the opposite side of the radiating dipole. The 50° angled expanded-arm structure results in a wide beam-width and broadband-matching characteristics. The more the arm angle is bent, the wider the beam-width pattern. Note that the expanded structure to the side of the dipole arm allows the wide beam-width of the radiation pattern. The printed dipole is then electromagnetically coupled with the fan-shaped feeder to obtain broadband-matching characteristics. To obtain additional broadband-matching characteristics, the circular cavity and the four-step tapered structures of the radiating printed dipole are carefully tuned by considering the coupled fields induced by the indirect feeding structure. The reflection coefficients are −14.6 dB and −11.9 dB at 1.575 GHz and 2.4 GHz, and the boresight gains are 4.8 dBi and 1 dBi, respectively. To confirm the DF capability of the proposed antenna, the pattern of the 4 × 4 arrays is observed by varying the steering angle.

This paper proposes a coupled-feed structure accompanied by cavity walls for an extremely small four-element array with an aperture size of less than 0.4 λ. The feeding loop of the proposed structure is connected to two output ports of a hybrid chip coupler, and the radiating loop is coupled to the feeding loop through near electromagnetic fields confined within the substrates. This structure allows to increasing the effective dielectric constant of the antenna, which helps to miniaturize the aperture size of the antenna. Another advantage of the proposed structure is that the effective dielectric constant can be adjusted by varying the height of the cavity walls. To verify the operating principles, an equivalent circuit is built, and variations of magnetic field distributions are also observed. Furthermore, performances on interference mitigation are evaluated based on the power inversion algorithm. The results confirm that the proposed structure is suitable to replace current single-antenna systems for an additional capability of effective interference mitigation in such a restricted area.

This paper investigates the scattering characteristics of periodic open cabinets in nuclear power plants using the mode-matching technique. The concept of a parallel-plate waveguide is adopted, and the power conservations at all junctions are confirmed. The incident power is almost equivalent to the summations of the reflected and transmitted powers at all junctions, and the differences in the power for all cases are almost zero. A multiregion problem is systematically applied to resolve the entire scattered fields, and the resulting contour plots for the field strength according to various modal incidences are displayed. Based on this paper, modal field distributions for multilayer cabinet structures can be extensively analyzed.

This paper proposes a novel iterative algorithm based on a Kernel regression as a suboptimal approach to reliable and efficient antenna optimization. In our approach, the complex and non-linear cost surface calculated from antenna characteristics is fitted into a simple linear model using Kernels, and an argument that minimizes this Kernel regression model is used as a new input to calculate its cost using numerical simulations. This process is repeated by updating coefficients of the Kernel regression model with new entries until meeting the stopping criteria. At every iteration, existing inputs are partitioned into a limited number of clusters to reduce the computational time and resources and to prevent unexpected over-weighted situations. The proposed approach is validated for the Rastrigins function as well as a real engineering problem using an antipodal Vivaldi antenna in comparison with a genetic algorithm. Furthermore, we explore the most appropriate Kernel that minimizes the least-square error when fitting the antenna cost surface. The results demonstrate that the proposed process is suitable to be used in antenna design problems as a reliable approach with a fast convergence time.

This paper proposes the design of a dual-band circularly polarized antenna with an exchangeable superstrate module to compensate for the unwanted frequency shift without the re-fabrication process. The proposed antenna consists of inner and outer circular ring patches printed on the same layer of a substrate, and the mushroom-shaped superstrate is inserted to the substrate hole placed in the middle of the inner ring patch. The proposed superstrate structure adaptively adjusts the resonant frequency by selecting appropriate heights of the superstrate module. By inserting the superstrate module with the height of 2 mm, the maximum frequency shift of 20 MHz was obtained with the improved gain of about 0.9 dB at 1.42 GHz without any deteriorations on the AR and radiation patterns.

This paper conducts an electromagnetic analysis of the closed cabinet used for instrumentation and control in nuclear power plants for the case of a parasitic electric-line current that is undesirably generated onto an interior digital module. Based on the Helmholtz equation in conjunction with both the separation of variables and superposition principle, we employed a mode-matching method to obtain the analytic solution to an electromagnetic interference problem. Using modal coefficients from a set of simultaneous equations by enforcing boundary conditions, we computationally derive electromagnetic-field distributions in terms of various geometric parameters. The results provide us with information useful for estimating the level of influence of the undesired current source on the adjacent digital modules.

This paper proposes a systematic method for estimating detection performances of a frequency-modulated continuous wave radar using electromagnetic simulations. The proposed systematic method includes a radar system simulator that can obtain range-Doppler images using the electromagnetic (EM) simulations in conjunction with a test setup employed for performance evaluation of multiple targets at different velocities in a traffic environment. This method is then applied for optimizing the half-power beamwidths of the antenna array using an evaluation metric defined to improve the detection strengths for the multiple targets. The optimized antenna has vertical and horizontal half-power beam widths of 10° and 60°, respectively. The results confirm that that the proposed systematic method is suitable to improve the radar detection performance with the enhanced radar-Doppler images.

This paper proposes a 5G glass antenna that can be printed on the thick window glass of a vehicle. The proposed antenna consists of a coplanar waveguide (CPW), a printed monopole radiator, parasitic elements, a linearly arrayed patch director, and a grid-slotted patch reflector. The linearly arrayed patch director and grid-slotted patch reflector are applied to improve the bore-sight gain of the antenna. To verify the performance improvement and feasibility, the proposed antenna is fabricated, and a reflection coefficient and a radiation pattern are measured and compared with the simulation results. The measured reflection coefficient shows broadband characteristics of less than −10 dB from 24.1 GHz to 31.0 GHz (fractional bandwidth of 24.6%), which agrees well with the simulation results. The reflection coefficients are −33.1 dB by measurement and −25.7 dB by simulation, and the maximum gains are 6.2 dBi and 5.5 dBi at 28 GHz, respectively. These results demonstrate that the proposed antenna has high-gain characteristics being suitable for 5G wireless communications.

In this paper, we propose an interface layer using the coplanar waveguide (CPW) between an array antenna and transmitting receiver modules (TRMs) for X-band military ship radar systems. To improve transmission characteristics, the interface layer with the CPW has three transition parts: Transition part A is between the sub miniature push-on (SMP) connector and the interface layer. Transition part B is the CPW in which the thickness gradually increases. Transition part C is for connecting the interface layer and the antenna. The measured reflection and transmission coefficients of the fabricated interface layer are −22.4 dB and −0.82 dB, respectively. To verify the proposed interface layer, we then apply the layer to a 2 × 2 X-band array antenna and measure the array antenna characteristics, such as reflection coefficients, array antenna gain, and half-power beam widths (HPBWs). The measured reflection coefficient is under −10 dB from 8.6 GHz to 10.2 GHz, and the bore-sight array gain of the 2 × 2 array antenna is 10.5 dBi at 9.5 GHz. In addition, the measured HPBWs under the same conditions are 47.8° and 39.1° in the zx- and zy-planes, respectively. The results demonstrate that the proposed interface layer using the CPW is suitable for X-band radar systems.

In this paper, a method for estimating atmospheric refractivity from sea and land clutters is proposed. To estimate the atmospheric refractivity, clutter power spectrums based on an artificial tri-linear model are calculated using an Advanced Refractive Prediction System (AREPS) simulator. Then, the clutter power spectrums are again obtained based on the measured atmospheric refractivity data using the AREPS simulator. In actual operation, this spectrum from measured reflectivity can be replaced with real-time clutter spectrums collected from radars. A cost function for the genetic algorithm (GA) is then defined based on the difference between the two clutter power spectrums to predict the atmospheric refractivity using the artificial tri-linear model. The optimum variables of the tri-linear model are determined at a minimum cost in the GA process. The results demonstrate that atmospheric refractivity can be predicted using the proposed method from the clutter powers.

In recent decades, novel and significant approaches to the design of antennas for various microwave and millimeter-wave applications have been attempted [...]

This paper proposes a Moiré-inspired metasurface lens system to focus electromagnetic power in the Fresnel near-field region. The proposed metasurface lens (MSL) system is composed of two MSLs and a square patch antenna source. The MSLs are modeled based on the transmit phase distributions of Moiré lens theory, and each unit cell structure (patch shape and Jerusalem cross slot shape) is determined to fit the calculated transmit phase distributions at each location. When changing the unit cell structure, phase and transmittance variations are achieved over 330° and −3 dB. The square patch antenna source is then designed to excite the field to the MSLs. The measured reflection coefficients are below −10 dB at 5.8 GHz while rotating the second MSL. The focal length can be adjusted from a minimum of 38 cm to a maximum of 110 cm according to the rotation angle of the second MSL. The proposed MSL system can be employed for wireless power transmission applications to focus electromagnetic power at various locations in the near-field region.

This article proposes the resonant transmission characteristic through the periodic subwavelength metal-insulator-metal (MIM) waveguide on a quartz plate at terahertz frequencies. By applying the multiregion problem to the mode matching technique (MMT), the total reflection and transmission characteristics of the periodic MIM waveguide can be resolved as functions of the thickness of the MIM waveguide, the gap width of the MIM waveguide, the thickness of the quartz plate, and frequency. To validate the results of the proposed MMT, the transmission results are compared with the results using a commercial electromagnetic simulation software (XFdtd). The similar results demonstrate that the proposed MMT is proper to compute the reflection and transmission characteristics of the periodic MIM waveguide on the real quartz plate and providing in-depth intuition for resonant transmissions using the modal approach.

In this paper, we propose a polarization-selective electromagnetic (EM) transparent mesh-type E-shaped antenna unit-cell in a shared aperture. The proposed antenna unit-cell, which can be expanded to a larger array in a modular way, has one S-band antenna on the upper layer and nine X-band antennas on the lower layers. The simple E-shaped structure, which has a low profile with a good bandwidth, is used for the antenna elements. However, due to the limited aperture size of the stacked configuration, the lower-layer elements can be physically blocked by the upper-layer element. To reduce this blockage effect, the S-band element is rotated 90 degrees with respect to X-band elements so that the polarizations between the S- and X-band elements are perpendicular to each other. Moreover, to minimize performance degradation due to the blockage effect, a mesh structure is applied for S-band elements for EM transparent characteristics, thereby improving EM transparency from −30 dB to −1.5 dB. The extended via cavity wall is also employed outside the nine X-band elements to minimize the mutual coupling and to reduce antenna size. To confirm the effectiveness of the proposed design, the proposed antenna unit-cell is fabricated, and the radiation characteristics are measured, in a full anechoic chamber. The average bore-sight gains in the S- and X-band are 5 dBi and 4.5 dBi, respectively. The results confirm that the proposed design is suitable for shared-aperture radar applications.

This paper proposes a design of small controlled reception pattern antenna (CRPA) arrays using circular microstrip loops with frequencyinsensitive characteristics. The proposed array consists of seven identical upper and lower circular loops that are electromagnetically coupled, which results in a frequency-insensitive behavior. To demonstrate the feasibility of the proposed feeding mechanism, the proposed array is fabricated, and its antenna characteristics are measured in a full-anechoic chamber. The operating principle of the proposed feeding mechanism is then interpreted using an equivalent circuit model, and the effectiveness of the circular loop shape is demonstrated by calculating near electromagnetic fields in proximity to the radiator. The results confirm that the proposed feeding mechanism is suitable to have frequency-insensitive behavior and induces strong electric and magnetic field strengths for higher radiation gain in extremely small antenna arrays.

In this paper, we propose a hemispherical reconfigurable frequency selective surface (FSS) using water channels. The switching between band-pass and band-stop states is possible since the water with a high dielectric constant can control the effective permittivity of the structure. We simulate and fabricate the FSS and measure the radiation pattern of FSS enclosed horn antenna to check the reconfigurable characteristic of the hemispherical FSS. The simulated results show a good agreement with the measured results.

This letter proposes a novel design for a printed 5G monopole antenna on a vehicle window glass. The proposed antenna consists of a coplanar waveguide (CPW), a monopole radiator, parasitic elements, and a lattice-structure reflector. The parasitic elements are placed on either side of the monopole radiator to improve the bore-sight gain. To solve the radiation pattern distortion problem that occurs due to the thick vehicle window glass, the lattice-structure reflector is printed on the opposite side of the monopole radiator. Through fabrication and measurement of the proposed antenna, it is confirmed that the design improves bore-sight gain, and minimizes the radiation pattern distortion. The results demonstrate that the proposed 5G monopole antenna with parasitic elements and the lattice-structure reflector is suitable for 5G communication in vehicle applications.

We investigate a target detection probability (TDP) using path loss of an airborne radar based on air-to-air scenarios in anomalous atmospheric and weather environments. In the process of calculating the TDP, it is necessary to obtain the overall path loss including the anomalous atmospheric environment, gas attenuation, rainfall attenuation, and beam scanning loss. The path loss including the quad-linear refractivity model and other radar input parameters is simulated using the Advanced Refractive Effects Prediction System (AREPS) software along the range and the altitude. For the gas and rainfall attenuations, ITU-R models are used to consider the weather environment. In addition, the radar beam scan loss and a radar cross section (RCS) of the target are considered to estimate the TDP of the airborne long-range radar. The TDP performance is examined by employing the threshold evaluations of the total path loss derived from the detectability factor and the free-space radar range equation. Finally, the TDPs are obtained by assuming various air-to-air scenarios for the airborne radar in anomalous atmospheric and weather environments.

This paper proposes a novel wideband leaf-shaped printed dipole antenna sensor that uses a parasitic element to improve the impedance matching bandwidth characteristics for high-power jamming applications. The proposed antenna sensor consists of leaf-shaped dipole radiators, matching posts, rectangular slots, and a parasitic loop element. The leaf-shaped dipole radiators are designed with exponential curves to obtain a high directive pattern and are printed on a TLY-5 substrate for high-power durability. The matching posts, rectangular slots, and a parasitic loop element are used to enhance the impedance matching characteristics. The proposed antenna sensor has a measured fractional bandwidth of 66.7% at a center frequency of 4.5 GHz. To confirm the array antenna sensor characteristics, such as its active reflection coefficients (ARCs) and beam steering gains, the proposed single antenna sensor is extended to an 11 × 1 uniform linear array. The average values of the simulated and measured ARCs from 4.5 to 6 GHz are −13.4 dB and −14.7 dB. In addition, the measured bore-sight array gains of the co-polarization are 13.4 dBi and 13.7 dBi at 4 GHz and 5 GHz, while those of the cross-polarizations are −4.9 dBi and −3.4 dBi, respectively. When the beam is steered at a steering angle, θ0, of 15°, the maximum measured array gains of the co-polarization are 12.2 dBi and 10.3 dBi at 4 GHz and 5 GHz, respectively.