Inspired by the 100-year-old Yagi-Uda antenna, the beamscanning directivity enhancement based on the strong interelement mutual coupling is proposed, explained, and verified in unequally spaced arrays with fixed configurations. First, the N-port characteristic model analysis is employed over ideal array models to investigate the effect of strong interelement mutual coupling on beamscanning directivities. Then, a 3.5-wavelength array of 1×8 dipoles with varying spacings is designed for verification. The time reversal (TR) synthesis is introduced as a non-iteration way to determine the optimal excitation with mutual coupling consideration for arbitrary array arrangements. The proposed unequal array enhances H-plane beamscanning directivities and realized gains with fixed array length and constant element number, achieving the defined superdirectivity ratio over unity. The angular and frequency ranges for enhancing beamscanning directivity of the proposed unequal array are also investigated. Diverse optimal arrangements are obtained for beamscaning from broadside to end-fire direction with the defined superdirectivity ratio from 1.1 to 3.5. The final experimental verification agrees with the simulated results. This work reveals that the strong interelement mutual coupling makes unequally spaced arrangements an effective way to enhance beamscanning directivity over fixed configurations, illustrating its potential for satellite communications and next-generation base stations.

In this paper, a corrugated Vivaldi phased array antenna in the 28 GHz frequency band is proposed for 5G communication applications. The presented configuration features an all-metal antipodal antenna structure with a broad bandwidth ranging from 26 to 30 GHz and beam steering capabilities from -30 to +30 degrees. The proposed antenna consists of a 4×4 array configuration, where each element has dimensions of 6.46 × 6.46 × 14.25 mm, resulting in an overall antenna structure with dimensions of 25.84 × 25.84 × 14.25 mm. The corrugation method is applied to minimize surface currents, resulting in a reduction in interelement mutual couplings. Therefore, the return loss in the array structure for central elements is decreased, and the antenna gain and radiation efficiency are improved. Moreover, the improved radiation efficiency allows for higher power transmission and reception from an antenna, resulting in potentially higher data rates and better performance.

This paper shows a high-gain planar deployable antenna ensuring air-gap to fold the antenna instead of commonly used way of folding transmission line. The air-gap works effectively not mechanically but also electrically. Proposed antenna has the volume constraints of folded width W, depth D, and height H, which are less than 150 mm and high directivity gain of 16.3 dBi.

We propose a retrodirective harmonic tag using a planar unidirectional dual-frequency antenna in a Van-Atta array. In applying the Van-Atta array to harmonic tags, we address the constraints on element spacing. In the effectiveness evaluation, we demonstrate both computationally and experimentally that the proposed design offers advantages in terms of gain and coverage range compared to a Van-Atta array using single-frequency antennas and an array without retrodirective characteristics.

This paper proposes a multiple-input multiple-output (MIMO) atmospheric radar utilizing orthogonal transmit signals. We focus on the Doppler division multiple access (DDMA) and the code division multiple access (CDMA) MIMO techniques, which are well-established for extending radar functionality and suitable for targets with low Doppler velocities. To validate these two methods, identical observations were conducted using the MU radar, a VHF-band phased array atmospheric radar with multi-channel receivers, enabling its operation as a MIMO radar with additional settings. A MIMO radar can create a virtual receive antenna aperture plane with transmit freedom, unlike actual antennas. When applying DDMA/CDMA systems, it is crucial to precisely adjust the phase between orthogonal transmit signals. We proposed and verified a transmit signal phase adjustment method compatible with each system. This process was validated by actual measurements of the beam pattern through analysis of the moon’s reflection echo after calibrating the phase adjustment for DDMA/CDMA. The results not only align with theoretical predictions, clearly demonstrating the efficacy of these techniques, but also highlight a shared essence among diverse methods for achieving orthogonality through proper transmit signal phase adjustment.

Polarimetric Synthetic Aperture Radar (PolSAR) is a radar that can identify and classify targets using the polarization scattering characteristics. The model-based scattering power decomposition, which is one of the PolSAR data analysis methods, estimates rough land cover conditions based on the ratio of fundamental polarimetric scattering components contained in the observation data. However, there is a problem that urban areas where building walls are not aligned parallel to the observation trajectory are misclassified as natural vegetation or forest. Although modified methods that applies polarimetric basis rotation to compensate the effect of the oblique angle of buildings in such urban areas has been proposed, the problem still remains. The cause of the misclassification is thought to be a mismatch between the scattering model and the actual scattering phenomenon, or bias in the polarimetric basis rotation for angle compensation of the urban area. In this paper, we propose a modified scattering model that takes into account the oblique angles of urban areas directly and evaluate the validity of the model theoretically. Furthermore, error in the orientation angle estimation is discussed by numerical examples and experimental results. The ALOS-2 dataset that is L-band fully polarimetric dataset is used in the experiment.

This paper answers the basic but burning question of whether or not the coupling quality factor (kQ) theory recently emerging for wireless power transfer is consistent with the traditional Friis formula. The Friis formula was established to predict how much power can be received out of the transmitted power in terms of the wavelength and the propagation distance taking the antenna gain into account. We now regard the two antennas as a wireless coupler between the transmitter and the receiver and observe the received-to-transmitted power ratio as the wireless power transfer efficiency; this enables us to juxtapose the kQ theory and the Friis formula fairly. Starting from the antenna structure, we give a series of formulations and flowcharts to describe how to estimate the maximum power transfer efficiency in two distinct routes. One is via the Friis formula, and the other is via the kQ theory. To exactly evaluate the two approaches for comparison, we give simple and persuasive examples of electromagnetic coupling systems between a pair of dipole antennas. We first find the far-field kQ formula between Hertzian dipoles: kQ = 3λ/4πd (λ: wavelength, d: propagation distance) as a crucial discovery. We then move on to practical-size antennas. The dipole element length is chosen to be 0.5, 1.0, and 1.25 λ since they are typically employed in practical wireless systems. The transmit-to-receive propagation distance is assumed to range from d = 1 mm to d = 10 m, which sufficiently covers the near- and far-field regions with respect to the wavelength of 10 cm or at the frequency of 3 GHz. The element radius is assumed to be only 1 mm; therefore we effectively use the method of moment for electromagnetic field simulation. The simulation results demonstrate that kQ = 50 for d = 1 mm and l = 125 mm; thus kQ almost monotonously decreases with the distance d. Accordingly, the maximum power transfer efficiency also decreases with d. A comprehensive simulation confirms that the two approaches, kQ and Friis, agree quite well in the far-field region. The efficiency stemming from kQ largely exhibits a convex curve, while that from Friis exhibits a straight line on a log-log chart. These curves and lines asymptotically get closer and closer toward d = ∞. Since there is no discontinuity on the line and the curve over the wide range, we conclude that the kQ theory for wireless power transfer is fully consistent with the Friis formula.

During emergencies, ensuring connection to emergency calls to contact an ambulance or fire brigade is crucial. Telecommunication networks face congestion in emergencies due to increased emergency and safety confirmation calls. Call admission control (CAC) has been proposed to handle these congested network environments. Our previous CAC method categorizes calls into emergency calls, calls from the disaster area, and calls from outside the disaster area in the Voice over Internet Protocol (VoIP) network. As a result, the optimal thresholds are derived that guarantee the quality of high-priority VoIP calls. However, the lowest-priority VoIP calls are also important calls in an emergency. In this paper, we propose a novel emergency CAC method with a waiting queue for lowest-priority VoIP calls that considers early departure. The early departure refers to the process of reneging in a queuing model with customer impatience. We analyze the connection and communication quality. From the analysis results, our proposed CAC method improves the connection quality of lowest-priority VoIP calls while maintaining the connection quality of high-priority VoIP calls and communication quality of all VoIP calls. Moreover, we analyze the characteristics of the proposed CAC method when the rate of early departure and the maximum number of the accommodated lowest-priority VoIP calls in the waiting queue change.

As we know, content discovery is one of the fundamental research topics in the field of communication networks such as P2P (Peer-to-Peer) networks and Information-Centric Networking. Traditional content discovery on a network aims at discovering content that exactly matches a query, i.e., a request, issued by a user. However, with the growth and diversification of the content space in recent years, it has become necessary to resolve queries flexibly and effectively. A promising approach to address this requirement is similarity searching, which resolves queries based on the similarity among contents. Therefore, in this paper, we incorporate the concept of similarity searching into content discovery on a network and study similar content discovery using a random walk on a graph. Specifically, we introduce a performance metric for similar content discovery, the s-content discovery time, which is defined as the time taken to discover content whose similarity is larger than or equal to a given similarity s, and derive it. We also analyze, through numerical evaluations, the trade-off between similarity and s-content discovery time. As a consequence, we reveal the relationship between the s-content discovery and the following factors: network topology, random walk mobility model, and distribution of content placement.

Covert communication, as an effective security method, had been widely introduced to improve the security of communication against fixed detection device in internet of vechicles (IOV). However, the application of mobile monitoring devices poses a huge threat to traditional covert communication. To solve this problem, we propose a vehicle mounted relay assisted covert communication location optimization method (VMRCCLOM). Specifically, the method first obtains detector’s optimal total error probability and detection threshold by pushing the monotonicity of the function, and then the expression of transmission rate is obtained according to the probability of transmission interruption. Finally, based on the objective function of maximizing the transmission rate, the optimal relay location is designed by geometric method. Experiment results indicate that our VMRCCLOM can effectively improve the transfer rate and concealment probability of communication compared with existing work.

This paper presents the physical layer cell identity (PCID) detection probability using polarization receiver diversity based on the primary synchronization signal (PSS) and secondary synchronization signal (SSS) of the New Radio (NR) interface for 3GPP Clustered Delay Line (CDL) channel models. We first validate the PCID detection probability in the CDL channel models with reference to those in the Tapped Delay Line (TDL) channel models that have the same power delay profile. Simulation results show that the loss in the required average received signal-to-noise power ratio (SNR) satisfying the PCID detection probability of 80% compared to that achieving the PSS detection probability of the same level due to the miss detection of the SSS sequence is only approximately 1.0 dB in the presence of a carrier frequency offset (CFO) in the CDL models. We also show that the PCID detection probability of 90% is achieved at the average received SNR of -2.2 dB, -5.6 dB, and -13.5 dB in the presence of a CFO with ε = 3 ppm at the carrier frequency of 4 GHz in the CDL-A, C, and E channel models, respectively. Through extensive simulation results, we show that the structure and sequence of the PSS and SSS based on the NR specifications are effective in achieving a high PCID detection probability for the realistic CDL channel models, in which the channel response of each path is characterized by the average signal power, delay time, random phase, and incident path angles, in the presence of the CFO with ε of up to 5 ppm at the carrier frequency of 4 GHz.

In this paper, we present a frequency sinogram data-based cancer recognition model employing a convolutional neural network (CNN) scheme for microwave-based breast cancer screening. As most cancer recognition schemes are based on radar image exploitation, these approaches have difficulty in discriminating a fibroglandular tissue from a malignant tumor, particularly in dense breasts, due to low contrast between tumor and fibro-glandular, in terms of dielectric properties. Thus, we introduce a straightforward recognition scheme involving the exploitation of a potential characteristic of backscattered frequency sinogram data. Furthermore, data augmentation schemes along an array rotation angle are introduced with a Fourier-based upsampling scheme to ensure high-accuracy recognition. The two-dimensional finite-difference time domain method using a realistic numerical phantom validates the effectiveness of our proposed approach.