This letter proposes a circularly polarized beamforming technique on volumetric random arrays with each antenna aligned deliberately. This technique seeks to advance the capabilities of spatially distributed antenna systems on mobile platforms. Sixteen microstrip patch antennas grouped as the tested array are adopted to investigate the fidelity of the developed beamforming technique. Each array element is distributed randomly and rotated freely to emulate the real mobile environment. Detailed and systematic beamforming procedures are provided and illustrated. Measured radiation patterns of the volumetric random array are compared to the simulated ones to benchmark their performance.

In this paper, we study an estimation method of the position of an unknown transmitter based on received signal strength. The original method considers only an omni-directional antenna pattern of the transmitter, so we extended the estimation method to take into account the directivity of the transmitting antenna. The estimation performance of the method is discussed by a computer simulation and an experiment. We showed that, when the transmitter has directivity, the accuracy of the position estimation was improved by considering the directivity.

This paper discusses the detection of the presence of paper inserted between the metal and the antenna. In order to clarify the feasibility of the sensing technique, we analyzed change of frequency characteristics of return loss in the presence or absence of paper near the antenna. Numerical analysis using the FDTD method was performed and experiments were carried out to compare the calculated and measured results. By the results, we confirmed detectable amount of change can be observed.

This paper presents gain enhancement of leaky wave antenna by parabolic reflector of photonic crystal. A leaky wave antenna has been proposed as an antenna for optical wireless communication. This antenna is excited by a parabolic reflector made of photonic crystals. This excitation method is very compact, resulting in some insertion loss. To improve the drawback, we propose a new reflector combined by photonic crystals and glass layer.

For effective computation of the total amount of interference from multiple nodes located in a wide area, we propose a scheme clustering multiple interference nodes and estimating the total interference power of the cluster. The total interference power is obtained by adding a margin to a reference power of limited number of representative nodes. In the scheme, the selection of the representative nodes is an important factor deciding frequency utilization efficiency. In the paper, we evaluated the amount of the excessively estimated power of several determination methods of the reference power by simulations and experiment. As a result, we show a method to determine the reference power with smaller overestimation.

An optimized MUSIC (MUtilple SIgnal Classification) is proposed, basing on Simplex search method. It can largely improve the scan speed of the conventional MUSIC and avoid the singularity of the Hessian matrix of the gradient based optimization methods. It also provides the possibility to distinguish the coherent signal with the acceptable time cost, in this case, we proposed an enumeration based coherence solver. Both simulations and experiments are carried out for RF localization purposes. The results shows that the proposed methods has faster computational speed with same numerical precision as the conventional MUSIC method does, which also confirms the feasibility of the proposed coherence solver.

For realizing automated monitoring of the behavior and preferences of residents for smart homes/smart building applications, device-free localization techniques using radio propagation characteristics have gained interest. In such techniques an environmental information should often be known in advance. This study developed the multi-dimensional Kirchhoff migration method to estimate a room geometry for indoor localization and the estimation accuracy was evaluated by ray-tracing simulations. By utilizing millimeter-wave radio systems, multi-dimensionality in terms of time-of-flight and angle-of-arrival/departure and high resolution in channel impulse responses offer high estimation accuracy. Moreover, the feasibility was demonstrated via the laboratory test measurements using directional channel sounder.

This paper presents an inverse method to reconstruct an antenna-excited electric field distribution of a dielectric object from measured field data, for the purpose of noninvasive SAR evaluation in the human phantom. The proposed method is a hybrid method combining the Boundary Integral Equation (BIE) and Finite Element Method (FEM). The BIE for the electromagnetic (EM) fields and equivalent currents of a radiating source are discretized using the method of moments (MoM) while EM fields in the scatterer and its surroundings are discretized using the FEM. The effectiveness of the method is tested numerically and experimentally using a dipole and a dielectric cuboid at 2.5 GHz. The numerical reconstruction achieves acceptably good agreement with that of reference as a whole. However, it is found from the experiment that the method is considerably sensitive to the measurement error. The factors that may have contributed to the errors are shortly discussed.

Highly efficient RF-DC conversion circuit is required for wireless power transmission. Since a diode with non-linear characteristics is used for the RF-DC conversion circuit, it is difficult to theoretically design a highly efficient RF-DC conversion circuit. Therefore, we have investigated automatic design by genetic algorism. As a result of automatic design, it was found that the impedance of the input circuit converges to a certain area when the input power and load are fixed. Furthermore, we constructed a measurement system and found that in a highly efficient RF-DC conversion circuit, there is a canceling relationship between the reactance of the input circuit and the diode.

Authors have proposed the internal electric field reconstruction method of dielectric objects based on the boundary integral equation and the method of moments’ implementation for the purpose of noninvasively estimating a specific absorption rate (SAR) in a human phantom. The validity of the method has been confirmed numerically and experimentally using simple-shaped convex dielectric objects with a very small loss. This paper assessed this method in three of more practical situations which is a concave model, a high-loss dielectric box, both for SAR estimation in the complex human phantoms, and also in a metallic enclosure with a window for the electromagnetic interference (EMI) applications. It is demonstrated numerically and experimentally that the electric field can be well reconstructed for all three situations without any methodological modifications. Hence, this method is expected to inherently possess high applicability for practical objects with a complicated geometrical shape in SAR estimation, and also for the EMI problems that includes the electric field reconstruction using the surrounding field data.

Recently, the magnetic coupling wireless power transfer technology has been attracting a lot of attention and is expected to have a wide range of applications in the electrical equipment around us. On the other hand, there have been reports on the application of metamaterials for the purpose of improving antenna gain and suppressing mutual coupling between antennas, and this study aim applying this technique to the magnetic coupling wireless power transfer system. In this paper, a magnetic wall by metamaterial suitable for a magnetic coupling wireless transfer system is proposed and its effect is demonstrated experimentally.

The EVM (Error Vector Magnitude) measurement is mandatory for radio equipment test. Signals transmitted from multiple antennas give high EVM value due to the phase difference in near field OTA (Over The Air) test. To overcome this difficulty, near field EVM measurement using channel estimation is examined in this paper.

We propose a method to accurately estimate microwave circuit parameters from observed amplitude of reflection characteristics. Characteristics of analog circuits are often not optimal because of the errors in circuit parameters. We develop a novel method to accurately estimate the circuit parameter values using the covariance matrix adaptive evolution strategy (CMA-ES) and evaluate its performance in comparison with conventional methods.

We propose a novel mushroom-type electromagnetic bandgap (EBG) structure with two stop-bands. The unit cell of the proposed EBG structure consists of a large mushroom and four small mushrooms, where the small ones are not stacked on but incorporated into the large one. The proposed dual-band EBG structure has the dual bandgaps of f₀-1.5f₀ and 3.2f₀-3.6f₀. It is shown that the electromagnetic interference between two antennas can be reduced by 10 dB or more at two frequency bands by installing the proposed EBG structure.

In this paper a deployable center-fed reflectarray antenna for mobile satellite communication systems is proposed. The proposed antenna consists of a main-substrate, four foldable sub-substrates, and a backfire antenna. This antenna can speedily be installed by attaching the backfire antenna and deploying the folded sub-substrates. The design results show that the antenna can satisfy the target gain by adjusting the deployment angle of the sub-substrates. In addition, the validity of the design is verified by measurements.

We propose a novel method to estimate source number used in Direction Of Arrival (DOA) estimator for Frequency Modulated Continuous Wave - Multiple-Input Multiple-Output (FMCW-MIMO) radar. The main principle is that the phase of the intermediate signals can be modified by the initial frequency of transmitted signals. We confirmed that our method can distinguish true and spurious sources when the number of sources is larger than the number of true sources.

This paper presents a method of thinning an Artificial Magnetic Conductor (AMC) substrate by applying the semicircle notch to the square patch. We analyze the reflection characteristics by changing the arc length of the semicircle. As a result, the frequency where a Perfect Magnetic Conductor (PMC) characteristics appears is shifted to the lower side as the arc length of the semicircle increases. It is confirmed that the proposed method is thinning the AMC substrate thickness about 15% compared with the AMC that has no semicircle notch. Furthermore, it was experimentally confirmed that the thin AMC substrate was thinning by semi-circle notch.

A Σ-Δ directional antenna array for electromagnetic(EM) energy harvesting is proposed in this paper. By applying the Σ-Δdirectional antenna array with the 180-degree hybrid circuit, it is possible to convert more electric power from the EM wave. The results of the consideration by the indoor environment using the ray tracing method are reported that the received electric power by the Σ-Δ directional antenna array is improved more than the single directivity antenna.

Recently, RFID (Radio Frequency IDentification) systems are expected to serve as the distribution management system of the alternative to bar-code systems. If tag antennas that can be identified even when attached to the surface of metal or high lossy dielectrics are developed, highly accurate automation of various product management can be expected. In this report, the development of the tag antenna for UHF-RFID system that can be attached to containers such as blood samples or liquid medicines is described.

This paper presents array antenna pattern synthesis with a fixed amplitude and limited phase range using genetic algorithm (GA). The array antenna can synthesize its pattern by controlling the amplitude and phase of each antenna element. However, a large phase shifter is required to control an arbitrary phase range of 360°. This proposed method can synthesize a cosecant squared beam (CSB) in the case of a 16-element, half-wavelength element spacing linear array with a fixed amplitude and limited phase range of less than 180°.

Dynamic spectrum allocation (DSA) between different radio systems is a promising method to efficiently use limited frequency resources. The approach of DSA is to allow different mobile network operators to use the same shared channel, without causing interference across base stations. However, existing methods to solve DSA are computationally very expensive. In this paper, we formulate the DSA problem for quantum annealing. Our evaluation demonstrates that momentum annealing as a high performance classical method of quantum annealing can obtain high accuracy solutions of the DSA problem in short time.

In this paper, the metasurface using the multi-layer ceramic capacitors (MLCCs) for monostatic radar cross section (RCS) reduction with broader bandwidth is proposed. By adjusting the width and the thickness of the inner electrodes, and the gap between staggered electrodes of the MLCC, two types of unit cell structures, the reflection phases of which have a phase difference of 180°, are designed. Next, by arranging the MLCCs in checkerboard patterns, the monostatic RCS reductions are simulated. Finally, the simulated results of the reflection phase difference and monostatic RCS reductions are compared with the measured results.

The antennas installed in mobile devices are small and low-profile compared to wavelength at the operating frequency. In general, low-profile horizontal elements and short monopole antennas have low radiation resistance. Low radiation resistance requires matching circuit between 50 Ω feed line and decreases radiation efficiency. By using the characteristic mode, excitation of the ground plane to improve the radiation resistance has been investigated. This paper proposes the structure with the modified folded dipole antenna, which is placed close to the metal casing. The surface current on the casing is excited by modified folded dipole antenna and contributes to the radiation.

A chaos modulation is a Gaussian modulation that achieves coding gains and physical layer securities. In the conventional method, a Bernoulli shift map, which is a chaos equation, is used for the modulation. However, the coding gain is limited to avoid an increase in the modulation complexity. In this paper, we propose a chaos modulation using a logistic map. Numerical results demonstrated that the proposed method increased the coding gain with the same amount of computation as that of the existing method.

High-order modulation is currently widespread since it increases spectral efficiency and data rate. In case of 8-ary signal set, the 8-ary phase shift keying having a constant envelope is useful but presents a poor performance in terms of power efficiency. In this letter, 8-ary modulation with a triangular lattice is investigated to improve the performance of 8-ary signaling and its power gains are elaborated analytically. According to results, the proposed 8-ary signal set provides the asymptotic power gains of 1.811 dB and 0.218 dB over the conventional 8-ary phase shift keying and quadrature amplitude modulation, respectively.

With the expansion of 5G mobile network, a large number of installation sites for small cell base stations are required, and the base station needs to be a more compact space. To solve this problem, we propose an S-plane configuration for the shared radio unit (RU) among mobile network operators. In addition, we propose the “Flunkey Clock” configuration as the PTP slave function mounted on the shared RU, and the feasibility of this system is verified and explained.

A method for ego-vehicle speed estimation using a fast chirp modulation (FCM) radar is proposed, which estimates the vehicle speed spectrum using a discrete Fourier transform and tracks the peak of the spectrum to estimate vehicle speed. Because it is applied to the intermediate-frequency signal, it can estimate vehicle speed without detecting objects. The proposed method can estimate low speeds which cannot be measured by wheel speed sensors. The estimated results of experiments using a vehicle were compared with those of in-vehicle sensors, revealing that the method can estimate vehicle speed using an FCM radar with low antenna elements.

In wireless feedback control systems, loss of control packets due to unreliable wireless channels is one of the most important problems. To cope with this problem, we propose a novel concept that combines a packetized model predictive control (MPC), which is control layer’s redundancy, and a forward error correction (FEC), which is communication layer’s redundancy. Simulation results show that under the same length of redundancy, there is a tradeoff performance between the packetized MPC and the FEC, and the proposed method can provide well-balanced tolerance to channel error.