Search

In this paper, effect of array configuration, directivity of element, control method, and losses in feeding cables on SINR characteristics of the adaptive array on a vehicle is examined. As the result, in most cases, it was clarified that X-type feeding network was the most excellent in feeding network, and MMSE had the most excellent performance in control methods.

This paper describes a metasurface designed utilizing either a Frequency Selective Surface (FSS) that has band-pass characteristics or one with band-rejection filtering characteristics in order to clarify the relationship between the filtering characteristics of the FSS and the Perfect Magnetic Conductor (PMC) characteristics of the metasurface. The effects of the filtering characteristics of the FSS on the PMC characteristics of the metasurface are described. Calculation results confirm that a low profile metasurface can be achieved using these FSSs. In addition, the effects of the size of the metasurface on the PMC characteristics of the surface are shown.

This paper proposes a novel blind multiuser detection scheme using CMA (Constant Modulus Algorithm) adaptive array. In the proposed scheme, the received signal is processed in two steps. In the primary step, only one user is captured by the CMA adaptive array, and at the same time, the other users' directions of arrival (DOA) are estimated. In the secondary step, initial weight vectors are set based on the estimated DOAs, and it processes with CMAs again to capture the other users in parallel. Thus, all the users are detected exactly and recovered separately. The Least-squares CMA is applied as an optimization algorithm to improve the performance of the proposed scheme, and the performances using the proposed scheme with linear arrays and circular arrays are discussed in detail. Simulation results are presented to verify the performance of the proposed scheme.

High-speed wireless communication systems have attracted much attention in recent years. To achieve a high-speed wireless communication system that utilizes an ultra-wide-frequency band, a broadband antenna is required. However, it is difficult to obtain an antenna that has uniform characteristics in a broad frequency band. Moreover, propagation characteristics are distorted in a multi-path environment. Thus, the communication quality tends to degrade due to the distortion in the frequency characteristics of the wideband communication system. This paper proposes a quasi-inverse filter (QIF) to improve the compensation effect for the transmitter antenna. Furthermore, we propose a method that employs the newly developed QIF that compensates for frequency characteristic distortion. We evaluate different configurations for the compensation system employing a pre-filter and post-filter in the wideband communication system. The effectiveness of the QIF in the case of severe distortion is verified by computer simulation. The proposed method is applied to a disc monopole antenna as a concrete example of a broadband antenna, and the compensation effect for the antenna is indicated.

This paper proposes the variable reflection angle meta-surface composed of the double layered FSS (Frequency Selective Surface) and the ground. The meta-surface can steer the reflection direction of the incident wave by shifting the lower FSS. It is clarified that the gradient of the reflection phase in the reflection direction steering plane (x-z plane) are changed by the shift amount of lower FSS. It is found that the reflection direction of the normal incident wave is obtained up to at 45 degrees by using the proposed meta-surface.

In recent years, interference of artificial noises from electrical power transfer becomes large and deterioration of sound quality of AM radio is worried. In this paper, a noise suppression system using quadrature demodulation techniques is proposed to reduce the effect of the interference. The proposed system utilizes the fact that the in-phase signal from the demodulator includes both of AM signal and interference, however, the quadrature signal includes only the interference. Thus, the interference in the in-phase signal could be canceled by the quadrature signal. Because of the sign of the both interference is different each other, Hilbert transformation is utilized to match the sign of the interferences. Validity of the proposed system is shown through computer simulation and experiments.

This paper shows the effects of noise on estimation accuracy in an object position estimation method using hyperbolas obtained from phase difference between elements of array antenna. It is shown that the contribution of antenna elements located at array ends to the position estimation is depend on the noise. It is shown that all antenna elements contributes effectively in case of the noise sufficiently small compared to the radiation power.

A meta-surface can reflect the incident wave with arbitrary reflection coefficient. This paper proposes a novel meta-surface which has polarization conversion function. A linearly polarized (LP) incident wave can be converted to a circularly polarized (CP) reflected wave by using a rectangular patches and the ground plane. In addition, the relationship between the frequency bandwidth and the structure are clarified. The maximum value of the frequency bandwidth is converged to approximately 87%.

This paper proposes a variable reflection angle meta-surface using double layered FSS (Frequency Selective Surface) for orthogonally polarized waves which can change the scattering pattern easily by shifting one layer. The reflection angle within range of about −20 deg. to −5 deg. is obtained in case of orthogonally polarized waves.

This paper focuses on an AMC (Artificial Magnetic Conductor) composed of a FSS (Frequency Selective Surface) and the ground plane, and describes the ideal filtering characteristics for realizing PMC (Perfect Magnetic Conductor) which is independent of frequency. The ideal filtering characteristics is derived from the condition for realizing the PMC in all the frequency using the relational expression between the filtering characteristics of a FSS and the PMC characteristics of the AMC. As the result, it is clarified that the ideal filter is a band pass filter. It is also shown that the optimum distance h between a FSS and the ground plane is a quarter wavelengths at the band pass frequency. On the other hand, it is found that the phase rotation direction is opposite compared with the conventional band pass frequency. It is found that the ideal filtering characteristics can be realized by using negative index material.

In order to realize the wireless broadband communication, a small antenna which has the ultra-wideband characteristics is required. The well-known planar monopole antenna features wideband characteristics, small size and simple structure. Thereby, planar monopole antennas of various shapes have been proposed. The paper proposes the T-shaped planar monopole antenna with a basis of rectangular planar monopole antenna. In addition, the structure of T-ledge which has the most broadband characteristics and the limitation of the broadband characteristics are clarified.

This paper proposes the variable reflection angle meta-surface using the double layered structure which can change the scatter pattern simply by sifting other layer. It is clarified that the gradients of the element vs. the reflection phase are changed by the relative position between two layers in double layered patch type FSS (Frequency Selective Surface). It is found that the reflection angle with range of about −34 deg. to −2 deg. is obtained in the proposed meta-surface.

This paper describes the printed dipole antenna impedance that is calculated using the ideal reflection phase of the AMC. Moreover, the optimum reflection phase of the AMC reflector for best relative bandwidth is described. From the result, the wide RBW was realized by the low distance of the printed dipole antenna and RBW PMC = 20∼30%. Moreover, the printed dipole antenna distance that had the widest RBW was shown.

A dipole antenna with a flat reflector can achieve unidirectional radiation pattern with a simple structure. However, the distance between a reflector and an dipole element is required 1/4 wavelength. In order to use in two or more frequency bands, it is necessary to use individual dipole element for each frequency band. This paper proposes a dipole antenna with dual flat reflectors. In addition, effect of the reflector structure on the beamwidth in dual frequency bands is clarified. Moreover, the effects of parasitic elements arranged close to the dipole element on the band characteristic of the VSWR is considered. Furthermore, it is shown that an impedance matching is realized in dual bands.

The artificially generated noise from the appliances has a periodicity in frequency domain. A noise suppression system, which is based on the PI(Power Inversion) algorithm and using frequency shift, has already been proposed. However, the system has a significant problem that the suppression effect can not be obtained when the frequency shift is not accurate. In this paper, reduction method of frequency shift error is proposed. Numerical results show that frequency shift error is reduced by the proposed method when the number of snapshots and the interval of sampling are set appropriately.

A new primary receiver detection method in cognitive radio for OFDM system is proposed in this paper. In the proposed method, the OFDM signal is modulated by load modulation at the primary system. Due to the modulation, spurious components appear in guard band of the OFDM system. Then, the secondary receiver detects the direction of the primary receiver through estimating the direction of the spurious components. Numerical results shows that the primary receiver in several meters from the secondary receiver can be detected using the radio wave of terrestrial digital broadcasting.

This paper describes the filtering characteristics of the alternated double layer patch type FSS (Frequency Selective Surface) in which a patch type FSS is arranged alternately at the surface and the back of a dielectric substrate. The equivalent circuit and the empirical equation of the coupling coefficient including dielectric substrate effect are proposed. It is also shown that the approximate equation is valid when the thickness of the dielectric substrate t/p less than 0.5.

A novel algorithm for an adaptive array that is suitable for a multi-carrier transmission will be proposed in this paper. In an adaptive array, signals received by antenna elements are weighted and combined together. In the proposed algorithm, distortion of a spectrum of the combined signal is detected and weight coefficients for each antenna element are controlled so that the spectrum of the combined signal becomes flat. Concept of the proposed algorithm can be interpreted as the CMA which is applied to signals sampled in the frequency domain. Furthermore, a configuration of the adaptive array will be shown. Signals separated in a receiver of the multi-carrier transmission are utilized to detect the distortion of the signal spectrum. By adopting the proposed configuration, the spectrum of the multi-carrier signal can be easily detected. In order to investigate the performance of the proposed adaptive array, computer simulation has been carried out. Numerical results show that; 1) A desired wave is captured well even if an interference wave is narrow band signal and is stronger than the desired wave. 2) Suppression performance for a co-channel interference wave depends on both a symbol timing and SIR of arrival waves. If the symbol timing of the interference wave greatly differs from the timing of FFT window of the receiver, the desired wave can be captured even if the co-channel interference wave is stronger more than 10 dB compared with the desired wave. The conventional CMA adaptive array has a serious problem that the narrow band interference wave is captured when it is stronger than the desired wave. On the other hand, it is extremely rare that the proposed adaptive array captures the narrow band interference wave. Therefore, it can be said that the proposed adaptive array is a robust system compared with the conventional system.

It is worried that the ITS may suffer interference from broadcast system or mobile communication system. Thus, we proposed a power inversion adaptive array which can suppress an interference wave in ITS propagation environment. However, the interference suppression performance is reduced due to multipath fading. As a countermeasure, we devised a continue control method for power inversion to follow the change of propagation environment. In this paper, the optimal snapshot number for properly estimating a correlation matrix is examined. As the result of examination, it is clarified that the optimal number of snapshots is about 30 times.

A high gain and low-profile antenna can be realized by using an AMC (Artificial Magnetic Conductor) reflector that has PMC (Perfect Magnetic Conductor) characteristics. Since a configuration of the AMC reflector must be adjusted for each antenna, studies on the configuration of the optimum AMC reflector are not enough yet. This paper describes the optimum AMC reflector configuration for high directive gain and low-profile dipole antenna with the AMC reflector. Here, the arranged unit cell area and the thickness of the AMC reflector are considered. The AMC treated in this paper are composed of the patch or loop type FSS (Frequency Selective Surface) and the ground plane. It is shown that the area of the arranged unit cell is one of the important factors to obtain the high directive gain. Moreover, it is shown that the high directive gain dipole antenna with the AMC reflector can be realized by the optimum area of the arranged unit cell.

This paper describes the equivalent circuit analysis of a double layer AMC (Artificial Magnetic Conductor) in consideration of mutual coupling between layers. The AMC with double layer patch type FSS (Frequency Selective Surface) is focused. This paper treats two type double layer structures. The one is stacked structure, and the other is alternated structure. It was shown that the calculated results by using the equivalent circuit well agreed with the results of the FDTD analysis. In addition, it was clarified that the stacked and alternated structures cause the common mode and the differential mode coupling, respectively. Moreover, it was shown that the miniaturization of the AMC is designed by setting the distance between the layers of double layer FSS as thin as possible.

In Wireless Body Area Network (WBAN) which is the network around a human body, Ultra Wide Band (UWB) communication is one of the candidates for a realizing a high transmission speed. However, the antenna characteristics can be degraded due to influence of the human body. Also, broadband antennas which cover the bandwidth of UWB are too large for WBAN's antennas in general. In this paper, an antenna with a slot of a bow-tie shape focused and downsizing technique discussed. In comparison with the basic shape, it downsized by approximately 10% in the y-direction, 68% in the z-direction. And, average Front to Back ratio of 1.95dB is obtained in band from 4.7 to 10.6GHz.

This paper describes the possibility of the miniaturized AMC (Artificial Magnetic Conductor) by the equivalent circuit analysis. The AMC with double layer patch type FSS (Frequency selective surface) is focused as the structure of AMC. It is clarified by the theoretical results that the operation frequency of the FSS becomes the half by using double layer patch type FSS. It is also shown that unit cell size of an AMC is miniaturized by the half.

A high gain and low-profile antenna can be realized by using an AMC (Artificial Magnetic Conductor) reflector that has PMC (Perfect Magnetic Conductor) characteristics. Since the configuration of the AMC reflector must be adjusted for each antenna, the configuration of the optimum AMC reflector has never been studied. This paper, describes the optimum AMC reflector configuration for high directive gain and low-profile dipole antenna with the AMC reflector. Here, the optimum number of AMC elements and the size of the ground plane of the AMC reflector are considered. And, a new arrangement of the elements for the AMC reflector is proposed. It was found by the simulation results that the highest directive gain was achieved by the dipole antenna with the AMC reflector with the 5×8 elements. Moreover, it was understood that the optimum AMC reflector didn't depend on the size of the ground plane. The directive gain of the optimum configuration of the AMC reflector was almost 11.6 dBi.

PCU (Power Control Unit) are installed in EV (Electric Vehicle) and HV (Hybrid Vehicle). Problems of inverter noise from the PCU become serious as popularization of the EV and H V. Especially, sound quality of AM radio is deteriorated due to the electrical noise because the AM radio utilizes relatively low frequency. As the countermeasure the authors proposed an inverter noise suppression system using a noise sensor and an adaptive filter. In this paper, the optimal tap interval of the adaptive filter in the proposed system is examined. As the result of examination, it is clarified that the optimal tap interval is 1/10 of the reciprocal of the frequency interval of the inverter noises.

This paper clarifies the effect of the metal wire on the channel capacity in the near-field MIMO system. The metal wire is placed near the dual-dipole arrays, which can adjust the HPBW (half-power beamwidth) of the element radiation pattern. It is verified that the metal wire placed at an appropriate location can even make the system channel capacity exceed that without a metal wire. And the optimum location of the metal wire and the maximum channel capacity are affected by the HPBW. It is found that the impacts of multiple metal wires in the system can be regarded as the accumulation of every single one.

In this paper, two types of sub-band technique to decrease the effect of antenna pattern distortion were proposed and evaluated; one was “Spectrum Averaging Method” and another was “Beam Averaging Method.” As the results, it was clarified that the estimation accuracy was greatly improved by “Spectrum Averaging Method”. It was also found that the accuracy of “Beam Averaging Method” was almost the same with “Spectrum Averaging Method” for phase error. Thus, the “Beam Averaging Method” is suitable for compensate the phase error of antenna elements.

EBG (Electromagnetic Band-Gap) structures composed of metal patches arranged at narrow intervals have been studied to apply to microwave components and antennas [1][2]. The EBG structures have the frequency-band-rejection characteristics and it can reduce the undesired radiation of electromagnetic waves [3]. In general, the EBG structure is made on the flat ground plane, and is not examined the design method when put on the curved surface. This paper describes the mutual coupling reduction effects of EBG structures located on cylindrical surface.

High resolution method for direction of arrival (DOA) estimation using array antenna is studied actively [1]. In almost previous studies, it is assumed that antenna elements have the same directional patterns. However, it is very difficult to make many antenna elements they have just the same directional patterns. Furthermore, the directional patterns are distorted due to mutual coupling between the elements [2]. The estimation accuracy is decayed if the directional patterns are distorted intensively.

Multiple-Input Multiple-Output (MIMO) and Multi-User MIMO (MU-MIMO) systems have been expected to improve the channel capacity over a limited bandwidth of existing networks [1], [2]. The effects on channel capacity of Single-User MIMO (SU-MIMO) systems in urban scenarios have been previously studied [3]. It has been clarified that the larger number of antennas cannot contribute the improvement on the channel capacity in urban SU-MIMO scenarios due to very high spatial correlation. In this paper, we focus on the MU-MIMO transmission because it can discriminate multiple users by the difference of Angle of Arrival (AoA). We compare the Multi Access Channel (MAC) capacity in uplink with the channel capacity in SU-MIMO by setting the total numbers of transmitting and receiving antennas of SU-MIMO and MU-MIMO to be the same. When the same numbers of antenna elements are used, the better performance is obtained with MU-MIMO in urban scenarios, unlike identical independent distributed (i.i.d.) channels which are generally assumed in MIMO transmission. We also clarify an interesting relationship between the channel capacity improvement of MU-MIMO compared with SU-MIMO and a path visibility.

A FSS (Frequency Selective Surface) is composed of metal patches arranged in narrow intervals, and has frequency-band-rejection and frequency-band-pass characteristics. It is known that the FSS with the ground plane has PMC (Perfect Magnetic Conductor) characteristics in a specific frequency band. The surface is referred to as a meta-surface and it can control the phase of the wave which is reflected at the surface. This paper proposes a design method to realize a low-profile meta-surface. In the proposed method, the FSS which has low-pass or high-pass filtering characteristics is utilized. The effects of the filtering characteristics of a FSS on PMC characteristics of a meta-surface are described. Based on the calculated results, it is confirmed that the meta-surface can be obtained by using the FSS. In addition, it is found that the thinner and more wideband meta-surface can be achieved by using the FSS which has low-pass filtering characteristics.

Multiple-Input Multiple-Output (MIMO) wireless communication technology has been expected to improve the channel capacity with a limited bandwidth for the future networks. Since the propagation environment or the propagation channel becomes very complex, it is difficult to simply estimate the channel capacity in urban MIMO systems. Hence, we introduce the characteristics of channel capacity in urban MIMO system by using a ray-tracing method. The simulation by this method with variable parameters can estimate various urban propagation characteristics and discriminate the effects of the urban model and antenna configurations. Moreover, we introduce path visibility, which is defined as the probability that at least one of the antenna elements of the mobile terminal (MT) can receive the direct wave when considering the downlink scenario, in order to make a measure in urban MIMO systems. It is represented in this study that the characteristics of the channel capacity can be figured out directly from the path visibility by the ray-tracing simulation. It also gives the guidance that the appropriate range of the base station (BS) antenna height can be determined from the path visibility.

Constant modulus algorithm (CMA) adaptive array has been proposed as a countermeasure to frequency selective fading; but since the evaluation function is nonlinear with respect to weight, the conventional steepest gradient method is being used for optimization. However, if there is a large variation in the eigenvalue of the correlation matrix of the input, then the convergence becomes very slow. In this paper, Marquardt's method of optimizing the CMA adaptive array is proposed. This method is based on a nonlinear least-square algorithm, and its dynamic characteristics are clarified by computer simulations. First, the fundamental characteristics of the algorithm are investigated. It is shown that this algorithm gives satisfactory convergence even for those cases where the convergence performance of the conventional steepest gradient method has degraded and where waves approach by multiple paths. Next, the performance of the algorithm is studied under the influence of Doppler shift or in the case where the wave conditions vary and satisfactory performance is obtained under frequency selective fading environment.

In this paper, effects of noise on performances of frequency characteristics compensation filter was evaluated. Three types of noise were considered in this paper and it was shown that the effect of the filter was greatly decreased by receiver noise. This is because of miss-estimation of transmission characteristics. To reduce the effect of receiver noise, averaging technique was introduced. It was varied through computer simulation that the effect of the filter was improved by the averaging. Almost the same performance without the miss-estimation was obtained when the estimated characteristics were averaged with 100 times.

This paper proposes the configuration of a polyhedral array antenna arranged on a polyhedron and describes the limitation of coverage gain of polyhedral antennas. Here, a cube, an octahedron, a dodecahedron, an icosahedron, the truncated icosahedron (soccer ball type), the polyhedron with 60 triangles, and the polyhedron with 80 triangles are considered. And, the relation between the minimum coverage gain and the size of an array antenna is discussed, and in order to achieve the higher minimum coverage gain, the several antenna element simultaneous excitation of a truncated icosahedron array is considered.

In this paper, we take up mushroom type EBG structures and clarify the frequency-band-rejection characteristics of the finite EBG structures on the finite ground plane, and we also compare that with the infinite EBG structures and the semi-infinite EBG structures. Here, we analyze the reflection characteristics of a normal incidence plane wave.

High speed wireless communication system attracts much attention in recent years. To realize the high speed wireless communication system utilizing ultra-wide-frequency bands, a broadband antenna must be required. However, it is difficult to obtain the antenna which has uniform characteristics in broad frequency band. More over, propagation characteristics are also distorted in multi-path environment. Thus, the communication quality tends to become worse because of distortion of the frequency characteristics of the wideband communication system. This paper proposes the compensation method for the frequency characteristics distortion in wideband communication system using pre-filter and post-filter, under considering frequency characteristics of both transmitting and receiving antenna, in addition radio propagation characteristics. And effectiveness of an approximately inverse filter in case of severe distortion is verified through computer simulation.

In this paper, we propose the system configuration in consideration of antenna directivity when four antennas are mounted on a vehicle and we experimentally demonstrate that the ISDB-T reception probability is improved while the vehicle moves at high speed.

This paper proposes a directional pattern control method that utilizes the direction of arrival (DOA) of an ultrasonic wave to control the base station of a communications system. Two kinds of waveforms are proposed for high resolution DOA estimation: A waveform with a raised cosine spectrum and a waveform with a binominal distribution spectrum. The simulation results show that the waveform with the binominal distribution spectrum is more appropriate for application to the Space Division Multiple Access system.

A disc monopole antenna has wideband characteristics and simple shapes. Therefore, such an antenna may be suited for ultra-wideband communication systems. When such a disc monopole element is rounded cylindrically, the rounded disc monopole antenna features the compactness and has also ultra-wideband characteristics This paper describes the ultra-wideband characteristics of a rounded circular disc monopole antenna and a rounded semicircular one, and also studies the effects of a finite ground plane on wideband characteristics. Based on the theoretical results, it was verified that a rounded disc monopole antenna on a finite ground plane had the ultra- wideband characteristics and higher gain. (5 pages)

There are some problems when adaptive arrays are applied to mobile terminals because they utilize several antenna elements on minute terminals. An analysis and evaluation of the effect of antenna element characteristics on SINR of the adaptive arrays is presented in this paper. It is shown that the influence of elements characteristics on the SINR depend on correlation between arrival waves. And it is also shown that a robust performance can be obtained by the MMSE in mobile environment.

The authors present a rapidly converging and well-conditioned algorithm based on the nonlinear least squares method referred to as the Marquardt method for the CMA (constant modulus algorithm) adaptive array. Computer simulation with a pi /4-shifted QPSK (quadrature phase-shift keying) signal verified its rapid and stable convergence characteristics for any radio environment. Taking into consideration the increase of computation for one weight update, the Marquardt method can reduce the convergence time by a factor of 10 to 100 compared to the steepest descent method. >

Lanthanide precipitates obtained by decomposition of Eu or Yb metal solutions in liquid ammonia were active at 393 K for the partial liquid-phase hydrogenation of benzene to cyclohexene with high selectivity (≥90%). When the reaction temperature decreased to 323 K, cyclohexadienes were preferentially formed. The reducing behavior was markedly enhanced by the addition of ammonia to the reaction system.

Multiple-Input Multiple-Output (MIMO) wireless communication technology is expected to improve the channel capacity over the limited bandwidth of existing networks. Since urban MIMO systems have complex propagation characteristics, the channel capacity cannot be estimated using a simple method. Hence, we introduce channel capacity characteristics to urban MIMO systems by using a combination of imaging and ray-launching methods as a ray-tracing scheme. A simulation based on these methods with variable parameters can reproducibly estimate various urban propagation characteristics and discriminate the effects of the urban model and antenna configurations. The characteristics of the Signal-to-Noise Ratio (SNR), the channel capacity, the spatial correlation, as well as the path visibility are then determined from the results of the simulation. The parameter called path visibility introduced in our previous study is considered again herein. We clarify that only this single parameter can be used to determine the channel capacity characteristics in urban MIMO scenarios. This parameter also provides guidance in determining the appropriate range for the base station (BS) height.