COMMISSION B: Fields and Waves (Nov. 2013 - Oct. 2016)
Edited by Jiro Hirokawa and Naobumi Michishita
This report presents a summary of Japanese contributions, including those of international
collaborations, in the field related to URSI Commission B during the last three years. It is not intended
to be an exhaustive survey of all relevant works, but rather an omnibus of important works around theauthors of each section or subsection.

B1. Scattering and Diffraction
1.1 Basic Electromagnetic Fields Analysis
In [Iwashige J., Barolli L., Iwaida M., and Kameyama S, 2014], estimation of the scatteringof electromagnetic waves by buildings and other obstacles is very important for wirelesscommunications in urban area. In our previous work, we have examined the diffracted fields by two
horizontal edges with an arbitrary angle. In this paper, we consider the diffracted fields by two edges
with an arbitrary angle which change in both horizontal and vertical directions. The numericalevaluation is carried out for two wedges and we compare the diffracted fields between parallel andarbitrary angle of edges. The results show that when the angle between two edges increases, relatively
strong orthogonal polarized wave components appear, but the principal components are almost thesame as the incident wave, and the effect of edge slant in vertical direction is smaller than horizontal
one.
In [Sygisaka J., Yasui T., and Hirayama K., 2016], an algorithm is proposed for the scattering
analyses of gratings with various local defects based on the difference-field boundary-element method(DFBEM). In the algorithm, the defect in the grating is partitioned, and the DFBEM is sequentiallyapplied for each defect section. The proposed algorithm is validated by demonstrating its flexibility
for various defect topologies for a locally deformed grating.
[Tamura Y., 2016] proposes a novel image integral equation of the first type (IIE-1) for a
TE plane wave scattering from periodic rough surfaces with perfect conductivity by means of themethod of image Green's function. This paper firstly points out that the branch point singularity of thebare propagator inevitably appears on the incident wavenumber characteristics of the scatteredwavefield and its related quantities just at the critical wavenumbers. [Nakayama J., and Tamura Y.,
2014b] proposes a new method to obtain a numerical solution that satisfies the reciprocity in the theoryof periodic gratings. Numerical examples are given for the diffraction of a transverse magnetic (TM)plane wave by a very rough periodic surface with perfect conductivity. By use of the average filter,the energy error is much reduced in some case.
(J. Hirokawa)1

1.2 Periodic Array Structures
Scattering and Guiding of periodic array structure such as photonic fiber and photonic
crystal waveguides is both theoretical and practical interest in many areas of physics and engineering.
In the scattering problem, Jandieri, Yasumoto and Cho [2013] proposed scattering andradiation from a line source placed inside the eccentric configuration of the cylindrical electromagnetic
bandgap (EBG) structure and plane wave incident on the cylindrical EBG structure is numericallystudied based on the method proposed by the authors in their early papers. Using the developed
formulation, it is shown first time that when the cylindrical EBG is illuminated by plane wave ofparticular resonance frequencies, the field are strongly enhanced or shaded inside the cylindrical EBG
structure and this effect depends on the angle of incidence of the plane waves. We give a deep physicalinsight into explanation of this phenomenon based on the Lorentz reciprocity relation for cylindricalstructures.
Meng, Yasumoto, and Liu [2014] investigated the scattering of TE polarized plane wave bymetal-coated dielectric nanocylinders with a particular emphasis on the enhancement of the near fields.
If the wavelength of illumination is properly chosen, two unique near field distributions can be excitedthrough the surface plasmon resonances. The enhanced near fields are localized along the inner orouter interface of the coating metal, being dependent on the wavelengths. It is shown that the scatteringcross-section of the nanocylinders is also enhanced when the illuminating field resonates to the surface
plasmons of the structures.
Nguyen-Huu, Cada, Pistora, and Yasumoto [2014] investigated the doubled-sided grating
structures including two identical single-layered metal gratings separated by a dielectric layer exhibit
enhanced optical transmission in the visible region for transverse magnetic polarized light. The
maximum transmission (71%) is attributed to a resonance of magnetic polaritons while the minimum
one (5%) is found to be caused by surface plasmons between metal and dielectric layers. The
transmission resonance of the grating structures is analyzed by varying their geometrical parametersand materials in order to evaluate different potential applications such as tunable optical filters,
polarizers, and selfsuspended-type plasmonic sensors.
Jandieri, Meng, Yasumoto, and Liu [2015] investigated the light scattering by a grating of
the metal (Ag)-coated nanocylinders supported on the dielectric substrate using an accurate andrigorous formulation based on the recursive algorithm combined with the lattice sums technique.
Special attention is paid to the three types of resonances: (a) surface plasmon resonances associatedwith the metal nanocylinders, (b) Rayleigh anomalies related with the periodic nature of the grating,and (c) resonances due to the coupling between the grating and the dielectric substrate. Physical insightis given to the localization of the field along the interfaces of the metal nanocylinders, formation of
the strong reflected field by the grating, and the field enhancement at the surface of the dielectric
substrate.
2

Jandieri, Yasumoto, Liu, and Pistora [2016] investigated scattering of light by metal-coateddielectric nanocylinders periodically distributed along a cylindrical surface both theoretically andnumerically. Scattering cross section and absorption cross section of three and four silver (Ag) coateddielectric nanocylinders periodically situated along a cylindrical surface are studied. Near field
distributions are investigated at particular wavelengths corresponding to the resonance wavelengths inthe spectral responses. Special attention is paid to the unique and interesting phenomena characterizing
the cylindrical structure composed of the metal-coated nanocylinders such as: a) localization of the
field; b) excitement of the field and c) strong confinement of the field inside the cylindrical structure.
Yokota and Matsumoto [2014] proposed an effective permittivity of the two-dimensional multilayered
periodic structures which consist of the rectangular dielectric cylinders is examined numerically. The
original periodic structure is replaced with a simple structure such as the dielectric slab. By using thereflectance of the periodic structure obtained by the FDTD method, the effective permittivity of thedielectric slab, which has the same reflectance as that of the periodic structure, is obtained by using
the transcendental equation. In order to reduce the procedure to obtain the reflectance from themultilayered periodic structures, the reflectance from one-layered structure is used. The range of theapplication and validity of this procedure is examined.
Sugisaka and Hirayama [2016] proposed an algorithm for the scattering analyses of gratings
with various local defects based on the difference-field boundary element method (DFBEM). In thealgorithm, the defect in the grating is partitioned, and the DFBEM is sequentially applied for eachdefect section. We validate the proposed algorithm by demonstrating its flexibility for various defecttopologies for a locally deformed grating.
Nakayama and Tamura [2014] proposed a new method to obtain a numerical solution thatsatisfies the reciprocity based on the shadow theory. The shadow theory states that the scattering factor
is an even function. However, a scattering factor obtained numerically becomes even function only
approximately. It can be decomposed to even and odd components, where an odd component
represents an error with respect to the reciprocity and can be removed by the average filter. Using evencomponents, a numerical solution that satisfies the reciprocity is obtained. Numerical examples are
given for the diffraction of a TM plane wave by a very rough periodic surface with perfect conductivity.
Tamura [2016] proposed a novel image integral equation of the first type (IIE-1) for a TE
plane wave scattering from periodic rough surfaces with perfect conductivity by means of the methodof image Green’s function. Since such an IIE-1 is valid for any incident wavenumbers including thecritical wavenumbers, the analytical properties of the scattered wavefield can be generally andrigorously discussed based on the shadow theory.
Komiyama [2014] analyzed the scattering of TE plane wave from the end-face of awaveguide system is treated by solving straightforwardly a wave equation for the electric field. The
unknown scattered field is expanded into a perturbation series. The first and second order terms are3

analytically derived and it is shown that the second order term is sufficiently small compared with thefirst order term and can be ignored. And also, [2015] the scattering of the ordered waveguide system
is numerically treated by a differential method. The results obtained by the perturbation method arecompared with the numerical results and the accuracy of the perturbation solution is clarified. For a
TM plane wave [2016a], the scattering by a dielectric grating is treated by the perturbation method
and the diffraction amplitudes are analytically derived. By comparing with the results obtained by thenumerical method it is shown that the properties of the high order diffraction amplitudes can be fairly
described by the perturbation solution. It is shown that the results obtained analytically by the
perturbation method are in relatively good agreement with the numerical results [2016b].
On the other hand, in the guiding problem, Ozaki and Yamasaki [2016a, 2016b] investigatedthe propagation constants at the first stop band region and the energy distribution at the guided area
for case with dielectric circular cylinders or dielectric hollow cylinder and equivalent rhombic cylinder
structure along a middle layer for TE mode by using the combination of improved Fourier series
expansion method and multilayer method. And they also, in the transient scattering problem forperiodic structure [2016c] analyzed the pulse response of plane gratings in the dispersion media byutilizing the parameters for permittivity properties of complex dielectric constants, and investigated
the influence of both dielectric and perfect conductor by using the fast inversion of Laplace transform
method and the point matching method. In addition, we confirmed the effectiveness and validity forpresent method comparing exact solution of perfect conductor plate in dispersion media.
Nakatake and Watanabe [2013] proposed a novel formulation for the modeling ofelectromagnetic wave propagation in pillar-type photonic crystal waveguide devices. The structure
under consideration is formed in an infinitely extended pillar-type photonic crystal and the wave
propagation is controlled by removing some cylinders from the original periodic structure. The
structure is considered as cascade connections of straight waveguides, and the input/output propertiesof the devices are obtained using an analysis method of multilayer structure. Each layer includes
periodic circular cylinder array with defects, and the transfer-matrix is obtained by using a spectraldomain approach based on the recursive transition-matrix algorithm with the lattice sums techniqueand the pseudo-periodic Fourier transform.
Naka and Nishimoto [2016] proposed an efficient sharply bent waveguide with amicrocavity constructed by an air-bridge type two-dimensional photonic crystal slab is analyzed. The
method of solution is the three-dimensional finite difference time domain (FDTD) method. The bent
waveguide has a microcavity structure that connects to an input and an output waveguide ports. The
radius and position of air-holes surrounding the microcavity are modified to adjust the resonant
frequency to the single-mode regime of the waveguides. It is confirmed that input optical power istransmitted efficiently to the output waveguide due to resonant tunneling caused by the microcavity.
Maeda, H., K. Tomiura, H. Chen, K. Yasumoto [2013], proposed the best configuration for4

bending part of the post wall waveguide. post wall waveguide is important structure for microwave
transmission of integrated circuits with multi-layered substrates. It has simple periodic array ofmetallic or dielectric cylinders between parallel conducting plates. In this study, loss of bending partwith the angle of 120° in post wall waveguide was evaluated both numerically and experimentally for
microwave.
Maeda, Chen, Tomiura, and Yasumoto [2014] investigated the numerical and experimental
study on confinement in Y-shaped post wall waveguides consist of dielectric or metallic cylinders for
microwave around 4 GHz. In straight waveguide with dielectric cylinders, confinement of microwave
is poor, when the post wall was composed of a pair of single row of cylinders. After confirming
confinement of the electromagnetic field, Y-shaped branches of post wall waveguide consisted ofdielectric cylinders for microwave were similarly investigated for dielectric rods. The confinement
was also improved by increase of post wall up to 3 layers. These results are applicable for fundamental
design and fabrication of integrated circuit for microwave and millimeter wave.
Jandieri, Yasumoto, and Pistora [2014] proposed a self-contained coupled-mode theory forthe coupled two asymmetric photonic crystal waveguides (PCWs). The first-order coupled-mode
equations are derived under a weak coupling assumption. The coupling coefficients are obtained
systematically by a matrix calculus using the modal solutions of each PCW in isolation. The coupledmode equations are solved for contra-directional coupling between two asymmetric PCWs formed bya hexagonal lattice of circular air holes in a dielectric medium. It is shown that the self-contained
coupled-mode analysis is useful to characterize a peculiar feature of the contra-directionally coupled
PCWs as a drop filter.
Arai, Shibazaki, and Kinoshita [2016] investigated the accuracy of the finite-differencetime-domain (FDTD) method for approximating a waveguide consisting of a periodic structure witha conducting iris of nonzero thickness. They consider a model for a single stage of a periodic structure– an individual conducting iris of nonzero thickness- and determine optimal grid spacings for FDTD
calculations. They also determine the optimal grid spacings using benchmark numerical solutions
obtained with the modified residue-calculus method (MRCM), an accurate solution procedure thatincorporates boundary conditions, and obtain agreement by choosing a grid spacing on the order of
1/100th of the wavelength.
(T. Yamasaki)

1.3 Cavity Structures
Cavity structures appear in many radar targets and it is important to investigate theirscattering phenomena in detail.
As a geometry that can be classified as cavity structures, Shirai et al. [2014, 2016b, 2016c]
considered a slit formed by two thick semi-infinite plates, and analyzed the plane wave scattering
5based on high-frequency asymptotic methods. They obtained solutions that are valid for the case where
the slit width is large compared with the wavelength. Based on the results, numerical examples on thefar field intensity are shown and scattering characteristics of the slit are discussed in detail.
Kobayashi [2015, 2016] considered a finite parallel-plate waveguide with material loading
as a geometry that can form cavities, and analyzed the plane wave diffraction with the aid of the
Wiener-Hopf technique. Numerical examples on the radar cross section (RCS) are presented forvarious physical parameters and far field scattering characteristics of the waveguide are discussed.
(K. Kobayashi)

1.4 Canonical Structures
Scattering and diffraction by canonical structures and their solutions are treated in some
papers. Goto et al. [2016b, c] discussed high-frequency scattering by a coated conducting cylinder
covered with a thin lossy medium. From an exact solution of this canonical structure, they derived afrequency-domain uniform asymptotic solution that is uniform in the transition region adjacent to theshadow boundary and is valid for a source point and/or an observation point located either near thecoating surface or in the far-zone. Goto et al., [2016d] and Hagiwara et al. [2016] also proposed afrequency-domain asymptotic solution for scattered field by a coated conducting cylinder when thecoating layer is thick compared with the wavelength. The obtained asymptotic solution includes
multiple reflected waves passing through the coating medium and its validity is confirmed bycomparing with an exact solution.
Nishimoto and Naka [2016] analyzed a scattering problem by a conducting circular cylinder
with inhomogeneous lossy dielectric coating by using the multilayer division method. By solving the
problem as a boundary value problem, an analytic solution for scattered field in frequency domain isderived. Using the solution, transient responses for incidence of ultra-wideband pulses are calculated.
Numerical results for some different inhomogeneous parameters are given and the relationshipbetween inhomogeneous parameters and corresponding waveforms is discussed.
(M. Nishimoto)B2. Inverse Scattering
2.1 Iterative Approach
Moriyama et al. [2014] proposed a new time-domain imaging approach that combines theregularization capabilities of the filtered FBTS (Forward-Backward Time Stepping) method with theinformation-acquisition features of the IMSA (Iterative Multi-Scaling Approach). Representative
numerical examples are presented. The accuracy and robustness of the proposed method are discussed.
Moriyama et al. [2015, 2016] proposed an inverse scattering approach for reconstructelectrical parameter profiles of unknown objects from only tangential component of total electric field6

collected on an observation surface. The reconstructions of relative permittivity distributions aredemonstrated in Moriyama et al. [2015]. The estimations of the size and location of unknown objects
are demonstrated in Moriyama et al. [2016].
(M. Tanaka)

2.2 Other Approach
Recent studies have focused on developing security systems using micro-Doppler radars todetect human bodies. However, the resolution of these conventional methods is unsuitable for
identifying bodies and moreover, most of these conventional methods were designed for a solitary or
sufficiently well-spaced targets. Saho et al. [2014] proposed a solution to these problems with an image
separation method for two closely spaced pedestrian targets. The proposed method first develops animage of the targets using ultra-wide-band (UWB) Doppler imaging radar. Next, the targets in theimage are separated using a supervised learning-based separation method trained on a data set
extracted using a range profile. They experimentally evaluated the performance of the image
separation using some representative supervised separation methods and selected the most appropriate
method. Finally, they reject false points caused by target interference based on the separation result.
The experiment, assuming two pedestrians with a body separation of 0.44 m, shows that their method
accurately separates their images using a UWB Doppler radar with a nominal down-range resolutionof 0.3 m. They described applications using various target positions, establish the performance, andderive optimal settings for their method.
A novel algorithm was proposed for separating multiple moving targets in radar images inthe slow time-range domain [Sakamoto et al. 2015a]. Target discrimination is based on an image
texture angle that is related to the target’s instantaneous velocity. The algorithm efficiency has beensuccessfully verified for targets with variable velocities.
Sakamoto et al. [2015b] demonstrated an accurate remote measurement of heartbeats using
an ultra-wideband radar system. Although most conventional systems use either continuous waves or
impulse-radio systems for remote vital monitoring, continuous waves suffer from non-stationary
clutters, while impulse-radio systems cannot detect heartbeats. Their ultra-wideband radar system hasa moderate fractional bandwidth intermediate of these systems, resulting in both the suppression of
clutters and high sensitivity in measuring accurate heart rates even in a dynamic environment. A
simultaneous measurement of the vital signal of a participant employing the ultra-wideband radar andelectrocardiography reveals the high accuracy of the radar system in measuring the heart rate varying
over time.
Sakamoto et al. [2015c] presented a method of imaging a two-dimensional section of awalking person using multiple ultrawideband Doppler radar systems. Although each simple radarsystem consists of only two receivers, different line-of-sight velocities allow target positions to be7

separated and located. The signal received using each antenna is processed employing time–frequency
analysis, which separates targets in the time–range–velocity space. This process is followed by adirection-of-arrival estimation employing interferometry. The data obtained using the multiple radarsystems are integrated using a clustering algorithm and a target-tracking algorithm. Through realistic
simulations, they demonstrated the remarkable performance of the proposed imaging method in
generating a clear outline image of a human target in unknown motion.
Sakamoto et al. [2015d] proposed a fast and accurate radarimaging algorithm that combines
Kirchhoff migration with Stolt’s frequency-wavenumber (F-K) migration. F-K migration is known asa fast-imaging method in the F-K domain, while Kirchhoff migration is reported to be more accurate.
However, Kirchhoff migration requires the reflection points to be located as a function of the antenna
position and the delay time. This prevents the use of fast Fourier transforms (FFTs) because Kirchhoff
migration must be processed in the time domain, and this can be extremely time consuming. The
proposed algorithm overcomes this hurdle by introducing the texture angle and the inverse boundary
scattering transform (IBST). These two tools enable the locations of the reflection points to be
determined rapidly for each pixel of a radar image. The radar signals are then modified according to
the Kirchhoff integral, before Stolt F-K migration is applied in the frequency domain to produce anaccurate radar image. To demonstrate the performance of the proposed method, the conventional
delay-and-sum (DAS) migration, Kirchhoff migration, Stolt F-K migration, and the proposed method
are applied to the same measured datasets.
Measurement of heartbeats is essential in cardiovascular magnetic resonance imaging
because the measurement must be synchronized with the phase of cardiac cycles. Many existingstudies on radar-based heartbeat monitoring have focused on echoes from the torso only, and suchmonitoring cannot be applied to subjects in magnetic resonance scanners because only the head andsoles can be seen from the outside. Sakamoto et al. [2015e] demonstrated the feasibility of the remotemonitoring of heartbeats from the subject’s soles using a 60-GHz ultra-wideband radar. The heartbeat
intervals measured using the radar are quantitatively compared with those measured using
conventional electrocardiography.
Microwave systems have a number of promising applications in surveillance and monitoring
systems. The main advantage of microwave systems is their ability to detect targets at distance underadverse conditions such as dim, smoky, and humid environments. Specifically, the wide bandwidth ofultra-wideband radar enables high range resolution. In a previous study, Yamazaki et al. [2016]
proposed an accurate shape estimation algorithm for multiple targets using multiple ultra-wideband
Doppler interferometers. However, this algorithm produces false image artifacts under conditions withsevere interference. They proposed a technique to suppress such false images by detecting inconsistent
combinations of the radial velocity and time derivative of image positions. They study the performanceof the proposed method through numerical simulations of a two-dimensional section of a moving
8human body, and demonstrate the remarkable performance of the proposed method in suppressing
false image artifacts in many scenarios.
Sakamoto et al. [2016a] proposed a method that can accurately estimate the human heart
rate (HR) using an ultrawideband (UWB) radar system, and to determine the performance of the
proposed method through measurements. The proposed method uses the feature points of a radar signal
to estimate the HR efficiently and accurately. Fourier- and periodicity-based methods are inappropriate
for estimation of instantaneous HRs in real time because heartbeat waveforms are highly variable,
even within the beat-to-beat interval. They defined six radar waveform features that enable correlation
processing to be performed quickly and accurately. In addition, they proposed a feature topology signalthat is generated from a feature sequence without using amplitude information. This feature topology
signal is used to find unreliable feature points, and thus, to suppress inaccurate HR estimates.
Measurements were taken using UWB radar, while simultaneously performing electrocardiographymeasurements in an experiment that was conducted on nine participants. The proposed method
achieved an average root-mean-square error in the interbeat interval of 7.17 ms for the nine participants.
The results demonstrate the effectiveness and accuracy of the proposed method. The significance of
this study for biomedical research is that the proposed method will be useful in the realization of aremote vital signs monitoring system that enables accurate estimation of HR variability, which has
been used in various clinical settings for the treatment of conditions such as diabetes and arterial
hypertension.
Sakamoto et al. [2016b] proposed a fast method of ultrawideband (UWB) radar imaging thatcan be applied to a moving target, having in mind such application as concealed weapon detection.
They demonstrated the performance of the proposed method using simulations and measurements withstatic and moving targets. They also compared the computational complexity of the proposed methodwith that of a conventional method to clarify the feasibility of applying the proposed method to theintended real-time systems.
(T. Sato)

B3. Computational Techniques
3.1 Integral Equation Methods
The integral equation methods such as the method of moments (MoM), the boundary
element method (BEM), and so on, are powerful and versatile solvers for various problems inelectromagnetics. In common with many other methods, computational costs become a serious issue
as the electrical size of objects increases and many attempts have long been made for this.
The one of effective approaches is the characteristic basis function method (CBFM). The
CBFM uses characteristic basis functions (CBFs) constructed by M-partitioning objects, to reduce theresulting MoM matrix to M2 * M2. Tanaka et al. [2016] developed improved primary characteristic
9basis functions (CBFs) to reduce the number of characteristic basis functions, and successfully
obtained high precision analysis results of monostatic radar cross section from a PEC plate. Konno
and Chen [2014b] formulated a higher-order CBF in a general form and applied it to analyses of largesized antennas in the vicinity of dielectric objects. The numerical results showed that the CPU time
can be saved without large degradation in accuracy.
An alternative technique was presented by Sekine [2014]. They applied isogeometricanalysis to MoM in order to take into account curved objects without mesh generation.
The integral equation methods in the time domain also attract much attention. Kawaguchi etal. [2014] presented an initial value problem formulation in 3D time domain boundary element method(TDBEM) to avoid the numerical instability and inaccuracy caused by the conventional TDBEM.
Maeda et al. [2014] adopted the compressed row storage matrix in TDBEM, which is suitable for a
message passing interface parallel processing. The numerical results showed the reduction of both
memory consumption and computation time. Kawaguchi et al. [2015] developed a four-dimensional
domain decomposition method for the TDBEM to save computational memory. Ohnuki et al. [2016]
utilized the fast inverse Laplace transform to obtain time-domain solutions. They formulated theintegral equations in the complex frequency domain and solved them by using the method of moments.
The advantage of this method is that the observation time can be selected independently and that theaccuracy does not depend on the observation time.
The one of attractive applications in the integral equation method is scattering problems
from multiple objects. Tanaka [2014] applied the multilevel algorithm for superposition solution
combined with the MoM to this type of problems. Yashiro [2015a, 2015b] adopted global basis
functions for analysis of multiple circular cylinders. Matsushima [2016] analyzed the light scatteringfrom nano-strips stacked in parallel by using the generalized boundary conditions, deriving singular
integral equations, and solving them by choosing the Legendre and Chebyshev polynomials as thebasis and testing functions.
(Y. Ando)

3.2 Modal Expansion Method
A modal expansion method is a quite powerful technique which is able to deal with a lot ofguided structures, antennas, and filters. A specific field or current are expanded as a sum offundamental field or current components, so-called modes. The modes associated with a specificstructure are obtained analytically or numerically and their coefficients are obtained numerically.
Ohnuki et al. [2014] have analyzed electromagnetic scattering problems using the point
matching method (PMM) with the mode expansion. A dielectric sphere with a PEC shell was
numerically analyzed using the PMM and excellent agreement between the numerical results and exact
Mie series solution was shown.
10

Fujita and Shirai [2015] have clarified a theoretical limitation of radiation efficiency forhomogeneous electrically small antennas using spherical wave functions. According to their study,
radiation efficiency of an antenna inside a sphere with a specific radius is less than that of a sphericalantenna with the same radius. In addition, it is indicated that a uniform current distribution is preferable
for high radiation efficiency.
Sato and Shirai [2016] have rigorously formulated a problem of electromagnetic plane wave
diffraction by loaded N-slits on thick conducting screen via eigen function expansion. Performance ofthe formulation is demonstrated and compared with that of the geometrical theory of diffraction (GTD).
Konno et al. [2014a-c] have analyzed an antenna in the vicinity of a dielectric object using
a characteristic basis function method (CBFM). The CBFM is able to reduce the size of the original
problem using a characteristic basis function (CBF), which is numerically obtained mode-like function.
Accuracy and computational cost of the CBFM have been clarified and enhanced in these studies.
Recently, a novel CBFM for a finite periodic structure has been developed and performed by Konno
et al. [2016].
(Q. Chen)

3.3 Finite-Difference and Finite-Element Methods
New FDTD modeling methods for Metamaterials have been developed. Arima et al. havedeveloped new modeling method for meta-surface [2016a]. This method has utilized Surface
Impedance of meta-surface. The effectiveness of this method is confirmed by analyzing dipole antenna
which is placed above the meta-surface.
An efficient FDTD algorithm for relatively low frequency (around 10MHz) range problem
has been developed by Asano et al. This method utilizes transfer function. In order to acetate
calculation time of the transfer function. The Auto Regressive Moving Average (ARMA) algorithm
has applied. This algorithm is named as ARMA-FDTD method. The effectiveness of ARMA-FDTD
method was confirmed by calculating lightning problem [2016].
New efficient FDTD algorithms have been developed. The partially implicit FDTD
algorithm was developed to the wideband analysis of spoof localized surface plasmons by Fujita[2015]. The effectiveness of the new FDTD algorithm has been confirmed in 3-D general orthogonal
grids by analyzing EM fields [2016a]. This new FDTD algorithm was named as Magnetically mixed
Newmark-Leapfrog (MNL-) FDTD method. Fujita applied this new FDTD algorithm for ESD
problem of small gap [2016b, 2016c]. A time signature of short gap ESD problem is also analyzed[2016d]. An efficient absorbing boundary condition (ABC) for this new FDTD algorithm has also beendeveloped [2016e].
Kushiyama et al. applied the FDTD method for metamaterial antenna development. The
developed metamaterial antenna was leaky wave antennas. Kushiyama et al. confirmed the11effectiveness of FDTD method for leaky wave metamaterial antennas [2015].
(T. Arima)

B4. High Frequency Technique
4.1 Wave Optics
In [Ali M., Kohama T., and Ando M., 2015]. Equivalent edge currents (EECs) for highfrequency diffraction analysis are intermediate concepts between ray theory and wave optics [physical
optics (PO)]. The methods of EEC present some ambiguity in the definition of currents at general edge
points, which do not satisfy the diffraction law. Modified edge representation (MER) is a uniqueconcept for a complete definition of EEC with simple and classical Keller-type knife-edge diffraction
coefficients. Although singularities in the definition of EEC exist, the line integration of MER EEC
results uniform and accurate fields everywhere including geometrical boundaries except for the caseof grazing incidence, where reflection and incidence shadow boundaries (RSB and ISB) are close toeach other. In this paper, fringe wave (FW) part of MER EEC is modified by introducing the weighting
in terms of Fresnel zone number (FZN) distance from the reflection point to improve the accuracy atand near shadow boundaries even in grazing incidence. The corner diffraction, a contribution comingfrom edge point which does not satisfy the diffraction law, is extracted in MER by introducing anotherweighting function using the FZN distance from scattering centers on edge. Its remarkable accuracy
fully validates MER EECs at general edge points. The dipole wave scattering from flat square andtriangular plates are discussed with numerical examples.
In [Kohama T., and Ando M., 2014], the physical optics (PO) approximation is one of thewidely-used techniques to calculate scattering fields with a reasonable accuracy in the high frequency
region. The computational load of PO radiation integral dramatically increases at higher frequencies
since it is proportional to the electrical size of scatterer. In order to suppress this load, a variety oftechniques, such as the asymptotic evaluation by the stationary phase method (SP), the equivalent edge
currents (EECs), the low-order polynomial expansion method and the fast physical optics (FPO), havebeen proposed and developed. The adaptive sampling method (ASM) proposed by Burkholder is also
one of the techniques where the sampling points in radiation integral should be adaptively determinedbased upon the phase change of integrand. We proposed a quite different approach named“Localization of the radiation integrals.” This localization method suggests that only the small portionsof the integration with a slow phase change contribute to the scattering field. In this paper, we newly
introduce the ASM in the localization method and applied the proposed method into the radar crosssection (RCS) analysis of 2-dimensional strip and cylinder. We have confirmed that the proposed
method provides the frequency-independent number of division in the radiation integrals andcomputational time and accuracy. As the starting point for extension to 3-D case, the application of
the proposed method for a reflection from an infinite PEC plane and a part of sphere was also examined.
(M. Ando)12

4.2 Ray Optics, and OthersHigh frequency reflection from and transmission through the wall is one of the important
problem for outdoor/indoor penetration analysis, since these rays experience the multiple bouncing
and lateral shift. This problem has been analyzed ray-optically by two dimensional slab structure [Satoet al., 2014a, b].
A high-frequency asymptotic method has been applied to formulate E-polarized plane wave
diffraction by a thick slit. The slit structure is regarded as an open-ended parallel plane waveguidecavity, and the excitation of the waveguide modes and their re-radiation are derived from a ray-mode
conversion technique. Comparison with another method reveals the validity and effectiveness of ourformulation [Hasegawa et al., 2014, Sato et al., 2014c, Shirai et al., 2014, 2016, Shimizu etl al., 2015,
Shirai et al., 2016a, b, c, d].
The above single thick slot problem has been extended to multiple slot cases to simulate theeffect of an array of windows on building walls [Sato et al.,2014b, 2016].
Diffraction from dielectric bodies become an important problem for high frequency regime,
since there is no rigorous analytical solution is available. Kirchhoff approximation has been applied
to obtain the diffraction field from dielectric cubic bodies to consider the effect of internal multiple
bouncing [Nguyen et al., 2015a, b]. Also, an effort has been made to estimate the shape of the dielectricbodies from their RCS variation [Kisumi et al., 2015].
The high-frequency scattering problem by a coated conducting cylinder covered with a thinlossy medium has been discussed in the papers by [Goto et al., 2016b, c]. The frequency-domain
uniform asymptotic solution (FD-UAS) is uniform in the transition region adjacent to the shadowboundary and is valid for a source point and/or an observation point located either near the coating
surface or in the far-zone.
The papers by [Goto et al., 2016d, Hagiwara et al., 2016] propose frequency-domain (FD)asymptotic solutions (FD-ASs) for scattered field by a coated conducting cylinder when a coating
layer is thick as compared with the wavelength. The FD-ASs newly include the multiple reflection
effect passing through the inner portion of a coating layer as compared with the FD-UAS [Goto et al.,2016b, c].
(H. Shirai)

B5. Transient Fields
Analysis of transient scattering phenomena from smooth curved conducting surfaces withedges or wedges plays an important role in developing ultra-wideband (UWB) (or short pulse) radars
and their associated antennas for remote sensing and target identification applications.
The paper by [Goto et al., 2014a] proposes a time-domain (TD) asymptotic analysis method
13for the transient scattered field excited by the edges of a cylindrically curved conducting open sheet.
Their proposed method is based on the Fourier transform method. The advantages of the proposed
method are: (1) Each TD asymptotic solution of pulse wave elements of which the transient scatteredfield is made up is obtained easily, (2) The TD asymptotic solution is effective in understanding thetransient scattering phenomena. The paper by [Goto et al., 2014b] investigates the arrival timedifference between a creeping wave (CW) propagating along a convex portion and a whisperinggallery (WG) mode propagating along a concave portion. They confirmed the interesting phenomenon
that the CW propagates along the curved sheet later than the WG mode. The papers by [Goto et al.,2014c, 2015a, 2016a] derive a novel TD asymptotic-numerical solution (TD-ANS) for transient
scattered field from a cylindrically curved conducting open sheet excited by a UWB pulse wave. The
advantages of the proposed method are: (1) The TD-ANS is highly accurate and a new reference
solution on engineering applications, (2) The TD-ANS can extract and observe each pulse wave
element from a response waveform, and (3) The computation rate of the TD-ANS is very fast ascompared with that of a reference solution which is obtained numerically from the method of moment(MoM) and the fast Fourier transform (FFT) numerical code.
A study of scattering and radiation from a conducting surface with dielectric loading is greatinteresting because it provides an understanding of the effects due to loading on the scattered fields.
Analysis of scattering phenomena from coating cylinders plays an important role in developing theapplication area such as the radar cross section (RCS), the development of radar absorbing material(RAM), and the radar target discrimination.
The papers by [Goto et al., 2016b, c] derive a frequency-domain (FD) uniform asymptotic
solution (FD-UAS) for scattered field by a coated cylinder with a thin lossy medium. The FD-UAS is
the high-frequency (HF) asymptotic solution applicable uniformly in the large area from the nearby
region relatively of the coating surface to the far-zone. The papers by [Goto et al., 2015b, c, d] develop
a time-domain (TD) asymptotic-numerical solution (TD-ANS) for a transient scattering problem byextending the FD-UAS.
The advantages of the TD-ANS are: (1) The TD-ANS is highly accurate and can extract andobserve each pulse wave element from a response waveform, namely, a direct geometric optical ray(DGO), a reflected GO (DGO), a pseudo surface diffracted ray (pseudo SD), and a lowest order SD,(2) The computation rate of the TD-ANS is very fast as compared with that of a reference solution
which is obtained from a FD exact solution and the FFT numerical code.
The papers by [Goto et al., 2016d, Hagiwara et al., 2016] propose frequency-domain (FD)asymptotic solutions (FD-ASs) for scattered field by a coated conducting cylinder covered with a thickdielectric medium. The FD-ASs newly include the multiple reflection effect passing through the inner
portion of a coating layer as compared with the FD-UAS [Goto et al., 2016b, c]. By extending the FDASs, the papers [Goto et al., 2014d, 2016e] develop a novel time-domain (TD) asymptotic-numerical14

solutions (TD-ANSs) which are composed of a geometric optical ray (GO) series solution and an
extended uninform geometrical theory of diffraction (UTD) series solution. The advantages of the TDANSs are highly accurate and useful because they can extract and interpret each pulse wave elementfrom a response waveform including the multiple reflection effect even when pulse wave elements
overlap mutually.
(K. Goto)

B6. Wave in random, inhomogeneous, nonlinear and complex media
6.1 Wave Propagation and Scattering in Random MediaThe conventional extinction theorem in grating theory does not work numerically for a
critical angle of incidence. This drawback was overcome by a new formulation using the image Green's
function. The extinction error field and the mean square extinction error were newly introduced asvalidity criteria and calculated numerically [Nakayama et al., 2014a]. Nakayama et al. [2014b]
proposed the average filter as a new numerical technique to make up a diffraction field solution withreciprocal property. It was found that the energy error is much reduced by use of the average filter insome case.
Tamura [2016] proposed a novel image integral equation of the first type (IIE-1) for a TE
plane wave scattering from periodic rough surfaces with perfect conductivity by means of the methodof image Green's function. Since such an IIE-1 is valid for any incident wavenumbers including thecritical wavenumbers, the analytical properties of the scattered wave field can be generally andrigorously discussed. Then, it is firstly pointed out that the branch point singularity of the barepropagator inevitably appears on the incident wavenumber characteristics of the scattered wave field
and its related quantities just at the critical wavenumbers. The proposed IIE-1 gives a numericalsolution satisfying sufficiently the optical theorem even for the critical wavenumbers. Moreover, it isthen confirmed that the branch point singularity clearly appears in the numerical solution. It is highly
expected that the IIE-1 be applied to numerical simulations of waves scattering from randomly roughsurfaces for low grazing angle incidences.
In order to analyze quantitatively the depolarization due to random medium, Nanbu et al.
[2016, 2014] derive an integral equation using the dyadic Green's function on the assumption that
there exists a random medium layer of which the dielectric constant is fluctuating randomly. On the
integral equation, the depolarized EM wave is analyzed by using a perturbation method, and the firstorder perturbed EM wave is given in a compact far-field form by using an ordered exponential function.
(S. Ohnuki)

6.2 Inhomogenenous, nonlinear and complex media
Ozaki et al. [2014] propose a method for deciding the parameters to satisfy the experiment15

values, and checked the effectiveness of this method based on Kramers-Kronig (K.K.) relation. In their
method, they expressed as matrix the Sellmeier's formula, and solved the simultaneous equation until
the satisfied the experiment value. The influence of pulse responses using the medium constants, which
can be found by proposed method, is shown numerically. Ozaki and Yamasaki [2016b] investigated a
new structure, which combines dielectric cylinders with air-hole cylinders array, and analyzed theguiding problem for periodically dielectric waveguides by arbitrary shape of dielectric constants inthe middle layer. In the numerical results, they examined an influence of the dielectric circular cylinder
along a middle layer by using the energy distribution and complex propagation constants at the firststop band region compared with hollow dielectric cylinder. In addition, we also investigated theinfluence of dielectric structure with equivalence cross section compared with dielectric cylinders, andclarified an influence of dielectric structures in the middle layer by energy distribution analysis forTE0 mode.
Nakayama and Tamura [2014b] proposed a new method to obtain a numerical solution ofdiffraction grating that satisfies the reciprocity. The shadow theory states that, by the reciprocity, them-th order scattering factor is an even function with respect to a symmetrical axis depending on theorder m of diffraction. However, a scattering factor obtained numerically becomes an even function
only approximately, but not accurately. It can be decomposed to even and odd components, where an
odd component represents an error with respect to the reciprocity and can be removed by the averagefilter. Using even components, a numerical solution that satisfies the reciprocity is obtained. Numericalexamples are given for the diffraction of a transverse magnetic (TM) plane wave by a very roughperiodic surface with perfect conductivity. It is found that, by use of the average filter, the energy error
is much reduced in some case.
Yokota and Matsumoto [2014] examined the effective permittivity of the two-dimensional
multilayered periodic structures, which consist of the rectangular dielectric cylinders, numerically. The
original periodic structure is replaced with a simple structure such as the dielectric slab. By using thereflectance of the periodic structure obtained by the FDTD method, the effective permittivity of thedielectric slab, which has the same reflectance as that of the periodic structure, is obtained by using
the transcendental equation. In order to reduce the procedure to obtain the reflectance from themultilayered periodic structures, the reflectance from one-layered structure is used. The range of theapplication and validity of this procedure is clarified.
(M. Yokota)

B7. Guided Waves
7.1 Dielectric and Optical Waveguides
PLC-based mode multi/demultiplexer devices are designed and fabricated based on a mode
coupling and/or incorporating a mode rotator to the mode-division multiplexing transmission in few
16mode fibers [Hanzawa, N., et al., 2013, Saitoh, K., et al., 2014, Hanzawa, N., et al., 2014, Hanzawa,N., et al., 2015]. Fiber-based multi/demultiplexer devices are also investigated for six modes based on
multi-core fiber couplers [Nishimoto, S., et al., 2016]. To realize a low bending loss, large effective
area, and large effective-index differences between core modes, optimized fiber parameters areinvestigated in few mode fibers [Kasahara, M., et al., 2013, 2014]. As for multi-core fibers, a simple
analytical expression for estimating a crosstalk in homogeneous [Ye, F., et al., 2014, 2016a, 2016b]
and an efficient design method are derived considering a low crosstalk, large effective area and singlemode operation in heterogeneous [Tu, J., et al., 2016] trench-assisted fibers. Optimized fiber designs
are investigated with a low crosstalk, large effective area, and low differential mode delay forheterogeneous trench-assisted few-mode multi-core fibers [Tu, J., et al., 2014, 2015]. Various fewmode multi-core fibers are also fabricated and demonstrated with spatial channel count of 36 with 3
modes × 12 cores [Sasaki, Y., et al., 2015], 108 with 3 modes × 36 cores [Sakaguchi, J., et al., 2016],
and 114 with 6 modes × 19 cores [Igarashi, K., et al., 2016]. Long-haul transmission over 500 km isachieved with spatial channel count of 36 with 3 modes × 12 cores employing a few-mode erbiumdoped fiber amplifier with low mode-dependent gain as well as a newly developed graded-index corewith low differential mode delay which is also compensated by a novel digital technique in few-mode
multi-core fibers [Shibahara, K., et al., 2016]. Aiming for suppression of group delay spread in strongly
coupled multi-core fibers, a group delay spread analysis and a novel fiber design are discussed[Fujisawa, T., et al., 2016]. As for all-solid photonic bandgap fibers, optimized structural parameters
for realizing large effective area are investigated while at the same time keeping single-mode operation
for high-power laser applications [Saitoh, S., et al., 2014].
A 3-D finite-element time-domain beam propagation method is developed, which enables
the analysis of transmission characteristics of any kind of photonic structures [Makino, S., et al.,2015a]. In order to calculate nonlinear Kerr effects rigorously in periodic optical waveguides, anonlinear guided mode solver is developed based on the 3-D finite element method [Sato, T., et al.,2014]. A rigorous definition of nonlinear parameter for high-index-contrast periodic opticalwaveguides is also proposed, which agrees well with the results by the rigorous nonlinear mode solver
and experiments [Sato, T., et al., 2015]. In order to suppress reflection of L-shaped photonic crystal
cavity-based all-optical diode, a simple design method is proposed using a linear numerical schemeand nonlinear coupled mode theory [Sato, T., et al., 2016]. Aiming for enhancing the opticalnonlinearity, a coupled resonator optical waveguide based on a slotted 1-D photonic crystal cavity is
proposed and analyzed [Makino, S., et al., 2015b]. For a novel light source expected in the future midinfrared photonics, material gain of GeSn/SiGeSn quantum wells is investigated by using the
microscopic many-body theory where GeSn becomes direct bandgap material without any strain anddoping contrary to Ge [Fujisawa, T., et al., 2015a]. Moreover, quantum-confined Stark effect of thematerial is analyzed for electroabsorption device applications such as a modulator, switch, and so on
17

[Fujisawa, T., et al., 2015b]. To reduce bend and transition losses, contribution of the adjustment of
the core location is discussed for a buried waveguide on a silicon substrate [Nito, Y., et al., 2016]. To
realize an ultra-broadband polarization beam combiner/splitter, a silicon waveguide structure is
proposed, composed of three identical directional couplers and two identical delay lines [Uematsu, T.,et al., 2014]. For an efficient optical coupling to fibers, a vertically curved Si waveguide coupler is
proposed and fabricated [Yoshida, T, et al., 2016]. To achieve a low loss wavelength-divisionmultiplexing and optical coupling between electroabsorption-modulator-integrated lasers and a singlemode fiber, a precise lens manipulation technique [Murao, T., et al., 2014], as well as a monolithic
integration technique with a low-loss cascaded Mach-Zehnder multiplexer [Fujisawa, T., et al., 2013]is proposed and demonstrated.
(T. Murao, M. Otsuka)

7.2 Transient Fields in Guided Waves
Shibayama et. al. [2014] calculate the transient electromagnetic fields of a plasmonic rod
waveguide and the reflection coefficients in a plasmonic grating, in which the dispersion is expressedby the Drude and Drude-Lorenz models, with the body-of-revolution finite-difference time-domain
method based on locally one-dimensional scheme.
Ohtera Y. [2016] investigates on the accuracy and computational performance of the FDTD
calculations for the transient electromagnetic field of the obliquely propagating waves in an air/Si subwavelength periodic structure.
(Y. Kogami)

B8. Antennas
8.1 Fundamental Antenna
Ito et al. [2016] have described the review of wearable antennas as well as implantableantennas that have been studied in their laboratory. Antennas for particular uses, Sekiguchi et al. [2016]
have developed a technique to reduce performance degradation of near field communication (NFC)
antennas nearby metal objects by modifying the magnetic sheet shape attached on the metal. Nguyen
et al. [2015] have proposed the space-saving design of built-in antennas for handset terminals basedon the concept of requisite design antenna volume. As the antenna theory topic, Fujita [2015] havederives the maximum radiation efficiency for homogeneous electrically small antennas using thespherical wave expansion. To analyze the radiation source of the EM interference, Nishina and Chen
[2016] have developed a method including near field measurement in time domain and matrix
inversion to estimate the equivalent current distribution of incoherent radiation source. In
computational electromagnetics, Konno and Qian [2014b] have formulated the higher-ordercharacteristic basis function method (HO-CBFM) to provide results accurately even if a block division18

is arbitrary.
(H. Arai)

8.2 Wideband Antennas
So et al. [2014] have proposed a sector base station antenna for mobile wirelesscommunication systems employing multiple woodpile metamaterial reflectors and a multiband
radiator that establishes the same beamwidth in the horizontal plane for more than two frequency
bands. Sumi and Cho [2014] have proposed a new small multiband printed antenna for wirelesstelecommunications modules that can realize Machine-to-Machine applications. Nguyen et al. [2015]
have presented the detailed investigations on a simple multi-band method that allows inverted-F
antennas (IFAs) to achieve good impedance matching in many different frequency bands. A tri-band
Multiple-input-multiple-output (MIMO) antenna system for LTE 700, LTE2500 and GSM 1800/1900
mobile handset application has been presented [Yang, et al., 2016].
A frequency-reconfigurable dipole antenna, whose dual resonant frequencies are
independently controlled, has been introduced [Onodera, et al., 2016]. The antenna's conductor
consists of radiating conductors, lumped and distributed elements, and varactors. The dual resonant
frequencies are controlled with the embedded series and shunt inductors.
Yamauchi and Fukusako [2016] have proposed design techniques to reduce the crosspolarization (XPOL) generated from a circular waveguide antenna using an L-shaped probe. As aresult, XPOL is reduced by around 10 dB, and CP is radiated over a wide angle range of 120-150°
covering frequencies from 7.35 to 9.75GHz.
(N. Michishita)

8.3 Antenna Elements
Monopole, microstrip, meander line, slit ring, inverted L, spiral, bowtie slot, body of
revolution (BOR), and loop antennas have been researched from novel engineering aspects. (1)Monopole antenna: Fujimoto et al. [2014] have proposed a monopole antenna for circular polarization,
while Yamamoto et al. [2015] have proposed a MIMO antenna composed of leaf-shaped monopoles
and notches. (2) Microstrip antenna: A circularly-polarized microstrip antenna has been proposed by
Fujimoto et al. [2015a], where dual-band operation is achieved by installing L-shaped slits at all edges
of a square patch. In addition, the same group has investigated a stacked microstrip antenna fed by an
L-probe for quadruple band operation [Fujimoto et al., 2015b]. Other researches on microstrip
antennas are found in the activities at Kumamoto and Hosei Universities. Maruyama et al. [2014] haverealized a broadband patch antenna that radiates a circularly polarized wave using an artificial groundstructure. Nakano et al. [2014b] have investigated a one-plate system composed of a patch antenna
and a single inhomogeneous plate in order to create a tilt beam. Furthermore, the same group has
19

revealed that a two-plate system creates a larger tilted beam than the one-plate system [Nakano et al.,2016a]. (3) Line antenna: Maema et al. [2014] have discussed the radiation efficiency of an electricallysmall and low-profile meandered-line antenna. This antenna uses a capacitive feed structure and two
meandered elements. (4) Split-ring Antenna: Lertsakwimarn et al. [2015] have designed an antennaconsisting of an inner small fed ring, an outer coupled split ring, and a ground plane, where an
omnidirectional radiation pattern with horizontal polarization to the ground is obtained. (5) Inverted L
antenna: Rohadi et al. [2014a] have investigated numerically and experimentally a low profile antenna
based on two inverted L elements, which are located on a square conducting plane. This antenna isapplied to a single-band MIMO antenna system. The same group has also investigated a dual-band
MIMO antenna system [Rahadi et al., 2014b]. (6) Spiral antenna: Tanabe [2016] has discussed theantenna characteristics of a two-arm Archimedean spiral antenna above a hybrid HIS-EBG reflector.
The hybrid HIS-EBG is effective for improving the input impedance and axial ratio. Nakano et al.
[2016b] have investigated a metaspiral antenna with unbalanced excitation. Simple equations arederived for the unbalanced excitation. (7) Bowtie slot antenna: The design of a wideband printed
antenna has been presented by Yamamoto [2014], where a leaf-shaped bowtie slot is employed as aradiating element. (8) BOR antenna: Nakano et al. [2014a] have introduced slots into a BOR-SPR
antenna to obtain a stop band within an extremely wide VSWR frequency band. The same technique
has been employed for an iCROSS antenna [Nakano et al., 2016c], which is a modification of the
BOR-SPR antenna. The advantages of the iCROSS are as follows: the low-profile structure, highstopband VSWR, small cross-polarization component in the azimuth plane, and low fabrication cost.
(9) Loop Antenna: Pal et al. [2014] have presented a dual-band low-proﬁle switched beam square-loop
antenna fed by capacitive coupling. The capacitively coupled feeding arrangement introduces
capacitance into the antenna input impedance and cancels the high inductance due to close proximityof ground plane and feeding probes. Hirose et al. [2015a] have discussed the radiation from a circularloop with parallel wires. When the distance between the parallel wires is appropriately chosen, theantenna radiates a circularly polarized wave. Subsequently, the same group has proposed a triangle
loop antenna as a circularly polarized element [Hirose et al., 2015b]. An application of the triangle
loop to a comb-line antenna is presented.
(H. Nakano)

8.4 Arrays and Phased Arrays
A novel technique to replace some elements in an array antenna with parasitic elements is
described [Takano et al., 2013]. First, the antenna characteristics are studied by simulation for a basic
unit array with one driven and two parasitic elements. The parasitic elements are excited by theneighboring driven elements through the electromagnetic coupling effect. It is shown that at the
optimal coupling condition, the radiation patterns are almost identical with those of an array antenna20

whose elements are all driven without coupling. The simulation result is confirmed by performing anexperiment at 5.8 GHz. Finally, a 12-element array is formed by combining four unit arrays. The
simulation results show that the maximum antenna gain indicates no penalty with respect to theantenna gain of a fully driven 12-element array. Therefore, the array antenna can be considerably
simplified by replacing 67% of its elements with parasitic elements.
A solar power satellite system as an application of a large-scaled phased array antenna is
described [Takano et al., 2013]. Key technologies are extracted, and their solutions are presented.
Consequently, a paradigm shift from a-la-carte production to mass-production is pointed out.
A novel method to generate a beamed wave by a phased array antenna is presented [Takano
et al., 2016]. Each radiating element of the antenna is fed with a phase correspondent to a sphericalwave front of a Gaussian beam. Simulation results reveal that the convergence characteristics arestrongly dependent on the transmitting antenna size, distance, and frequency. This work could be usedin wireless power transmission through a long distance.
The design and radiation properties of a linearly polarized radial line microstrip antenna
array (RL-MSAA) with U-slot circular microstrip antennas are presented [Kimura et al., 2014]. A
circular microstrip antenna (C-MSA) with U-shaped slot is used as a radiation element of the RLMSAA. Radiation phase of the U-slot C-MSA is controlled by tuning the radius of the C-MSA anddimensions of the U-slot on the C-MSA; therefore, the desired phase distribution of the RL-MSAA
can be realized. In the paper, a linearly polarized RL-MSAA with three concentric rows of C-MSAs
at a spacing of 0.65 wavelengths is designed for 12 GHz operation. In order to realize uniform phase
distribution, the U-slot C-MSAs are arranged for inner two rows and normal C-MSAs are arranged
for the termination row. Validity of the linearly polarized RL-MSAA with U-slot C-MSAs for radiation
phase control is demonstrated by simulation and measurement.
Parallel-plate slot array antenna fed by rectangular waveguides at its lower-edge sides has
been proposed [Akbar et al., 2016]. This antenna panel can be applied for dual circularly polarized
deployable synthetic aperture radar (SAR) antenna onboard small satellite. As to confirm thefeasibility of the antenna implementation, a development of one panel antenna system with single
polarization (RHCP) has been conducted. The antenna design with simplified model by highfrequency structure simulator (HFSS) and antenna measurement results are explained in this paper. It
is shown that antenna with gain and efficiency of 34.9 dBic and 54%, respectively, are achieved at thetargeted center frequency (9.65 GHz).
A partially dielectric-filled structure of low-temperature cofired ceramics (LTCC) oversizedrectangular waveguide slot array antenna with air layers both in the radiating and the feeding parts ispresented [She et al., 2015]. It has a new structure of partially filled coupling junctions in the feeding
waveguide. The efficiency evaluation shows that the air-layer addition reduces the transmission loss
both in the radiating and the feeding parts. The gain and bandwidth have been enhanced. The effective
21

dielectric constant is reduced and it broaden the bandwidth of the series-fed feed junctions and the slot
array. Using the LTCC with εr = 6.6 and tanδ = 0.013, the dielectric losses of the feeding waveguideare reduced from 4.5 to 0.5 dB. The losses of the radiating waveguide are reduced from 3.7 to 0.45
dB. Experimentally, the gain was shown to increase 5.5 dB. The 3-dB-down bandwidth was improved
from 1.4 to 2.1 GHz.
A point-to-point fixed wireless access (FWA) system with a maximum throughput of 1 Gbps
has been developed in the 39 GHz band [Zhang et al., 2014]. A double-layer plate-laminatedwaveguide slot array antenna is successfully realized with specific considerations of practicalapplication. The antenna is designed so as to hold the VSWR under 1.5. The antenna input as well as
feeding network is configured to reduce the antenna profile as well as the antenna weight. In addition,
integrating the antenna into a wireless terminal is taken into account. A shielding wall, whose
effectiveness is experimentally demonstrated, is set in the middle of the wireless terminal to achieve
the spatial isolation of more than 65 dB between two antennas on the H-plane. 30 test antennas arefabricated by diffusion bonding of thin metal plates, to investigate the tolerance and mass-productivityof this process. An aluminum antenna, which has the advantages of light weight and anti-aging, is alsofabricated and evaluated with an eye to the future.
A double-layer waveguide slot array antenna is developed for a 40-GHz-band directional
division duplex (DDD) system, which exhibits extremely high utilization efficiency of frequency[Zhang et al., 2016]. To minimize the interference from the surrounding buildings, the Taylor
distributions are adopted in both longitudinal and transverse directions over the antenna aperture to
suppress the sidelobe levels (SLLs) below −30 dB. A four-corner-fed structure instead of the typicalcenter-feed one is introduced for wideband operation. The perfect magnetic conductor (PMC)
terminations are also adopted at the center of feeding waveguides due to the symmetric feed fromright-and-left ends. As the predicted antenna performance using HFSS, the antenna gain of more than
31.8 dBi and the reflection of less than −10 dB are estimated over the operating frequency range of39.5-41.0 GHz. The test antennas are fabricated by diffusion bonding of copper plates. As themeasured antenna performance, the antenna gain higher than 30.6 dBi and the reflection lower than
−10 dB are achieved over the desired frequency range. The sidelobes are suppressed below −30 dB,
and the isolation between two antennas arranged in H-plane is achieved at the level of more than 76
dB.
A 16 x 16-element corporate-feed waveguide slot array antenna in the 60-GHz band isdesigned to achieve broadband reflection and high antenna efficiency [Tomura et al., 2014]. The subarrays consisting of 2 x 2-elements are designed to improve the reflection bandwidth by implementing
lower Q and triple resonance. The designed antenna is fabricated by diffusion bonding of thin copper
plates. A wide reflection bandwidth with VSWR less than 2.0 is obtained over 21.5%, 13.2 GHz (54.767.8 GHz). The measured gain is 32.6 dBi and the corresponding antenna efficiency is 76.5%. The
22

broad bandwidth of more than 31.5-dBi gain is realized over 19.2%, 11.9 GHz (56.1-68.0 GHz). The
gain in bandwidth covers the whole of the license-free 60-GHz band (57-66 GHz).
A 45° linearly polarized hollow-waveguide 16 x 16-slot array antenna is proposed for pointto-point wireless communication in the 71–76 GHz and 81–86 GHz bands [Tomura et al., 2014]. The
antenna is composed of an equally-split corporate-feed circuit and 2 x 2-element sub-arrays whichradiate the 45° linear polarization. Low sidelobe characteristics are obtained in the E-plane by diagonalplacement of the square antenna rotating by 45 degrees. To suppress cross polarization, a radiating
narrow-slot pair is adopted. The sub-array is designed by a genetic algorithm and 25.7% reflection
bandwidth for VSWR < 1.5 is obtained by decreasing the Q of two eigenmodes of the radiating element.
A 16 x 16-element array is fabricated by diffusion bonding of thin copper plates. The total thickness
is 3.2 mm which is less than 1 free space wavelength. A high gain of 32.9 dBi, high antenna efficiencyof 86.6% and low sidelobe characteristics of -27.1 dB first sidelobe levels are measured at the center
frequency of 78.5 GHz. Further, the broadband characteristics of reflection (VSWR < 2), show a gainof more than 31.4 dBi, and low cross polarization of less than -30 dB are achieved over the 71-86 GHzband.
A single-layer corporate-feed slot array antenna is presented [Sano et al., 2014]. The singlelayer structure is realized by adopting hollow rectangular coaxial lines for the corporate-feed circuit
and placing the feeding circuit and the radiating elements in the same layer. Based on this, a 16 x 16element slot array for the 60-GHz band is designed and fabricated by diffusion bonding of laminatedthin copper plates. A 32.3 dBi gain and 72.2% antenna efficiency are confirmed at the design frequencyof 61.5 GHz in the measurements. The 1-dB down gain bandwidth is 8.8%. The conductor loss of theantenna is estimated to be 0.85 dB at 61.5 GHz.
High gain antennas having broad bandwidth characteristic for the 120 GHz band is proposed[Kim et al., 2014]. The proposed antennas are fabricated by diffusion bonding of laminated thin copper
plates which have the advantages of high precision and low loss characteristic even in a high frequency
region such as the 120 GHz band. For stable fabrication using diffusion bonding, we propose a feeding
structure which has a double layer. A 32 x 32-element array antenna shows more than a 38 dBi antenna
gain with over 60% antenna efficiency and 15 GHz bandwidth (119.0�134.0 GHz) and a 64 x 64element array shows a higher than 43 dBi antenna gain with over 50% antenna efficiency and 14.5
GHz bandwidth (118.5-133.0 GHz), respectively.
A slot array antenna for dual-polarization operation in the 60 GHz band is proposed. To
realize the dual-polarization, cross-shaped radiating slots and a multilayer feeding structure are
employed [Kim et al., 2014]. A 16 x 16-element array is fabricated by diffusion bonding of laminatedthin copper plates, which has the advantages of high precision and low loss characteristics. To suppress
the grating lobes, we employ several design techniques, such as a thick cavity structure and dense
element spacing. The high antenna gain higher than 32.0 dBi and the antenna efficiency near 80.0%
23

are obtained over 60.0-64.0 GHz for two different polarizations. The 1-dB-down gain bandwidths
reach 10.4% and 10.9%. High isolation above 50 dB is achieved between the two input ports.
A 12 x 16-element corporate-feed slot array is presented [Ito et al., 2016]. The corporatefeed circuit for the 12 x 16-element array consists of cross-junctions and asymmetric T-junctions,whereas the conventional one is limited to arrays of 2m x 2n slots by its use of symmetric T-junctions.
Simulations of the 12 x 16-element array show a 7.6% bandwidth for reflection less than −14 dB. A
31.7-dBi gain with an antenna efficiency of 82.6% is obtained at the design frequency of 61.5 GHz.
The 12 x 16-element array is fabricated by diffusion bonding of laminated thin metal plates.
Measurements indicate 31.1-dBi gain with 71.9% antenna efficiency at 61.5 GHz.
(K. Hashimoto)8.5 Systems
Recently, the wireless power transfer (WPT) systems including SSPS are very remarkable
and the relating papers have been reported.
An independent electrical coupled resonance WPT system to further increase such systems’power transfer distance is proposed [Yang and Tsunekawa, 2015]. The proposed system’s powertransfer function, critical coupling point, and resonance frequency splitting are investigated via theequivalent circuit, simulation, and experiment. Moreover, the input impedance characteristic of twoelectric coupled resonance antennas is also analyzed according to the transfer distance. In the regionof under coupled, an appropriate impedance matching method is required to achieve effective powertransfers. Further, a fixed configuration type matching loop with a series-connecting variablecapacitance that can be added into both the source and load antennas is proposed. Experimental results
demonstrate that the proposed matching loop can convert the two electric coupled resonance antennas’
input impedance to the feed port impedance very well at varying transfer distances; these results arein good agreement with the simulation results.
Magnetic resonant coupling between two coils allows effective wireless transfer of powerover distances in the range of tens of centimeters to a few meters. The strong resonant magnetic fieldalso extends to the immediate surroundings of the power transfer system. When a user or bystander is
exposed to this magnetic field, electric fields are induced in the body. For the purposes of human andproduct safety, it is necessary to evaluate whether these fields satisfy the human exposure limits
specified in international guidelines and standards. The effectiveness of the quasistatic approximation
for computational modeling human exposure to the magnetic fields of wireless power transfer systems
is investigated [Laakso et al., 2015]. It is shown that, when valid, this approximation can greatly reducethe computational requirements of the assessment of human exposure.
“Disk-repeater” is proposed as a new structure alternative to the conventional resonator
repeater [Sawahara et al., 2015]. Disk-repeater has a simple structure comprised of just copper plates
24and wire, non-resonant structure. First, coupling coefficients are measured as functions of disk
diameter and wire length to characterize the basic performance of Disk-repeater. It is explained byseveral experimental evidences that Disk-repeater and resonator are not magnetically coupled but
electrically coupled. It is also shown that the transmission distance extends dramatically longer thanthat of conventional resonator repeater. Further, two-dimensional arrangement, where multiple disks
are connected, shows very high efficiency and uniform transmission characteristic regardless of
positions of receiving resonator. Disk-repeater gives possibility of unprecedented versatile application
with the simple structure.
A method for measuring the magnetic field strength for human exposure assessment closer
than 20 cm to wireless power transfer (WPT) systems for information household appliances isinvestigated based on numerical simulations and measurements at 100 kHz and 6.78 MHz [Ishihara etal., 2015]. Four types of magnetic sources are considered: a simple 1-turn coil and three types of coils
simulating actual WPT systems. A magnetic sensor whose cross sectional area is 100 cm2 as prescribedin International Electrotechnical Commission 62233 is used. Simulation results show that the magnetic
field strength detected by the magnetic sensor is affected by its placement angle. The maximum
coefficient of variation (CV) is 27.2% when the magnetic source and the sensor are in contact. The
reason for this deviation is attributable to the localization of the magnetic field distribution around themagnetic source. The coupling effect between the magnetic source and the sensor is negligible.
Therefore, the sensor placement angle is an essential factor in magnetic field measurements. The CV
due to the sensor placement angle is reduced from 21% to 4% if the area of the sensor coil is reduced
from 100 to 0.75 cm2 at 6.78 MHz. However, the sensitivity of the sensor coil is decreased by 42.5
dB. If measurement uncertainty that considers the deviation in the magnetic field strength due to thesensor placement angle is large, the measured magnetic field strength should be corrected by theuncertainty. If the magnetic field distribution around the magnetic source is known, conservative
exposure assessments can be achieved by placing the magnetic sensor in locations at which the spatial
averaged magnetic field strengths perpendicular to the magnetic sensor coils become maximum.
A novel resonator design that uses tightly coupled parallel coils to improve the quality factor(Q factor) in coupled magnetic resonance wireless power transfer is proposed [Yang and Tsunekawa,
2016]. Depending on the characteristics of the tightly coupled parallel-connected coils, the proposedresonator can offer significantly reduced resistance with very little self-inductance loss. A double-layer
spiral coil structure is used for resonator design and evaluating its characteristics. Measured results
show that a resonator consisting of two identical, tightly coupled parallel double-layer spiral coils canmatch the Q factor of a conventional double-layer spiral coil with the same number of turns, eventhough its equivalent resistance is approximately 75% less. Moreover, the system power transfer
performance of the resonator was measured under the impedance matching condition. To further
reduce the resistance, we propose another resonator comprising of three parallel and tightly coupled25

double-layer spiral coils, and measure its equivalent resistance characteristics for different wire gap
sizes.
A technology and system which can be used for feeding electric vehicles by wireless means
is proposed [Takano et al., 2015a]. In the system, input power is converted to microwave, andpropagates in the form of a beam. At the receiving site, the microwave is reconverted to DC or AC
power, and is output to users. The system analysis shows that the beam can be focused in a relatively
short haul so that the receiving antenna can be made small in size. Concentration of power in a beam
is beneficial to lessen the interference with other radio systems. Semiconductors in the input and output
which should handle a large microwave power are studied. Finally, a concrete application of thetechnologies to a car feeding system is shown.
The design method of the antennas for beamed power transfer via radio wave is proposed[Takano et al., 2015b]. The transmission antenna is composed of arrayed radiating elements of which
the phase is designed to form a concave phase front. The simulation analysis clarifies thecharacteristics of the transmitted beam. Accordingly, the focusing capability is dependent on the sizeof the transmission antenna, frequency, and the distance. The reception antenna is determinedaccording to the obtained beam profile.
The COP 21 requires no total emission of man-made CO2 gas, which necessitates newenergy systems without fossil fuel. A solar power satellite system (SPSS) is one of powerful solutions.
At this stage, realistic SPSS models looking back R&D activities in the past is shown [Takano, 2016c].
In the future, we should demonstrate sending a weak beamed power from a satellite to earth, thenincreasing the power, and finally the system integrity of the commercial satellite. As an SPSS is a hugesystem, its R&D plan is deliberated to lessen the cost and risks, and to satisfy business conditions.
(S. Makino)

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36

Nito Y., Yatabe B., Yamauchi J., and Nakano H. [2016], “Reduction in bend losses of a buried
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Saho K., Homma H., Sakamoto T., Sato T., Inoue K., and Fukuda T. [2014], “Accurate Image
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Sakamoto T., Sato T., Aubry P., and Yarovoy A. [2015d], “Ultra-Wideband Radar Imaging using a
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Sato R. and Shirai H. [2016], “Electromagnetic plane wave diffraction by loaded N-slits on thickconducting screen,’’ IEICE Trans. Electron., vol.E99-C, no.1, pp.72-75.

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41

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