高橋 応明

The Finite Difference Time Domain (FDTD) method is widely used for analyzing an electromagnetic scattering problem, antennas including a antenna on dielectric substrate, and so on. However, a staircase error increases when a bend antenna is included in computational region. In order to overcome this difficulty, the contour path (CP) method was proposed. However, and extremely smaller cell is required when a very accurate resonance frequency of the antenna is needed even if the CP method is used. This reason is that the electromagnetic field near the edge of the antenna conductor changes very rapidly. In order to improve the accuracy of the FDTD calculation, we have proposed the new technique which is the quasi-static approximation is incorporated to FDTD cells near the conductor edges. In this paper, the proposed method is applied to bend antennas on dielectric substrate, and the validity of the proposed method is confirmed.

Planar microwave discharges using a multi-slotted planar antenna are investigated. A three-dimensional finite difference time domain code is developed for the calculation of wave propagation in nonuniform plasmas. The enhancement of the microwave fields near the plasma resonance is revealed in accordance with the theory of the resonant absorption. The global wave electric field is obtained for various excitation modes of the antenna. By operating the antenna with transverse electric mode, where the field is rotating in the azimuthal direction, and by minimizing the reflected power from the antenna, highly uniform overdense plasmas can be produced in a wide range of gas pressures and microwave powers.

With recent advances in electrical and electronic devices, they are proliferating in the office environment. In turn, electromagnetic interference, mixing, and information leakage due to the use of wireless LAN have become problematic. Electromagnetic wave absorbers based on glass have been investigated using resistive films. In this paper, the electromagnetic wave is cut off by placing metallic wires on windowglass so that a low-cost shielding material easily manufactured can be developed. First, only the frequency of 2.45 GHz for wireless LAN is considered in the discussion of shielding. Further, MMAC (Multimedia Mobile Access Communication Systems) has been considered as a future wireless LAN. In order to also cut off 5.2 GHz for the MMAC frequency, a method for cutting off two frequencies is proposed in which circular conductors and crossed conductors are combined. © 2002 Wiley Periodicals, Inc. Electron. Comm. Jpn. Pt. 1.

FDTD法はモデル化が簡単で実用的なレベルでの精度が容易に得られることから,パッチアンテナなどの平面アンテナの解析にしばしば用いられてきた.しかしながら,パッチアンテナの共振周波数を極めて正確に求めようとすると,セルサイズを非常に細かくしなければならない.これはアンテナ導体端部近傍の電磁界の変化が急激になるためであると考えられる.そこで本論文では,方形パッチアンテナの導体エッジ近傍セル内の電磁界を準静近似し,電磁界の空間的な変化をFDTD法に組み入れることにより,セルサイズを細かくすることなく高精度に解析する手法を提案する.

Large-area and uniform plasma production is of crucial importance for achieving large-scaled material processing. In particular, with the progress of memory sizes of micro-processors, the uniformity of plasma parameters over large-area is an essential problem for high speed and high quality process. A rotating mode radial line slot antenna (RLSA) with densely arrayed slots has already been proposed for plasma processing system and the basic characteristics were confirmed. In our previous work, however, the feeding circuit using cylindrical waveguide to excite rotating mode was very large and bulky. In order to make the most of the advantages of small and low profile apparatus by using RLSAs, improvement of the size of feeding circuit as well as of the plasma chamber is required. Moreover, enhancement of the rotational symmetry by optimizing the feeding circuit is also required. This paper proposes a novel feeding circuit using cavity resonator in plasma processing RLSAs. The rotational symmetry of field intensity generated in parallel plate as well as the input impedance is evaluated by using mode matching technique. Excellent rotational symmetry with the amplitude deviations of less than 2dB and good matching with a coaxial waveguide is realized at the same time. The design of reflection characteristics is confirmed by Ansoft-HFSS.

The present direction-finding equipment has insufficient accuracy and resolution, so that accurate evaluation of the direction of arrival and the position cannot be carried out. Although each radar signal has a narrow bandwidth, the entire bandwidth for various radars used exceeds four octaves. In order to search all of these, equipment for each bandwidth is used at present so that the entire frequency range is covered. However, it is more effective from the standpoint of equipment size and cost to cover the entire spectrum with a single kind of equipment. It is desirable to realize high-accuracy high-resolution direction finding over a broad bandwidth. In realization, broadband antennas are used, and high-gain antennas are also needed in a low-SIN environment. Since the dimensions of high-gain and broadband antennas are large, an array configuration with a half-wave spacing may not physically be possible. Thus, the array spacing becomes more than a half-wavelength. If the range of direction estimation is -90 to +90°, the phase difference exceeds 360° so that ambiguity occurs. As a method to resolve this ambiguity problem, a nonuniformly spaced array is effective. In this paper, the array conditions for a nonuniformly spaced array are determined in the case of one arriving wave. Next, the case of several arriving waves is discussed and the array conditions for several arriving waves are derived. © 2001 Scripta Technica, Electron. Comm. Jpn.

In the communication systems expected to be used indoors, such as PHS, wireless LAN and MMAC, degradation of the communication quality by transmitting waves from the exterior to the room and the information leaks by the electromagnetic waves from the room to the exterior are of concern. Absorption and shielding of the electromagnetic waves with structural elements such as walls are required so that the indoor reflection is suppressed and the transmission of the electromagnetic waves in both ways between the room and the exterior are reduced. For this purpose, this paper proposes dome-shaped walls that are modifications of the surface shape of the concrete wall such that dome-shaped protrusions are placed orthogonally with the planar concrete wall. The characteristics are studied by the FD-TD method. It is found that the domed wall can suppress the reflection and transmission for an arbitrary polarization. Also, the insertion interval is confirmed to maintain a high absorption effect of the electromagnetic wave even when iron wires are inserted. Finally, the effectiveness of the FD-TD simulation is confirmed by experiment. © 2002 Wiley Periodicals, Inc. Electron. Comm. Jpn. Pt. 1.

If it is possible to derive the complex permittivity of a dielectric material by measurement of the coefficient of reflection from the aperture of a flanged rectangular waveguide attached to a conductor-backed lossy dielectric sheet, an effective nondestructive measurement method can be established. In this paper, by solving simultaneous equations derived by an application of the spectral domain method, contour maps for derivation of the complex permittivity of a lossy dielectric from the reflection coefficient are formed and their characteristics are studied. The effectiveness of these contour maps is confirmed by experiments. In the region within the contour chart where the permittivity can be determined with good accuracy, it can be determined with an error of about 5% by means of a general-purpose network analyzer. Further, the attenuation of the electromagnetic wave within the lossy dielectric in the direction of propagation is studied in order to derive the dimensions of the sample and flange needed for actual measurement. © 2001 Scripta Technica.

PHS・無線LAN・MMACなどの室内での使用が予想される通信システムでは, 壁・床・天井等での室内における多重反射や, 外部から室内へと透過波による通信品質の劣化, 内部から壁等を透過していく電磁波による情報漏洩(えい)が懸念されており, 室内での反射をおさえ, かつ室内外双方向の電磁波の透過を軽減するため, 壁などの建材で電磁波をしゃへい・吸収することが必要とされている.この対策として, 本研究では, コンクリート壁の表面形状を変形させ, 平面コンクリート壁に直交するドーム状の突起を配列したドーム突起壁を提案し, その特性についてFD-TD法を用いて検討を行った.その結果, ドーム突起壁は, 任意偏波に対応し, 高い反射・透過抑制効果が明らかとなった.また, 鉄線を挿入した状態でも高い電磁波の吸収効果が維持される挿入間隔を確認した.最後に, 実験によりFD-TDシミュレーションの有効性が確認された.

Planar microwave discharges using a multi-slotted planar antenna are investigated. The enhancement of the microwave fields near the plasma resonance is observed in accordance with the theoretical prediction of the resonant absorption. By operating the antenna with TE11 mode, where the field is rotating in the azimuthal direction, highly uniform overdense plasmas can be produced without being affected by eigenmode structures of surface waves.

In this paper we describe the application of the spectral domain approach to the electromagnetic fields in a lossy dielectric sheet, sandwiched between a rectangular waveguide with an infinite width flange on the aperture and a metal back, on which is incident the dominant mode from the waveguide. We show that it suffices if 12 higher-order mode terms are used to solve the simultaneous equations for the reflection coefficients in the aperture plane. Based on these results, the field distributions for five characteristic thicknesses are calculated from the thickness dependence of the occurrence rates of the modes, and the relationships between the propagating modes in the dielectric and the sheet thickness are determined from the field components along the coordinate axes.

The recent miniaturization of communication equipment has resulted in circuits that are extremely dense with many discontinuities of microstrip lines (MSL), such as bends, branches, and linewidth changes in printed circuits. The electromagnetic waves radiated by these discontinuities cannot be neglected. In this paper, the bending sections of the MSL are discussed as an example of these discontinuities. The conditions as regards linewidth and the shape of the bends for reducing unwanted radiation are discussed. It is found that the unwanted radiation can be reduced by increasing the radius of curvature and decreasing the linewidth.

近年の通信機器の小型化に伴い回路が高密度化され,プリント基板回路内ではマイクロストリップ線路(MSL)の曲がり・分岐・線路幅変化などの不連続点が多数存在する.この不連続部により放射される電磁波は無視できない.本論文では,不連続部の一例としてMSLの曲がり部に着目し,線路の幅や,曲がり部の形状による不要電磁波の軽減条件を検討した.その結果,曲率半径を大きくし,線路幅を細くするとこにより,不要放射を軽減できることを明らかにした.

衛星放送受信用に開発されたラジアルラインスロットアンテナ(RLSA)は円形の平面アレーアンテナである.1層構造RLSAはスロットの長さ,位置等の最適化により,アンテナ効率80%以上を実現し市販化されている.RLSAの応用の一例として,マイクロ波回線等への使用を考え低サイドローブ化の検討を行った.RLSAはマルチモードの導波管構造を用いているため,導波管内の内部電磁界を乱さないように設計する必要がある.本論文では,励振振幅にテイラー分布を応用した設計法を示すとともに,例として開口径50cm(12GHz),第1サイドローブレベル-25dB,効率60%以上のアンテナを試作し,低サイドローブ化とアンテナ効率65%を実現したので報告する.

A radial line slot antenna (RLSA) is a high efficiency and high gain planar antenna. The efficiency of RLSA becomes lower as the aperture size reduces due to rotational asymmetry of the illumination. A concentric array RLSA (CA-RLSA) was proposed to overcome this difficulty. It adopted three new techniques; (1) not spirally but concentrically arrayed slots, (2) a rotating mode feed circuit, (3) matching slot pairs eliminating termination loss. This paper proposes the basic slot design for (1) and (2) of CA-RLSA. Excellent characteristics of very small CA-RLSAs based upon this design are confirmed by measurements.

A Radial Line Slot Antenna (RLSA) is a planar antenna for DBS reception [1]. It is a kind of slotted waveguide arrays. The conductor loss is so small that high efficiency is expected irrespective of the aperture diameter. On the other hand, since a RLSA utilizes the traveling waves, the frequency bandwidth is limited by the long line effect [2], particularly for a larger antenna. A new Wide-Band RLSA (WB-RLSA) is proposed which halves the waveguide length and widens the frequency bandwidth [3]. This paper presents the design and experimental results of a model antenna. A gain of 33.7 dBi is measured at the edge of 800 MHz bandwidth and its high potential is demonstrated.

A radial line slot antenna (RLSA) is a circularly polarized high efficiency planar array. Two types of RLSA's, a single-layered and a double-layered one, have been released commercially for 12 GHz band DBS reception, The former adopts nonuniform slots excited by a radially outward traveling wave, while the latter has uniform ones excited by an inward traveling wave, This paper merges the two into a novel, dual circularly polarized RLSA. Minimum antenna gain of 33.5 dBi in DBS bandwidth of 500 MHz is measured for a 0.55 m diameter antenna.