The theoretical studies conducted mainly by the author are reviewed on (1) derivation of arbitrary order moment equations and solutions of some equations, (2) scattering by many particles and the effective medium constant of random medium, (3) scattering by a conducting body in random media and (4) spatially partially-coherent wave scattering, with application to satellite communications, artificial material development, and sensing and radar technology. The leading research results are described with many references; and also unsolved subjects in the above four studies are touched.

View full abstract

This paper studies scattering and diffraction of a TE plane wave from a periodic surface with semi-infinite extent. By use of a combination of the Wiener-Hopf technique and a perturbation method, a concrete representation of the wavefield is explicitly obtained in terms of a sum of two types of Fourier integrals. It is then found that effects of surface roughness mainly appear on the illuminated side, but weakly on the shadow side. Moreover, ripples on the angular distribution of the first-order scattering in the shadow side are newly found as interference between a cylindrical wave radiated from the edge and an inhomogeneous plane wave supported by the periodic surface.

View full abstract

A rigorous semi-analytical approach for the scalar field in a microstructured optical fiber, which is formed of layered cylindrical arrays of circular rods symmetrically distributed on each concentric cylindrical layer, is presented. The method uses the T-matrix of a circular rod in isolation and the generalized reflection and transmission matrices of cylindrical arrays. Numerical examples of the mode index for three-layered hexagonal structure of circular air holes are demonstrated and compared with those obtained by a variational method.

View full abstract

The Fourier series expansion method is a useful tool to approach the problems of discontinuities in optical waveguides, and it can apply to analyze the Floquet-modes of photonic crystal waveguides. However, it has known that the Floquet-mode calculation with large truncation order is limited because of the roundoff errors. This paper proposes a novel formulation of the Floquet-modes propagating in two-dimensional photonic crystal waveguides formed by circular cylinders. We introduce a periodic boundary condition as same with the conventional method, and the fields are expressed in the Fourier series expansions. The present formulation also introduces the cylindrical-wave expansions and uses the recursive transition-matrix algorithm, which is used to analyze the scattering from cylinder array. This makes us possible to obtain very high accuracy without the use of large truncation order for Fourier series expansion. The presented formulation is validated by numerical experiments.

View full abstract

For achieving low cross-polarization component in addition to circular-coverage pattern in compact structure, this paper proposes a novel multimode horn with arbitrary coaxial-corrugation configuration which plays two roles of mode converters and chokes. The proposed horn can be designed by iteration of non-linear optimization procedure based on generalized scattering matrices pre-calculated by the mode-matching technique. We show a compact horn with four coaxial corrugations for shaping circular-coverage beam over frequency range of bandwidth 20%. The effectiveness of the designed horn is discussed by evaluating VSWR and radiation characteristics in X-band numerically and experimentally.

View full abstract

This paper is concerned with the estimation of radio communication distance when both the transmitter and receiver are arbitrarily distributed on a random rough surface such as desert, terrain, sea surface and so on. First, we simulate electromagnetic wave propagation along the rough surface by using the discrete ray tracing method (DRTM) proposed by authors recently. Second, we determine three parameters by conjugate gradient method (CGM) combined with the method of least-squares. Finally, we derive an analytical expression which can estimate the maximum communication distance when the input power of a transmitter and the minimum detectable electric intensity of a receiver are specified. Random rough surfaces are assumed to be Gaussian, pn-th order power law or exponential distributions.

View full abstract

The coupled mode equation describing the propagation of light in a disordered waveguide system composed of randomly different cores in size is analytically solved by the perturbation method and the average amplitude of light is derived. In the summation of a perturbation series only successive scatterings from different cores are taken into account. The result obtained shows that the average amplitude behaves as if in an ordered waveguide system composed of identical cores at short distance and decreases exponentially with increasing distance at large distance. The result is compared with the result obtained by the coherent potential approximation and the both results are in good agreement with each other. The results are also compared with the results obtained by numerically solving the coupled mode equation.

View full abstract

This paper presents unconditionally stable and conformal FDTD schemes which are based on the alternating-direction implicit finite difference time domain (ADI-FDTD) method for accurate modeling of perfectly electric conducting (PEC) objects. The proposed schemes are formulated within the framework of the matrix-vector notation of the finite integration technique (FIT), which allows a systematic and consistent extension of finite difference solution of Maxwell's equations on dual grids. As possible choices of second-order convergent conformal method, we apply the partially filled cell (PFC) and the uniformly stable conformal (USC) schemes for the ADI-FDTD method. The unconditional stability and the rates of convergence of the proposed conformal ADI-FDTD (CADI-FDTD) schemes are verified by means of numerical examples of waveguide problems.

View full abstract

The present study proposes a quasi-static finite-difference time-domain (FDTD) method for dosimetry in humans due to contact current at low frequencies (∼10kHz). Our attention focused on wave sources which can reduce computational time. The computational time was found to be reduced using a voltage source of a step function with smooth start. The computational time required for the proposed method was smaller than a quasi-static FDTD method proposed in a previous study. Comparison between our computational results and those in a previous study suggested the effectiveness of our proposal. The difference in in-situ electric field due to different human models was a factor of 2 or so.

View full abstract

A new technique to estimate the Poynting vector distribution from near-magnetic-field measurement is proposed. To calculate the Poynting vector, both electric and magnetic field should be known. In the proposed method, only magnetic-field measurement of three orthogonal axes is required. Electric field is estimated from the measured magnetic field by using the Maxwell's equation. The modified Yee cell is employed to estimate electric field from the measured magnetic field. Finally, the Poynting vector is calculated from the measured magnetic field and the estimated electric field. Since the proposed method enables us to understand propagation direction of electro-magnetic energy, it can be utilized to locate an emission source and to investigate a mechanism of undesired emission. Experiments are carried out to discuss the accuracy and to validate practical usefulness.

View full abstract

Phase information on wave scattering is not unique and greatly depends on a choice of the origin of coordinates in the measurement system. The present paper argues that the center of scattering for polygonal cylinders should not be a geometrical center of the obstacle such as a center of gravity but be a position that acts as a balance to the electrostatic field effects from edge points. The position is exactly determined in terms of edge positions, edge parameters and lengths of side of polygons. A few examples are given to illustrate a difference from the center of geometry.

View full abstract

Radar cross sections of polygonal cylinders are investigated by using a kind of mode matching methods. Applying two types of novel field-decomposition techniques, electromagnetic scattering analysis can be performed very precisely. We will discuss computational accuracy of our proposed method and the proper choice of field-decomposition techniques for a rectangular cylinder with various shapes of wedge cavities and bumps.

View full abstract

Existence of backward TE volume modes which are to be identified as Magnetostatic Wave (MSW) in anisotropic single-negative slab with partly negative permeability tensor component have already been revealed by present authors. In this paper, detailed modal analysis has been carried out for this kind of TE volume modes to find out their novel and peculiar properties. From these numerical results, it has been clarified that dispersion curve of the lowest order mode for thicker slab has a frequency of turning point below which both forward and backward waves can be simultaneously observed and also there is a critical slab thickness for each order of TE volume modes to exist.

View full abstract

A method for reducing ground clutter contribution from ground penetrating radar (GPR) data is proposed for discrimination of landmines located in shallow depth. The algorithm of this method is based on the Matching Pursuit (MP) that is a technique for non-orthogonal signal decomposition using dictionary of functions. As the dictionary of function, a wave-based dictionary constructed by taking account of scattering mechanisms of electromagnetic (EM) wave by rough surfaces is employed. Through numerical simulations, performance of ground clutter reduction is evaluated. The results show that the proposed method has good performance and is effective for GPR data preprocessing for discrimination of shallowly buried landmines.

View full abstract

Gaussian rough surfaces can be characterized by two roughness parameters, the root-mean-square height and correlation length. For accurate estimation of these parameters from measured surface height-profile, data samples with sufficiently long record length are necessary. In this letter, an expression of correlation length in terms of a surface slope function is introduced in order to estimate correlation length and analytical expression of the data record length required for accurate estimation is derived. The result shows that the method using the slope function can reduce the data record length approximately 60% as compared to the commonly employed method using the correlation function. In order to check the result, a Monte Carlo simulation is also carried out and the validity of the result is confirmed.

View full abstract

We present a 60-GHz wireless through-repeater system based on self-heterodyne transmission scheme with the potential to optimize the carrier-to-interference and noise ratio (CINR) performance according to the transmission distance. The phase-noise degradation through a 60-GHz repeater link is not a serious concern when we employ the self-heterodyne transmission scheme. Multichannel interferences caused by third-order intermodulation distortions are efficiently suppressed by setting a high power ratio of LO carrier to RF signals in the self-heterodyne transmission. However, this high power ratio results in a lower carrier-to-noise ratio (CNR) and becomes unsuitable for improving link performance if the transmission distance increases. In order to facilitate a solution, we propose and make an embodiment of 60GHz self-heterodyne transmitters that provide flexible control over the power ratio of LO to RF in a range of 10dB ranges. With them, we successfully demonstrate terrestrial digital broadcasting signals on five channels and optimize their performance for wireless through-repeater applications.

View full abstract

This paper presents a numerical approach to the time-domain analysis of N-branch-line couplers. The approach is based on the modified central difference (MCD) method combined with internal boundary treatments, which consist of the time-domain scattering matrix for the three-port junction discontinuity. The behavior of the signal propagation including multiple reflections on the N-branch-line coupler with and without line loss is analyzed and demonstrated in the time domain. Additionally, the S-parameters obtained from Gaussian pulse responses of the N-branch-line directional couplers are shown. The simulated results are in good agreement with those of the commercial simulator.

View full abstract

We have developed an easy fabrication method of Si field effect transistors (FETs) with poly (methyl methacrylate) (PMMA) gate films for science education. In this process, we can easily fabricate the silicon FETs only by means of metal deposition and thermal diffusion without any lithography processes. The organic isolation films of PMMA can be deposited by casting or painting at room temperature in air. The metal-organic-semiconductor FETs with PMMA exhibited almost the same drain current — gate voltage characteristics as those of conventional Si metal-oxide-semiconductor FETs, which are suitable for the education material of semiconductor engineering. The organic gate Si FETs can be used not only for education but also as thin film transistors for active matrix displays.

View full abstract

Analytical solutions for the frequency-dependent transmission line model parameters of a stranded coaxial cable, which are not trivial due to the complex geometry, are presented and discussed in this paper. A frequency-dependent effective conductor radius of a stranded wire coaxial cable is proposed to estimate the internal impedance using the Bessel function solutions of a solid wire coaxial cable. The performance of the proposed model is verified by electromagnetic field solver simulation and by experimental measurement. The results show that the proposed model successfully calculates the broadband frequency-dependent RLGC model parameters and characteristic impedance of a stranded wire coaxial cable with high accuracy.

View full abstract

A CMOS wireless transceiver operating in the 14-18GHz range is proposed. The receiver uses direct conversion architecture for demodulation with a fast carrier and symbol timing recovery scheme. The transmitter uses a PLL and an up-conversion mixer to generate BPSK modulated signal. A ring oscillator is used in the PLL to make faster switching for burst transmission obtaining high speed low power operation. The transceiver operation has been verified by system simulation while the transmitter test-chip was fabricated in 65nm CMOS technology and verified with measured results. The transmitter generates a bi-phase modulated signal with a center frequency of 16GHz at a maximum data rate of 4Gb/s and consumes 61mW of power. To the best knowledge of authors, this is lowest power consumption among the reported transmitters that operate over 1Gb/s range. The transceiver is proposed for a target communication distance of 10cm.

View full abstract

A circuit technique to correct V_dd/PM distortion and improve efficiency as supply modulation of cascode class-E PAs has been proposed. The experimental result shows that the phase distortion can be improved from 20 degrees to 5 degrees. Moreover, a system co-simulation result demonstrated that the EVM can be improved from -17dB to -19dB.

View full abstract

A digital 3Gbps 0.2V differential transmitter is proposed using a voltage-mode pseudo-LVDS output driver. The delay mismatch between two pre-drivers is digitally calibrated by a modified digital DLL with the duty cycle correction. The height and width of eye opening are improved by 103% and 46%, respectively. The power consumption is 11.4mW at 1.2V with 0.18µm process.

View full abstract

This paper proposes a wide-locking range divide-by-3 injection-locked frequency divider (ILFD) fabricated in the 90nm 1P9M CMOS technology. The divider consists of an nMOS cross-coupled LC oscillator and two injection MOSFETs in series with the cross-coupled nMOSFETs. The ILFD is formed with two linear mixers which share the same dc current so that a low power ILFD can be designed. At the supply voltage of 0.7V, the free-running frequency is from 10.18 to 11.56GHz, the current and power consumption of the divider without buffers are 2.8mA and 1.96mW, respectively. At the incident power of 0dBm, the total operational locking range is 4.94GHz, from the incident frequency 29.96 to 34.9GHz.

View full abstract

This paper presents a design of a monolithic transformer using bond wires. The proposed transformer structure has several advantages such as high power handling and high efficiency. It shows that the measured insertion loss at the 1.9GHz range is -1.54dB (70%), which is higher than the spiral transformer of the same size. Also, it shows a phase error of less than 1 degree.

View full abstract

A high performance highly integrated sub-GHz wideband differential low-noise amplifier (LNA) for terrestrial and cable digital TV tuner applications is realized in 0.18µm CMOS technology. A noise-canceling topology using a feed-forward current reuse common-source stage is presented to obtain low noise characteristics and high gain while achieving good wideband input matching within 48-860MHz. In addition, linearization methods are appropriately utilized to improve the linearity. The implemented LNA achieves a power gain of 20.9dB, a minimum noise figure of 2.8dB, and an OIP3 of 24.2dBm. The chip consumes 32mA of current at 1.8V power supply and the core die size is 0.21mm².

View full abstract

A CMOS current-mode nth-switchable-root circuit composed of a compact logarithm circuit, a divide-by-n circuit, and a compact exponential circuit is proposed. The n can be selected from 5 values by three switches. Simulation results indicate that the compact nth-switchable-root circuit has a wide input-current range for relative errors less than 3%, low power dissipations below 630µW, and high bandwidth over 330MHz.

View full abstract

This paper reports a current-reused pseudo-differential (CRPD) programmable gain amplifier (PGA) that demonstrates small size, low power, wide band, low noise, and high linearity operation with 4 control bits. Implemented in 0.18um CMOS technology, the PGA shows the gain range from -9.9 to 8.3dB with gain error of less than ±0.38dB. The IIP3, P1dB, and smallest 3-dB bandwidth are 10.5 to 27dBm, -9 to 9.5dBm, and 250MHz, respectively. The PGA occupies the chip area of 0.04mm² and consumes only 460 µA from a 1.2V supply.

View full abstract

The electrical properties of poly-Si thin film transistors (TFTs) using rapid thermal annealing with various gate oxide thicknesses were studied in this work. It was found that Poly-Si TFT electrical characteristics with the thinnest gate oxide thickness after RTA treatment exhibits the largest performance improvement compared to TFT with thick oxide as a result of the increased incorporated amounts of the nitrogen and oxygen. Thus, the combined effects can maintain the advantages and avoid the disadvantages of scaled-down oxide, which is suitable for small-to-medium display mass production.

View full abstract