An image NRD guide-fed dielectric rod antenna, which is suitable for use at millimeter-wave frequencies, is presented in this paper. The antenna is composed of a linearly tapered dielectric rod connected to the image NRD guide. First, radiation characteristics of the dielectric rod antenna directly protruded from the end of the image NRD guide are investigated by FDTD analysis and measurements at 30 GHz band. For this case, the degradation of the radiation pattern and the decrease of the gain, which are due to the strong radiation from the guide-to-antenna discontinuity, are observed. In order to minimize this radiation and to realize reasonable radiation characteristics, a transition from the image NRD guide-to-rod antenna is proposed. A simple procedure to determine the optimum dimensions of the transition is described. This procedure is based on parametric study of the transition's dimensions, and is performed using FDTD analysis. Based on the results, the dielectric rod antenna having a length of 10 λ₀ is designed, and its performance is analyzed and measured. The results show that radiation patterns with the half power beamwidth of 22, sidelobe level of -21 dB and reasonable gain of 18.5 dBi can be realized by employing the transition having the optimum dimensions.

A high permittivity LSE-NRD guide was applied to a planar antenna at 60 GHz. Emphasis was placed on compatibility between the high permittivity LSE-NRD guide and the conventionally used low permittivity LSM-NRD guide. Performance of the transition between two such types of NRD guides was optimized by using an electromagnetic simulator and the validity was experimentally demonstrated. A simple radiator, consisting of a tapered high permittivity LSE-NRD guide was fabricated and evaluated as to radiation characteristics. Since the radiator has a broad radiation pattern, it was employed in a primary radiator of a two-dimensional parabolic reflector to develop a new type of folded planar antenna at 60 GHz. This planar antenna has a double-layered structure. In the upper layer, a metalized dielectric substrate with a slotted array is excited by a rectangular-shaped oversized waveguide, and in the lower layer, an offset parabolic reflector is fed by the radiator. Measurement showed the half-power beam width of the fabricated antenna to be 2.5 degrees in the E and H planes, respectively, and the gain to be 35.3 dBi, thus indicating that a good pencil beam antenna was successfully developed in this manner.

This paper presents a framework for the analysis of multi-antenna communication systems with mutually-coupled elements. The approach uses a network model that includes the coupled antennas, the propagation channel, the receiver matching network, a realistic noise model for the receive amplifiers, and externally generated interference. The general scheme is applied to diversity receivers, multiple-input multiple-output, and adaptive array architectures. Application of the formulation to coupled dipole antennas illustrates the impact of both mutual coupling and receiver matching on the performance of several representative multi-antenna applications.

In order to achieve a transponder antenna for intersection collision avoidance systems in Intelligent Transport Systems, a lens horn antenna that generates a cosecant squared beam is developed. This paper clarifies the method for designing the antenna to achieve accurate radiation pattern synthesis. A H-plane sectral horn is selected. The ray tracing method is employed in the design of the lens shape. The aperture of the horn is determined to be seven wavelengths based on a comparison of calculated radiation patterns and the desired cosecant squared beam shape. Accurate electrical performance, such as radiation patterns and electrical fields in the horn, is calculated using Finite Difference Time Domain software. Electrical field disturbances caused by reflected waves at the lens surfaces expanded widely inside the small horn. As a result, sidelobe levels of the radiation patterns are increased. In order to eliminate these disturbances, matching layers are attached to the shaped lens surface. Then, electrical field distributions in the horn are recovered and disturbances disappear. Measured radiation patterns become almost the same as that designed using the ray tracing method. The results show that application of the ray tracing method to radiation pattern synthesis of a small lens horn antenna is effective. We clarify the electrical field disturbances caused by reflections at the lens surfaces and show that eliminating the reflection at the lens surface by attaching matching layers is very important to achieving radiation pattern synthesis.

Recently, dielectric lens antennas are paid attentions in ITS applications. Many lens shape designing methods were already developed. And electrical performances were estimated through a ray tracing method. Here, arbitral lens shapes were expressed by a system of power series. In the case of ray tracing, time-consuming three-coordinate root-finder programs were needed to find intersection points of rays on the lens surfaces. In order to calculate complicated structures such as zoned lenses and complicated rays such as multiple reflections between lens surfaces, simple ray tracing methods are requested. In this paper, a simple ray tracing method that utilizes directly designed discrete points of lens surfaces is developed. In this method, a refracted ray is automatically determined for a given incident ray. As for an intersecting point of a lens surface for an outgoing ray, the nearest point to the refracted vector is found out by employing a simple searching procedure. This method is time-saving compared to the previous three-coordinate root-finding program. Through calculated results of focal points and radiation patterns in wide angle beam steering, effectiveness of a developed method is ensured. Application of the developed ray tracing method of complicated multiple reflections are studied. Reflecting points are found out speedily by the same searching procedure. A calculated example of doubly reflected rays is obtained. Through comparing calculated and measured results of wide angle radiation patterns, effectiveness of a developed method is ensured.

Propagation modeling and advanced channel characterization techniques represent integral parts of significant impact in advancing progress in enabling next generation wireless communication technology and realizing its much anticipated broader application and economic benefits. In this paper we describe advances in developing computationally efficient ray-tracing channel modeling procedures, and also describe recent results in characterizing challenging propagation environments including transmission through windows and propagation through walls of complex structures. The impact of these realistic propagation environments as well as the antenna mutual coupling effects on the estimation of channel capacity in a MIMO-based communication system is also evaluated. Significant difference between realistic and statistical channel models are identified and quantified for the special cases of the channels modeled in this study.

Research in smart antenna technology has progressed over the past few years and is gradually reaching the phase of practical use. We have developed a smart antenna test bed for wireless local area network (LAN) that is based on the IEEE802.11b. The objective is to improve anti-multipath fading performance and expand communication distance. Using this test bed, we carried out field tests in two environment. One environment is an office in an non line of sight (NLOS), and another environment is an outdoor in a line of sight (LOS). In this paper, we explain the outline of the test bed, the measurement method, and present the results of the field tests. In the office environment, we measured the performance of each set with a different number of antenna elements. The results show that the dead-spots where communication becomes impossible disappear if the number of antenna elements is more than or equal to two. In addition, a greater number of elements indicates better performance. The total average throughput is 1.6 times as efficient when two elements are used, and 1.9 times when four elements are used. Cold spots where the throughput is slower than 1 Mbps are reduced by 80-90%. In the outdoor LOS environment field test, it is shown that by using four-element smart antenna for both transmitter and receiver, the communication distance reached 1km with an average throughput of 4 Mbps. These results prove that the smart antenna drastically improves the performance of a wireless LAN system, i.e. the IEEE802.11b.

Point-to-point optical and millimeter wave communication has recently been of interest, especially in urban areas. Its benefits include simpler and easier installation compared with a land-based line. However, this technology suffers when adverse weather conditions are present, such as rain, fog and clouds, which induce scattering and absorption of the optical wave. The effects of scattering and absorption degrade the quality of the communication link resulting in increase of bit-error-rate. Therefore, there exists a need for accurate channel characterization in order to understand and mitigate the problem. In this paper, radiative transfer theory is employed to study the behavior of amplitude modulated signal propagating through a random medium. We show the effect of the medium to a modulated signal and relate the outcome on the quality of the communication link.

A novel parallel acceleration technique is proposed based on intrinsic parallelism characteristics of shooting-and-bouncing ray launching (SBR) algorithm, which has been implemented using the MPI parallel library on common PC cluster instead of dedicated parallel machines. The results reveal that the new technique achieves very large speedup gains and could be the efficient and low-cost propagation prediction solution.

An ultra wide band channel sounder has been developed and has attained the time delay resolution of 0.5 ns which enables the propagation path discrimination in indoor wireless propagation environments as well as the direction-of-arrival measurements by power delay profile measurements.

Unlike most of the previous work for smart antennas that covered each area individually (antenna-array design, signal processing and communications algorithms and network throughput), this paper may be considered as a review of comprehensive effort on smart antennas that examines and integrates antenna array design, the development of signal processing algorithms (for angle of arrival estimation and adaptive beamforming), strategies for combating fading, and the impact on the network throughput. In particular, this study considers problems dealing with the impact of the antenna design on the network throughput. In addition, fading channels and tradeoffs between diversity combining and adaptive beamforming are examined as well as channel coding to improve the system performance.

For future high-speed wireless communications using orthogonal frequency division multiplexing (OFDM), two major system requirements will emerge: throughput improvement and rich interference elimination. Because of its broadband nature and limited frequency allocations worldwide, interference from co-located wireless LAN's operating in the same frequency band will become a serious deployment issue. Adaptive array antenna can enhance the performance by suppressing the co-channel interference even when interference may have a large amount of multipath and also have similar received power to the desired signal. There are typically two types of adaptive array architecture for OFDM systems, whose signal processing is carried out before or after FFT (Fast Fourier Transform). In general, the pre-FFT array processing has low complexity, but in rich multipath and interference environments, the performance will deteriorate drastically. In contrast, the post-FFT array processing can provide the optimum performance even in such severe environments at the cost of complexity. Therefore, complexity-reduction techniques combined with the achievement of high system performance will be a key issue for adaptive array antenna applications. This paper proposes novel adaptive array architecture, which is a complexity-reduction technique using subcarrier clustering for post-FFT adaptive array. In the proposed scheme, plural subcarriers can be clustered into a group with the same spatial weight. Simulation results show that the proposed architecture is a promising candidate for real implementation, since it can achieve high performance with much lower complexity even in a rich multipath environment with low signal to noise plus interference ratio (SNIR).

DOA (Direction Of Arrival) estimation is a useful technique in various positioning applications including the DOA-based adaptive array antenna system. This paper presents a practical implementation of FPGA (Field Programmable Gate Array) based fast DOA estimator for wireless cellular basestation. This system incorporates spectral unitary MUSIC (MUltiple SIgnal Classification) algorithm, which is one of the representative super resolution DOA estimation techniques. This paper proposes a way of digital signal processor design suitable for FPGA and its real hardware implementation. In this system, all digital signal processing procedures are computed by the only fixed-point operation with finite word-length for fast processing and low power consumption. The performance will be assessed by hardware level simulations and experiments in a radio anechoic chamber.

Integrated implementation of RF front-end components has been shown to posses many benefits. Furthermore, it presents a new way of approaching RF design. This paper will discuss the recent developments by the author's group in the field of RF front-end technology. This will include stand-alone RF front-end components such as a self-heterodyne mixer as well as more functional front-end circuitry such as digital beamformer arrays, retrodirective arrays and an array error calibration scheme.

This paper introduces a new type of microwave isolator. The operation is based on the two phenomena; the ferrite edge-mode and the photo-generated plasma on silicon substrate. Conventional ferrite edge-mode isolator has been made of the ferrite and the resistive material. The later is used to absorb the reverse-propagating wave of the isolator. An inadequate choice of the resistive body leads to the imperfect absorption; the isolation ratio decreases. In this paper, the isolation-variable isolator is introduced by using this change of isolation. The control is realized by the change of the surface resistance on the silicon. On this isolator, the frequency response is investigated both experimentally and numerically. The numerical analysis is conducted by FDTD method. The experiment is carried out on the prototype isolator. Both experimental and numerical results have shown that the isolation ratio can be controlled for 39 dB at 12 GHz by the irradiation.

Intensity-noise characteristics of stable multi-mode Fabry-Perot semiconductor lasers are analyzed experimentally and theoretically. Mode-partition noise caused by optical filtering and propagation through optical fibers is investigated by evaluating the relative intensity noise and signal-to-noise ratio. The experimental results indicate that the simplified two-mode analysis provides a good approximation. Suppression of the mode-partition noise by nonlinear gain is experimentally confirmed.

This paper presents a new method to improve the resonant characteristics of a microstrip resonator. The improved characteristics have been achieved by inserting two dielectric rods between strip conductor and the ground plane. Dielectric rods to be inserted have higher relative permittivity than that of the substrate. Therefore, it is suitable to realize by Low-Temperature Cofired Ceramics (LTCC) technique. Several model of microstrip resonators employing the proposed method are analyzed by a Finite-Difference Time-Domain (FDTD) method, and their resonant characteristics are discussed. One of the advantages of the proposed method is that an attenuation pole (f_l or f_h) in each side of the fundamental resonant frequency (f_r) and improved-spurious responses can be realized together by a capacitive-coupling tapped resonator loaded with dielectric rods. The proposed method is also effective to achieve sharp skirt characteristics and wide stopband of a direct-coupling tapped resonator which can be used either as a wideband lowpass filter or a band-elimination filter. Another interesting feature of the analyzed resonators is that about 60% reduction in resonator's length has been obtained compared to a basic half-wavelength (λ/2) microstrip resonator. Therefore, wide exploitation of the proposed method can be expected in the filter design based on the LTCC technique.

Subcircuits designed for integrated silicon DCS1800/ PCS1900 base station receivers have been reconfigured into hybrid and single-chip Doppler radar transceivers. Radar chips have been fully integrated in 0.25 µm silicon CMOS and BiCMOS processes. These chips have been used to monitor heart and respiration activity without contact, and they have successfully detected heartbeat and respiration rate up to 1 m from the subject. This monitoring device may be useful in home monitoring, continuous monitoring, and physiological research.

An RF front-end using a six-port circuit is a promising technology for realization of a compact software defined radio (SDR) receiver. Such a receiver, called a six-port direct conversion receiver (DCR), consists of analog circuit and digital signal processing components. The six-port DCR itself outputs four different linear combinations of received and local signals. The output powers are measured at each port, and the received signal is recovered by solving a set of linear equations. This receiver can easily cover a wide frequency band unlike the conventional DCR since it does not require the precise orthogonality that the conventional one does. In this paper, we propose a novel calibration method for a six-port system that includes nonlinear circuits such as diode detectors. We demonstrated the demodulation performance of a six-port DCR by computer simulation and experiments at 1.9, 2.45, and 5.85 GHz.

A new hybrid formulation has been derived for analyzing biological electromagnetic compatibility (Bio-EMC) problems by combining the frequency-domain Method of Moments (MoM) and the Finite-Difference Time-Domain (FDTD) method. This hybrid form is different from, and more direct than, the method previously proposed by Mangoud et al. Some numerical examples are given for the human head exposure field due to a half wavelength dipole and a one-wavelength loop antenna. Our iterative method is found to have fast convergence. In addition, our method works well for cases when the radiation antenna wires are not aligned with the FDTD lattice.

An iterative method is proposed to solve integral equations (IEs) of the second kind with Picard-kernel in linear complexity, i.e.O(N). The particular IE considered describes the process of scattering of a plane wave incident on an inhomogeneous slab. The collocation method with triangle basis functions is used to derive a linear system of equations, which is solved for a test problem with the BiCGSTAB method. To reduce the number of iterations, an efficient preconditioning operator is introduced.

Novel high-frequency asymptotic solutions for the scattered fields by a dielectric circular cylinder with a radius of curvature sufficiently larger than the wavelength are presented in this paper. We shall derive the modified UTD (uniform Geometrical Theory of Diffraction) solution, which is applicable in the transition regions near the geometrical boundaries produced by the incident ray on the dielectric cylinder from the tangential direction. Also derived are the uniform geometrical ray solutions applicable near the geometrical boundaries and near the caustics produced by the ray family reflected on the internal concave boundary of the dielectric cylinder. The validity and the utility of the uniform solutions are confirmed by comparing with the exact solution obtained from the eigenfuction expansion.

The scattering problem by metallic gratings has become one of fundamental problems in electromagnetics. In this paper, a thin metallic grating placed in conical mounting is treated as a lossy dielectric grating expressed by complex permittivity and thickness. The solution of the metallic grating by using the matrix eigenvalue calculations is compared with that of the plane grating by using the resistive boundary condition and the spectral Galerkin procedure, and the availability of the resistive boundary condition for thin metallic gratings in conical mounting is investigated. In order to improve the convergence of the solutions of thin metallic gratings, the spatial harmonics of flux densities which are continuous function instead of electromagnetic fields are used.

In this paper, we present the interlaced fast Fourier transform (FFT) method to parallelize the adaptive integral method (AIM) algorithm for the radar cross-section (RCS) computation of large scattering objects in free space. It is noted that the function obtained after convolution is smoother as compared to the original functions. Utilizing this concept, it is possible to interlace the grid current and charge sources in AIM and compute the potentials on each set of interlaced grid independently using FFT. Since the potentials on each interlaced grid are smooth functions in space, we can then interpolate the potentials to every other nodes on the original grid. The final solution of the potentials on the original grid is obtained by summing the total contributions of all the computed and interpolated potentials from every individual interlaced grid. Since the potentials of each interlaced grid can be computed independently without much communication overheads between the processes, such an algorithm is suitable for parallelizing the AIM solver to run on distributed parallel computer clusters. It is shown that the overall computation complexity of the newly proposed interlaced FFT scheme is still of O(N log N).

Superluminal group velocity in dispersive media has long been controversial. A partial source of confusion seems to be the absence of high precision numerical results concerning the waveform of the transmitted signal. This paper gives the precise waveforms of a causal half-sine-modulated pulse and a triangle-modulated pulse propagating in the Lorentz medium. Thus, the effects of analyticity of signal are clarified, which the analysis using Gaussian pulse cannot. Further, to deepen understanding of the mechanism of superluminal group velocity, we give a network theoretic consideration.

We describe elements of a fast integral equation solver for large periodic and partly periodic finite array systems. A key element of the algorithm is utilization (in a rigorous way) of a block-Toeplitz structure of the impedance matrix in conjunction with either conventional Method of Moments (MoM), Fast Multipole Method (FMM), or Fast Fourier Transform (FFT)-based Adaptive Integral Method (AIM) compression techniques. We refer to the resulting algorithms as the (block-)Toeplitz-MoM, (block-)Toeplitz-AIM, or (block-)Toeplitz-FMM algorithms. While the computational complexity of the Toeplitz-AIM and Toeplitz-FMM algorithms is comparable to that of their non-Toeplitz counterparts, they offer a very significant (about two orders of magnitude for problems of the order of five million unknowns) storage reduction. In particular, our comparisons demonstrate, that the Toeplitz-AIM algorithm offers significant advantages in problems of practical interest involving arrays with complex antenna elements. This result follows from the more favorable scaling of the Toeplitz-AIM algorithm for arrays characterized by large number of unknowns in a single array element and applicability of the AIM algorithm to problems requiring strongly sub-wavelength resolution.

Scattering of the two dimensional electromagnetic waves is studied by the infinite sequences of zeros arising on the complex plane, which just correspond to the null points of the far field pattern given as a function of the azimuthal angle θ. The convergent sequences of zeros around the point of infinity are evaluated when the scattering objects are assumed to be N-polygonal cylinders. Every edge condition can be satisfied if the locations of zeros are determined appropriately. The parameters, which allow us to calculate the exact positions of zeros, are given by the asymptotic analysis. It is also shown that there are N-directions of convergence, which tend to infinity. An illustrative example is presented.

High frequency (HF) diffraction is known as local phenomena, and only parts of the scatterer contribute to the field such as the edge, corner and specular reflection point etc. Many HF diffraction techniques such as Geometrical Theory of Diffraction (GTD), Uniform Theory of Diffraction (UTD) and Physical Theory of Diffraction (PTD) utilize these assumptions explicitly. Physical Optics (PO), on the other hand, expresses the diffraction in terms of radiation integral or the sum total of contributions from all the illuminated parts of scatterers, while the PO currents are locally defined at the point of integration. This paper presents PO-based visualization of the scattering and diffraction phenomena and tries to provide the intuitive understanding of local property of HF diffraction as well as the relations between PO and the ray techniques such as GTD, UTD etc. A weighting named "eye function" is introduced in PO radiation integrals to take into account of local cancellation between rapidly oscillating contributions from adjacent currents; this extracts important areas of current distribution, whose location moves not only with the source but also with the observation point. PO visualization illustrates both local property of HF scattering and defects associated with ray techniques. Furthermore, careful examination of visualized image reminds us of the error factor in PO as applied for curved surfaces, named fictitious penetrating rays. They have been scarcely recognized if not for visualization, though they disturb the geometrical shadow behind the opaque scatterer and can be the leading error factors of PO in shadow regions. Finally, visualization is extended to slot antennas with finite ground planes by hybrid use of modified edge representation (MER) to assess the significance of edge diffraction.

This study proposes a 3 dB branch-line coupler using radial stubs to achieve reduced coupler size and simplified stub arrangement. As the electrical lengths of stubs used here are less than 90at center frequency, a method of comparing input impedances to obtain radial stubs that are equivalent to straight stubs is discussed. The frequency characteristics of the proposed coupler are derived by combining classical transmission line theory with the computed data of radial stub input impedances. The methods presented here increase possibilities for realizing reduced branch-line couplers by means of stub design. Experimental results agree well with theoretical results except for slight differences in the high frequency region.

First we introduce the high-frequency equivalent circuit model of the Fine Pitched Ball Grid Array (FPBGA) bonding for frequencies up to 20 GHz. The lumped circuit model of the FPBGA bonding was extracted based on S-parameters measurement and subsequent fitting of the model parameters. The test packages, which contain probing pads, coplanar waveguides and FPBGA ball bonding, were fabricated and measured. The suggested π-model of the FPBGA bonding consists of self-inductor, self-capacitor, and self-resistor components. From the extracted model, a solder ball of 350 µm diameter and 800 µm ball pitch has less than 0.08 nH self-inductance, 0.40 pF self capacitance, and about 10 mΩ self-resistance. In addition, the mutual capacitance caused by the presence of the adjacent bonding balls is included in the model. The FPBGA solder ball bonding has less than 1.5 dB insertion loss up to 20 GHz, and it causes negligible delay time in digital signal transmission. The extracted circuit model of FPBGA bonding is useful in design and performance simulation of advanced packages, which use FPBGA bonding.

This paper analyzes program and erase mechanisms for Floating Channel type Surrounding Gate Transistor (FC-SGT) Flash memory cells for the first time. In FC-SGT Flash memory cell, control gate, floating gate, drain and source is arranged vertically on the substrate. The body region is isolated from the substrate by the bottom source region. The cell is programmed by applying a high positive voltage to the control gate electrode with drain and source electrodes grounded. Erasing is performed by applying a high positive voltage to the drain and source electrodes with the control gate electrode grounded. The physical models for program and erase operations in FC-SGT Flash memory cell are developed. Program and erase operations based on the developed physical models are simulated by utilizing a device simulator. Program and erase characteristics obtained from the device simulation agree well with the results of analytical models. The FC-SGT Flash memory cell can realize program and erase operation with a floating body structure.

In this paper, the magnetic field properties around household appliances are investigated with the single coil model and equivalent source model, which are used as main source models in the European standard EN50366 (CENELEC). The accuracy of the field properties is conducted for the coil model (defined in the EN50366), by comparing with the results of the equivalent source model, which allow the reproduction of the complicated inhomogeneous magnetic field around the appliance with full generality (i.e. supports three dimensional vector fields).

A cryogenic Whispering Gallery sapphire resonator oscillator has been investigated using a 4 K pulse-tube cryocooler. The turnover temperature of the chosen mode in the sapphire crystal was 9.17 K with an unloaded Q-factor of 710⁸. The prototype sapphire-loaded cavity oscillator was designed to oscillate at 9.195 GHz. A fractional frequency stability of 210^-13 was measured at integration times of 10 s.

An output load VSWR (voltage standing wave ratio) protection circuit for SiGe power amplifiers (PA) is presented by using the relatively low collector-emitter avalanche breakdown characteristic of SiGe HBT. Unlike the conventional diode-type switch, the new protection circuit completely eliminates the undesirable dc leakage current during the normal operation of the PA. Simulations and measurements show the proposed protection circuit enhances the ruggedness of the PA at harsh operating condition while it imposes only minor performance degradation at normal operating condition.

A Power on Reset signal generation circuit referencing threshold voltage without standby current consumption has been proposed. The POR signal is generated when supply voltage is larger than the sum of threshold voltages of N- and P-MOSFET.

A readout circuit involving new two step current mode background suppression is studied for 2-dimensional long wavelength infrared focal plane arrays (LWIR FPA's). Buffered direct injection (BDI) and feedback amplifier structure are adopted for input circuit and background suppression circuit, respectively. The pixel circuit is simple and has very small skimming error less than 0.1%. Enough calibration range over 50% as well as long integration time over 1.75 ms can be obtained using this readout circuit.