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A method for evaluating the mean effective gain (MEG) of mobile antennas in line-of-sight (LOS) street microcells with low base station antennas is investigated. The received power patterns of incident radio waves along typical streets measured in actual street microcells in urban areas of Tokyo are presented to clarify the proper distribution model for the incident radio waves. A two-dimensional statistical distribution model is proposed based on the measured received power patterns for the incident radio waves that follow a Gaussian distribution in the azimuth angle, but are concentrated in the horizontal plane in the elevation angle. The two-dimensional theoretical expression of the MEG that consists of the incident distribution model function and the radiation patterns in the horizontal plane of the mobile antennas is derived to evaluate easily the MEG. We show that the MEG values in street microcells are not defined as only one value and form the MEG pattern because the MEG values are changed by the relative direction of the radio waves arriving at the mobile station antennas. The measured and calculated MEG values (MEG patterns) of the whip antennas used in the experiments are in good agreement. The average error between the measured and calculated MEG values is within approximately 4.5 dB at maximum. The results show that the MEG degradation of the mobile station antennas due to the effect of the human body is properly evaluated by the proposed distribution model. The proposed statistical distribution model is valid and effective in both estimating the MEG values of mobile antennas and designing the LOS street microcell systems with low base station antennas.

An enhanced microstrip antenna is proposed that incorporates a patch that rotates around the inner conductor of the coaxial line or dielectric shaft and a novel coaxial line feeding technique that offers constant electromagnetic coupling. This proposal addresses the disadvantages in our previous patch antenna in which the resonant frequency diverges from the center frequency of the personal handy-phone system (PHS) band and the bandwidth decreases as the patch rotates because of the changing electromagnetic coupling between the patch and microstrip line due to the patch rotation. We verify that this enhanced patch antenna achieves the antenna gain of approximately 0 dBd, which is the same as that of the previously proposed antenna, while suffering no significant gain degradation due to unit inclination over inclination angles from plusmn45deg compared to a conventional quarter-wavelength whip antenna, which experiences a degradation of approximately 2.7 dB. We show that the maximum resonant frequency separation from the center frequency of the PHS band is reduced to 15 MHz from 31.4 MHz of the previous antenna using the novel coaxial line feeding technique. The effective bandwidth needed for PHS is achieved over the inclination angles of -20deg to +40deg. Approximately 93% of the total bandwidth needed for PHS is achieved while the previous microstrip line type achieved only 58% coverage; accordingly, an adequate bandwidth for PHS use is obtained.

A fully integrated direct conversion DVB-H tuner is realized in a 0.5-mum SiGe BiCMOS technology. To meet the stringent linearity requirement while keeping low power consumption, novel linearization techniques for a variable-gain low-noise amplifier (VG-LNA) and a mixer are proposed. The proposed linearized VG-LNA has a variable gain range of over 50 dB, noise figure of less than 2.6 dB over the frequency range from 200 to 1000 MHz, and IIP3 of more than -10 dBm at a current consumption of 2.1 mA. The quadrature mixer with the proposed linearization technique achieves OIP3 of more than 25 dBm at a current consumption of 5 mA. In addition, a new offset-cancel feedback is introduced for the baseband block of a direct conversion receiver, which keeps the high-pass cutoff frequency independent of the baseband VGA gain. The fabricated tuner IC satisfies all the DVB-H requirements at a power consumption of 184 mW

The Multi Sector Monopole Yagi–Uda Antenna (MS-MPYA) can be used to realize low profile, multi-sector antennas. The MS-MPYA has an interesting feature; we can sharpen the beams by using the adjacent array effect if we set metallic fins between the arrays so as to hide the excitors. Otherwise, without the fins, undesired radiation from the adjacent arrays causes beam division. This paper shows the radiation mechanism by using transient solutions in the time domain calculated by the FDTD method to examine how electromagnetic waves interact with the directors, adjacent arrays, and fins in real time. We introduce the transient solutions for three types of MS-MPYA: with adjacent array and with fins, without adjacent array but with fins, and with adjacent arrays but without fins. The transient solutions show that the adjacent array's action is changed by the existence of the fins and caused beam division. Without fins, the adjacent arrays act as directors of the active array and cause beam division. With fins, the adjacent arrays reflect the wave coming from the main array and sharpen the beam. Copyright © 1999 John Wiley & Sons, Ltd.

A novel beam combination method for wide-band digital indoor communication systems such as wireless LANs and wireless ATMs is proposed. Crossed fan beams are used at the base station (BS) and personal stations (PSs). The beam combination method provides better transmission quality than the traditional pencil-beam combination and eliminates complex beam control in the BS. Maximum dispersion distributions in a transmission frequency bandwidth are calculated by a three-dimensional (3-D) indoor propagation delay simulation algorithm. A prototype fan-beam antenna for the PS is fabricated and measured at 20 GHz.

This paper proposes a four-branch height and polarization diversity configuration that achieves almost constant received signal power over any terminal inclination in a street microcell communication environment. An example of the four-branch diversity antenna is also presented. Our measurement results in cell-size comparison among height diversity, polarization diversity, and height and polarization diversity configurations confirm the effectiveness of the proposed diversity configuration.

In this paper, we propose a novel electromagnetically coupled microstrip antenna with a rotatable patch to overcome the problems associated with the conventional whip antenna for the personal handy-phone system (PHS). The structure of the newly developed antenna installed in actual PHS units is described. Its fundamental characteristics such as radiation pattern, bandwidth, and gain are shown. The performance of the antenna in actual propagation environments is also clarified. It is shown that this novel antenna is superior to the conventional whip antenna and achieves efficient performance in commercial PHS service.

Activities since August 1989 are covered. Included are antennas for mobile communication, multibeam earth station antennas, satellite-borne antennas for communication, and for earth remote sensing, direct broadcast satellite antennas, and propagation studies for land mobile radio, mobile satellite systems, fixed satellite systems, and terrestrial propagation. >

BACKGROUND AND PURPOSE: Fluid-attenuated inversion recovery (FLAIR) MR imaging has advantages to detect meningeal lesions. FLAIR MR imaging was used to detect pachymeningeal thickening and thin bilateral subdural effusion/hematomas in patients with spontaneous intracranial hypotension (SIH). MATERIALS AND METHODS: Eight patients were treated under clinical diagnoses of SIH. Chronologic MR imaging studies, including the FLAIR sequence, were retrospectively reviewed. RESULTS: Initial MR imaging showed diffuse pachymeningeal thickening as isointense in 6 cases, hypoisointense in 1 case, and isohyperintense in 1 case on the T1-weighted MR images, and hyperintense in all cases on both T2-weighted and FLAIR MR images. Dural (pachymeningeal) hyperintensity on FLAIR MR imaging had the highest contrast to CSF, and was observed as linear in all patients, usually located in the supratentorial convexity and also parallel to the falx, the dura of the posterior fossa convexity, and the tentorium, and improved after treatment. These characteristics of diffuse pachymeningeal hyperintensity on FLAIR MR imaging were similar to diffuse pachymeningeal enhancement (DPME) on T1-weighted imaging with gadolinium. Initial FLAIR imaging clearly showed subdural effusion/hematomas in 6 of 8 patients. The thickness of subdural effusion/hematomas sometimes increased transiently after successful treatment and resolution of clinical symptoms. CONCLUSION: Diffuse pachymeningeal hyperintensity on FLAIR MR imaging is a similar sign to DPME for the diagnosis of SIH but does not require injection of contrast medium. FLAIR is useful sequence for the detection of subdural effusion/hematomas in patients with SIH.

A single chip direct conversion DVB-H tuner with a distortion compensated variable gain LNA is implemented in 0.5mum SiGe BiCMOS. The LNA exhibits 0dBm IIP3 and 2.8dB NF at 860MHz. A new offset cancel feedback is introduced that keeps the cutoff frequency independent of the baseband gain. The IC consumes 184mW at 2.8V while achieving a sensitivity of -96dBm for QPSK, CR=1/2 signal

An automatic tuning method for active-RC base-band filters used in direct conversion receivers is proposed. Filter calibration is realized by setting the phase delay for a reference frequency of 4.5 MHz to -360deg. The proposed method is accurate and area efficient, since it does not require a replica filter but uses the filter itself. In addition, monotonic control of the capacitor arrays makes fast tuning possible. A pair of base band filters for DVB-H receivers including this automatic tuning method was fabricated using a 0.5mum SiGe Bi-CMOS process. The accuracy of the tuning is limited by the resolution of the binary capacitor-array and is 12deg. This corresponds to a worst case cutoff frequency deviation of 300 kHz. The tuning takes 113.8musec

A 160mW low-IF single-chip tuner for a mobile ISDB-T receiver is realized in SiGe BiCMOS. Its 25mW variable gain LNA shows 2.7dB NF and 62dB variable gain range. The 20mW switched-capacitor channel selection filter exhibits 80dB out-of-band rejection and 11nV//spl radic/Hz input referred noise.

Technological features of InGaP power HBTs for 5 GHz wireless-LAN applications are described. These features include self-aligned device structure, small-sized via-holes located adjacent to each transistor finger, and bias and feedback circuits for the reduction of distortion. These technologies improve both the gain and the linearity of power HBTs, producing high linearity and high power added efficiency in power amplifier MMIC.

A simple method is proposed to calculate the beam scanned angle of a dual reflector antenna due to subreflector statement displacement. After noting that beam scan by subreflector displacement is equivalent to beam scans by displacements of the feed horn and main reflector, the subreflector movement is translated into feed and main reflector displacement and the beam scanned angle is then the sum of an equivalent feed displacement component and an equivalent main reflector focal-point displacement component. The proposed formula is similar to that used in the case of a single parabolic reflector. >

A simple superdirective antenna structure that does not require an impedance tuner is proposed. The proposed design concept for broadside superdirective antennas was used to fabricate five-element arrays of d = 0.2/spl lambda/ and 0.3/spl lambda/ by combining self-resonating dipole elements, /spl lambda//4 parallel line matching circuits and a feed network. A d = 0.3/spl lambda/ antenna realized the designed radiation pattern with a theoretical gain (8.1 dBi) which confirmed the exact superdirective excitation. However, when d = 0.2/spl lambda/, the radiation pattern was deformed and the gain was about 4.5 dB lower than the designed value for lossless material. This decrease in gain is consistent with the calculated ohmic loss of the antenna elements and the loss caused by pattern synthesis errors, which is higher when the Q factor is high. >

This paper proposes the DP-BIRA (dual-polarized bidirectional rod antenna) which has the optimum antenna beam shape for street microcells and minimizes degradation in the received signal power caused by the polarization mismatch at the street microcell base stations. The theoretical results given by the multi-ray model are verified; the optimum antenna configuration for the street microcell base station is a bidirectional rod antenna (BIRA) composed of radiating elements arrayed in the E-plane (vertical). When the inclination angle of the handy-phone antenna is 90 degrees, the signal power of the height diversity collinear antenna (HCA), which is commonly used for diversity reception at the PHS base stations, degrades up to about -15 dB, and the HCA cell length is reduced by almost half from that of the vertically-polarized incident wave. On the other hand, the DP-BIRA holds the received signal power almost constant against inclination, so almost the same cell length is realized regardless of the handy-phone inclination. A DP-BIRA is fabricated and tested in a street cell environment in an urban area to verify the validity of our design method and the usefulness of the DP-BIRA.

A new analysis model of a portable radio antenna is proposed to investigate the characteristics of the antenna; the influence of the feeding circuit and the box covering the circuit are considered. The existing model used to analyze half wavelength whip antennas ignores the feeding circuits as radiating elements. However, recent radio equipment has become much smaller, and the existing analysis model and the real structure of the radio unit are diverging from the view points of the electrical design. Since the feeding circuits are not completely enclosed in modern units, coupling between the antenna element and the feeding circuit occurs and some unbalanced current mode in the circuit may radiate, but these phenomenon cannot be analyzed using the existing model. This paper proposes a new analysis model of portable radio antennas. A numerical analysis is carried out by using the FDTD method. This model is based on the concept of integrating the necessary parts for the analysis and includes the transmission line and the matching circuit, as well as the radiation element and the metal box of the radio unit. Some fundamental numerical data are presented and it is shown that the model produces a more realistic analysis of portable radio antennas. >

A dual-frequency low-profile printed dipole Yagi-array which can be attached at the back of a rear-view mirror within a vehicle interior is proposed. The relation between its configuration parameters and electrical performance is studied by numerical analysis. Although the dimensions of the antenna are very small, a frequency bandwidth, defined by a VSWR (voltage standing wave ratio) of less than 1.5 of 10% was achieved. Virtually identical radiation patterns with directivity of 4 dB/sub i/ were achieved in both frequency bands. By combining the output of two of the proposed antennas, diversity reception can be achieved. >

Suppressing multiple reflected waves in an indoor propagation environment is now in great demand because multiple reflected waves significantly degrade the transmission quality of wide-band wireless communication systems. This paper clarifies that adaptive arrays with M+1 elements can completely suppress the multipath waves whose delay times are up to M times greater than the inverse of the signal transmission speed (1/baud) regardless of the number of incoming waves in an indoor environment. Furthermore, it is also shown that the adaptive antenna technique can miniaturize an ordinary base station antenna obtaining a specified average bit-error-rate (BER) performance.

Wide-band digital indoor communication systems, such as wireless LANs and wireless ATMs, are being developed in the quasi-millimeter and millimeter wave frequency bands. In such high-speed systems, the degradation of transmission quality by multipath fading is a significant problem. Since wireless communication users operate their terminals without knowing the direction of the other station, the antennas should cover all directions with narrow beams. In addition, the antenna gains should be equalized in all directions. A sector antenna consists of narrow beams radially oriented and the beams are electrically switched to select the best signal. Therefore, its hardware is not complex and control is fairly simple. This paper shows a new methodology for realizing planar sector antennas. The sector antenna uses two kinds of beams formed by two kinds of antennas: planar 4-beam subarrays and planar single-beam subarrays. In order to equalize the antenna gains in all sectors, the beam shapes are carefully designed to offset the movement experienced by portable terminals. The 4-beam subarray is a multi-beam antenna integrated with a planar Butler matrix feeding circuit. The design method of the subarray and an evaluation of its characteristics in the 19 GHz band are discussed.

This paper proposes a three-dimensional active antenna configuration for a front-end module of a high-speed wireless communication system at millimeter and quasi-millimeter-wave frequencies. The active antenna is integrated with a microstrip antenna array on multilayer alumina-ceramic, individual MMIC chips including transmit/receive amplifiers, time division duplex switches, and a filter on multilayer polyimide. The three-dimensional structure achieves an unrestricted RF-circuit design on multilayer polyimide.

The performance of a newly developed microstrip antenna is investigated by FDTD analysis and experiments. The proposed new antenna consists of a patch, a shaft, a bearing, a weight and a microstrip line. The patch can rotate freely around the shaft. When the portable telephone unit is inclined, the patch rotates and remains vertical because of the weight. Therefore, the polarization direction of the new microstrip antenna is always kept vertical and there is no effective gain degradation due to the inclination. This new antenna also decreases the effective gain degradation due to the proximity of the operator's body. This is because its radiation pattern is very directional with low levels towards the operator. Furthermore, this new antenna is very easy to handle and resists breakdown. This is because it is built into the portable telephone unit.

An InGaP/GaAs two-stage HBT linear power amplifier MMIC for the 5GHz Wireless-LAN Application was developed. By using a novel linearizer and a small-size via-hole technology, the power amplifier showed high output power (19dBm) with high power-added-efficiency (PAE : 18.5%), sufficient gain (21.0dB) and high linearity (4.78% error vector magnitude : EVM) at supply voltage 3.3V. It is the highest PAE in the power amplifier MMIC for the 5GHz Wireless-LAN application ever reported.

New concepts are required to realize really effective antennas for broadband wireless access systems. Broadband wireless access system antennas cannot be the same as existing wireless system antennas, such as those for fixed terrestrial systems and narrow band mobile communication systems. The difficulties arise because broadband systems need tracking wireless terminals and mitigating multi-path phenomena. Differences in design procedure for broadband wireless antennas are described and it is pointed out that the design objects of antennas must be determined by evaluating all transmission line phenomena. Practical and effective antennas for broadband wireless access systems are described which have been developed in the NTT Wireless System Laboratories. The possibility of developing an adaptive antenna is also investigated as a powerful antenna of the future.

The Personal Handy-phone System (PHS) has been put into service in Japan. In this system, rod antennas are commonly used as the base station antennas because of their easy installation and low cost. This paper proposes a new base station antenna for base stations located on a slope or beside a cliff. The proposed antenna is a rod antenna that has axis-asymmetrical radiation patterns. To realize such radiation patterns, pattern syntheses of a linear array antenna are introduced that consider the influence of the metal plate (one part of the antenna), as determined by the moment method analysis. Two types of antennas are considered. One has a bidirectional radiation pattern in the slant direction, and the other has beams in the horizontal and slant directions. The results of the moment method analysis verify that the proposed antenna has the desired radiation patterns.

This paper proposes a new antenna structure named MS-MPYA that consists of a multi-sector monopole Yagi-Uda array on a circular ground plane. To numerically analyze MS-MPYA and clarify mutual sectors interaction when the antenna uses multiple sectors, the moment method which combines patch and wire models, is used. This paper introduces the following results. The beam width is reduced by 10.0 degrees in the horizontal plane due to mutual sectors interaction (compared to the single sector configuration). Setting metallic fin reflectors between each array is effective in eliminating the strong reflection that causes pattern instability. The MS-MPYA realizes a low-profile multi-beam antenna that offers a 30 degree beam with twelve sectors; the antenna height is 0.6 /spl lambda/ (/spl lambda/:wave length), ground plane diameter is 10.1 /spl lambda/, and array length is 3.5 /spl lambda/. Experimental results confirm the accuracy of the analysis method used.

Colinear antennas which have omnidirectional radiation patterns in the horizontal plane are used for base station antenna in personal communication systems because of their easy installation and low cost. For street microcells, which are formed using low base station antenna heights in urban areas, however, colinear antennas yield rather small microcell zones. Zone size can be efficiently increased by using bidirectional antennas which preferentially radiate the antenna beam along the street. The configuration of a bidirectional antenna is automatically determined by the shape of the antenna beam. Accordingly, the optimum beam shape must be determined for realizing the optimum antenna for street microcells. This paper describes the optimum beam shape for street widths ranging from 30 to 60 m, and proposes a base station antenna that yields the desired beam shape. We examine the relation between antenna beamwidth and microcellular zone size. The discussion is based on the theoretical results given by the multi-ray model technique assuming a street microcell model with infinite concrete walls. A bidirectional narrow patch antenna (BNPA) element is developed to realize a bidirectional rod array antenna (BIRA). The validity of the design method used and the antenna's performance are verified by laboratory measurement of a fabricated BIRA operating in the 1.9 GHz band, and field test results.

A planar inverted F antenna (PIFA) fed by electromagnetic field coupling, which has the advantage of compactness and simplicity of feeding structure, is presented. Analysis of this rather complicated antenna was successfully carried out by the FD-TD (finite-difference time-domain) method. The effectiveness of this antenna was demonstrated by numerical data of input impedance and radiation pattern. >

The electrical performance of an antenna located near a conductor or a dielectric material is affected by those obstacles. How the directional antenna can reduce the influence of the dielectric cylinder is investigated. First, an analysis method for the current distribution of an N-element dipole array located near the lossy dielectric cylinder is discussed. In this analysis, simultaneous integral equations, whose unknown functions are the currents on each element and whose kernels are the dyadic Green's functions for the dielectric cylinder, are derived. Second, numerical calculations are performed in the case when the directional antennas are two-element Yagi arrays. The input impedance and radiation pattern of these directional antennas are compared to those of the single dipole, and it is shown that the change of input impedance and radiation pattern of the directional antenna located near the cylinder is much smaller than those of the single dipole. >

The authors present a numerical analysis of correlation coefficient characteristics with antenna separation and incoming wave distribution for a built-in diversity antenna system comprising two planar inverted-F antennas (PIFAs) mounted on both sides of the radio case. It was found that even small antenna separation yields a sufficiently low correlation coefficient. Mutual couplings between the two antennas were found to play a major role in obtaining low correlation coefficients. It was also found that the built-in diversity antennas have good performance in terms of effective gain. The calculated results were in fairly good agreement with experimental results. >

A newly developed method of design for a shaped reflector antenna is described. A conventional quadratic reflector configuration is assumed; the reflectors are then modified to yield the desired aperture shape and field distribution by introducing shaping functions. This method is useful for designing antennas with an arbitrary shaped beam, such as an elliptical-beam antenna, and has been verified through a 4.7 m * 2.3 m (equivalent to 3.3 m diameter) dual-band (30-20 GHz) earth-station antenna for the Japanese domestic satellite system CS. The measured aperture efficiency is more than 76%, and the ratio of the major and minor axes of the elliptical beam is 2:1. >

The relations between the radiation pattern and feeding method in quadrifilar helical antennas is discussed. As a result, it is found that by changing the phase of each wire the helical antenna can achieve two radiation modes; both backfire and endfire radiation. These patterns do not have a difference except in radiation direction. Antenna polarisation of quadrifilar helical antenna depends only on the helical winding direction.

An experimental one-way multiaddress data communication system accommodating many small receive-only terminals is described. In this system, a digital facsimile is used as the output equipment. A simple one-way transmission protocol adopting the flag synchronization method has been developed so that facsimile equipment of different speeds can be used. The receive-only terminal comprises an antenna, an RF receiver, a demodulator, and a channel selector. The antenna is an offset parabolic type with an effective diameter of 60 cm and uses a printed spiral type primary radiator. Dimensions of the terminal are 70 cm wide, 88 cm deep, and 126 cm high. The satellite channel bit rate is 64 kbits/s in order to transmit multiple facsimile data simultaneously. Experiments using the Japanese "CS" satellite have been carried out to verify the system feasibility. The normal bit error rate was less than 10-6and line errors occurred less than once in three facsimile transmissions.

The system design and operational results of a 30/20 GHz band small Earth station for integrated services satellite digital network (ISSDN) experiments are presented. The Earth station has a high efficiency offset Cassegrain antenna with elliptical beam, a high power klystron amplifier with 1 kW output power and an uncooled parametric low noise amplifier with 200 K noise temperature. Experiments were performed using the medium capacity communications satellite for experimental purposes (CS). Performance on the Earth station was high. Effective radiation power (ERP) was greater than 88.1 dBW, and the receiving figure of merit (G/T) was larger than 30.6 dB/K. Good transmission characteristics were obtained through the satellite link for demand assigned time-division multiple access (DA-TDMA) with 20 Mbit/s bit rate.