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Numerous ways to analyze the pull-in range of the phase-locked system have been proposed. These include harmonic balance, the phase plane method and numerical analysis. In most of these methods, however, it was difficult to determine the actual pull-in range with high accuracy. This is because of the limitations in the applicable phase detector characteristics and loop filters, or the need to perform a complex numerical analysis. This paper proposes Galerkin's procedure to determine the pull-in range of the phase-locked system, demonstrating that the pull-in range can be determined with a high accuracy in a relatively simple way. Galerkin's procedure is a method of numerical analysis which can determine the periodic function for the nonlinear ordinary differential equation. By applying the procedure, the periodic solution of the second kind, corresponding to the out-of-lock condition of the system, is determined. From the critical input-output detuning for the solution to exist, the pull-in range is determined. From the critical input-output detuning for the solution to exist, the pull-in range is determined. This method can be applied to any phase-detector characteristics and loop filters, and by taking higher harmonics into consideration, a highly accurate solution can be determined. In this paper, as examples, the pull-in ranges are determined for a wide range of natural angular frequency and damping factor, for the phase detector characteristics which are sinusoidal, triangular, tanlock and sawtooth with fast jilter. [ABSTRACT FROM AUTHOR]

When tracking radar is used for tracking a low-altitude target, fading due to multipath propagation consisting of the direct wave and the waves reflected from the sea surface (or the ground) is generated so that tracking becomes difficult. In this paper, as a remedy to this problem, a space-frequency maximum-ratio combining method is proposed that combines frequency hopping with an array antenna. In order to reduce the size of the transmission and reception system, and also to reduce the computational overhead for maximum-ratio combining, a subarray configuration is used for the array antenna and the maximum-ratio combining is applied to the subarray. By means of computer simulation, the effects of the space-frequency maximum-ratio combining in the full DBF and in the subarray configuration are compared. It is confirmed that a power level higher than that in free space can be obtained by the proposed method under the constraint of a distance of 5000 to 40,000 m for a target at an altitude of 100 m (constant) by letting the frequency hopping range be 20%. It is also confirmed that the diversity gain degradation due to the subarray configuration is small. © 2004 Wiley Periodicals, Inc. Electron Comm Jpn Pt 1, 87(5): 75–85, 2004; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ecja.10143 [ABSTRACT FROM AUTHOR]

The M-sequence (maximum length sequence) is often used as a ranging signal in radar and other systems. This paper considers the case where an M sequence ranging signal is detected by an MPD (matched pulse detector), which is a digital correlator, and analyzes the probabilities for miss detection and for false detection due to bit error. Previously, this correlation function has not been derived analytically. In this paper, a procedure is presented where the threshold for the miss detection and false detection probabilities is determined by a simulation result for the correlator. An experiment is attempted in which a single M-sequence is detected in satellite communication using VSAT (very small aperture terminal). It is shown that the experimental results and analysis almost agree for a single M-sequence with a 31-bit code length. © 1998 Scripta Technica. Electron Comm Jpn Pt 1, 82(2): 82–89, 1999 [ABSTRACT FROM AUTHOR]

This paper proposes the differential detection type direct sequence/code-division multiple-access (DS/CDMA) adaptive interference canceller (AIC) that can track the fast fading. The proposed AIC is composed of the fractionally chip-spaced code-orthogonalizing filter (COF) with tap length corresponding to several bit periods and the differential detector. The COF makes adaptively the tap weight orthogonal to all spreading codes of other users as a despreading code of the desired user so that the interferences from other users are cancelled and the signal component of the desired user is extracted. The differential detector compensation the carrier phase variation due to finding in the desired user's signal at the COF output. By such a structure, the tracking performance of AIC to the channel variation can be improved to the limit of the tracking performance of the differential detector. This paper evaluates the basic ability of the proposed AIC in the fast-fading channel. The AIC is especially expected to be utilized in the DS/CDMA mobile communications since the receiver is of the signle-user type, where no information concerning other users is needed. [ABSTRACT FROM AUTHOR]

The microwave displacement meter based on the principle of phase interferometer has a high sensitivity in detection, However, in the conventional system the measurable displacement width is limited to the order on e haft-wavelenght of the microwave, and quantitative information can not be obtained without calibration. In the system proposed in this paper, a two-phase microware Doppler sensor (10.525 GHz) is used for detecting the reflected signal from the object as a vector, and displacement is measured directly from the phase.Which the high sensitivity of the phase interferometric method is maintained, the measurable width is improved significantly and quantitative measurement is possible. However, in the present method, the offset caused by the existence of unwanted reflectors other than the object can be a problem. Since this is depent on the measurement environment, the problem is expecially severe for biological measurement. In the this papers, this offset is calculated by estimation and is shown to be removable. Next, a recurrence formula is derived that is used calculating the displacement from the phase of the signal vector. The propotype system can measure the displacement width of 36 cm with the resolution of 90 um. As an example of biological measurement, two-dimension body movement measurement in the balacing function test is presented. Finally, the accurancy and resolution of the present method are studied. [ABSTRACT FROM AUTHOR]

We describe the α–β filter, which is a tracking method in one-dimensional space that estimates the true values of the position and velocity from observations of the target position. We disclose a tracking method, known as the observed noise multiplication method, that multiplies a constant l not limited to being greater than 1 by the observed noise covariance matrix in the calculation of the smoothed error covariance matrix in a Kalman filter. The α–β filter is obtained from this observed noise multiplication method. The tracking performance of this α–β filter was evaluated by the tracking accuracy of a target with constant-velocity linear motion based on the condition that the steady-state tracking error for a constant-acceleration target is constant (equivalent to a constant gain β). The gain α of the observed noise multiplication method is a function of the constant l. We see from the evaluation result that a constant l exists where the tracking accuracy of the α–β filter derived from the observed noise multiplication method is optimized. However, it is unclear whether this constant l generally optimizes the tracking accuracy of the general α–β filter or not. In this paper, we improve the α–β filter derived from the observed noise multiplication method so that the optimum gain α is uniquely determined. We see from this result that the variance of the tracking error is about one-fourth that of an α–β filter derived from the conventional observed noise multiplication method. © 2006 Wiley Periodicals, Inc. Electron Comm Jpn Pt 1, 89(10): 34–43, 2006; Published online in Wiley InterScience (www.interscience. wiley.com). DOI 10.1002/ecja.20273 [ABSTRACT FROM AUTHOR]

One of the techniques for detecting malicious communications from network traffic is to use a network-based intrusion detection system (IDS). However, since an existing IDS handles a low-risk alert for which an attack failed and a high-risk alert for which an attack succeeded in a similar manner, malicious communications cannot be detected properly unless a risk analysis is performed for each alert. This means that as the number of detection targets of the IDS increases, the cost of the risk analysis for every alert also increases proportionally. In other words, as the number of detection targets continues to increase, it becomes difficult to effectively deal with network incidents by using the IDS. In this paper, the authors focus on the fact that by continuously monitoring communications after an attack, the success or failure of the attack can be determined from the responses. They define these continuous communications as a session and design and implement a session-based IDS that enables the risk to be evaluated immediately and automatically. They also evaluate the effectiveness of the session-based IDS in an actual operating network. The results showed that this research lowered the operational cost of the IDS and enabled network incidents to be dealt with effectively. © 2005 Wiley Periodicals, Inc. Electron Comm Jpn Pt 1, 89(3): 46–58, 2006; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ecja.20251 [ABSTRACT FROM AUTHOR]

When vehicles and ships are observed by radar, echoes from the target are buried in the echoes (clutter) from the ground and the sea surface in the background and detection becomes difficult. Previously, a method known as a Polarimetric Whitening Filter (PWF) was proposed as a target detection technique that focuses on the difference in the polarizations of the clutter and the target and verified its effectiveness. In addition, the authors proposed the Polarimetric Notch Filter (PNF) as a clutter suppression scheme in an environment with a low signal-to-clutter power ratio (SCR) and verified the achievement of superior improvement in the SCR performance. In this paper, we propose a target detection algorithm that obtains a constant probability of false alarm by whitening the polarization characteristic of the residual clutter power after suppressing the clutter power by the PNF. From the results of evaluations by computer simulation, we see that the SCR improvement factor of the proposed method was on average about 1.5 dB better than conventional PWF, but the target detection probability was nearly identical. In addition, the results of the performance evaluation of the polarization data of the noise of asphalt and vehicles acquired by polarimetric FMCW radar in the 95-GHz band where the SCR improvement factors of PNF and PWF were 7.44 and 5.85 dB, respectively, and the SCR improvement factor of PNF was 1.59 dB better. Although the target detection probability was somewhat higher for PNF than PWF, they were nearly identical. © 2004 Wiley Periodicals, Inc. Electron Comm Jpn Pt 1, 88(3): 33–43, 2005; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ecja.20158 [ABSTRACT FROM AUTHOR]

With the progress in electronic equipment, evaluation of the electromagnetic compatibility (EMC) of the equipment has become an important issue. To evaluate the EMC it is necessary to accurately understand the electromagnetic field surrounding the equipment. Therefore, various sensors for measuring the electric field have been developed. Among them, since the electric field sensor using a Mach–Zehnder interferometer features wide bandwidth, high sensitivity, and high resolution, its application in EMC measurement is expected. However, its sensitivity changes at a frequency higher than a few megahertz due to unknown reasons and this makes the intensity measurement of the electric field much more difficult. In this paper, the sensitivity variation is considered to be caused by the resonance due to the piezoelectric effect of the optical crystal substrate used to form the optical modulator. By comparing the measured and theoretical resonance frequencies it is found that the sensitivity variation is due to the resonance in the width direction of the substrate. Based on this result, a method is proposed to suppress the resonance by varying the width of the substrate along the propagating direction. Finally, the improvement of the frequency response is demonstrated by using an optical interferometer with a variable width crystal substrate as the electric field sensor. © 2000 Scripta Technica, Electron Comm Jpn Pt 1, 83(11): 76–84, 2000 [ABSTRACT FROM AUTHOR]

The (4,12) circular- signal-set constellation [or (4,12) QAM] has been proposed for 16APSK in view of both the minimum Euclidean distance between mapped signal points and the realization of differential phase detection. Usually, the optimum value of the ring ratio, which is the ratio of the inner and outer ring level of signal constellation, is decided as one of the parameters of 16APSK by using the geometrical approach when the channel SNR is assumed to be quite large. However, the optimum value should be calculated by its symbol error rate to realize the best performance over all channel SNRs. From this point of view, symbol error rates of (4,12) QAM for three detection schemes are analyzed theoretically, and the optimum ring ratios for these detections are indicated in this paper. The performance of the envelope amplitude detection is expressed as the sum of PSK's performance and the effect of amplitude detection, which causes degradation of its performance. The optimum ring ratio for envelope detection is smaller when the channel SNR is lower, although the optimum value for ideal coherent detection becomes larger. The procedure used to analyze (4,12) QAM can also be adapted for star QAM, which is a conventional signal constellation of 16APSK. © 2000 Scripta Technica, Electron Comm Jpn Pt 1, 83(10): 19–28, 2000 [ABSTRACT FROM AUTHOR]

When several moving targets are detected by two two-dimensional angle sensors (elevation and azimuth angles) separately spaced, three-dimensional tracking of each target is possible if the range to each target is computed by triangulation. What is important in such a step is correlation processing to find out which pairs of sensor information are obtained from the same target. Especially, if several targets enter a region that can be considered within the same plane seen from the two angle sensors, a false intersection with no actual target, namely, a ghost, is generated among the intersections of the line of sight from the sensor to the target so that the correlation process becomes difficult. In this paper, the angle and angular velocity of the target with respect to each sensor are tracked by an angle tracking filter. The proposed system for the correlation process carries out discrimination of the same target by using the angle tracking results. By means of simulation, the performance of the proposed system is investigated. It is made clear that the proposed system can effectively eliminate the ghosting when several targets enter temporarily the same plane. © 1998 Scripta Technica, Electron Comm Jpn Pt 1, 82(2): 30–38, 1999 [ABSTRACT FROM AUTHOR]

With the progress in mobile communication as the background, researchers have become interested in digital signaling techniques. The quadrature modulator and the quadrature demodulator are employed in those techniques. This paper aims at the suppression of the waveform distortion in such a quadrature modulator/demodulator and proposes the affine transformation distortion compensation for the linear distortion (ADC). The linear distortion is attributed to: (i) dc offset in the baseband signal; (ii) unbalance of I/Q amplitudes; and (iii) phase offset of quadrature reference carrier. It is shown that those can be eliminated by ADC. A method is shown which estimates the ADC parameters of the quadrant modulation from the output of the level detector for the modulated wave. A method is also shown which estimates the ADC parameters for quadrature demodulation from the detected component in the received wave. ADC is actually implemented in the QPSK transmission system using the decision feedback equalizer. The characteristics are examined experimentally, and the usefulness of the method is demonstrated. [ABSTRACT FROM AUTHOR]

Radar polarimetry is considered a new subject of study in the field of microwave remote sensing. This paper describes a measurement method to obtain polarimetric microwave backseattering characteristics of random media using a power-measuring type, indoor-use microwave scatterometer. In general, the polarimetric backscattering characteristics are measured in the form of scattering matrices. However, in the method here, modified Mueller matrices ot random media were obtained by measuring backscattering coefficients for multiple polarizations. For transmitting and receiving polarizations, the horizontal linear, vertical linear, left-handed circular, right-handed circular, 45 degrees tilted linear, and 135 degrees tilted linear were combined. In comparing the measurement method to obtain scattering matrices, the method here- in has these features: i) the modified Mueller matrices which represent the back- scattering characteristics of random media are derived directly; ii) since phase measurement is avoided, the measurement system is simple and the calibration technique becomes stratight forward. In this paper, the measurement method, also with the fabricated scatterometer for the C band and the experimental results for backscatters from the random media composed of needle-shaped scatters are discussed, [ABSTRACT FROM AUTHOR]

Although optical fiber communication systems have recently been utilized in many fields, most of these have been realized by using a light source-detector pair. There- fore, two fibers have been needed f or 51- directional communication. Alternately, for small-scale systems such as communication between personal computers and measuring systems, for which not too high a speed is required, a single-fiber half-duplex optical communication can be realized by using an LED as source and detector. However, the LED as source stores many excess charge carriers, and the LED as detector has a large depletion capacitance. Therefore, the transceiver must be constructed to minimize these effects for possible high-speed communication. This paper proposes a transceiver applied to a multivibrator, which has both functions of switching between transmitting- and receiving-mode and modulating the data to FSK signal. The characteristics of trial system including the methods of data-input and demodulation are investigated. Although the transmitting speed by the proposed method depends on the LED characteristics, we have established a transmitting speed of about 200 k-bit/s in unidirection by the trial system. [ABSTRACT FROM AUTHOR]

This paper describes the analysis and design method 1 or a new biased rectifier amplifier (BRAM). The BRAM is driven by a high-frequency square wave, employs a new self-biased circuit configuration, and simulates dc detection characteristics using equivalent circuits. Design parameters of the core and operating frequency are studied to obtain a high conversion ratio of 2750. Applying the BRAN to a dc current detector gives a highly accurate, constant current dc--dc converter. [ABSTRACT FROM AUTHOR]

This paper proposes a new adaptive suppression scheme for radar clutters. This scheme applies a multisegment MEM which has been known as a means for power spectral analysis and for classification of radar clutters. This adaptive suppression scheme is applied to the multisegment MEM based on the work by Zhang and Haykin who assumed that clutter data in neighboring range rings have a high correlation. Actual clutter data (ground, sea, and weather clutters) collected by an experimental L-band radar with a low PRF wave were used. A comparison was made of performances based on improvement factors between the new suppression scheme for clutters and the suppression scheme used by Zhang and Haykin. The new processing method is shown to give an improved level by a few decibels for the numerical values of improvement factors. This was confirmed by the detection efficiency of an object signal which was buried in clutters using topological figures. It was clarified that the new suppression scheme for clutter possesses an enhanced capability in detecting the object signal easily compared with the method of Zhang and Haykin. [ABSTRACT FROM AUTHOR]

In this paper, with regard to a resonant sensor of a three-parallel line type consisting of a snow probe sensor array placed in snow for long-term measurement of the complex permittivity profile of accumulated snow layers at UHF frequencies, a derivation of an approximate formula for estimating the constant permittivity on the basis of the method of moments and experimental verification results are presented. The measured snow dielectric constant profile over a period of about 2 weeks at Aomori Airport is described. In particular, the change from dry snow to wet snow associated with snow melting is acquired. Hence, the effectiveness of the probe sensor for long-term measurement of the snow dielectric constant is confirmed. © 2004 Wiley Periodicals, Inc. Electron Comm Jpn Pt 1, 88(4): 10–19, 2005; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ecja.20186 [ABSTRACT FROM AUTHOR]

This paper considers the concept of an MSCS (metastable information communications system) for remote transmission of measured data with gradual variations of the transmission frame cycle and proposes a signal integration method for improvement of the transmission characteristics. Based on the proposed method, a signal integration algorithm for a system remotely transmitting measured sensor data from on board a moving body is derived. An improvement of the received SNR (signal-to-noise ratio) is demonstrated by simulation. As a specific example, the integration effect and limitation of the number of integrations determined by the relationship between the error ellipse and the speed of movement is derived with a GPS as a measurement sensor. An example result includes a maximum of 7 integrations for an allowable error of ±16 m for the GPS sensor measurement, a frame period of 1 s, and a speed of movement of 2.5 m/s, with the bit error rate improved by 8 dB when the input SNR is 0 dB. © 2004 Wiley Periodicals, Inc. Electron Comm Jpn Pt 1, 88(3): 44–52, 2005; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ecja.20154 [ABSTRACT FROM AUTHOR]

Multiuser detection using decorrelating detectors in CDMA systems have favorable performance when a few channels are in the synchronized state. However, when there are many channels, the performance degrades due to the effect of intersymbol interference in the unsynchronized state and the effect of noise emphasis. In this paper, we propose a method that reduces the effects between adjacent symbols by adding a guard chip interval while not increasing the processing computational load of the decorrelating detector even in the unsynchronized state. In addition, we propose a method that applies quasi-maximum likelihood estimation, a simplification of maximum likelihood estimation, to reduce the degradation in the noise emphasis. The result of an evaluation of the BER performance by a computer simulation verified the removal of interference nearly equal to the synchronized state even in the unsynchronized state. Even if the performance is degraded by the effect of noise emphasis with many channels, we verified that the performance can be improved to some degree by applying quasi-maximum likelihood estimation. [ABSTRACT FROM AUTHOR]

As a sensor that can measure the signals at around several gigahertz propagating on a printed circuit board, a near-field sensor with a patch antenna configuration is conceived. The tested sensor is the first to measure the electric field component perpendicular to the transmission line dominant near the microstrip line. In the range from 1 to 10 GHz, the signals on the microstrip line can be measured with a variation level of less than 4 dB. In this paper, the effect of the physical shape of the sensor on the characteristics is verified by the FDTD numerical calculations. The effectiveness of the sensor is demonstrated by test fabrication. Since the present sensor has a configuration without a balun, it is possible to increase the operating frequency by selecting the permittivity of the material used for the sensor and by reducing the size. © 2004 Wiley Periodicals, Inc. Electron Comm Jpn Pt 1, 87(11): 57–67, 2004; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ecja.20143 [ABSTRACT FROM AUTHOR]

In this paper, a simple input current waveform shaping method for a rectifier with a high power factor using the induced voltage of a flyback transformer is proposed. The duty ratio of the present shaping circuit is obtained by comparison of the integration signal of the rectified induced voltage and the ramp carrier waveform with a negative slope. By means of the proposed method, the input voltage sensor, current control loop, multiplier, and inductance current sensor can be eliminated, simplifying the control circuit. In order to confirm the proposed method, a flyback rectifier circuit for 100 W is fabricated for an experimental investigation. The results confirm that the input current waveform of the rectifier becomes closer to a sinusoidal shape and harmonic components become smaller by the use of the present shaping method. [ABSTRACT FROM AUTHOR]

When MTI (Moving Target Indicators) and AMTI (Adaptive MTI) are used in the pulse radar for searching, the staggered trigger scheme that transmits pulses at nonequal intervals in order to reduce the blind speed region is often used. As a clutter suppression process when the staggered trigger scheme is used, a method using the time variable coefficient filter is commonly chosen. However, in this method, a higher-order time-varying filter is needed in order to suppress several different clutters received at the same time. As a result, the computational effort to derive the filter coefficients for the desired characteristics increases, making real-time processing difficult. As a solution to this problem, this paper proposes a method of realizing a clutter suppression filter by means of a cascade connection of several low-order time-varying filters with their zero frequencies adjusted by zero frequency offset. First, the frequency characteristics of this filter are analyzed. It is made clear that the zero multiplicity cannot be obtained, so that the clutter suppression performance is degraded in the case of a configuration consisting of a cascade connection of several time-varying filters with the same zero frequencies. The effectiveness of zero frequency offset is presented. Next, it is shown by computer simulation that a time-varying AMTI that provides the desired clutter suppression performance can be realized by means of the proposed method, while the computation effort can be reduced. © 2004 Wiley Periodicals, Inc. Electron Comm Jpn Pt 1, 87(9): 75–86, 2004; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ecja.10153 [ABSTRACT FROM AUTHOR]

To measure the frequency stability of an atomic oscillator having high-frequency stability, a technique using a pair of mixers and a time interval counter is widely used. This technique shares the signals of a local oscillator, uses a pair of mixers to convert the signals of the reference oscillator and the signals of the test oscillator to beat signals, and then uses a time interval counter to measure the phase difference between the beat signals. In this paper, the authors propose a frequency stability measuring technique that uses a two-channel audio band digitizer in place of the time interval counter. This technique uses the local oscillator and pair of mixers to convert the test signals and reference signals to audio-band beat signals, and then performs an analog-to-digital conversion on the beat signals. When the phase difference between two beat signals is numerically calculated, not only the effect of the local oscillator's phase noise can be eliminated, but the DC offset voltage generated from the mixers is not a critical problem for frequency stability measurements. The authors developed a prototype frequency stability analyzer based on this technique and obtained an Allan deviation (square root of the Allan variance) of σy(τ) = 5 × 10-17 at τ = 1000 seconds as a result of measuring its residual noise at a frequency of 100 MHz. This technique can be used to analyze a wide range of properties such as the clock quality of digital devices that operate at high speed, as well as the frequency stability of atomic oscillators at arbitrary nominal frequencies. © 2003 Wiley Periodicals, Inc. Electron Comm Jpn Pt 1, 87(1): 21–33, 2004; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ecja.10097 [ABSTRACT FROM AUTHOR]

In this paper, we propose a multiple radar target tracking system that uses a mobile station, which is effective in reducing cross-range errors. The mobile station is an airplane equipped with radar and tracks the target by radar while in flight. By controlling the motion of the mobile state according to the proposed algorithm, the beams from the radars to the moving target can be orthogonal to or nearly orthogonal to each other compared to a multiple radar target tracking system that uses only conventional stationary stations. Combining the measurements from radars placed so that their beams to the target are orthogonal or nearly orthogonal can lessen the effect of increases in the cross-range errors and can obtain excellent tracking accuracy. Computer simulations compare the proposed method to a multiple radar target tracking system that used only conventional stationary stations and demonstrate its ability to obtain excellent tracking accuracy for distant targets. © 2002 Wiley Periodicals, Inc. Electron Comm Jpn Pt 1, 85(8): 1–12, 2002; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ecja.1113 [ABSTRACT FROM AUTHOR]

Crosshole borehole radar measurement is needed to compensate the antenna transfer functions in polarimetric single-hole radar measurement with combinations of a dipole antenna and a cylindrical conducting slot antenna. This paper presents a method to estimate the antenna transfer functions from the single-hole measurement alone. A small dipole model in a homogeneous medium is used to approximate the relationship between the direct coupling wave in the single-hole measurement and the direct wave in crosshole measurement (antenna transfer function). We show that the far field crosshole signal approximately has the same frequency dependency as the time derivative of the direct coupling signal measured via single-hole measurement. We experimentally demonstrate that the measured far field waveforms have good agreement with the time derivative of the measured direct coupling waveform for dipole–dipole and slot–slot arrangements with an antenna separation of 1.6 m. © 2000 Scripta Technica, Electron Comm Jpn Pt 1, 83(11): 11–21, 2000 [ABSTRACT FROM AUTHOR]

An electric field sensor using a Mach-Zehnder interferometer can be made compact, used for wide-band applications, and does not disturb the surrounding electromagnetic field. Because of these merits, its application to EMC measurement is promising. However, because it is not clear how to adjust the operating point (optical bias angle) of the optical modulator used for the electric field sensor, its dynamic range is limited. This paper proposes a method to adjust the operating point by applying force to a point on the optical crystal substrate used for the optical modulator. First, the relationship between the applied force and optical bias angle is theoretically analyzed, taking into account the change in waveguide length and change in the refractive index when load is applied. Then, it is shown that the change in the waveguide length is more dominating than the change in the refractive index. An electric field sensor was actually fabricated to show that the optical bias angle can be adjusted as theoretically predicted and that its temperature dependence is comparable to that of a conventional electric field sensor. © 2000 Scripta Technica, Electron Comm Jpn Pt 1, 83(8): 53-61, 2000 [ABSTRACT FROM AUTHOR]

Tracking systems with phased-array antennas have used α-β filters. An α-β filter can reliably estimate the target position and velocity operation in real time. When the target maneuvers, the quality of the position and velocity estimates provided by an α-β filter degrades significantly. For tracking maneuvering targets, an α-β filter combined with circular prediction has been proposed. However, there is the problem that the estimates of the α-β filter combined with circular prediction are degraded when tracking maneuvering targets because the smoothed positions that are input to the circular prediction filter are adversely affected by increasing linear prediction errors. In this paper, we propose an adaptive-gain α-β tracker combined with circular prediction to improve tracking quality compared with conventional filters. The filter gain of our proposed scheme is variable by the use of a maneuver detector. Simulation results for various target profiles are included to compare the performance of our proposed scheme with that of conventional tracking filters. © 1999 Scripta Technica, Electron Comm Jpn Pt 1, 82(12): 20–29, 1999 [ABSTRACT FROM AUTHOR]

Weibull distribution and log normal distribution among others have been used to describe the amplitude distribution in clutter. The K-distribution, proposed more recently attracts attention because its parameters are able to explain the physical nature of clutter. The relationship between the K-distribution parameters and the nature of geographical features is clarified in this paper. Differences in experimental conditions and small amounts of non-object clutter in the geographical features influence the parameters. We show that this influence can be reduced by a limiter related to average electric power. We show that the distribution, obtained by pulse integration and unification processing, and using a limiter several times, conforms to a gamma distribution. In these experiments, this method, using the same radar, is applied to clutter from various geographical features to obtain the K-distribution parameter. The K-distribution parameter is used to compare the relation between various geographical features. Finally we show that the power distribution before pulse integration or the clutter voltage distribution conforms to a K-distribution with the same shape and scale parameter as the gamma distribution. © 1998 Scripta Technica, Electron Comm Jpn Pt 1, 82(2): 57–65, 1999 [ABSTRACT FROM AUTHOR]

The electric field sensor using an optical modulator makes possible accurate measurement without disturbing the electromagnetic field to be measured and is expected to have applications in EMC measurement. In this paper, a theoretical analysis of the sensitivity of the electric field sensor using an LiNbO3 modulator and the error factors are described. First, the electric field sensor consisting of a rod, an optical modulator, an optical source, and an optical detector is expressed by an equivalent circuit. Next, of the equivalent circuit parameters, those related to the sensor rod are derived by a numerical analysis using the method of moments. Those related to the optical modulator are derived by the theoretical analysis and measurement. A method is presented for determination by measurement in regard to the optical source and the detector. An electric field sensor is fabricated and its characteristics are evaluated. It is found that the difference between the measured value and the theoretical value of the sensitivity is about 8.2 dB. The causes of the difference are the input capacitance and the insertion loss of the optical modulator. These two parameters are measured beforehand and used in the calculation. Then, the sensitivity of the electric field sensor can be estimated with an accuracy of 1 dB. The analysis method used in this paper is found to be effective for sensitivity analysis of the electric field sensor. © 1997 Scripta Technica, Inc. Electron Comm Jpn Pt 1, 80(12): 79–89, 1997 [ABSTRACT FROM AUTHOR]

When a flying object tracks a target, the location and velocity of the target are estimated based on a target detection process using radar. In general, the constant false alarm rate (CFAR) is used in the target detection process. However, if a high power interference wave is received in addition to the object signal, the target cannot be detected, so that tracking fails. This is caused by an uncontrolled increase in the threshold level at the time of target detection due to the interference component mixed in the reference cells. After the CFAR process, tracking of the target is possible by the use of a tracking filter as long as the existing target signal component is detected, even if the interference wave is evaluated as the target signal component. In this paper, an interference adaptive CFAR is discussed in which the CFAR process is carried out and the interference component mixed in the reference cell is detected and eliminated. The relationship between the threshold coefficient and the false alarm probability and a computation method for the CFAR loss are formulated in this paper. By means of the derived relationships, several case studies are carried out and the nature of the interference adaptive CFAR is discussed. © 1997 Scripta Technica, Inc. Electron Comm Jpn Pt 1, 80(10): 29–37, 1997 [ABSTRACT FROM AUTHOR]

There are two methods for improving the resolution in the scan axis direction of the subsurface radar, i.e., the F-K migration method and the phase-shift method. The resolution can be improved significantly by the F-K migration method if the propagation velocity of the radio wave in the ground is uniform and by the phase-shift method if the propagation speed varies in depth and is known. In general, the propagation speed of the radio wave often changes in depth and its distribution is unknown. In this paper, a method is proposed in which the radar image is divided in the depth direction and the propagation time difference up to the divided block is compensated for so that the F-K migration method is applied to each block. The propagation speed of each block is estimated as the case in which the maximum reflection value of the reconstructed image is the largest after the F-K migration process is carried out for several candidate values of the propagation speed. By means of this method, the distribution of the propagation speed can be estimated and a reconstructed image with high resolution can be obtained. This reconstructed image is of sufficiently good quality in comparison to the one by the phase-shift method using the empirical propagation speed distribution. The processing time excluding the propagation speed estimation is reduced to one-seventh that needed for the phase-shift method. [ABSTRACT FROM AUTHOR]

Traffic monitoring systems employ, as sensors, infrared image systems, visible light image systems, and so on. But observation with such monitoring systems are limited to highway interchange areas and intersections of large roads. Also, such systems often fail to detect vehicles hidden by obstacles such as roadside trees because the sensors are easily affected by weather conditions such as rain and dense fog. This paper discusses sensors using 94-GHz millimeter-wave radar in traffic observation systems. These sensors make it possible to observe hidden cars and to reduce the influence of weather and are unaffected by night and day conditions. In addition, it is possible to improve the observation ability by using both the current system and 94-GHz millimeter-wave radar for unattended observation of traffic within the range of 1 km. [ABSTRACT FROM AUTHOR]

It has been considered impossible to demodulate a fast frequency-hopping (FFH) spread-spectrum signal coherently in a frequency selective fading channel as a result of difficulties with making the receiver local oscillator track the phase of a received signal that lacks phase continuity. This paper proposes a coherent demodulator for both FFH-PSK (phase-shift keying) and FFH-FSK (frequency-shift keying) signal employing a method in which the received signal is noncoherently downconverted and phase-adjusted by an adaptive algorithm. Computer-simulations show that performance is better than in the case of noncoherent demodulators and that the interference-rejection effect of the adaptive algorithm produces strong protection against interferences from other CDMA users. [ABSTRACT FROM AUTHOR]

When observation of a direct lightning strike to a building is performed or in an experiment for applying lightning using a building, one needs current sensors that can measure the current in building columns, girders, and walls. As the current sensor, the Rogowski coil commonly is used. The coil is placed around the object to be measured, and the inductive voltage is obtained. Although there are many commercially available units, these sensors are too small for measuring building columns and girders. This paper studies Rogowski coils which are long enough to encircle the building columns and girders and flexible enough to set up the structure according to the practical situation. First, the coil and the integrator are described by their lumped element equivalent circuits. In addition, the target values were set for the frequency bandwidth and the sensitivity. A structure optimum for these characteristics was found. From the results, a hollow core coil using a vinyl pipe was fabricated. A Rogowski coil 1 to 10 m long was realized which has a frequency of 300 kHz and a current-voltage conversion factor of 1/100. Further, the position dependence of the current to be measured was observed. Sufficiently practical characteristics were obtained with the present coil with a long structure. [ABSTRACT FROM AUTHOR]

An increase in the size of on-board antenna reflectors is a key technology in providing economical services by miniaturized portable equipment in future mobile satellite communication systems. In practice, a mesh antenna can be used as the on-board antenna. However, since the reflector surface of this antenna is supported by the cable and the mesh, and its size is larger, the surface is subject to larger thermal deformation in orbit than is the solid antenna reflector. Conventional compensation methods such as passive thermal control or rotation of the antenna reflector cannot maintain the required antenna performances. Various methods have been reported to compensate for the deterioration of antenna performance by thermal deformation. This paper describes a static shape control system for a 10-m diameter antenna which actively compensates for the deformation by using a shape-measuring sensor and shape-compensation actuator. The configuration of the sensor and the experimental results by a functional model are described to confirm the design validity. The shape-compensation method by the actuator was cone firmed to be useful in achieving a required surface accuracy. [ABSTRACT FROM AUTHOR]

To improve the coverage and the resolution of the baseband pulse radar system, it is important to predict accurately the characteristics of the transmitting and receiving antennas due to a pulse and the electromagnetic transient field scattered by a target. In this paper, a moment method and Fourier transform are presented to solve the problem of transient coupling between two orthogonally and resistively loaded dipole antennas and a thin-wire target, both placed in free space. Numerical results show that if resistances with optimum values are loaded in both arms of the dipoles, the multiple reflections arising between their ends and their feeder can greatly be suppressed. Based on these results, the coverage method for such a pulse radar system using resistively loaded dipoles as well as the near field patterns at the first resonant frequency are examined. [ABSTRACT FROM AUTHOR]

A tracking system consists of an observation part such as a radar and a filter part such as a Kalman filter. To date, numerous adaptive filters have been studied for improving the tracking accuracy. However, the parameters related to the observed data have been fixed. If, on the other hand, one uses a digital beamforming (DBF) radar as the observation part so that the coherent integration number has a degree of freedom, these observation parameters can be adjusted according to the situation to improve the accuracy of the tracking system. From the viewpoint of requirement on the filter, the observation period and the observation accuracy, both of which are functions of the coherent integration number, are opposite to each other, and hence the optimization of the integration number is a problem. In this paper, a DBF radar is used for observation and a Kalman filter as the filter, and a study is made to determine how the angular position prediction accuracy in such a tracking system varies by the coherent integration number. It is shown that there exists an optimum coherent integration number for the entire tracking system. [ABSTRACT FROM AUTHOR]

When an ultrasonic wave is irradiated perpendicularly by a coherent light beam, the ultrasonic wave behaves as a phase diffraction grating, and the light is phase-modulated. Since the degree of modulation of the light is proportional to the line integral value of the sound pressure in the light-beam path, the sound field can be reconstructed by measuring it in various directions and by applying the CT method. This paper describes a development of the light beam CT system for measuring ultrasonic fields and the obtained results. A system to measure the projection data from various directions was developed, and sound fields produced by various transducers were reconstructed. The results were compared with the experimental data obtained by a hydrophone and the numerically calculated values. The degrading of the quantitativity of this method due to the fact that the ultrasonic wavefront is not really a plane (this is a crucial point in the method), was examined by using a computer simulation. The results show that the errors are negligible in the far-field region of a plane-type transducer or in the focal plane of a concave-type transducer. However, the errors are significant in the rest of the region. [ABSTRACT FROM AUTHOR]

In conventional radio interference measuring apparatus, the direct-QP detection method is used. In this method, intermediate frequency output is added directly to a quasi-peak detector to obtain an output corresponding to the quasi-peak level of the interference. However, a new type of QP detection method has recently been used in the radio interference measuring apparatus as demonstrated in the spectrum analyzer with the quasi-peak detection capability. In this method, the intermediate frequency output is first added to an envelope detector and then to quasi-peak detector. But it is not yet known if this measuring apparatus with its combination of detector, the envelope-QP detector, satisfies all standards, including present CISPR specifications. The latter is determined based on the response characteristics of the direct-QP detector system. In this paper, theoretical computer comparison has been made between the direct-QP detector system and the envelope-QP detector system to study responses to Gaussian noise and the repeated pulse input. It is found that the measuring apparatus with an envelope QP detector does not easily satisfy the present CISPR specifications. To improve the response characteristics of this new apparatus having the envelope-QP detector, guidelines have been indicated for the bandwidth and the charge and discharge time constants. [ABSTRACT FROM AUTHOR]

FM demodulators using digital signal processing (DSP) technology are advantageous over analog type FM demodulators because they have stable behavior, high-reliability, compactness by LSI, and no need for adjustment. In this paper, we propose a new FM demodulator called SIN type FM demodulator which uses DSP technology. It reduces hardware complexity compared with TAN type FM demodulator which has the best characteristic among many FM demodulators using DSP. For example, SIN type needs only one A/D converter, while TAN type needs two. As for ROM, SIN type needs one-third of ROM which TAN type requires. The circuit of SIN type required for phase detector is substantially simplified. First, the circuit configuration and operation principle of SIN type will be described and SIN type circuit is shown to be significantly simplified compared with TAN type circuit. Then, compared with TAN type circuit. Then, through computer simulation the performance of SIN type is shown to be much better than the Digital Quadrature type, which has the simplest structure of all the FM demodulators using DSP. [ABSTRACT FROM AUTHOR]

There is a great demand for electric field sensors with bandwidth wider than 1 GHz in order to evaluate electromagnetic fields near wireless equipment and to investigate EMC test equipment. An electric field sensor using an optical modulator is suitable for this purpose because it has a wide bandwidth and is compact. This paper describes an electric field sensor with a 10-mm-long element fabricated by depositing a nichrome layer on a glass substrate. First, based on the equivalent circuit of an electric field sensor, the frequency characteristic of the sensor was analyzed by the moment method and the relationship between the element length and frequency characteristic was clarified. Then, the characteristics of a fabricated sensor were analyzed. It was found that the sensor sensitivity was constant within ±4 dB at frequencies up to 4 GHz. The measured frequency characteristic of the sensor was close to the analytical result obtained by taking into account the dielectric constant of the material in which the sensor is mounted. It was also found that the sensor sensitivity was 16 mV/m, about 100 times higher than that of conventional sensors with a similar size element. The directionality of this sensor was equivalent to that of a tunable dipole antenna and the spatial resolution was comparable with the element length. © 1997 Scripta Technica, Inc. Electron Comm Jpn Pt 1, 80(12): 69–78, 1997 [ABSTRACT FROM AUTHOR]

The monopulse method is widely used to obtain the arrival angle of a target echo, which is required in radar measurements of target height. The monopulse method uses the fact that the angle error signal obtained from the signals received by the sum and difference antenna patterns is a monotonically increasing function of the echo arrival angle. However, in measuring a low-elevation target, in addition to the direct echo from the target, the measurement is affected by indirect echoes arriving at the radar system after reflection from the sea or ground surface. In this case, the angle error signal is a complex function, which leads to a higher measurement error than the conventional monopulse method. In particular, if the angle range of the dual lobe (in the difference antenna pattern) is wider than that of the main lobe in the sum antenna pattern, the received signal for the difference antenna pattern suffers from interference with indirect echoes. This paper offers an analysis of the complex angle error signal in the monopulse method for such antenna patterns and proposes a method to obtain the direct echo arrival angle with suppressed interference from the indirect echoes. A computer simulation was used for comparison with the conventional method. It is confirmed that the proposed method yields reduced error. © 1997 Scripta Technica, Inc. Electron Comm Jpn Pt 1, 80(9): 25–33, 1997 [ABSTRACT FROM AUTHOR]

Typical problems for subsurface radar sensing are the existence of strong surface clutter and the difficulty in detection of deep targets due to the attenuation of electromagnetic waves underground. This paper proposes a method of enhancing deep target echo strength for FM-CW radar so that the radar sensitivity is proportional to the range. This technique is similar to the time sensitivity control circuits used for pulse radar, and is based on the differentiation property of the beat signal with respect to time. First, we show that this amplitude compensation approach is feasible both theoretically and experimentally in free space. Next, the validity of this method is confirmed by a subsurface target detection experiment using sandy ground. Finally, a hardware implementation in the FM-CW radar is described. © 1997 Scripta Technica, Inc. Electron Comm Jpn Pt 1, 80(6): 1–7, 1997 [ABSTRACT FROM AUTHOR]

This paper uses measured data to analyze the relationship between the depth of the snowpack and the brightness temperature in the snowpack observation by microwave scanning radiometers (MSRs) on Marine Observation Satellite-1 (MOS-1) that is one of the satellite-borne microwave radiometers. In the analysis, a model is established in which the brightness temperature observed by the MSR captures mainly the effect of attenuation by scattering and absorption when the microwave radiated from the underlying ground passes through the snowpack. The measured data are statistically processed by taking into account the fluctuations of the data caused by the effect of various factors other than snowpack on brightness temperature. The MSR data from observations of the Hokkaido region from January to March in 1988 and the snowpack depth data observed on the ground are compared. It is found that the relationship between snowpack depth and the brightness temperature can be approximated by a straight line with a negative slope. The slope of the approximated straight line varies seasonally and this change reflects variations of the snowpack condition. Further, it is shown that there is a strong correlation between the average brightness temperature of the inland part of Hokkaido and that of the ocean surrounding Hokkaido. A possibility is suggested that the effect of atmospheric radiation can be estimated from the average brightness temperature of the nearby ocean. © 1997 Scripta Technica, Inc. Electron Comm Jpn Pt 1, 80(3): 58–66, 1997 [ABSTRACT FROM AUTHOR]

This paper extends the function of Amari-Takeuchi's model by adding an inhibitory cell with nonlinear characteristics to their self-organizing model of the feature-detecting cell. The generalized model is shown to separate even patterns in mutually inclusive relation, forming the feature-detecting cells for each of the patterns. It is shown that when a learning parameter in the model is modified, it can perform classifications under various criteria based on the similarity. Then an associative model based on the feature-detecting cell is proposed. The model is composed of three subsystems: the feature-detecting cell formation subsystem to convert in a self-organizing way the input pattern to the specified feature set; the learning subsystem, which associates in a multiple way two kinds of signals by cross-correlation; and the decoding learning subsystem, which restores the original pattern from the coded signal. The behavior of the model was examined under a multiple-associative environment. The model can handle the mutual and self recalls in a unified way, and the memorized patterns associated with the key pattern are recalled successively. The result indicates a role of the feature-detecting cell in the associative memory. It is also suggested that the model can be a basis for accounting for the high-level associative function through association of high-level notions. [ABSTRACT FROM AUTHOR]

Along with the development of optical circuit elements, the problem of coupling these elements to optical fibers, light sources and detectors is very important in the further realization of highly efficient malfunction optical transmissions systems. In conjuction with the coupling of optical circuit elements to fiber, this paper reports on fusion splicing using the heat of a C02 gas laser. The circuit elements employ deposited silica waveguide (DS guide), which is excellent with regard to loss, fabrication precision, stability, etc. For coupling of multimode graded-index fiber to multimode DS guide the average loss of fusion splices was 0.18 dB. Measurement of the reflected light from the splices confirmed that fusion caused the disappearance of reflections. The average loss of fusion splices between single-mode fiber and single-mode DS guide was 0.19 dB. A multiple splice of 10 fibers to 10 multimode DS guides spaced 200 µm apart shows the prospect of realizing high-density multiple fusion splices. [ABSTRACT FROM AUTHOR]

A neural processing-type optical wavelength division multiplexing (WDM) demultiplexer (NP-ODEMUX), which consists of diffraction grating, detector array, and neural network LSI, is proposed in order to improve receiver sensitivity while maintaining flexible demultiplexing characteristics. In previous work, a neural processing-type optical WDM demultiplexer using a multimode optical waveguide was proposed. This conventional NP-ODEMUX and the proposed grating-type NP-ODEMUX are compared using power penalty calculation simulations. The results show that receiver sensitivity is improved using the proposed grating-type NP-ODEMUX. Also, a standard diffraction grating demultiplexer without neural processing is compared with the proposed NP-ODEMUX using power penalty and it is shown that the proposed NP-ODEMUX can demultiplex WDM signals without degrading receiver sensitivity. Next, the results of the demultiplexing experiment for six-channel WDM signal which has been directly modulated at 150 Mb/s using nonreturn to zero (NRZ) pseudorandom signal by grating-type NP-ODEMUX prototype are described. Bit-error rate measurement for both the conventional diffraction grating demultiplexer and the grating-type NP-ODEMUX using neural processing for the unequally spaced WDM signals revealed that the receiver sensitivity can be greatly improved and that it can flexibly compensate wavelength change. [ABSTRACT FROM AUTHOR]

For automobile safety, supplemental equipment such as seat belts and air bags is used. These devices are activated after an accident. In contrast, from the point of view of accident prevention, automotive radar has been developed for collision avoidance. Presently, typical radars are the frequency-modulated type and the pulse-modulated type. It is known that measurement of an object over short range is difficult with these types of radar. Here, we propose a method of realization for radar using a standing wave that can measure a moving target within 2 m at a speed of 0 km/h to 100 km/h in simulations, within the specification of low-power radio equipment to detect moving objects at 24 GHz with a narrow bandwidth of 76 MHz. This radar is not subject to the problems of FMCW radar such as leakage of the transmitted signal and false targets due to nonlinearity of the mixer. © 2006 Wiley Periodicals, Inc. Electron Comm Jpn Pt 1, 89(5): 52–60, 2006; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ecja.20165 [ABSTRACT FROM AUTHOR]

In order to reduce the number of preamble bits required for synchronization at correct positions, a method of synchronization by deselecting the candidate positions for synchronization is proposed. As decision methods for each preamble bit, a method using the threshold detection and a method using chip level detection are discussed. Both methods make use of the fact that the preamble bit is the bit “1”: any synchronization position judged not to be a “1” bit even once is deselected as a candidate. In this way, the only position eventually remaining without being deselected is judged to be the synchronization position. As a result, it is possible to carry out synchronization with fewer preamble bits than the conventional method in which bit decision is based on the logarithmic likelihood ratio of the continuously transmitted preamble bits. A theoretical analysis is made under the assumption that the output of the photodetector follows a Poisson distribution. It is found that the proposed method can perform synchronization within a shorter time than the conventional synchronization method. Further, in the method using chip level detection, it is shown that synchronization is achieved in a shorter time even if the bit decision threshold is fixed. © 2004 Wiley Periodicals, Inc. Electron Comm Jpn Pt 1, 88(3): 21–32, 2005; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ecja.20160 [ABSTRACT FROM AUTHOR]

Since the autocorrelation function of radar clutter between cells usually attenuates rapidly compared to that of the signal, the waveform after detection has larger changes in the clutter than the signal. Improving the signal-to-clutter ratio (SCR) in conventional radar relies on the integration effect of the amplitude, but here we tried to use the differences in the frequency components of the waveforms. We compared the output after detection obtained from aircraft flying over the ocean by asynchronous detection shipborne radar to the waveform that used Daubechies wavelet, and verified the effect. Next, we defined the signal area and the SCR and quantitatively calculated the improvement. Although we were able to verify an improvement of several decibels for a nearby target, the effect could not be obtained for a distant target. We could provide nearly the same improvement for all of the targets by changing the filter that varies the cutoff frequency with distance. In experiments, we were able to demonstrate a similar improvement by using wavelets in the detected output of the experimental Airport Surface Detection Equipment set up at Sendai Airport. © 2002 Wiley Periodicals, Inc. Electron Comm Jpn Pt 1, 85(10): 23–32, 2002; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ecja.1128 [ABSTRACT FROM AUTHOR]