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FMCW (frequency-modulated continuous wave) radar is a radar system which can achieve high resolution by relatively low signal processing load. The authors have reported on clutter suppression by FMICW (FM interrupted CW) radar, where the transmission/reception of FMCW radar in pulse waveform is switched in order to assure transmission/reception isolation and to suppress undesired waves from short distances. This paper proposes the FM staggered PRI system, in which the pulse repetition interval (PRI) is randomized for each pulse in order to suppress the interference when FMICW radars are congested within the search distance. The target-signal in the FM staggered PRI system is formulated. Conditions such as the average PRI and the possible range of staggering are derived from requirements such as the maximum search distance. The output S/I is statistically evaluated by computer simulation, with the average PRI, the pulse width, the number of interference waves, and the input S/I (signal-to-interference ratio) as variables. The effectiveness of the FM staggered PRI system is demonstrated. © 2007 Wiley Periodicals, Inc. Electron Comm Jpn Pt 1, 90(12): 86–100, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ecja.20326 [ABSTRACT FROM AUTHOR]

The detection of received radar signals uses Doppler filtering as the correlation process on the received echoes for many transmitted pulses in addition to the pulse compression process which is the correlation process in the range direction. Normal radar echoes become blips widened in the azimuth direction, but the Doppler filtering process is not the optimum process from the perspective of improving the signal-to-noise ratio. Furthermore, compression of the spread in the azimuth direction of the signal is demanded in order to detect the azimuth. In this paper, we show that the azimuth beam width compression process can be implemented by filtering which satisfies the maximum SNR based on the zero sidelobe constraint condition applied to pulse compression. In addition, we theoretically explain the weighting matrix derived by this design method and use simulations to compare with the pulse compression process of the characteristics of a zero sidelobe correlation function. © 2007 Wiley Periodicals, Inc. Electron Comm Jpn Pt 1, 90(10): 25– 35, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ecja.20373 [ABSTRACT FROM AUTHOR]

In general, it is difficult to measure short distances by radar, which has a minimum detection distance of several meters. The standing wave radar proposed by the present authors has a minimum detection distance of about 2 m when the frequency bandwidth is 76 MHz. A solution to reduce the minimum detection distance is to increase the frequency bandwidth. This is not realistic due to limits imposed by radio regulations. The authors have proposed a method with measurable distances down to 0 m without enlarging the bandwidth and have presented the configuration and the measurement principle. The measurement principle has been verified by numerical simulation. In the present paper, the measurement principle is experimentally verified by using an actual standing wave radar and the realizability of a standing wave radar with measurement capability down to 0 m is confirmed. It is shown that the distance to the target at locations closer than the minimum detection distance of 2 m (0.14, 0.3, 0.5, and 1 m) can be measured with an error of several centimeters for a frequency bandwidth of 76 MHz at 24 GHz. For distances less than 0.14 m, the target could not be placed closer than 0.14 m due to positional interference of the target and the antenna in the present experimental environment so that physical confirmation was not possible. However, at the confirmed distance, the range spectrum predicted from the theory is obtained. Hence, it is considered possible to make measurements without special restrictions. © 2007 Wiley Periodicals, Inc. Electron Comm Jpn Pt 1, 90(9): 25– 34, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ecja.20375 [ABSTRACT FROM AUTHOR]

In forward-looking radars such as automotive radars, it is necessary to suppress the reflected undesirable signal (clutter) from such objects as the ground surface (especially hills), guard rails, and buildings, in order to detect moving targets ahead. When using a pulse-Doppler filter (PDF), which is the conventional method for clutter suppression, separation is difficult when the velocity of the target relative to the clutter is small. In this paper, as a high performance clutter suppression method for such low-velocity targets, we propose element-localized Doppler space time adaptive processing (ELD-STAP), which includes a PDF in the preprocessing, and which uses an array antenna. In the proposed ELD-STAP, only the PDF output corresponding to the Doppler frequency breadth of the clutter, predicted from the speed of the vehicle on which it is mounted, is selected for applying STAP, and hence the dimension of the data vector, which is the greatest difficulty in the application of STAP, can be reduced. By reducing the dimension of the data vector, not only the computation load, but also the number of cells that must be referenced to estimate the clutter correlation matrix (called secondary cells), can be reduced. Computer simulation reveals that the proposed ELD-STAP yields an improvement factor better than that provided by the combination of PDF and multibeam forming (MBF). © 2006 Wiley Periodicals, Inc. Electron Comm Jpn Pt 1, 90(1): 77–89, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ecja.20221 [ABSTRACT FROM AUTHOR]

A problem in radar is the significant degradation in system performance when the power of jamming electromagnetic signals is larger than the desired signal. To address this problem, we herein propose a blind jamming signal suppression method using an array antenna. The proposed method determines the matrix that projects onto the space orthogonal to the signal subspace of the jamming signals from the eigenvectors of the correlation matrix of the received signal composed of the jamming signal component. Then the projection transform is applied to the received signal vector containing the desired signal. By using the eigenvector corresponding to the maximum eigenvalue of the correlation matrix of the output signal vector of the transform as the weighting coefficients, the signal-to-noise ratio (SNR) is improved by maximum ratio combining of the desired signal component. Based on a performance evaluation by computer simulation, the jamming signal suppression capability exhibits improvement compared to the power inversion adaptive array of the same blind processing. © 2006 Wiley Periodicals, Inc. Electron Comm Jpn Pt 1, 89(12): 45–53, 2006; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ecja.20303 [ABSTRACT FROM AUTHOR]

In order to perform recognition of a moving target with a satellite-borne synthetic aperture radar, the use of a PN (Pseudorandom Noise) sequence is proposed. By employing two different PN sequences alternately, in-pulse modulation is performed. The pulse wave transmitted from a satellite with a specified PRF (Pulse Reception Frequency) is used for illumination of several targets and the received backscattered wave signal is demodulated with the same PN sequences as those for the transmitted pulse wave. The demodulated signal components have substantial correlation with the signal components from the target, so that pseudosignals leaking from adjacent pulses and moving clutter can be suppressed sufficiently. The signal components demodulated by the newly proposed PN sequence are aperture-synthesized in a manner similar to that used in the conventional method. The target is approximated by a point target and the difference between the front and back pulse demodulated signals of the backscatter from the target is subjected to the wavelet transform. In this way, the recognition of stationary and moving targets and identification of the radial speed of moving targets are possible. © 2006 Wiley Periodicals, Inc. Electron Comm Jpn Pt 1, 89(11): 12–23, 2006; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ecja.20290 [ABSTRACT FROM AUTHOR]

MUSIC superresolution algorithm can estimate the DOAs (directions of arrival) of multiple waves closing less than the beam width. However, the MUSIC algorithm is usually applied to a DBF (digital beam forming) array antenna, and it was difficult to apply the method to scanning beam radar, which has simpler structure and lower cost than DBF radar. This paper proposes a MUSIC DOA estimation algorithm intended to improve DOA estimation performance by separating mixed signals in a scanning beam radar. In this paper, we assume a scanning beam radar transmitting and receiving FMCW modulated waves, which are often used for modulation. The principle of the proposed method is described. The accuracy and resolution of DOA estimation by the proposed estimation method are evaluated by computer simulation, and it is verified that a resolution 5 times as great as that of the conventional method can be achieved. © 2006 Wiley Periodicals, Inc. Electron Comm Jpn Pt 1, 89(10): 24–33, 2006; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ecja.20289 [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]

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]

We explain a tracking method that uses a linear filter to estimate the true values of the position and the velocity with the target position as the radar observation. One rep- resentative example is a Kalman filter for three-dimen- sional space. The α-β filter with its easily analyzed performance is widely used in one-dimensional space. In a tracking method, the tracking precision must be evaluated when sufficient time has elapsed since the initial calculation, that is, in the steady state. The equation for calculating the variance of the errors in the predicted position in the steady state has been reported for radar observations of a constant-velocity linear motion target by an α-β filter. In addition, a Kalman filter can obtain the variance of the errors in the predicted position in the steady state by the Riccatti equation. In this case, however, a premise is the presence of drive noise that indicates the ambiguity of the motion model. There is no equation for calculating the variance of the errors in the predicted position in the steady state for the radar observations of a constant-velocity linear motion target. In this paper, we present an equation for calculating the covariance matrix of the prediction errors in the steady state of the position and velocity for the radar observations of the constant-velocity linear motion target in a 3D spatial linear filter. The results calculated in this paper present an extension of a conventional α-β filter. [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]

In a multiple target tracking system combining several radars, the errors in the radar observation coordinates and in the radar position due to alignment of each radar significantly affect the tracking performance. In this paper it is assumed that the former error is negligible. The difference in the position of an aircraft observed simultaneously by the radars in question is linearly approximated. A method is proposed to estimate the bias error of the relative position in several three-dimensional radars by means of a Kalman filter. When several radars are positioned far away, the reference direction and the absolute horizontal plane of the coordinate axis in reference to each radar are inclined due to the curvature of the earth, so that the bias error estimation accuracy is degraded. The slope of the coordinate axis due to the curvature of the earth is specifically corrected for estimation of the bias error of the relative radar position. Also, by means of simulation, the method is compared with that in which the sea surface altitude of an aircraft is calculated from the observed values (range and elevation angle) and the effect of the inclination of the coordinated axis is corrected. It is shown that the estimation accuracy is improved by 3.7 m for a radar range of 10 km and 19.5 m for 30 km. © 2004 Wiley Periodicals, Inc. Electron Comm Jpn Pt 1, 87(9): 64–74, 2004; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ecja.10159 [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]

As radiating elements for a phased array consisting of radiating elements placed along a straight line, a quasi-Yagi antenna that has a reflector behind the dipole and a parasitic element in front is used. The length of the parasitic elements and the distance between the parasitic element and the dipole are optimized by the genetic algorithm in such a way that the gain deterioration due to beam scanning is the minimum. Further, the quasi-Yagi antenna is applied in the array antenna for direction-of-arrival estimation using such subarrays as ESPRIT. The parameters optimizing the direction-of-arrival estimation accuracy are derived by the genetic algorithm. The array antenna with quasi-Yagi antenna optimized by the genetic algorithm can significantly improve the beam scanning characteristics and improve the accuracy and resolution when used for direction-of-arrival estimation by ESPRIT. This is confirmed by computer simulation and test evaluation. © 2003 Wiley Periodicals, Inc. Electron Comm Jpn Pt 1, 87(3): 39–49, 2004; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ecja.10158 [ABSTRACT FROM AUTHOR]

The α–β filter estimates the true values of the position and velocity of the target from the observed target position. If the driving noise indicating the ambiguity of the target motion differs, then various different α–β filters can be derived from a Kalman filter that uses a constant-velocity linear motion model. On the other hand, the MV filter is an α–β filter that minimizes the variations of the steady error of the predicted value of the target position for a target in constant-velocity linear motion, under the condition that the steady tracking error for the target with constant acceleration is constant. This MV filter cannot be derived from the Kalman filter. Note that there are methods of increasing the sampling rate and of improving observation accuracy for improvement of tracking capability. However, when multiple targets are tracked at the same time, the electromagnetic illumination time per target is necessarily reduced. In this paper, the tracking capability of the above α–β filter with constant gains is evaluated in terms of the tracking accuracy for a target in constant-velocity linear motion under the condition that the steady tracking error for a target in constant-acceleration motion is constant. It is found advantageous to increase the sample rate rather than to improve the observation accuracy if the electromagnetic illumination time is constant. © 2003 Wiley Periodicals, Inc. Electron Comm Jpn Pt 1, 86(10): 10–20, 2003; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ecja.10113 [ABSTRACT FROM AUTHOR]

Sea ice clutter was measured using a millimeter wave radar. To determine the sea ice clutter amplitude, we introduce the Akaike Information Criterion (AIC). It is found that the sea ice clutter amplitude obeys the log-Weibull distribution which was newly proposed by us for both all data and data within the beam width of an antenna. To suppress such clutter, we have applied the log-Weibull/CFAR procedure to the observed data. It is shown that radar target embedded in sea ice clutter is detected. © 2003 Wiley Periodicals, Inc. Electron Comm Jpn Pt 1, 86(9): 9–16, 2003; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ecja.10101 [ABSTRACT FROM AUTHOR]

There have been different methods to suppress radar clutter depending on its amplitude distribution. This paper describes a two-dimensional weighted moving average filter and a two-dimensional moving filter for clutter having a k-distribution, both with weighted samples of a reflected signal from an illuminated surface. A genetic algorithm is used for the weighting, since its optimum value is obtained in a relatively short time. To simulate various field conditions, two kinds of data were used: data of reflected waves from objects in the green belt of an airport, and composite data of reflected waves from objects in clear weather (no clutter) and reflected waves from a field on a rainy day. The two-dimensional weighted moving average improves the signal-to-clutter ratio significantly: by 0.5 to 2.3 dB compared with a two-dimensional moving average without weighting; and by 0.9 to 3.7 dB compared with no averaging treatment. © 2003 Wiley Periodicals, Inc. Electron Comm Jpn Pt 1, 86(8): 58–67, 2003; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ecja.1172 [ABSTRACT FROM AUTHOR]

Inverse Synthetic Aperture Radar (ISAR) is a well-known technique for acquiring images of a moving target by using the synthetic aperture method. This radar improves the angle resolution based on the Doppler effect accompanying the relative motion with respect to the target, estimates the target motion from the echoes, and must compensate for the range migration during the observation and the fluctuations in the Doppler frequency. However, the problem faced when multiple targets, such as a formation of airplanes, are simultaneously observed is that the echoes of targets having slightly different motions interfere and degrade the estimation of the motion and the image resolution. Here, we propose an algorithm capable of separating the echo of each target, estimating the motion of each target, and compensating for the unwanted motion of each target based on the motion estimates even when multiple targets are simultaneously observed by utilizing the two-dimensional discrete Fourier transform. We conducted computer simulations and demonstrated the ability to generate the images from two target echoes and confirmed the effectiveness of the proposed method. © 2003 Wiley Periodicals, Inc. Electron Comm Jpn Pt 1, 86(7): 1–10, 2003; Published online in Wiley InterScience (www.interscience.wiley. com). DOI 10.1002/ecja.10090 [ABSTRACT FROM AUTHOR]

The phased array antenna can instantaneously direct a radar beam into a desired direction without mechanically moving the antenna. Anticipating an application to a phased array radar, adaptive control of the sampling interval for the tracking object is considered. Reducing the sampling interval for a target with high maneuverability prevents degradation of the tracking accuracy. For a target in straight-line motion, the sampling interval is increased so that the number of observations is reduced for an efficient operation of radar resources. In this paper, the M3 (Multiple Maneuver Model) filter is used as one of the tracking algorithms based on the multiple motion model, and a control scheme is proposed with a sampling interval based on the tracking error covariance matrix. By means of simulation, the tracking performance is compared with the case where the sampling interval is fixed. As a result, the tracking accuracy is improved by 15% during a maneuvering motion without increasing radar resources. © 2002 Wiley Periodicals, Inc. Electron Comm Jpn Pt 1, 85(10): 44–54, 2002; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ecja.1130 [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]

Joint search data technology by geographically separated radars has drawn attention. In this technique, the observation data of several radars placed in a geographically wide area are collected for tracking processing. A characteristic of this technique is the reduction of the cross range error that is a problem in single radar. Hence, improved tracking capability is expected. However, for realization it is necessary to take into account the deviations of the coordinate axes between the state variable vector of the target and the observation vector for the observation model of the tracking filter. In this paper, the difference in the coordinate axes is studied. JPDA (Joint Probabilistic Data Association), a multitarget tracking algorithm making use of the observation information of radars placed at several locations, is studied. In order to evaluate the effectiveness of the present technique, computer simulation is carried out. It is found that the tracking performance is improved over the conventional method of using only one radar. © 2002 Scripta Technica, Electron Comm Jpn Pt 1, 85(5): 34–47, 2002 [ABSTRACT FROM AUTHOR]

The present direction-finding equipment has insufficient accuracy and resolution, so that accurate evaluation of the direction of arrival and the position cannot be carried out. Although each radar signal has a narrow bandwidth, the entire bandwidth for various radars used exceeds four octaves. In order to search all of these, equipment for each bandwidth is used at present so that the entire frequency range is covered. However, it is more effective from the standpoint of equipment size and cost to cover the entire spectrum with a single kind of equipment. It is desirable to realize high-accuracy high-resolution direction finding over a broad bandwidth. In realization, broadband antennas are used, and high-gain antennas are also needed in a low-S/N environment. Since the dimensions of high-gain and broadband antennas are large, an array configuration with a half-wave spacing may not physically be possible. Thus, the array spacing becomes more than a half-wavelength. If the range of direction estimation is -90 to +90°, the phase difference exceeds 360° so that ambiguity occurs. As a method to resolve this ambiguity problem, a nonuniformly spaced array is effective. In this paper, the array conditions for a nonuniformly spaced array are determined in the case of one arriving wave. Next, the case of several arriving waves is discussed and the array conditions for several arriving waves are derived. © 2001 Scripta Technica, Electron Comm Jpn Pt 1, 85(3): 1–8, 2002 [ABSTRACT FROM AUTHOR]

An important requirement for tracking filters is the ability to maintain tracking under dense environments. The JPDA (Joint Probabilistic Data Association) using the positional measurements is conceivable. However, if the number of observation data to be processed simultaneously is increased, incorrect correlation takes place and the tracking performance deteriorates. In this paper, in order to improve the problem of incorrect correlation in the JPDA, the JPDA using the range rate measurement is proposed. Through several simulations, the validity of this method has been confirmed with respect to tracking success rates and tracking accuracies. © 2001 Scripta Technica, Electron Comm Jpn Pt 1, 85(3): 19–29, 2002 [ABSTRACT FROM AUTHOR]

A time sidelobe (TSL) reduction technique in binary code pulse compression is proposed. A code with a small peak sidelobe (PSL) is searched. Many codes have been obtained that have much smaller PSL than the conventional binary code with the compression ratio in the range from 5 to 16. Simulations are carried out for some of these codes and the optimum IF filter bandwidth is evaluated. It is confirmed that the waveform is stable for Doppler and the PSL value is kept small. © 2001 Scripta Technica, Electron Comm Jpn Pt 1, 84(12): 52–60, 2001 [ABSTRACT FROM AUTHOR]

With the practical development of automobile collision avoidance radars, there is a need for a radio wave absorber in the 60-GHz band with excellent environmental robustness, to be used in covering guard rails and similar objects to prevent false operation of the radar. This study describes epoxy-modified urethane rubber with excellent environmental robustness and attempts to realize a wave absorber in the 60-GHz band using this material. The reflection attenuation and the complex relative dielectric constant are measured by the free space method. It is found that the fabricated material can realize a high reflection attenuation of approximately 16 to 46 dB at the maximum for incidence angles of 5 to 50°, thus verifying experimentally that the wave absorber can be realized in the 60-GHz band using the proposed material. © 2000 Scripta Technica, Electron Comm Jpn Pt 1, 84(4): 32–38, 2001 [ABSTRACT FROM AUTHOR]

Tracking of highly maneuvering targets in a cluttered environment is a difficult problem. It has been previously reported that the target motion model defined as superposition of multiple constant acceleration vectors on a constant velocity straight line motion model using an automatic optimization of the target correlation gate in response to the target maneuvering based on the Multiple Maneuver Model Probabilistic Data Association (M3PDA) proved to be an effective method for severely cluttered conditions. On the other hand, due to the recent developments in the area of sensor technologies it became possible to use highly accurate angle sensors (such as infrared sensors) for target tracking. It is expected that the use of such sensors will greatly improve the tracking performance of radar systems. In this study, we propose an algorithm based on an expanded M3PDA formed by the six-dimensional state vector consisting of the target position and velocity components using three-dimensional observation data from the radar and two-dimensional observation data from angle sensors. We also demonstrate the advantages of the proposed method compared to conventional ones using a simulation of tracking of one maneuvering target. © 2000 Scripta Technica, Electron Comm Jpn Pt 1, 84(2): 99–109, 2001 [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]

This paper proposes a method that calculates the approximate cross-correlation between two discrete sequences with high speed. The method is evaluated by applying the idea to range compression in the SAR image reconstruction process. When the sequences are very long, tremendous computation time is required, even if the cross-correlation function is calculated through the frequency domain. This is a problem when real-time processing is required. In such a case, however, it is often more important to determine the approximate value with high speed than to determine precisely the value of the cross-correlation function. From this viewpoint, this paper proposes a method in which the wavelet transform is applied to the two sequences, and the correlation function for the obtained short sequences is defined as an approximation to the original correlation function. By forming a hierarchy of wavelet functions, a hierarchy of approximate values is formed according to their accuracy. It is also possible, by successively improving the accuracy starting from a coarse approximation, to finally obtain the accurate value. The algorithm for such an idea is presented. Then, by applying the idea to the SAR range compression, the proposed method is experimentally evaluated. © 2000 Scripta Technica, Electron Comm Jpn Pt 1, 83(6): 10–20, 2000 [ABSTRACT FROM AUTHOR]

A simultaneous transmission and reception system is studied in which transmission and reception are always possible without preventing the functions of the receiver near the transmitter, and a method is proposed for eliminating the interference wave as an important technical challenge in this system. The proposed system is an interference suppression method using a nonlinear circuit. Interference suppression by a nonlinear circuit is assigned to each element of the array antenna. After the interference wave is eliminated in the nonlinear circuit, the intermodulation components due to nonlinearity and the residual interference are suppressed by spatial averaging so that only the desired wave is extracted. In this method, no correlation is used for discrimination of the interference and the desired wave, nor are complex calculations required. Therefore, interference elimination is accomplished instantaneously. Also, in principle no phase adjustment is needed in the interference elimination. Therefore, the method is extremely effective for a broadband FM noise interference wave. The improvement characteristics of the interference elimination in this system are studied theoretically. Experiments are carried out for the conventional echo canceller system and the proposed system. The superiority of the interference elimination characteristics of the proposed system is described qualitatively. © 1999 Scripta Technica, Electron Comm Jpn Pt 1, 83(3): 13–24, 2000 [ABSTRACT FROM AUTHOR]

Inverse synthetic aperture radar is an imaging radar in which the radio image is derived by utilizing the Doppler effect produced by change of the target aspect. When the target is accelerated, the resolution in this radar is degraded due to the frequency modulation of the received signal. In order to avoid this, the phase of the received signal must be compensated. In general, however, the motion of the target cannot be predicted, and the amount of correction must be determined by a certain evaluation index derived from the received signal. Such a method, where the amount of correction is derived from the received signal and the resolution is improved, is generally called autofocus. In conventional synthetic aperture radar, there is a method in which the peak luminosity of the image is used as the evaluation index in compensating the frequency modulation of the received signal produced by vibration of the platform. In this article, it is proposed to use the entropy of the image, and the result is compared to the conventional method. It is shown by a computer simulation that the probability of compensation failure can be reduced to the same value or decreased to approximately 1/100 of the conventional method. In other words, it is shown that the entropy, rather than the peak luminosity, of the image should be used as the evaluation index for the autofocus. © 1999 Scripta Technica, Electron Comm Jpn Pt 1, 83(2): 97–106, 2000 [ABSTRACT FROM AUTHOR]

In order to realize an azimuth resolving imaging method which is adequate for automotive radars, a novel holographic imaging method using two antenna arrays for both the transmitting and the receiving antennas is proposed and investigated. It is analytically shown that high-quality images can be obtained at high speed by using antenna arrays with a small number of elements placed at large intervals with this method. We also show the validity and advantage of the imaging principle with computer simulations. © 1999 Scripta Technica, Electron Comm Jpn Pt 1, 82(12): 1–9, 1999 [ABSTRACT FROM AUTHOR]

The inverse synthetic aperture radar (ISAR) uses the Doppler effect caused by the rotation and translation of the target to improve the cross-range resolution. Usually, these two motions have not been distinguished and have been processed in one dimension in the cross-range compression of the ISAR. In this paper, it is shown that Doppler components caused by these two motions can be separated, so that two-dimensional cross-range compression by elevation compression due to rotation and azimuth compression due to translation is possible for a target such as a boat that moves slowly in translation with rolling. Further, the boundary condition is derived that enables image reconstruction from the Doppler effect caused by the two motions, rotational and translational. For radar parameters such as the transmission wavelength λ, the resolution Δ of the ISAR image, and the range D to be visualized, two-dimensional cross-range compression becomes possible if the relationships $$\alpha > { \lambda \over {4 \pi \Delta}}, \ \ \ \nu \leq { {\lambda R_0} \over {2 T_0 D }}$$ hold for target parameters such as the maximum rolling angle α, rolling period T0, translation speed v, and relative distance R0 from the radar. By computer simulation, an image reconstruction example using the two-dimensional cross-range compression algorithm is presented. © 1999 Scripta Technica, Electron Comm Jpn Pt 1, 82(9): 10–18, 1999 [ABSTRACT FROM AUTHOR]

In this paper a stepped-FM pulse radar for vehicular collision avoidance is proposed, providing anti-interference capability and high range resolution. Wide-band VCO devices have in general a linearity error over the bandwidth, which is critical issue for high-range-resolution radar. We also suggest a compensation scheme based on the LMS method for the VCO linearity error. © 1999 Scripta Technica, Electron Comm Jpn Pt 1, 82(6): 1–7, 1999 [ABSTRACT FROM AUTHOR]

In a multiple sidelobe canceler (MSLC) designed to suppress several interference waves incident on the radar, the number of auxiliary antennas equal to or greater than the number of interference waves is needed. On the other hand, in the TDL (Tapped Delay Line)-MSLC using delay lines, only one auxiliary antenna is needed, and hence this system is economical, with the further advantage that the convergence time for the adaptive weights does not depend on the directions of incidence of the interference waves. In this paper, for the case where two interference waves are incident on a TDL-MSLC with one delay line, the relation between the convergence time of the adaptive weights and the product of the time delay in the delay line and the frequency difference of two interference waves is investigated. Furthermore, a TDL-MSLC using Gram-Schmidt processing is proposed. It is confirmed by simulations and hardware experiments that this configuration can reduce the effect of the frequency difference of the two interference waves on the convergence time of the adaptive weights, so that the convergence of the adaptive weights can be made faster. © 1999 Scripta Technica, Electron Comm Jpn Pt 1, 82(5): 24–33, 1999 [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 a new pulse compression code and presents a numerical analysis and simulation results. The proposed code has the features that both the sidelobe level and the sidelobe power are very small compared to the Barker code and other polyphase codes at small compression ratios. Consequently, it is useful where the short-range search is required, as in millimeter wave radar. © 1998 Scripta Technica, Electron Comm Jpn Pt 1, 82(1): 74–86, 1999 [ABSTRACT FROM AUTHOR]

The quasi-optical antenna-mixer system transforms a radio frequency (RF) signal into an intermediate-frequency signal as soon as the system receives the RF and local oscillator's (LO) signals spatially. We propose a novel beam scanning system with a quasi-optical antenna-mixer array. The traditional phased array needs RF circuits such as phase shifters for beam scanning, but our system can steer the beam without them. RF arrival direction is steered by changing the LO incidence angle and/or frequency. Therefore, not only are losses reduced in RF circuits, but the system is easily designed because of its simple structure. First, we describe the principle of beam scanning with concrete model. Next, a fabricated model working in the microwave band is tested to verify beam-scanning performance. The experimental results agree with the theory very well and our proposal is confirmed. © 1998 Scripta Technica, Electron Comm Jpn Pt 1, 81(12): 1–8, 1998 [ABSTRACT FROM AUTHOR]

A low-profile Yagi-Uda antenna composed of a driven inverted-F antenna and two parasitic inverted-L antennas, which is used for the antennas of SSR (secondary surveillance radar) and mounted on an airplane, is proposed. The wire antenna is analyzed by the moment method, while the printed antenna is analyzed by the FD-TD method. The wire-type antenna has Gd/Gr = 18.1 dB, Gd = 8.3 dBi, bandwidth defined by VSWR ≤ 2 is 9.6%, with dimensions of 0.08λ0 (height) × 0.51λ0 (length), where Gd and Gr denote the directive gain of director orientation and reflector orientation, respectively. It is also shown that the characteristics of a print-type antenna fabricated on a dielectric substrate (εt = 1.7) are similar to those of a wire-type antenna. © 1998 Scripta Technica, Electron Comm Jpn Pt 1, 81(12): 28–36, 1998 [ABSTRACT FROM AUTHOR]

This paper discusses new pulse compression codes in which the modulation phase is monotonoically increased or decreased and the phase difference between the neighboring modulated codes is compressed to polyphase. In the proposed coding system, the sidelobe is small when the compression ratio is relatively low. Even in the high Doppler frequency region in which the pulse shape of the 13-bit Barker codes is largely deformed, the shape of the compressed pulse is stable and the sidelobe is always smaller than in the 13-bit Barker code. © 1998 Scripta Technica, Electron Comm Jpn Pt 1, 81(10): 41–49, 1998 [ABSTRACT FROM AUTHOR]

Cartesian coordinates are discussed in the finding of target position from radar signals. The Cartesian coordinates are used for the tracking algorithm of radar signal under the cluttering condition by PDA (Probabilistic Data Association) method. The possibility of transforming some dimensions of PDA using one Cartesian coordinate to the other Cartesian coordinate has not as yet been reported. Dimensions are the estimated values of position, velocity, and some other variables of movement of the target, and the covariance matrix as the evaluation of their errors in estimation. The Cartesian coordinate system which takes the true north as the first coordinate, or the one which takes the vector toward the target position as the first coordinate have been proposed in order to find the coordinate system of the best tracking ability. In this paper, it is proved that PDA of one Cartesian coordinate can be transformed to the other by the mathematical reduction method of sampling time, and also the range of target estimation and correlation probabilities between target and observed vector is the same under any Cartesian coordinate. Then, it is not necessary to make mutual comparisons of performance and evaluation of PDA in different Cartesian coordinates. Furthermore, transformation formulas are derived for dimensions of target movement, covariance matrices of errors, and gain matrices in these coordinates. © 1998 Scripta Technica, Electron Comm Jpn Pt 1, 81(9): 47–57, 1998 [ABSTRACT FROM AUTHOR]

An adaptive moving target indicator, AMTI, is a filter that automatically suppresses the moving clutter contained in a received radar signal. In AMTI based on an adaptive filter, the amplitude and the phase of the filter weight are simultaneously adjusted and this enhances the effect of the adaptation error. For this problem, this paper proposes weight-magnitude-constrained AMTI, where only the phase of the filter weight is adjusted in real-time as a parameter in order to improve clutter suppression performance. We then consider an environment in which the power of the desired signal is not negligible compared to the clutter power. In order to reduce the estimation error for the clutter center frequency, weight-magnitude-constrained AMTI introducing a median filter is proposed. The effectiveness of this approach is demonstrated by computer simulation. A situation is considered, where the received noise is modulated by a moving target indicator (MTI) that suppresses the static clutter in AMTI pre-processing; an algorithm for clutter center frequency estimation is presented for which the estimation accuracy is guaranteed. © 1998 Scripta Technica. Electron Comm Jpn Pt 1, 81(5): 41–50, 1998 [ABSTRACT FROM AUTHOR]

In the conventional target signal detection method using noncoherent integration, the integration is carried out using all of the output signals from the envelope detector. Therefore, the fluctuations in intensity of the output signals from the envelope detector form a substantial component of the pulse signals received. Although desirable, no integration is performed for the reflected signal from fluctuating targets. In the conventional method, if high intensity (high SN ratio) pulsed signals are received, even the low intensity (low SN ratio) signals received are unnecessarily used in the integration. Therefore, the average SN ratio of the received signals used in the noncoherent integration is degraded so that there is a reduced possibility for improvement in target detection probability. In this paper, in order to solve this problem, a threshold is used before noncoherent integration, so that only output from the envelope detector with an intensity exceeding the threshold is used in noncoherent integration. When, in this method, the envelope detection is linear and the model for the fluctuation of the target reflection signal is Swerling Case 2, the target detection probability is found to be improved over the target signal detection method using conventional noncoherent integration. © 1998 Scripta Technica. Electron Comm Jpn Pt 1, 81(3): 11–21, 1998 [ABSTRACT FROM AUTHOR]

This paper discusses preprocessing in a tracking filter to estimate the parameters of target motion, such as position and velocity. We use orthogonal coordinates, with the target position as the radar observation data. Typical examples of tracking filters are the Kalman filter and the α-β filter. In a Kalman filter, although the tracking accuracy is high, the computation load is heavy. Consequently, a simplified version of the Kalman filter, the α-β filter, is used. The α-β filter has problems in tracking accuracy, although the computation load is low. Another difficulty with the α-β filter concerns its application to radar tracking when the observation noise varies with sampling time or when the sampling interval is non-uniform. In such cases, the Kalman filter must be used to achieve adequate tracking performance. This paper proposes a method in which the tracking filter consists of a Kalman filter with preliminary integration of multiple observation data, obtained at different sampling times, into a single observed datum. It is shown that the proposed tracking filter can be approximated by a tracking filter in which a Kalman filter is used for each sample. The tracking accuracy and the computation time are evaluated by computer simulation. © 1998 Scripta Technica. Electron Comm Jpn Pt 1, 81(2): 33–44, 1998 [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]

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]

Using the target location and the target range rate as radar observation data, a tracking filter based on the extended Kalman filter is discussed. For this tracking filter, the Cartesian coordinate will be used, with the north as one axis, the one with the object position vector as one axis, or the one with the target velocity vector as one axis. However, it has not been reported if the computed variables (estimate values of the motion parameters of the object, such as location and velocity, and the error covariance matrix as the evaluation value of the estimation error) in a tracking filter using a specific Cartesian coordinate can be converted to the parameters in the tracking filter using another Cartesian coordinate. Because it remains to discover whether conversion is possible, research still continues to find a Cartesian coordinate that has good tracking performance. It is proven here, using a mathematical induction method in regard to the sampling time, that no matter which Cartesian coordinate is used in the forementioned tracking filter, its computational parameters can be converted to those of the tracking filter using an arbitrary Cartesian coordinate. As a result, comparison and evaluation of the tracking filter performance are unnecessary when different Cartesian coordinates are used. In addition, the equations are derived for conversion of the target motion parameters, covariance matrix, and gain matrix between these tracking filters. © 1997 Scripta Technica, Inc. Electron Comm Jpn Pt 1, 80 (4): 51–61, 1996 [ABSTRACT FROM AUTHOR]

This paper discusses the tracking filter that estimates the true values of the states of the target such as position and velocity by Cartesian coordinates with the target position used as the observation value of the radar. A typical example is a Kalman filter or an α-β filter. A Kalman filter has a good tracking accuracy but a heavy computational load, whereas the α-β filter has a light computational load and is practical, although it has a problem in tracking accuracy. If the α-β filter with a light computational load has a tracking accuracy similar to the one for a Kalman filter, this filter becomes even more practical. Therefore, in this paper, the conditions are discussed where the α-β filter can approximate a Kalman filter. In this paper, the radar coordinates, where the target position vector is one axis, is used for calculation of the smoothing values (estimated values of the states for target motion at the present sampling time). It is proven that the α-β filter can approximate a Kalman filter if the angular velocity of the target and the rotation of the radar coordinates with the coordinate axis rotated with the target motion are infinitesimal and the process noise (a parameter indicating the ambiguity of the target motion model) is independent and the same between the coordinates. This result indicates that the α-β filter can approximate a Kalman filter if the target is at a low speed, the target range is large, or the target is proceeding toward the radar in a straight line. © 1997 Scripta Technica, Inc. Electron Comm Jpn Pt 1, 80(3): 67–77, 1997 [ABSTRACT FROM AUTHOR]

The necessity for a multiple sidelobe canceller (MSLC) that suppresses several interference waves incident corresponding to complex radio environment is increasing. In the MSLC, there exists interference incident directions for which the suppression capability is degraded substantially, depending on the arrangement of auxiliary antennas. In this paper, the problem of degradation of the suppression capability of several interference waves depending on the direction of incidence is studied in the case where the two interference waves are suppressed by the MSLC with two auxiliary antennas. The relationship of the suppression capability to the receiving phase difference between the auxiliary antennas for each interference wave is discussed. Further, based on the results, an arrangement method of the auxiliary antennas minimizing the suppression capability degradation is presented. It is shown by numerical calculations that the suppression capability degradation can be improved by means of the configuration of the auxiliary antennas obtained by this method. © 1997 Scripta Technica, Inc. Electron Comm Jpn Pt 1, 80 (1): 100–111, 1997 [ABSTRACT FROM AUTHOR]

The fundamental characteristics of signals reflected from objects buried in the ground were measured with a CW radar system. In this measurement system, the reflected signals from buried objects are detected synchronously so that the measurement of amplitude and phase of the reflected signals is possible. From the results of measurement, it was found that the reflected power from buried objects is almost proportional to the minus fourth power of the equivalent distance and that the phase variation agrees almost with the result anticipated from Snell's law under a plane wave approximation. From these observations, it is found that the measurement of the reflected signals from buried objects is possible with a CW radar system, and that underground remote sensing also is possible. [ABSTRACT FROM AUTHOR]