Seiji Mano

An improved thinning method for density tapering of planar array antennas

A thinning method is presented to realize the desired aperture distribution in a planar array antenna with elements fixed on an array lattice. In this method elements to be excited are determined by quantizing cumulative weights which are calculated from the desired aperture distribution. At first, this method is applied to density tapering on orthogonal axes of a planar array. Radiation patterns of the planar array determined by this method are compared with those by the desired amplitude distribution, and the results show good coincidence. Next, this method is extended to density tapering on four axes, that is, orthogonal and diagonal axes of a planar array. Moreover, this method is applied to density tapering with multi-amplitude level elements in order to enhance directive gain of thinned array. Lastly, a rectangular planar array was fabricated, and its radiation patterns were measured. Measured results were in good coincidence with calculated ones, and the usefulness of this method was verified.

Kalman Filter and ?-? filters for radar tracking

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.

An adaptive moving target indicator using median filters

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.

Null points adjusting method providing low sidelobe patterns in conformal array antennas

A novel pattern synthesis method (null points adjusting method) for providing a low sidelobe pattern in a conformal array antenna is presented. This method is based on the principle that the level of sidelobe between null points can be determined by controlling their positions. The usefulness of this method is verified by synthesizing a low sidelobe pattern of a hemispherical array antenna. Using the proposed method, even if in a large-scale or complexly shaped conformal array antenna which cannot be characterized by a single curve, the optimum excitation amplitude and phase of elements can be easily determined.<<ETX>>

A CARTESIAN COORDINATE CONVERSION ALGORITHM FOR RADAR TRACKING WITH RANGE RATE MEASUREMENT

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.

Multiple target tracking using adaptive multiple maneuver model joint probabilistic data association

The M3JPDA (multiple maneuver model joint probabilistic data association) system is a multiple target tracking algorithm that can cope with maneuvering targets. The system includes a straight-line constant-velocity movement model as well as multiple accelerated movement models, to be used in parallel, where the models are utilized according to their reliability. It sometimes happens in M3JPDA, however, that when the targets move in straight lines with constant velocities, the multiple tracking performance is worse than in the conventional JPDA using the straight-line constant-velocity movement model. This paper proposes adaptive M3JPDA to remedy this point. In this method, the target acceleration is estimated and is smoothed. If the resulting value is large, the conventional M3JPDA is used. If the value is small, the reliability of each motion model is calculated and the choice of models is based on the difference between the reliabilities of the conventional M3JPDA accelerated motion models and the straight-line constant-velocity motion model. Using the proposed algorithm, the reliability of the straight-line constant-velocity motion model is improved when the target executes straight-line constant-velocity motion. As a result of evaluation by simulation, it is seen that the proposed algorithm is capable of tracking two crossing targets in straight-line constant-velocity motions, as well as two targets rapidly maneuvering with 7 g accelerations, in contrast to JPDA based on the straight-line constant-velocity motion model and M3JPDA.

A multiple sidelobe canceler using tapped delay line with Gram‐Schmidt processing

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.

A multiple sidelobe canceller using tapped delay line with Gram-Schmidt processing

A multiple sidelobe canceller (MSLC) that can suppress multiple interferences received by a radar needs more auxiliary antennas than the number of interferences. The use of several auxiliary antennas increases the cost of an MSLC. An MSLC using tapped delay line (TDL type MSLC) that has only one auxiliary antenna reduces cost and has an advantage that the convergence time does not depend on incident directions of interferences. In this paper, we show the relation between the convergence time and the product of frequency difference of interferences and time delay, and propose a TDL type MSLC with Gram-Schmidt processing. Simulation results show that the effect of frequency difference and time delay on convergence time is reduced.