The design, manufacture, and test results are presented for a 90polarization-rotating Van Atta array reflector with suppressed scattered field for the 1.27-GHz band. The reflector consists of 48 element antennas, half for horizontal polarization and half for vertical polarization. It receives a horizontally or vertically polarized wave and retransmits a vertically or horizontally polarized wave, respectively. The measured cross-polarized radar cross section of the reflector was 15.8 dBm2 on average, which agreed well with a theoretical prediction. Although the suppression of the scattered field was limited to about -20 dB relative to the retransmitted field, we could suppress more the scattered field by accurate positioning and careful characteristics adjustment of element antennas. Theoretical calculations showed that total phase errors of the element antennas including positioning errors and impedance characteristics errors have to be within 7.5to suppress the scattered field by less than -30 dB.

Imaging techniques for robots are important and meaningful in the near future. Pulse radar systems have a great potential for shape estimation and locationing of targets. They have an advantage that they can be used even in critical situations where optical techniques cannot be used. It is thus required to develop high-resolution imaging algorithms for pulse radar systems. High-resolution imaging algorithms utilize the carrier phase of received signals. However, their estimation accuracy suffers degradation due to phase rotation of the received signal because the phase depends on the shape of the target. In this paper, we propose a phase compensation algorithm for high-resolution pulse radar systems. The proposed algorithm works well with SEABED algorithm, which is a non-parametric algorithm of estimating target shapes based on a reversible transform. The theory is presented first and numerical simulation results follow. We show the estimation accuracy is remarkably improved without sacrificing the resolution using the proposed algorithm.

Identification of targets using sequential high range-resolution (HRR) radar signatures is studied. Classifiers are designed by using hidden Markov models (HMMs) to characterize the sequential information in multi-aspect HRR signatures. The higher-order moments together with the target dimension and the number of dominant wavefronts are used as features of the transient HRR waveforms. Classification results are presented for the ten-target MSTAR data set. The example results show that good classification performance and robustness are obtained, although the target features used here are very simple and compact compared with the complex HRR signatures.

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

Matching Pursuits (MP), a technique for signal decomposition using a dictionary of functions, is applied to ground penetrating radar (GPR) signals in order to remove noise and clutter included in the signals and to extract target responses. A wave-based dictionary composed of wavefronts and resonances is employed. Noise reduction performance and the removal of ground-surface reflection are evaluated through numerical simulations. The results show that the MP approach performs well and offers an effective method for feature extraction from GPR signals.

Radars utilizing ultra-wide-band (UWB) pulses are attractive as an environment measurement method for various applications including household robots. Suitable filtering is essential for accurate ranging, which requires an accurate waveform estimation. This paper presents a high-resolution algorithm of estimating target location and scattered waveforms, whose accuracies are interdependent. The technique relies on iterative improvements of estimated waveforms. Description of the algorithm is followed by statistical simulation examples. The performance of the algorithm is contrasted with conventional ones and statistical bounds. Results indicate that our proposed algorithm has a remarkable performance, which is close to the theoretical limit. Next, we clarify the problem of applying HCT to multiple targets. HCT for multiple targets can not be used as an estimated waveform because of interference waves from other targets. We propose an interference suppression algorithm based on a neural network, and show an application example of the algorithm.

Modern spaceborne precision radar altimeters transmit radio signals of a spectrum bandwidth up to 300 MHz, but the bandwidth should be still increased for precise estimation of the roughness of the sea surface. In this research, the influence of the ionosphere on wideband radar signals is investigated and then it is shown that the signals are strongly influenced by the dispersive distortions in the atmosphere of the Earth even in Ku-band. Finally, the allowable bandwidth of a space borne precision radar altimeter signals is estimated, at which we could ignore the presence of these distortions.

Environment measurement is an important issue for various applications including household robots. Pulse radars are promising candidates in a near future. Estimating target shapes using waveform data, which we obtain by scanning an omni-directional antenna, is known as one of ill-posed inverse problems. Parametric methods such as Model-fitting method have problems concerning calculation time and stability. We propose a non-parametric algorithm for high-resolution estimation of target shapes in order to solve the problems of parametric algorithms.

This paper presents an imaging technique using the MUSIC algorithm to localize cylindrical reflectors in cross-borehole radar arrangements. Tomographic measurement, in which a transmitting and a receiving antenna are individually moved in separate boreholes, can be considered as a combination of a transmitting and a receiving array. A decorrelation technique with the transmitting array, which has been proposed for imaging point reflectors, is applied for imaging cylindrical reflectors using the MUSIC algorithm. Simulated and experimental results are shown to verify the validity of this algorithm for cylindrical targets. We analyze the evaluation error caused by the increase in the radius of the cylinder.

In this letter, the concept of cross-entropy is introduced for unsupervised polarimetric synthetic aperture radar (SAR) image classification. The difference between two scatterers is decomposed into three parts, i.e., the difference of average scattering characteristic, the difference of scattering randomness and the difference of scattering matrix span. All these three parts are expressed in cross-entropy formats. The minimum cross-entropy principle is adopted to make classification decision. It works well in unsupervised terrain classification with a NASA/JPL AIRSAR image.

Range resolution for radar is determined by bandwidth. One of the various super-resolution techniques for improving resolution is bandwidth extrapolation (BWE). In this technique, a linear prediction model is fitted to the data, and the model is used to extrapolate the bandwidth. In this paper, we extend BWE, and propose a new algorithm that we call polarimetric bandwidth extrapolation (PBWE) applicable to polarimetric radar data. We show through numerical simulations that utilization of fully polarimetric information allows PBWE to improve the resolution beyond the conventional BWE method. Some results of a physical simulation experiment using a W-band polarimetric FMCW radar and corner reflectors are shown to confirm the advantage of PBWE.

A simple non-destructive depth estimation method for a crack on a metal surface has been proposed. This method is based on our finding that the electromagnetic back scattering from a narrow trough (crack model) on the ground plane causes periodical nulls (dips) as the frequency changes, and the first dip occurs when the depth of the crack becomes nearly one half of the incident wavelength. Dependencies of the crack's aperture and the incident angle have also been studied from rigorous and numerical analyses, and considered as our depth estimation parameters. A simple estimation formula for a crack depth has been derived from these studies. Test measurement has been made to check the accuracy of our estimation formula. Time domain gating process is utilized for isolating the crack scattering spectra buried in the measured frequency RCS data. Tested crack types are a narrow rectangular, a tapered, and a stair approximated crack shapes. It is found that the depth of these cracks can be measured within 3 percent error by our estimation method.

This paper describes a method for the fast evaluation of the Sommerfeld integrals for modeling a vertical dipole antenna array in a borehole. When we analyze the antenna inside a medium modeled by multiple cylindrical layers with the Method of Moment (MoM), we need a Green's function including the scattered field from the cylindrical boundaries. We focus on the calculation of Green's functions under the condition that both the detector and the source are situated in the innermost layer, since the Green's functions are used to form the impedance matrix of the antenna. Considering bounds on the location of singularities on a complex wave number plane, a fast convergent integration path where pole tracking is unnecessary is considered for numerical integration. Furthermore, as an approximation of the Sommerfeld integral, we describe an asymptotic expansion of the integrals along the branch cuts. The pole contribution of TM01 and HE11 modes are considered in the asymptotic expansion. To obtain numerical results, we use a fast convergent integration path that always proves to be accurate and efficient. The asymptotic expansion works well under specific conditions. The Sommerfeld integral values calculated with the fast evaluation method is used to model the array antenna in a borehole with the MoM. We compare the MoM data with experimental data, and we show the validity of the fast evaluation method.

For radar tracking, the α-β filter and the Kalman filter, both of which do not require large computational requirements, have been widely utilized. However these filters cannot track a maneuvering target accurately. In recent years, the IMM (Interactive Multiple Model) algorithm has been proposed. The IMM is expected to reduce tracking errors for both non-maneuvering and maneuvering target. However, the IMM requires heavy computational burden, because it utilizes multiple Kalman filters in parallel. On the other hand, the α-β filter with an acceleration term which can estimate maneuver acceleration from the past target estimated positions using the kinetic model, has been proposed. This filter is not available for tracking targets under clutter environment, since it does not calculate the covariance matrix which is needed for gate setting. In this paper, we apply the acceleration estimate to the Kalman filter, and propose the hybrid Kalman filter with a constant-velocity filter and an acceleration estimation filter, and it integrates the outputs of two filters using the normalized distance of the prediction error of each filter. The computational requirement of the proposed filter is smaller than that of the IMM since the proposed filter consists of only two Kalman based filters. The proposed method can prevent deteriorating tracking accuracy by reducing the risk of maneuver misdetection when a target maneuvers. We evaluate the performance of the proposed filter by computer simulation, and show the effectiveness of the proposed filter, comparing with the conventional Kalman filter and the two-stage Kalman filter.

A microstrip array antenna with 45-degree inclined linear polarization is proposed for automotive radars. The proposed antenna has the advantages of high aperture efficiency, low profile and ease of manufacture. The rectangular radiating elements inclined at 45 degrees to the straight microstrip line are directly connected to it at their corners in the proposed array antenna. The radiating element has a feature that radiation conductance for co-polarization is controlled widely enough to set desired amplitude distribution keeping excited mode for cross-polarization negligibly small. The feed line loss of the linear array antenna having 15 wavelengths is estimated 0.9 dB in the design taking the loss of the microstrip line into account. The performance of two types of developed antennas, for electrical and mechanical scanning radars, is presented. The fan beam subarray antenna for electrical scanning radars has an aperture efficiency of 53% with gain of 22.5 dBi at 76.5 GHz. For mechanical scanning radars, the two-stage series feeding circuit is also proposed for lower feed line loss and setting desired amplitude distribution. The pencil beam array antenna has an aperture efficiency of 39% with gain of 32.2 dBi at 76.5 GHz.

A pilot needs operational information about wind over sea as well as wave height to provide safety of hydroplane landing on water. Near-surface wind speed and direction can be obtained with an airborne microwave scatterometer, a radar designed for measuring the scatter characteristics of a surface. Mostly narrow-beam antennas are applied for such wind measurement. Unfortunately, a microwave narrow-beam antenna has considerable size that hampers its placement on flying apparatus. In this connection, a possibility to apply a conventional airborne radar altimeter as a scatterometer with a nadir-looking wide-beam antenna in conjunction with simultaneous range Doppler discrimination techniques for recovering the wind vector over sea at low speed of flight is discussed, and measuring algorithms of sea surface wind speed and direction are proposed. The principle considered and algorithms proposed in the paper can be used for creation an airborne radar system for operational measurement of the sea roughness characteristics and for safe landing of a hydroplane on water.

This paper proposes an automated 3D visualization method of embedded tubes applicable to the scanned result of pulse-radar Non-Destructive Testing (NDT). The proposed method consists of three stages. First, our method defines the processing region which includes a pattern generated by a tube. This region is determined by referring to the composition of a received wave. Second, after expert knowledge of a tube is translated into fuzzy inference rules, the positions of embedded tubes are identified by inferring them. Third, 3D links of the identified positions are formed to visualize the continuous shape of the tubes. Consequently, the tubes are extracted, and their 3D shapes are visualized. The experimental result on the specimens shows that our method was able to find all tubes that exist in the radiograph and the schematic. Our method could thus provide the internal information of concrete with sufficient accuracy required in the practical construction work.

We present theoretical and experimental results for a microwave photonic oscillator (MPO) that provides a microwave signal and a modulated optical wave simultaneously. Among the different techniques currently in use for optically generating a microwave signal, we have chosen a ring configuration based on an electro-optical Mach-Zehnder modulator (EOM) driven by a 1.55 µm DFB laser diode. An accurate modelling of EOM and the contributions from all noise sources in the oscillation loop allows us to predict performances of our designated MPO in a very good agreement with the measured oscillation power (up to 22 dBm, depending on the DC bias voltage) and phase noise spectral density (-130 dBc/Hz @ 10 kHz away from the carrier). We propose this hybrid microwave photonic source to be used as a local oscillator for a coherent laser radar operating at 1550 nm. A good compromise between a very high tunability range (1-8 GHz) and a high spectral purity (> -120 dBc/Hz @ 10 kHz) is obtained through a dual-loop configuration for the MPO.

Polarimetric SAR interferometry has been successful and attractive for forest parameters (tree height and canopy extinction) estimation. In this paper, we propose to use the ESPRIT algorithm to extract the interferometric phase of local scatterers with polarimetric and interferometric SAR data. Two or three local scattering waves can be extracted at each image patch when a fully polarimetric data set (HH, HV, VV) is available. Furthermore, the ESPRIT can estimate two dominant local scattering centers when only a dual polarimetric data set (e.g., VV and VH) is provided. In order to demonstrate effectiveness the proposed technqiue, we examined the relation between local scattering centers extracted by this method and complex coherence of the coherent scattering model for vegetation cover. The results show that the three-wave estimation can be more accurate than the two-wave case. The extracted interferometric phases with full and dual polarization data sets correspond to effective ground and canopy scattering centers. In this investigation, SIR-C/X-SAR data of the Tien Shan flight-pass are used.

In this paper, a new method is proposed for supervised classification of ground cover types by using polarimetric synthetic aperture radar (SAR) data. The concept of similarity parameter between two scattering matrices is introduced for characterizing target scattering mechanism. Four similarity parameters of each pixel in image are used for classification. They are the similarity parameters between a pixel and a plane, a dihedral, a helix and a wire. The total received power of each pixel is also used since the similarity parameter is independent of the spans of target scattering matrices. The supervised classification is carried out based on the principal component analysis. This analysis is applied to each data set in image in the feature space for getting the corresponding feature transform vector. The inner product of two vectors is used as a distance measure in classification. The classification result of the new scheme is shown and it is compared to the results of principal component analysis with other decomposition coefficients, to demonstrate the effectiveness of the similarity parameters.