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.

The radar cross section (RCS) of a dielectric-coated cylindrical cavity was measured and the measurements were compared with those calculated according to the iterative physical optics (IPO). The IPO analysis used the equivalent-impedance boundary condition (EIBC) based on transmission-line theory which takes into account the thickness of the coating. It was consequently found that this condition is much more effective than the ordinary-impedance boundary condition based on the intrinsic impedance of the material.

This paper introduces an automatic and multi-instrument snowfall observation system and proposes techniques that could be used in the estimation of snowfall characteristics. The instruments used in this study include two microwave radars, an optical lidar, a CCD camera based imaging system and high-accuracy electrical balances for reference data. The emphasis has been on obtaining good temporal resolution and synchronization accuracy of separate datasets. In most research done so far, this has not been a principal point, either because only very long snowfall events have been measured, or wide area estimates were desired, or due to limitations in manual sampling methods and other technical issues. The measurements were also contained in a small area to make sure that all instruments record data from the same target. One radar and the optical lidar recorded an atmospheric profile up to 6000 m, while the other radar, the imaging system and the two balances recorded snowfall on the ground level. The combination of optical, microwave and direct visual observations of snowfall show that a change in cloud conditions can result in snowfall having different characteristics. The lidar backscatter was used as main indicator of transitions in cloud conditions. A direct visual evaluation of snowflake size distribution using a CCD camera shows that it is extremely helpful in order to interpret radar data. The camera observed velocity distribution showed no large variations between snowfall events, however, it could be useful in detecting graupel and hail precipitations which have much faster terminal velocities. This paper will conclude with a discussion on further elaborating the use of lidar and visual data to complement radar observations of snowfall.

A multi-range resolution radar using sideband spectrum energy is investigated. The basic system consists of a sharpening processor and least-error energy shaping filters. First, the sharpening processor makes long flat pulses sharpened. Next, the least-error shaping filters compress the input pulse into the desired pulse width. Then the output pulse width can become narrower than the reciprocal of the input bandwidth, because the least-error shaping filters make the equivalent bandwidth expanded by the enhancement of the sideband spectrum energy and the suppression of the main spectrum. The transmitted signals with simple phase modulation are studied to obtain the multi-range resolution where the pulse is compressed into a pulse with the same bandwidth and another pulse width equal to the reciprocal of the input bandwidth. The peak-to-sidelobe ratio after the pulse compression and the improvement factor of the output signal-to-noise ratio are measured. Further, the experimental results are shown to verify our proposed technique.

We observed the log normal, log-Weibull and K-distributed sea-clutter from high sea state 7 with an X-band radar for grazing angles between 3.1 and 17.5. To determine the sea-clutter amplitude statistics, we introduced the Akaike Information Criterion (AIC), which is more rigorous fit of the distribution to the data than the least-squares method.

A 5.3-GHz klystron has been recently designed and fabricated. In many countries, the transmitting frequency of 5.6 GHz (5,600 to 5,650 MHz) is commonly used for C-band meteorological radars. However, 5.3 GHz is generally used in Japan. To detect low-level wind shears by a Doppler radar, it is essential to use a MOPA (Master Oscillator and Power Amplifier) that generates stable coherent microwaves. The klystron is most suitable for this purpose. However, there are no commercially available klystrons in C-band that operate at 5.3 GHz. We developed a klystron for this band, making use of a simulation technique originally devised for S- and X-bands. The klystron operates at frequencies between 5,250 and 5,350 MHz. The typical operating parameters are a peak output power of 200 kW, a pulse width of 1 µs, and an RF duty cycle of 0.002. The klystron, including the electromagnet for focusing the magnetic field, is approximately 67 cm long with a diameter of 40 cm and a weight of 162 kg. Phase modulation is suppressed below 20% of the phase change required for the minimum resolution of Doppler velocity measurement by the radar for which this klystron is employed. The klystron shows favorable performance for Doppler radars operated in major airports in Japan.

The concept of the equi-phase curve is introduced for the cross-polarized channel case. It is proved that the equi-phase curves are a series of half circles on the Poincare sphere, and that all these curves have two common ends. Based on the introduced concept, this letter demonstrates the distribution of the received voltage's phases on the Poincare sphere. In addition, it is shown theoretically that the cross-polarized phase of the off-diagonal elements of a scattering matrix is unstable for most natural targets. Therefore, the cross-polarized phase information cannot be used for extracting target characteristics in polarimetric radar remote sensing.

A novel power spectral density accumulation (PSDA) method for estimating the bandwidth of the clutter spectra is proposed, based on a priori knowledge of the shape of the clutter spectra. The comparison of the complexity and the performance between the PSDA method and the general ones is presented. It is shown that the PSDA method is effective for the short-time clutter data in the practical application.

A stabilized local oscillator is one of the key components for any radar system, especially for a Doppler radar in detecting slowly moving targets. Based on hybrid semiconductor/superconductor circuitry, the HTS local oscillator produces stable, low noise performance superior to that achieved with conventional technology. The device combines a high Q HTS sapphire cavity resonator (f=5.6 GHz) with a C-band low noise GsAs HEMT amplifier. The phase noise of the oscillator, measured by a HP 3048A noise measurement system, is -134 dBc/Hz at 10 kHz offset at 77 K.

The periodicity of a target scattering matrix is studied when the target is rotated about the sight line of a monostatic radar. Except for the periodicity and invariance of the scattering matrix diag(a,a), it is proved that only helixes have the quasi-invariance, and that only N-targets have the quasi-periodicity, demonstrating that a target with some angle rotation symmetry also has the scattering matrix form diag(a,a). From this result, we conclude that it is impossible to extract the shape characteristics of a complex target from its scattering matrix or its Kennaugh matrix.

Synthetic aperture radar interferometry have been established in the past two decades, and used extensively for many applications including topographic mapping of terrain and surface deformation. Vegetation analysis is also a growing area of its application. In this paper, we propose an polarimetric SAR interferometry technique for interferometric phase extraction of each local scatterer. The estimated position of local scattering centers has an important information for effective tree height estimation of forest. The proposed method formulated for local scattering center extraction is based on the ESPRIT algorithm which is known for high-resolution capability of closely located incident waves. The method shows high-resolution performance when local scattered waves are uncorrelated and have different polarization characteristics. Using the method, the number of dominant local scattering centers and interferometric phases in each image pixel can be estimated directly. Validity of the algorithm is demonstrated by using examples derived from SIR-C data.