Byung-Lae Cho

Automobile-based SAR/InSAR system for ground experiments

An automobile-based synthetic aperture radar (SAR) system named AutoSAR is described. It is an experimental SAR system operating on the ground, which was developed by the Pohang University of Science and Technology, Korea. AutoSAR can also operate as an interferometric SAR (InSAR) when one additional receiving antenna is used. The swath of AutoSAR is less than 1 km, and the azimuthal coverage is limited only by the storage capacity of the system. SAR and InSAR images obtained at a test site near Pohang, Korea, are presented. Being on an automobile, this system can easily obtain SAR data of any target area with a straight road nearby

Interpolation using Optimum Nyquist Filter for SAR Interferometry

Interpolation is necessary for image registration in interferometric synthetic aperture radar (InSAR). In this letter, the raised cosine (RC) function used in digital communications is proposed as a new interpolation kernel for SAR interferometry. Theoretical and simulation results are compared for the new interpolation kernel and the classical ones, and the proposed kernel shows the best result in interpolation accuracy even with much smaller window sizes.

Multilook Coherence Estimation Using Adaptive Weighted Window in Interferometric SAR

The coherence between two SAR images is an important factor in the interferometric SAR processing. As a previous step to the phase unwrapping, multilook averaging is widely used as the coherence estimator, and in general, a k × k square window is used. In this letter, it is shown that the performance of the coherence estimator can be improved by using an adaptive weighted window, which is originally developed for SAR speckle reduction. The proposed method was tested using the InSAR data obtained by an automobile-based SAR system.

Target angle estimation of multifunction radar in search mode using digital beamforming technique

We propose a new target angle estimation method for a multifunction radar in search mode using the digital beamforming technique. The conventional center of mass-based method (CM method) used in mechanical scanning radar or two-dimensional digital beamforming radar is not very useful for a three-dimensional multifunction radar due to many problems. We suggest a three-beam-based angle estimation method (3B method) to reduce the target angle estimation error by the CM method. The 3B method estimates the target angle in search mode with less error than the CM method for all Swerling cases and signal-to-noise ratio.

Unambiguous angle estimation of unresolved targets in monopulse radar

This paper presents an important improvement on Shermans method for angle estimation of two unresolved targets when using monopulse radar. The graphical or numerical solution for the 6th-order polynomial equation is replaced with a quadratic equation that has exact algebraic solutions for nonfluctuating or slowly fluctuating targets. The proposed method can also estimate the angle for a single target without ambiguity and can estimate the angles when two targets are positioned at the same azimuth or elevation angle, in contrast with previous techniques. The proposed method is validated using simulations.

Feasibility Study of Forward-Looking Imaging Radar Applicable to an Unmanned Ground Vehicle

This study describes the design and verification of short range UWB(Ultra Wideband) imaging radar that is able to display high resolution radar image for front area of a UGV(Unmanned Ground Vehicle). This radar can help a UGV to navigate autonomously as it detects and avoids obstacles through foliage. We describe the relationship between bandwidth of transmitting signal and range resolution. A vivaldi antenna is designed and it`s radiation pattern and reflection are measured. It is easy to make array antenna because of small size and thin shape. Aperture size of receiving array antenna is determined by azimuth resolution of radar image. The relation of interval of receiving antenna array, image resolution and aliasing of target on a radar image is analyzed. A vector network analyzer is used to obtain the reflected signal and corner reflectors as targets are positioned at grass field. Applicability of the proposed radar to UGV is proved by analysis of image resolution and penetrating capability for grass in the experiment.

Effective Detection and Suppression of Low-Amplitude Interference in FMCW Radars

As many radar systems are simultaneously operated with overlapping frequency bands, interference between systems inevitably occurs. Because interference can degrade radar performance, suppression of interference is a critical issue in radar systems. In this letter, a new interference detection and suppression method using a short-time Fourier transform and an adaptive notch filter is proposed. An experiment is carried out to validate the proposed method and the results demonstrate that the proposed method is suitable for application in real FMCW radars.

K-Band Radar Development for the Ground Moving Vehicle

This paper presents a K-band radar system installed on the ground moving vehicle to detect and track a high-speed target. The presented radar is separated into three search regions to satisfy a wide area detection and a limitation of the installing space of the radar, and each region performs detecting the target independently and tracking the detected target automatically. The presented radar radiating K-band FMCW waveform acquires range and velocity information of the target at the every dwell and receiving antenna of the radar is applied the multiple baseline interferometer to extract the precise angle information of the target. 3-dimensional tracking accuracy of the radar is 0.25 m RMSE measured actually through a fire experiment of an imitation target.

Ultra-wideband imaging radar to reveal obstacles concealed in vegetation to improve navigation of unmanned ground vehicles

To increase mobility of an unmanned ground vehicle (UGV), this study describes the use of forward-looking imaging radar applying ultra-wideband radar technology. If radar is able to visualize images with high resolution in front of a UGV, the radar can be used to support the vehicle by detecting obstacles through foliage. This system employs the multi-input/double-output configuration with two transmitting horn antennas to increase cross-range resolution. Also, two rows of physical receiving antenna arrays provide the height information of targets using an interferometer principle. For visualizing objects in front of the radar, the back-projection method is applied to the data acquired from the receivers. A field test is used to verify the effectiveness of the new radar system. The performance of the radar is proved experimentally by the analysis of image resolution, grass-penetrating capability, and target height information.

A Study on Bistatic SAR Imaging Using Bistatic-to-Monostatic Conversion in Wavenumber Domain

This study describes an omega-K algorithm for focusing bistatic synthetic aperture radar(SAR) data using bistatic-to-monostatic conversion. Bistatic SAR system considered in this study consists of a transmitting antenna and a physical array of several receiving antennas. The length of the physical array is identical to the SAR synthetic aperture. Unlike the monostatic case, an omega-K algorithm for the bistatic case is difficult to obtain the exact equation in the 2D wavenumber domain. The key of the proposed algorithm is converting the bistatic data into a monostatic one. The effectiveness of the proposed algorithm is proved by simulation and real measurement data.