Single-reference near-field calibration procedure for step-frequency ground penetrating radar

The antenna system of ground penetrating radar is usually positioned in the vicinity of the ground surface to obtain sufficient spatial resolution for detecting small targets. Therefore, received signals are subject to errors caused by unwanted reflections and coupling. A near-field calibration procedure taking into account these effects as well as antenna dispersion is presented. For practical convenience, only a metal plane is used here as a calibration standard. Calibration data are measured for a set of distances between the antenna and metal plane. The reference reflections in all positions are computed using polynomial representation of the reflected signal. Then, error coefficients are obtained by a solution of a linear system of equations in the least squares sense. Experimental verification of the proposed calibration technique demonstrated efficient removal of artefacts caused by unwanted reflections. Moreover, peaks in the radar range profile become sharper after calibration if the antenna is dispersive. Consequently, the ground response in the form of an exponential term can be effectively subtracted from the received signal. This helps to reveal and discriminate shallow underground targets obscured by strong reflection of the ground surface. Experimental examples are given to illustrate the performance of the method.     

A practical millimeter-wave radar calibration target

A simple rectangular-plate millimeter-wave radar calibration target gives RCS values ranging from hundreds to thousands of square meters. This enable tests over extended ranges and with equipment having modest output power. Precise mechanical alignment mechanisms and an optical sight are mandatory, due to the narrow beamwidth. Absorber collars provide an easy way of adjusting the actual RCS according to specific mission requirements, and effectively reduce edge-diffraction effects. The measured V-band calibration uncertainty was less than 0.5 dB, and the pointing resolution was better than 0.05/spl deg/.     

A new 94-GHz six-port collision-avoidance radar sensor

A new 94-GHz collision avoidance radar sensor is proposed. The receiver front-end module is based on a six-port phase/frequency discriminator (SPD). The SPD, composed of four 90/spl deg/ hybrid couplers, is manufactured in a metal block of brass using a computer numerically controlled milling machine. Simulation and measurement S-parameters of the SPD are presented in the frequency band. New SPD computer models are generated and used in the system simulations. Preliminary measurements and system simulations performed to obtain the relative velocity of the target and its distance are presented. Statistical evaluations show an acceptable measurement error of this radar sensor.     

A radar cross-section model for power lines at millimeter-wave frequencies

The knowledge of radar backscatter characteristics of high-voltage power lines is of great importance in the development of a millimeter-wave wire detection system. In this paper, a very high-frequency technique based on an iterative physical optics approach is developed for predicting polarimetric radar backscattering behavior of power lines of arbitrary strand arrangement. In the proposed scattering model the induced surface current is obtained using the tangent plane approximation in an iterative manner where the first-order current, obtained from the incident wave, is used as the source for the second-order current and so on. The approximation is valid for frequencies where the cable strand diameter is on the order of or larger than the wavelength. It is shown that the copolarized backscatter is dominated by the contribution from the first-order PO currents, whereas the cross-polarized backscatter is generated by the second- and higher order PO currents. Using this model, the effects of radar antenna footprint, surface irregularities, and cable sag (when suspended between towers) on radar backscatter are studied. To verify the validity of the proposed model, theoretical results are compared at 94 GHz with experimental results and are found to be in good agreement.     

A short-range, high-resolution millimeter-wave surface movement radar

Today’s Air (and Airport traffic) management needs an advanced surveillance function for the airport’s surface. Among the different sensors to be integrated for this function just the surface movement radar is able to detect the presence, and determine the position, of non co-operating targets. Present-day smr’s are considered aged and inadequate. In this paper we propose a novel short range radar, operating at frequencies around 95 GHz, to be used in a distributed surface surveillance system. Its main characteristics and the trade-off considerations involved in its design are discussed.     

毫米波雷达DBS回波信号仿真

为了在实验室内完成多普勒波束锐化（DBS）技术的评估、验证及优化,阐述了多普勒波束锐化（DBS）技术的基本原理及DBS图像拼接算法,结合目标DBS回波理论模型及毫米波雷达的特点,采用Matlab工具对目标的DBS回波信号进行了计算机仿真,得到目标DBS回波数据,运用DBS成像技术完成回波仿真数据的成像处理,实现了不同波束内不同方位的目标回波仿真及成像,验证了DBS回波仿真算法的正确性。为DBS回波仿真的工程应用奠定了基础。     

一种毫米波二维电扫有源相控阵雷达

采用多波束开关馈线与相控波束扫描相结合的技术实现了一种低成本毫米波 二维电扫描有源相控阵雷达。该雷达主要包含电扫的关键组件Rotman透镜与多端口TR组件, 配以高 性能的模块化数字信号处理机。试验结果表明,该雷达能实现动目标检测与跟踪、前斜视调 频步进SAR成像与扇扫成像。     

A new generation of SIS receivers for millimeter-wave radioastronomy

A new generation of low-noise, dual-polarization heterodyne receivers covering all atmospheric windows between 68 and 300 GHz has been developed for the 12-m telescope on Kitt Peak, AZ, operated by the National Radio Astronomy Observatory (NRAO). A modular approach to the receiver construction has been used. Each receiver channel is constructed as a self-contained insert which is mounted in a dewar equipped with a closed-cycle 4 K refrigerator capable of cooling up to eight inserts, thereby enabling several frequency bands to be contained within one dewar. The telescope and receiver optics are so arranged that switching between frequency bands may be accomplished rapidly by rotating the optical elements placed in the signal path. Single-sideband noise temperatures ranging from 50 to 400 K are obtained across the frequency range     

A multistatic microwave radar sensor for short range anticollisionwarning

An adequate radar technology for the detection and localization of obstacles before, behind and on the sides of a moving car is of primary importance to realize on-board devices able to perform different tasks such as parking, stop and go, and pre-alarm of the frontal air-bags. In these situations, the radar must acquire the position of the obstacles located at short distances from the car. This acquisition must be carried out with high radial and angular resolution; the former needs large radio frequency bandwidth, the latter requires large antennas and this means that the investigation area of the radar is certainly in the near field of the antenna. It is for this reason that traditional anti-collision systems based on phase array antennas prove to be unsuited to perform these tasks in the short range. The solution that we are proposing is based on several independent microwave radar sensors with wide angle of view connected to a central processing unit able to define the position and the relative velocity of the nearest obstacles. This prototype works in the 13.4-14 GHz frequency range at low power (16 dBm cirp) in accordance with the ETSI and CEPT/ERC Recommendations and it has been realized with microstrip technology so that thanks to its reduced size each device can be embedded easily in a bumper     

A new view of millimeter-wave satellite communication

Italian satellite results have broad implications for millimeter-wave satellite communication. We apply their results to high-elevation satellite systems, and find that attractive frequencies extend well beyond the Ka band, to emphasize 40-47 and 85-98 GHz     

Estimate of the subglacier dielectric constant of an ice shelfusing a ground-penetrating step-frequency radar

The mass balance of the Antarctic ice cap, its stability, and the role of the surrounding ice shelf in bottomwater mass formation is, to a large extent, dictated by processes associated with subsurface freezing and melting, where the submerged ice meets the surrounding ocean. It is demonstrated how multifrequency ground-penetrating radar data collected at the Riiser-Larsenisen can be used to examine the physical conditions of the ice-shelf subsurface. The received radar signal from three different frequency intervals, 10-30, 155-170, and 330-360 MHz (range of wavelengths from 15 to 0.5 m in the ice), was analyzed by using a plane reflector model. It is demonstrated that the data can be successfully used to distinguish between types of ice at the ice-ocean interface, such as for freezing marine ice, melting marine ice, melting meteoric ice from the ice cap, and melting firn/ice. The data analysis shows that the subsurface can be regarded as rough on length scales in the order of 1 m     

A FM-CW radar proximity sensor for use in mechatronic products

The need for a low cost medium range proximity sensor for use in mechatronic products is identified and discussed with particular reference to automotive applications. One candidate solution to this need, a 27 GHz frequency modulated continuous wave radar system, is presented for use as a range finder. The method of releasing the range information from the returned signal is described together with the results from off-line data analysis. A real-time system for implementation in a typical product is outlined.     

一种新型雷达天线方位转台

提出一种全新的雷达天线方位转台结构方案。由于所有功能都集中在一台新型的少齿差行星减速器上，所以该方位转台结构紧凑、体积小、重量轻、精度高以及承载能力强，而且有利于模块化设计。     

A new system model for radar polarimeters

The validity of the 2×2 receive R and transmit T model for radar polarimeter systems, first proposed by H. Zebker et al. (1987), is questioned. The model is found to be invalid for many practical realizations of radar polarimeters, which can lead to significant errors in the calibration of polarimetric radar images. A more general model is put forward, which addresses the system defects which cause the 2×2 model to break down. By measuring one simple parameter from a polarimetric active radar calibration (PARC), it is possible to transform the scattering matrix measurements made by a radar polarimeter to a format compatible with a 2×2 R and T matrix model. Alternatively, the PARC can be used to verify the validity of the 2×2 model for any polarimetric radar system. Recommendations for the use of PARCs in polarimetric calibration and to measure the orientation angle of the horizontal (H) and vertical (V) coordinate system are also presented     

一种新的雷达重频模式识别方法

针对雷达重频模式识别中存在的问题,提出了一组新的二维特征向量,对重频固定、重频抖动、重频参差、重频分组和重频滑变5种典型的重频模式进行了识别。仿真结果表明,该方法正确识别率高,为工程应用提供了一种新的思路。     

An ultrafast wide-band millimeter-wave (MMW) polarimetric radar for remote sensing applications

With the advent of high-frequency radio frequency (RF) circuits and components technology, millimeter-wave (MMW) radars are being proposed for a large number of military and civilian applications. Accurate and high-resolution characterization of the polarimetric radar backscatter responses of both clutter and man-made targets at MMW frequencies is essential for the development of radar systems and optimal detection and tracking algorithms. Toward this end, a new design is developed for ultrafast, wide-band, polarimetric, instrumentation radars that operate at 35 and 95 GHz. With this new design, the complete scattering matrix of a target (magnitude and phase) can be measured over a bandwidth of 500 MHz in less than 2 /spl mu/s. In this paper, the design concepts and procedures for the construction and calibration of these radars are described. In addition, the signal processing algorithm and data-acquisition procedure used with the new radars are presented. To demonstrate the accuracy and applicability of the new radars, backscatter measurements of certain points and distributed targets are compared with their analytical radar cross section (RCS) and previously measured /spl sigma//spl deg/ values, respectively, and good agreements are shown. These systems, which can be mounted on a precision gimbal assembly that facilitates their application as high-resolution imaging radar systems, are used to determine the MMW two-way propagation loss of a corn field for different plant moisture conditions.     

System feasibility study of a microwave/millimeter-wave radar for space debris tracking

A 35 GHz millimeter-wave radar system has been studied for space debris tracking. The objective is to track the particles ranging in size from 4 mm to 80 mm up to a range of 25 km. The system requires various state-of-the-art technologies including phased arrays, monopulse tracking, pulse compression, high power transmitters, low noise receivers, and pulse integration signal processing techniques.