Polish radar technology

Polish radar research and development since 1953 is reviewed, covering the development and production of surveillance radars, height finders, tracking radars, air traffic control (ATC) radars and systems, and marine and Doppler radars. Some current work, including an L-band ATC radar for enroute control, a weather channel for primary surveillance radar, signal detection in non-Gaussian clutter, adaptive MTI filters and postdetection filtering, and a basic approach to radar polarimetry, is examined.<>     

Japan's CS (Sakura) Communications Satellite Experiments

The Japanese Communications Satellite (CS), called Sakura, is a "Medium Capacity Communications Satellite for Experimental Purposes" and is the first experimental communications satellite in which 30/20 GHz bands were adopted and were developed for practical domestic use. Large scale field trials have been carried out for more than three years in order to evaluate 30/20 GHz (Ka-band) and 6/4 GHz (C-band) domestic satellite communications system technologies under actual operational conditions by using the CS Sakura launched in December 1977. Through the various experiments on Kand C-band large fixed and small transportable Earth station systems, satellite control experiments, and Ka-band propagation measurements, it has been verified that the medium capacity satellite communications system meets the design objectives.     

First spaceborne demonstration of BeiDou-3 signals for GNSS reflectometry from CYGNSS constellation

The full constellation of Chinese Global Navigation Satellite System (GNSS) BeiDou-3 has been deployed completely and started fully operational service. In addition to providing global Positioning, Navigation and Timing (PNT) services, the BeiDou-3 satellites transmissions can also be used as the sources of illumination for Earth Observation (EO) with a bistatic radar configuration. This innovative EO concept, known as GNSS reflectometry (GNSS-R), allows to measure the Earth surface characteristics at high resolution via the reflected L-band radar signals collected by a constellation of small, low cost and low Earth orbiting satellites. For the first time in orbit, earth reflected BeiDou-3 signal has been detected from the limited sets of raw data collected by the NASA’s Cyclone GNSS (CYGNSS) constellation. The feasibility of spaceborne BeiDou-3 reflections on two typical applications, including sea surface wind and flooding inundation detection, has been demonstrated. The methodology and results give new strength to the prospect of new spaceborne GNSS-R instruments and missions, which can make multi-GNSS reflectometry observations available to better capture rapidly changing weather systems at better spatio-temporal scales.     

A chirp scaling approach for processing squint mode SAR data

Image formation from squint mode synthetic aperture radar (SAR) is limited by image degradations caused by neglecting the range-variant filtering required by secondary range compression (SRC). Introduced here is a nonlinear FM chirp scaling, an extension of the chirp scaling algorithm, as an efficient and accurate approach to range variant SRC. Two methods of implementing the approach are described. The nonlinear FM filtering method is more accurate but adds a filtering step to the chirp scaling algorithm, although the extra computation is less than that of a time domain residual compression filter. The nonlinear FM pulse method consists of changing the phase modulation of the transmitted pulse, thus avoiding an increase in computation. Simulations show both methods significantly improve resolution width and sidelobe level, compared with existing SAR processors for squint angles above 10 deg for L-band and 20 deg for C-band     

ATS-6 Satellite Instructional Television Experiment

The Satellite Instructional Television Experiment (SITE) is scheduled for the second year of satellite operation. Applications Technology Satellite (ATS-6) will receive C-band video signals frorn Abmedabad and Delhi, India, and will retransmitt the video and two audio sub-carriers at 860 MHz to 6 clusters of 400 direct-receive stations for a total of 2400 direct-receive stations. Morning programs of 1.5 hours per day are designed for classroom use, and evening programs of 2.5 hours duration are designed for village adult education. Indian production antennas and television sets have been tested and found to meet specifications, and a successful experiment is anticipated.     

A Rader Clutter Model: Average Scattering Coefficients of Land, Snow, and Ice

A model has been developed for average radar backscatter from terrain based on recent carefully controlled wide-bandwidth measurements of vegetation, snow-covered ground, and sea ice and on a comparison with measurements over North America by the Skylab S-193 scatterometer. The models for the thiree cases take the form ?° dB = A + B? + Cf+ Df?, 20° ? angle of incidence ? 70°, where the constants vary depending on polarization and terrain class. They also differ above and below a critical frequency (6 GHz for general terrain, 8 GHz for sea ice, and between 8 and 12 GHz for snow). For angles of incidence of 0° (vertical) and 10°, the model is of the form ?° dB = M(?) + N(?)f over the range 1 to 18 GHz. Hundreds of thousands of measurements contributed to the general (vegetated terrain) model, and smaller numbers contributed to the snow and sea ice models. Since 1974 all measurements have been made with University of Kansas microwave spectrometers. A brief discussion of fading shows that insufficient data are available to describe the ranges adequately.     

Foliage penetration experiment

This series papers describes analyses of a foliage penetration experiment undertaken by MIT Lincoln Laboratory to assess the ability of synthetic aperture radar (SAR) to detect targets under trees. Data were taken using the NASA/JPL UHF, L-, C-band fully polarimetric SAR over a forested area in Maine in July 1990. Future experiments are planned to measure the polarimetric properties of clutter and targets using the latest ultrawideband sensors with submeter resolutions and fully polarimetric data collection capabilities     

可实时重构的国际C站卫星模拟器

我国自行研制的国际标准C频段统一测控系统,配置了功能齐全的卫星模拟器,但其一星一模拟器的方式已不能适应当前多星管理和未来星座管理的需要。本文旨在探讨利用现有的微波宽带器件技术和软件无线电技术,用一套硬件系统,根据需要实时重构成所需卫星的模拟器,达到多星共用一套模拟器,实现小型化、实时性的目的。     

Adaptive Clutter Suppression in Step Scan Radars

Clutter echoes with unknown power spectra (from weather, sea, chaff disturbances) can be suppressed only adaptively. The use of the discrete Fourier transform (DFT) for clutter suppression in step scan radars is investigated by use of a clutter model that is derived in analogy to measured clutter data of a radar with a rotating antenna.     

New Developments in Radar and Radio Sensors for Aircraft Navigation

Recent developments in airborne Doppler and ground mapping navigation radars and ground and satellite based radio systems are described. Simultaneous lobing and slope tracking techniques can remove the well-known Doppler sea bias error in fast and slowly moving vehicles. Doppler velocity information can be extracted from coherent forward-looking mapping radars, and high position fixing accuracy can be achieved by synthetic aperture radars. In radio navigation systems, such as Loran, Omega, and satellite systems, direct-ranging and differential techniques greatly reduce the geometric dilution and propagation effects which have plagued conventional radio navigation systems. The advantages gained by mixing of the data from these and other navigation sensors in a digital multisensor system are discussed and approaches for processing these data are suggested.     

The chemical profiles of polar ice on Earth and Mars: What we read from the first; what we could read from the second

An analogy is drawn between the current knowledge on terrestrial snow and ice-cap chemistry and the possible composition of snowfall and ice caps of Mars. Terrestrial snowfall reflects the composition of the Earth's atmosphere. Snow cover further interacts with the atmosphere and is the recipient of aerosol and particulate fall-out. The snow is transformed to firn and ice and the chemical signatures become locked into the perennial ice sheets. The chemical profiles of ice thus constitute environmental records of the Earth's past. By considering the present knowledge on the hydrologie cycle of Mars and the chemistry of the atmosphere, a simple analogous model for the chemical profile of the North polar ice cap is proposed. Three major constituents of the ice are discussed: water ice, dust, and occluded air bubbles. The seasonal fluctuations and interannual variability of these components are examined as possible chemical signatures for the dating of ice, elucidating hydrologie processes, and recording long-term climatic change. The model of the north polar cap in summer consists of water-ice fine-dust layers (30–200 m thick) sandwiched between annual dust layers of variable size distribution and thickness (< 1m– > 66 m). The water ice is subjected to metamorphism and grain growth. The interpretation of the physico-chemical profile could lead to increased knowledge on the recent climatic past (1,000–2,000 years), hydrologic reservoirs, and seasonal cycles in the atmospheric dynamics of the planet.     

Spiky sea clutter at high range resolutions and very low grazingangles

X-band (9.5-10.0 GHz) backscatter at near grazing incidence (0.2 deg) from the sea off the coast of Kauai, Hawaii, was measured with a radar characterized by a high spatial resolution in range (0.3 m) and a high temporal resolution (2000 Hz pulse repetition frequency (PRF)). Extensive amounts (over 20 min per measurement) of vertically and horizontally polarized sea clutter data were taken with upwind (UP) and crosswind (CR) transmit geometries during the collection campaign. Specific but representative examples of the clutter were statistically and phenomenologically analyzed over time scales varying from long (200 s), to intermediate (5 s), to short (50 ms), and over range swaths varying from full (160 m), to partial (30 m), to a single range cell (0.3 m). All analyses and results presented here are noncoherent, involving only the clutter amplitudes. Each type of clutter exhibited the characteristic spiky behavior which has come to be expected from microwave sea backscatter observed at low grazing angles and high range resolutions, while showing, between themselves, marked transmit geometry and polarization dependent contrasts, with the horizontally polarized clutter, measured with an UP transmit geometry, being especially notable for its frequently occurring, significant high frequency spectral content. Within the same clutter type, differences were observed in the probability distributions of radar cross sections (RCS) of spatially and temporally extended spiking events     

Medium PRF Performance Analysis

A discussion of various types of x-band airborne radars is presented together with their systematic development through the years to the present time. Starting with simple, low pulse-repetition frequency (PRF) radars for measuring radar-target range, airborne radar development proceeded with more sophisticated high PRF Doppler radars where radar-target range and range rate were measured simultaneously. The use of Doppler (frequency) in signal processing allowed the separation of moving from nonmoving targets (ground), enabling the detection of moving targets in the presence of ground clutter. More recent developments in waveform generation and selection has resulted in the development of medium PRF radars, whereby a greater degree of tactical flexibility in target detection is achieved by combining the desirable features of both low and high PRF radars. Part of the available literature gives an overview, together with a specific example of the design and performance of an airborne medium PRF radar. Here, however, the systematic evolution of these radars is emphasized and the necessary theoretical background is developed for their performance calculations. Modern day airborne radars may be equipped with all three modes of operation, low, medium, and high PRF, allowing the operator to utilize the mode best suited for the tactical encounter. Low PRF and high PRF radars have been described elsewhere and are given here primarily for the sake of completeness and for the necessary background for developing medium PRF radar equations. They are also needed for developing the reasons why medium PRF radars came into being.     

Probability of Pulse Coincidence in a Multiple Radar Environment

Elementary probability theory is used to develop three formulas for the probability of two or more pulses being coincident at an observer's aircraft position in a multiple radar environment. The first formula is for nonscanning tracking type radars with different pulsewidths (PWs) and pulse repetition frequencies (PRFs), the second is for generically identical nonscanning radars with similar PWs and PRFs, and the third is for scanning type radars such as air search radars with similar PWs and PRFs. The probability of coincidence is related to the mean-time-between-coincidences (MTBC) and to the average coincidence rate. Two sample problems are given.     

Generalized approach to resolution analysis in BSAR

Bistatic synthetic aperture radars (BSARs) have been the focus of increasing research activity over the last decade. The generalized ambiguity function (GAF) of bistatic SAR is introduced here. First, the GAF for BSAR is represented in the delay-Doppler domain, and is then expanded to the spatial (coordinates) domain. From the GAF, comprehensive knowledge regarding the resolution of BSAR can be extracted, including the range and azimuth resolutions, as well as the area of a resolution cell of BSAR. These general results are also applied to the performance analysis of several particular BSAR geometries, including the space-surface-BSAR (SS-BSAR) system, to demonstrate the potential ability of this newly introduced system.     

The Lunar Reconnaissance Orbiter Miniature Radio Frequency (Mini-RF) Technology Demonstration

The Miniature Radio Frequency (Mini-RF) system is manifested on the Lunar Reconnaissance Orbiter (LRO) as a technology demonstration and an extended mission science instrument. Mini-RF represents a significant step forward in spaceborne RF technology and architecture. It combines synthetic aperture radar (SAR) at two wavelengths (S-band and X-band) and two resolutions (150 m and 30 m) with interferometric and communications functionality in one lightweight (16 kg) package. Previous radar observations (Earth-based, and one bistatic data set from Clementine) of the permanently shadowed regions of the lunar poles seem to indicate areas of high circular polarization ratio (CPR) consistent with volume scattering from volatile deposits (e.g. water ice) buried at shallow (0.1–1 m) depth, but only at unfavorable viewing geometries, and with inconclusive results. The LRO Mini-RF utilizes new wideband hybrid polarization architecture to measure the Stokes parameters of the reflected signal. These data will help to differentiate “true” volumetric ice reflections from “false” returns due to angular surface regolith. Additional lunar science investigations (e.g. pyroclastic deposit characterization) will also be attempted during the LRO extended mission. LRO’s lunar operations will be contemporaneous with India’s Chandrayaan-1, which carries the Forerunner Mini-SAR (S-band wavelength and 150-m resolution), and bistatic radar (S-Band) measurements may be possible. On orbit calibration, procedures for LRO Mini-RF have been validated using Chandrayaan 1 and ground-based facilities (Arecibo and Greenbank Radio Observatories).     

一种新的周期性运动部件调制谱估计方法

目标内部运动部件对雷达回波产生的周期性运动部件调制 (PMPM )为目标识别提供了丰富的特征信息。但由于大多数雷达均采用多目标工作方式 ,因此 ,通常情况下只能从雷达获得不连续的目标回波脉冲串 ,这极大增加了根据目标回波频谱提取PMPM特征的难度。针对含PMPM目标回波频谱具有简单结构这一特点 ,提出了基于最小熵准则的交替迭代反卷积方法(AIDME)用于扩展目标雷达回波频谱估计。结果表明 :与傅里叶谱分析方法相比 ,该方法能够有效消除卷积核函数的不利影响 ,获得逼近目标回波真实谱的良好谱估计结果     

基于随机文法的多功能雷达识别方法

 针对多功能雷达采用复杂体制而造成的辐射源不能正确识别问题,提出了一种基于随机文法(SG)的辐射源识别算法。该算法基于多功能雷达的句法模型,将威胁数据库中的多功能雷达文法分为随机正则文法(SRG)和随机上下文无关文法(SCFG)两种情况,并分别构造随机有限自动机(SFA)和随机下推自动机(SPDA)对测量辐射源进行识别。仿真实验表明,该方法不仅能识别出多功能雷达辐射源的型号及模式,而且能识别出雷达辐射源的功能状态,并进而推断出雷达辐射源的威胁等级。     

国外机载海面监视雷达发展现状与趋势

首先对目前西方国家装备的较先进的机载海面监视雷达进行了介绍,总结了它们的技术特点。现役机载海面监视雷达具有多功能和多工作模式的特点,除增强了对高海况下的小目标检测能力外,还新增了气象探测、SAR/ISAR和HRRP等先进功能。最后指出了机载海面监视雷达未来发展趋势。     

Target Image Frequency Spectrum in Doppler Radars

A mathematical model to study target image return frequency spectrums in Doppler radars is described. The model includes the effects of eclipsing, sea surface slope distribution, and surface reflectivity characteristics. The procedure of calculations has been computerized and the analytical results are compared to flight-test values obtained from flights over the ocean. The calculated values of amplitude-frequency spectrums of target image returns correspond reasonably well with the respective recorded flight-test data.