On the Optimal Filters for a Fixed-Range Radar

The jointly optimal filters of a filter-sampler-filter system, representative of a fixed-range radar, are shown to each have impulse-response functions of the form a · cos(at), 0 ? t ? ?/2a.     

Range Resolution of Targets

The problem of resolving targets in range is formulated as a hypothesis-testing problem. A generalized likelihood approach is developed and very good results are obtained, e. g., targets separated by more than a pulsewidth can almost always be resolved, Specifically, simulations showed that when using a sampling rate of 1.5 samples per pulsewidth, two 20 dB nonfluctuating targets can be resolved at a resolution probability of 0.9 and at a false-alarm probability of 0.01 at separations varying between ? and ? of a pulsewidth, depending on the relative phase difference between the targets. The effect of increasing the sampling rate was investigated and it appears that there is only marginal benefit in increasing the sampling rate beyond 1.5 samples per pulsewidth. Finally, the generalized likelihood approach was compared to several easily implemented adhoc approaches and an adhoc approach involving fitting a pulse shape to the data is only slightly (approximately 10%) less accurate than the likelihood approach.     

Radar Track Acquisition Range

The track acquisiton range of a track-while-scan radar is defined as the range at which the cumulative probability of M detections in N scans is 90 percent. Track acquisition ranges for 2 out of 3, 2 out of 4, and 3 out of 4 detection criteria are presented for Swerling 0, 1, and 3 target models.     

Minimum Peak Range Sidelobe Filters for Binary Phase-Coded Waveforms

Linear programming techniques are utilized to determine the optimal filter weights for minimizing the peak range sidelobes of a binary phase-coded waveform. The resulting filter is compared with the filter obtained by use of the least square approximation to the ideal inverse filter. For a test case using the 13-element Barker code the linear programming filter is found to have peak sidelobes as much as 5 dB lower than the least squares filter of the same length.     

Improved Global Range Alignment for ISAR

An improved global range alignment is presented for inverse synthetic aperture radar (ISAR) imaging. The shifts of the echoes are modeled as a polynomial, and the coefficients of this polynomial are chosen to optimize a quality measure of range alignment. The shift in the time domain is carried out by introducing a phase ramp in the frequency domain in order to remove the limitation of integer steps. Because the quality measure of range alignment is calculated directly in the frequency domain, this method is computationally more efficient than the original global method.     

Ambiguity Resolution for Satellite Doppler Positioning Systems

The implementation of satellite-based Doppler positioning systems frequently requires the recovery of transmitter position from a single pass of Doppler data. The least-squares approach to the problem yieds conjugate solutions on either side of the satellite subtrack. It is important to develop a procedure for choosing the proper solution which is correct in a high percentage of cases. A test for ambiguity resolution which is the most powerful in the sense that it maximizes the probability of a correct decision is derived. When systematic error sources are properly included in the least-squares reduction process to yield an optimal solution the test reduces to choosing the solution which provides the smaller valuation of the least-squares loss function. When systematic error sources are ignored in the least-squares reduction, the most powerful test is a quadratic form compasison with the weighting matrix of the quadratic form obtained by computing the pseudoinverse of a reduced-rank square matrix. A formula for computing the power of the most powerful test is provided. Numerical examples are included in which the power of the test is computed for situations that are relevant to the design of a satellite-aided search and rescue system.     

Range Resolution of Targets Using Automatic Detectors

When two targets are closely separated in range, automatic detectors will declare the presence of only one target. To increase the-probability of resolving targets in range, log video should be used and the threshold should be of the form T = ? + F, where the mean ? is the smaller of the two means calculated from reference cells on either the greater range side or the lesser range side of the test cell and F is a fixed number. When the adjacent-detection merging algorithm is used, the probability of resolving targets does not rise above 0.9 until the targets are separated in range by 2.5lse-pulsewidths.     

Optimization of Surveillance Radar with Instrumented Range

The influence of the instrumented range on the selection of the radar parameters for maximal detection range is described. Procedures for optimization of the performance of the radar by an appropriate setting of its parameters, for specified instrumented range, are presented.     

Atmospheric Lens Effect; Another Loss for the Radar Range Equation

A small additional loss for radar range calculations at low grazing angles is described. This loss results because the variation in atmospheric refraction versus altitude makes the atmosphere act like a lens, causing thinning of radar signal energy to and from the target, independent of frequency. The magnitude of loss is derived and is plotted versus grazing angle and range. The maximum two-way loss, occurring at zero degrees grazing angle and a range well beyond the atmosphere, is 2.9 dB.     

Recent Breakthroughs in RF Photonics for Radar Systems

Radar systems require transmission of very high purity signals. Photonics is now mature enough to achieve analog transmission with very low noise, strong immunity, and wide-bandwidth even in harsh environments. We present our recent developments of optimized optical links dedicated to radar and multifunction systems     

Faraday Loss for L-Band Radar and Communications Systems

The mechanism of Faraday rotation as it affects radar and communication propagation has been extensively treated (1, 7). The purpose of this paper is to point out the magnitude of the effect and its possible consequences which have not been appreciated. Contrary to what many believe, the two-way Faraday rotation angle and loss can be large at L-band for ground-based, linearly polarized radar systems observing targets above the ionosphere. Similarly, the one-way Faraday rotation and loss for linearly polarized, ground-to-space pace communication links at comparable frequencies can be large. The magnitude of the rotation loss depends on the location of the radar or communication station in latitude and longitude, the condition of the ionosphere, and the elevation and azimuth angles of the target. For example, based on the total electron content in 1970 (a peak sunspot activity year) at L-band, a two-way Faraday rotation greater than 50°a loss greater than 3.8 dB is calculated to occur at 60° N, 70° W, 75 percent of the time between the hours of 10 A.M. and 4 P.M. for nine months, and 22 percent of the total time for the entire year, when looking toward the south magnetic pole at low elevation angles. For the same year this rotation and loss at 15°N, 150° is calculated to occur 48 percent of the total time when looking south at low elevation angles.     

Artificial Beam Sharpening Technique for Radar Beacon Systems

A method of improving angular discrimination artificially in radar beacon systems, without going to extremely high frequencies of operation or using unreasonably large interrogator antennas, involves the use of a null-type antenna pattern superposed on a normal directional beam. The effective are over which replies are obtained is determined by an amplitude discriminator circuit within the beacon which compares the amplitude of the pulse signals received on the null pattern with those received via the directional beam. Only if the latter exceed the former by a predetermined amount does the beacon produce a reply. The method, which has been tried experimentally and its theory verified, produces an increase in traffic handling capacity, as well as improved angular resolution, by reducing unwanted triggering and, hence, clutter on the display and the over-interrogation of transponder beacons. An antenna is described which eliminates triggering on sidelobes by providing the proper current distribution to the radiating elements to cause the null pattern to cover the sidelobes of the normal beam. Triple-pulse amplitude discriminators have been built and tested in a double-pulse interrogation system. Some theoretical considerations and design curves and equations for use in designing nulltype antennas are given in the Appendix.     

Optimal Digital Beam Splitting for Radar Beacon Systems

Beam splitting for a radar beacon system that scans in azimuth is investigated from a theoretical viewpoint. The video output is quantized into two levels corresponding to a detection and no detection. Further, the antenna sensitivity profile is described by sin ?/?. For this system, a digital method of beam splitting that minimizes angular error is developed. Prior information about the probable location of targets can be included. Both Bayesian and minimax approaches are developed. The minimax estimate of the target azimuth is the average of the angles at which beacon signals are detected. The antenna beam can be interpolated by a factor of 10 when the signal power is 3 dB above the noise and without prior azimuth information The interaction of beam splitting and detection is discussed.     

Improved Antenna Systems for ILS Localizers

For many years Norwegian airports have been equipped with instrument landing system (ILS) localizers of conventional type. Most of the localizers, however, were found not to perform very well on these sites. The course bends were too large and even moderate amounts of snow and ice could cause the localizer to fall out of operation. To overcome these difficulties, the requirements for localizer operation at these airports were analyzed and a new and improved antenna system developed. After a long period of operational testing, during which it was made clear that a substantial improvement in performance had been achieved, the new localizer antenna system is now in operation at 13 Norwegian airports.     

改进 K-均值算法在雷达辐射源信号预分选中的应用

雷达辐射源信号分选是电子对抗领域一个关键技术,随着电子技术的发展,电磁环境日趋复杂,信号分选的难度越来越大,在这样的条件下,我们应该寻求新的解决问题的方法.本文首先概述了雷达辐射源信号分选意义、系统组成和分选流程,然后介绍了改进 K-均值算法.为了有效实现信号分选,提出了基于改进K-均值算法的信号分选方法,该方法可对到达角、载频和脉宽参数进行分选.最后进行了仿真实验,结果表明该方法实现简单,分选效果较好     

一种基于高分辨率距离像自动目标识别新方法

提出了一种基于高分辨率距离像的联合对准与识别新方法。该方法结合功率变换的使用，在利用8米雷达目标实测数据进行的识别实验中，获得了较高的正确识别率。