New radar technology to free-up radio spectrum

New radar technology could help free up highly sought after radio spectrum currently used for air traffic surveillance.

The government has tasked the Civil Aviation Authority (CAA) with investigating options that would allow it to release bandwidth in the current air traffic radar spectrum allocation – in the ‘S Band’ between 2.7 and 2.9 GHz – to help meet its aspiration to free up 500 MHz of public spectrum by 2020.

In response, Cambridge technology firm Aveillant has been awarded a contract by the CAA to demonstrate the ability of its Holographic Radar technology to provide a spectrum-efficient alternative to S-band radar.

At present each radar typically has its own frequency assignment, but Aveillant hopes to demonstrate a surveillance system that can enable all air traffic control radars in the UK to operate through a single frequency assignment, separate from the ‘S Band’.

The firm’s radars use the L band frequency as opposed to the highly congested S band, used by current air traffic control radars and highly sought after by mobile phone operators.

Gordon Oswald, chief technology officer at Aveillant, said: “This is not a simple problem to solve, but based on our experience with Holographic Radar we’re confident that we are best placed to do so.

“Air traffic control radars cannot be simply shifted to another frequency, such as L band: this would then itself become too congested. At the same time, a much higher frequency is less suitable for long-range air traffic control radar due to atmospheric effects.

“This problem is ripe for a solution that changes the way air traffic radars occupy bandwidth. It’s going to be a demanding project to show how this solution will work – but one that we’re well equipped to handle.”

According to the firm, its 3D Holographic Radar is also proven to successfully mitigate the effect of wind farms on radar and has excelled in trials held by US and UK aviation stakeholders.

Source

1954 - This is "shipboard radar"!

This is "shipboard radar"! A simple phrase for some of the most fantastic electronic equipment of our age.

Distant Early Warning Line- Alaska

'Warning Star'

Listening! by artist Robert Riggs

DEW Line radar- Thule AFB- Greenland

USAF- Michael Tolzman

1950 -rubber-fortress

artist - Frank Tinsley

Ми-28Н с модифицированной РЛС

Новейшая фотография известного боевого вертолета Ми-28Н (бортовой номер "36 желтый", серийный номер 01-05, заводской номер 34012835105), используемого ОАО "Московский вертолётный завод имени М.Л. Миля" для отработки бортовой РЛС Н025 в надвтулочном обтекателе. Данный борт стал первым экземпляром вертолета Ми-28Н, получившем РЛС Н025, начав испытательные полеты с ней в феврале 2007 года. На данной фотографии, сделанной 2 апреля 2012 года, заметно, что обтекатель антенны РЛС несколько отличается деталями от ранее использовавшегося, что заставляет сделать вывод о начале испытаний доработанного варианта РЛС Н025.

Ми-28Н (бортовой номер "36 желтый", серийный номер 01-05, заводской номер 34012835105) с модифицированной РЛС Н025. Панки, 02.04.2012 (с) kabuki/russianplanes.net

Fundamentals of radar signal processing by Mark A. Richards

Source

Annotated bibliography - "Pulse compression in Radars"

Listing are chronological

• Woodward, P.M., Probability and Information Theory, With Applications to Radar, New York: McGraw-Hill Book Co. (1955).
  Fundamentals of resolution theory and ambiguity functions, including linear-FM pulse.
• Cook, C.E., "Modification of Pulse-Compression Waveforms," Proc. NEC 14, 1958, pp 1058-67.
  Basic paper on linear FM pulse compression technique.
• Cook, C.E., "Pulse Compression-Key to More Efficient Radar Transmission," Proc IRE 48, No 3, Mar. 60, pp 310-316.
  Basic paper on linear-FM pulse compression technique. Reprint Paper No. 1 in Source.
• Westerfield, E.C., Prager, R.H. and Stewart, J.L. "Processing Gains Against Reverberation (Clutter) Using Matched Filters," IRE Trans IT-6, No 3, Jun 1960, pp 342-349.
  Use of Woodward ambiguity function to calculate signal-to-clutter ratio in radar and sonar systems.
• Klauder, J.R. et. al., "The Theory and Design of Chirp Radars," BSTJ 39, No 4, Jul 1960, pp 745-808.
  Basic paper on linear-FM pulse compression theory, sidelobe reduction, and error effects. Reprint Paper No. 2 in Source.
• Klauder, J.R., "The Design of Radar Signals Having Both High Range Resolution and High Velocity Resolution," BSTJ 39, No 4, Jul 1960, pp 809-820.
  Derivation of waveform having circularly symmetric ambiguity function. Required amplitude modulation precludes efficient transmission.
• Key, F.L., Fowle, E.N. and Haggarty, R.D., "A Method of Designing Signals of Large Time-Bandwidth Product," IRE Conv Record, 1961, Pt. 4, pp 146-154.
  Design of signals for which envelope shape and autocorrelation function are separately specified.
• Ramp, H.O. and Wingrove, E.R., "Principles of Pulse Compression," IRE Trans M/L-5, No 2, Apr 1961, pp 109-116.
  Basic paper on linear-FM pulse compression principles and applications. Reprint Paper No. 3 in Source.
• Cook, C.E., "General Matched-Filter Analysis of Linear FM Pulse Compression," Proc IRE 49, No 4, Apr 1961, p 831.
  Considers effect of Doppler shift on output waveform of filter matched to linear-FM signal, including bandwidth restriction.
• DiFranco, J., "Closed-Form Solution for the Output of a Finite-Bandwidth Pulse-Compression Filter," Proc IRE 49, No 6, Jun 1961, pp 1086-87.
  Evaluation of integrals leading to output waveform in band limited cases.
• DiFranco, J.V. and Rubin, W.L., "An Interpretation of 'Paired Echo Theory' for Time-Domain Distortion in Pulsed Systems and an Extension to the Radar 'Uncertainty Function'," Proc IRE 49, No 9, Sep 1961, pp 1432-1433.
  Description of spurious outputs caused by frequency-domain and time-domain distortions.
• Reed, J., "Long-Line Effect in Pulse Compression Radar," Microwave Journal 4, No 9, Sep 1961, pp 99-100.
  Effect of transmission line mismatch on phase-vs-frequency response of radar system. Reprint Paper No. 4 in Source.
• Ramp, H.О. and Wingrove, E.R., "Performance Degradation of Linear FM Pulse Compression," Proc IRE 49, No 11, Nov 1961, p 1693.
  Analysis of output waveform of Doppler shifted signal, including second-order Doppler terms which can be important for large time-bandwidth product.
• Cook, C.E., "Effects of Phase-Modulation Errors on Radar Pulse Compression Signals," IRE Conv Record, 1962, Pt 4, pp 174-184.
  Analysis and experimental data on effect on sinusoidal phase errors on output waveform.
• Thor, R.C., "A Large Time-Bandwidth Product Pulse Compression Technique," IRE Trans MIL-6, No 2, Apr 1962, pp 169-173.
  Use of logarithmic, rather than linear, frequency modulation is shown to permit use of greater time-bandwidth products on targets with large radial velocity. Reprint Paper No. 5 in Source.
• DiFranco, J.V. and Rubin, W.L., "Analysis of Signal Processing Distortion in Radar Systems," IRE Trans MIL-6, No 2, Apr 1962, pp 219-227.
  Describes effects of phase and amplitude distortion on ambiguity function shape and sidelobe levels.
• Cook, C.E. and Heiss, W.H., "Linear FM Pulse Compression Doppler Distortion Effects," Proc IRE 50, No 6, Jun 1962, pp 1535-1536.
  Further discussion of dispersive Doppler effect and different viewpoints of Cook (1961) and Ramp and Wingrove (1961).
• Fryberger, D., "On the Use of Pulse Compression for the Enhancement of Radar Echoes from Diffuse Targets," Proc IRE 50, No 9, Sep 1962, pp 1993-1994.
  Compares effect of pulse compression on SNR and resolution for diffuse and discrete targets.
• Rubin, W.L. and DiFranco, J.V., "The Effects of Doppler Dispersion on Matched Filter Performance," Proc IRE 50, No 10, Oct 1962, pp 2127-2128.
  Expressions are derived for the difference between simple frequency shift and Doppler shift with dispersion, and it is shown that this difference is negligible for time-bandwidth products less than 1000.
• Fowle, E.N. el. al., "A Pulse Compression System Employing a Linear FM Gaussian Signal." Proc IEEE 51, No 2, Feb 1963, pp 304-312.
  Design and equipment considerations for low-sidelobe pulse compression systems using approximations to Gaussian weighting.
• Cook, C.E., "Pulse-Compression Paired-Echo Experiments," Proc IEEE 51, No 2, Feb 63, pp 383-384.
  Experimental verification of paired-echo response caused by sinusoidal phase errors in pulse compression signal.
• Temes, C.L. et. al. "Pulse Compression System for a Down-Range Tracker," IEEE Conv Rec 1963, Pt 8, pp 71-81.
  Description of 4 MHz 2 ms pulse compression waveform for 425 MHz instrumentation radar.
• Cook, C.E., "Transmitter Phase Modulation and Pulse Compression Waveform Distortion," Microwave Journal 6, No 5, May 1963, pp 63-69.
  Analysis of paired-echo effect of sinusoidal phase error, and sidelobe increase caused by localized phase error in chirp signal. Reprint Paper No. 6 in Source.
• Minis, W.B., "The Detection of Chirped Radar Signals by Means of Electron Spin Echoes," Proc IEEE 51, No 8, Aug 1963, pp 1127-1134.
  Theory and experimental results using compression filter based on paramagnetic resonance line at 6.7 GHz.
• Bernfeld, M., "Pulse Compression Techniques," Proc IEEE 51, No 9, Sep 63, p 1261.
  Comparison of systems using series and parallel dispersive elements to generate large time-bandwidth products.
• Lurin, E.S., "Digital Pulse Compression Using Polyphase Codes," Proc IEEE 51, No 9, Sep 63, pp 1262-1263.
  Implementation and ambiguity function of digital equivalent of linear and triangular-FM pulse compression.
• Fowle, F.N., "The Design of FM Pulse Compression Signals," IEEE Trans IT-10, No 1, Jan 1964, pp 61-67.
  Discusses design of waveform having arbitrary transmitted envelope, to produce given autocorrelation function.
• Cook, C.E. and Paolillo, J., "A Pulse Compression Predistortion Function for Efficient Sidelobe Reduction in a High-Power Radar," Proc IEEE 52, No 4, Apr 1964, pp 377-89.
  Describes use of increased sweep rate on leading and trailing edges of pulse to reduce paired-echo sidelobes.
• Cook, C.E., "A Class of Nonlinear FM Pulse Compression Signals," Proc IEEE 52, No 11, Nov 1964, pp 1369-1371.
  Analysis of nonlinear chirp to achieve sidelobe reduction, showing sensitivity to Doppler shift.
• Bernfeld, M. et. al., "Matched Filtering, Pulse Compression and Waveform Design," Microwave Journal, Oct, Nov, Dec 1964; Jan 1965, pp 57-64, 81-90, 70-76, 73-81.
  Thorough discussion and analysis of linear and nonlinear FM and discrete code waveforms and their ambiguity functions. Reprint Paper No. 7 in Source.
• Bogotch, S.E. and Cook, C.E., "The Effect of Limiting on the Detectability of Partially Time Coincident Pulse Compression Signals," IEEE Trans M/L-9, No 1, Jan 1965, pp 17-24.
  Theory and experimental results on suppression of small signals by overlap of expanded pulse from large, adjacent signal which would be resolvable except for receiver limiting. Reprint Paper No. 8 in Source.
• Peebles, P.Z. and Stevens, G.H., "A Technique for the Generation of Highly Linear FM Pulse Radar Signals," IEEE Trans M/L-9, No 1, Jan 1965, pp 32-38.
  A method is described for generating a staircase FM waveform, closely approximating linear sweep with very high accuracy.
• Rihaczek, A.W., "Radar Signal Design for Target Resolution," Proc IEEE 53, No 2, Feb 1965, pp 116-128.
  Relationships between resolution and measurement uncertainty are explored for different signals and clutter environments.
• Rihaczek, A.W., "Range Accuracy of Chirp Signals," Proc IEEE 53, No 4, Apr 1965, pp 412-13.
  It is shown that the diagonal ambiguity of chirp signals does not lead to range uncertainty on targets of unknown Doppler if the range reading is interpreted as applying at a time displaced from the actual echo time. Reprint Paper No. 9 in Source.
• Jacob, J.S., "Graphical Comparison of a Doppler-Shift Advantage for Three Pulse-Compression Techniques," Proc 9th Natl Conv on Military Electr, IELE, Wash, D.C., 1965, pp 382-387.
  Degradation in SNR with Doppler shift is compared for three waveforms, and linear FM is shown to be affected less than phase-coded or frequency-stepped waveforms.
• Ward, M.X., ''Matched Scan Rate Pulse-Compression Analysis," Proc IEEE 54, No 4, Apr 1966, pp 707-708.
  Derives output waveform for compression filter with arbitrary impulse response duration, showing approach to (sin x)/x shape for long durations.
• Rihaczek, A.W., "Doppler-Tolerant Signal Waveforms," Proc IEEE 54, No 6, Jun 1966, pp 849-857.
  Discussion of non-linear FM modulations and pulse trains for which Doppler distortions can be ignored.
• Hollis, E.E., "Comparison of Combined Barker Codes for Coded Radar Use," IEEE Trans AES-3, No 1, Jan 1967, pp 141-143.
  Sidelobe levels are determined for sequences of four 13-bit Barker Codes and thirteen 4-bit codes, showing maximum amplitude 13/52 times main lobe.
• Lipman, M.A. "A Useful Property of the Generalized Chirp Signal Ambiguity Function," Proc IEEE 55, No 7, Jul 1967, pp 1241-1242.
  Ambiguity function generalized to include mismatched sweep rate as well as delay and Doppler shift.
• Cook, C.E. and Bernfeld, M. Radar Signals, New York: Academic Press, 1967.
  Basic text on pulse compression principles and implementation.
• Kibbler, G.O.T.H., "The CLFM: a Method of Generating Linear Frequency-Coded Radar Pulses," IEEE Trans AES-4, No 3, May 68, pp 385-391.
  Describes coherent linear frequency modulator used in active generation of chirp signals and in conversion of received signals to constant frequency.
• Mitchell, R.L. and Rihaczek, A.W., "Matched-Filter Responses of the Linear FM Waveform," IEEE Trans AES-4, No 3, May 1968, pp 417-432.
  Equations and three-dimensional plots of ambiguity functions with and without weighting and mismatch.
• Rihaczek, A.W., and Mitchell, R.L., "Design of Zigzag FM Signals," IEEE Tram AES-4, No 5, Sep 1968, pp 680-692.
  Presents three-dimensional plots of ambiguity functions of simple and multiple-segment zigzag FM waveforms.
• Haggarty, R.D., Hart, L.A. and O'Leary, G.C, "A 10.000 to 1 Pulse Compression Filter Using a Tapped Delay Line Linear Filter Synthesis Technique," IEEE EASCON Rec, 1968, pp 306-314.
  Synthesis procedure and experimental results on delay-line filters for large time-bandwidth product pulse compression and other applications. Reprint Paper No. 10 in Source.
• Belknap, D.J., "An Experimental Measurement of the Detection Capability of a Linear FM Pulse Compression System," IEEE EASCON Rec, 1968, pp 315-318.
  Detection performance of 1000:1 pulse compression system is compared with ideal matched filter and with Doppler filter bank. Results are within a fraction of a dB of the matched filter.
• Ruttenberg, K. and Chanzit, L., "High Range Resolution by Means of Pulse-To-Pulse Frequency Shifting," IEEE EASCON Record, 1968, pp 47-51.
  Method of obtaining resolution in system using agile magnetron rather than intrapulse FM. Reprint Paper No. 11 in Source.
• Leith, E.N., "Optical Processing Techniques for Simultaneous Pulse Compression and Beamsharpening," IEEE Trans AES-4, No 6, Nov 1968, pp 879-885.
  Combined processing for synthetic aperture resolution and pulse compression, using two-dimensional optical filter.
• Bechtel, M.E., "Generalized Paired-Echo Analysis for Band-pass Systems," Proc IEEE 57, No 2, Feb 1969, pp 204-205.
  Description of phase and amplitude distortion terms in bandpass systems in terms of advanced and delayed replicas of ideal signal.
• Palmieri, C.A. and Cook, C.E., "The Ambiguity Properties of Multiple-Segment Linear FM Signals," Proc IEEE 57, No 7, Jul 1969, pp 1323-1325.
  Approximate analysis of mainlobe and near-sidelobe response of multiple-segment FM waveforms.
• Vannicola, V.C., "Range Dependent Waveform of an Active Weighted Pulse Compression Receiver," IEEE Trans AES-5, No 5, Sep 1969, pp 847-864.
  Output waveforms for pulse compression systems in which the signal is time weighted by a function not exactly centered on the received signal. Reprint Paper No. 12 in Source.
• Nathanson, F.E., Radar Design Principles, New York, McGraw-Hill, 1969.
  Text covering radar clutter and resolution requirements, with chapters devoted to phase coding and to linear-FM processing techniques.
• Rihaczek, A.W., Principles of High-Resolution Radar, New York: McGraw-Hill, 1969.
  Basic text on waveform design and results in resolution, detection and measurement in clutter.
• Campbell, B.D., "High-Resolution, Radar Coherent Linear FM Microwave Source," IEEE Trans AES-6, No 1, Jan 1970, pp 62-72.
  Design of BWO generator for 16 Hz FM Sweep at S-band.
• Millett, R.E., "A Matched-Filter Pulse-Compression System Using a Nonlinear FM Waveform," IEEE Trans AES-6, No 1, Jan 1970, pp 73-78.
  Design and test data on low-sidelobe pulse compression waveform having 0.1 dB mismatch loss. Reprint Paper No 13 in Source.
• Cohen, S.A., "Generalized Response of a Linear FM Pulse Compression Matched Filter," IEEE Trans AES-6, No 5, Sep 1970, pp 708-712.
  Curves are derived which show losses in peak output caused by mismatch of pulse width, sweep rate and center frequency.
• Caputi, W.J., Jr., "Stretch: A Time-Transformation Technique," IEEE Trans AES-7, No 2, Mar 1971, pp 269-278.
  Technique for very high resolution with relatively simple processor covering a limited range window. Reprint Paper No. 14 in Source.
• Hartt, J.K. and Sheats, L.F., "Application of Pipeline FFT Technology in Radar Signal and Data Processing," IEEE EASCON Record 1971, pp 216-221.
  Pipeline FFT processors for pulse compression and Doppler filtering are described. Reprint Paper No. 15 in Source.
• Halpern, H.M. and Perry, R.P. "Digital Matched Fitters Using Fast Fourier Transforms," IEEE EASCON Record 1971, pp 222-230.
  A 10-MHz bandwidth digital filter, suitable for high-resolution pulse compression, is described. Effects of different word lengths for signal and reference waveforms are explored by simulation. Reprint Paper No. 16 in Source.
• Woerrlein, N.H., "Spurious Target Generation Due to Hard Limiting in Pulse Compression Radars," IEEE Trans AES-7, No 6, Nov 1971, pp 1170-1178.
  Method and results for calculating spurious outputs caused by hard limiting of three overlapping signals, using phase-coded waveform.
• Rihaczek, A.W., "Radar Waveform Selection-A Simplified Approach," IEEE Trans AES-7, No 6, Nov 1971, pp 1078-1086.
  Waveforms are divided into four classes, each with distinct resolution properties, permitting a systematic approach to waveform selection. Reprint Paper No 17 in Source.
• Jones, W.S., Kempf, R.A. and Hartmann, C.S., "Practical Surface Wave Chirp Fillers for Modern Radar Systems," Microwave Journal, May 1972.
  Design, application and performance of surface acoustic wave filters for 8 MHz x 12.5 usec and 2 MHz x 25 usec pulse compression. Reprint Paper No 18 in Source.
• Ackroyd, M.H. and Ghani, F., "Optimum Mismatched Filters for Sidelobe Suppression," IEEE Trans AES-9, No 2, Mar 1973, pp 214-218.
  At some expense in complexity and small loss in SNR, time sidelobes can he reduced without amplitude weighting on transmit.
• Powell, Т.Н., Jr. and Sinsky, A.I., "A Time Sidelobe Reduction Technique for Small Time-Bandwidth Chirp," IEEE Trans AES-10, No 3, May 1974, pp 390-392.
  Digital filter design to compensate for effect of Fresnel ripples in spectrum of chirp signal.
• Hollan, M.G. and Claiborne, L.T., "Practical Surface Acoustic Wave Devices," Proc IEEE 62, No 5, May 1974, pp 582-611.
  Tutorial discussion of SAW devices and their application, with extensive bibliography.
• Fitzgerald, R.J., "Effects of Range-Doppler Coupling on Chirp Radar Tracking Accuracy," IEEE Trans AES-10, No 4, Jul 1974, pp 528-532.
  Describes interaction of chirp range-Doppler coupling with truncation error of GHK filler, such that positive chirp slope leads to reduced error of filtered data.
• Caputi, W.J., "Stabilized Linear FM Generator," IEEE Trans, AES-9, No 5, Sep 1973, pp 570-578.
  Closed-loop technique for controlling slope of linear frequency sweep generator, as applied to 240 MHz x 120 usec active pulse-compression waveform generator.

Source: Radars. Vol 3. Pulse Compression. By David K. Barton. Dedham: Artech House, Inc., 1975.

An Evaluation of Two NEXRAD Wind Retrieval Methodologies and Their Use in Atmospheric Dispersion Models

Two entirely different methods for retrieving 3D fields of horizontal winds from Next Generation Weather Radar (NEXRAD) radial velocities have been evaluated using radar wind profiler measurements to determine whether routine wind retrievals would be useful for atmospheric dispersion model applications. The first method uses a physical algorithm based on four-dimensional variational data assimilation, and the second simpler method uses a statistical technique based on an analytic formulation of the background error covariance. Both methods can be run in near–real time, but the simpler method was executed about 2.5 times as fast as the four-dimensional variational method. The observed multiday and diurnal variations in wind speed and direction were reproduced by both methods below 1.5 km above the ground in the vicinity of Oklahoma City, Oklahoma, during July 2003. However, wind retrievals overestimated the strength of the nighttime low-level jet by as much as 65%. The wind speeds and directions obtained from both methods were usually similar when compared with profiler measurements, and neither method outperformed the other statistically. Within a dispersion model framework, the 3D wind fields and transport patterns were often better represented when the wind retrievals were included along with operational data. Despite uncertainties in the wind speed and direction obtained from the wind retrievals that are higher than those from remote sensing radar wind profilers, the inclusion of the wind retrievals is likely to produce more realistic temporal variations in the winds aloft than would be obtained by interpolation using the available radiosondes, especially during rapidly changing synoptic- and mesoscale conditions.- Reference

Maximum Position Alignment Method for Noisy High-Resolution Radar Target Classification

In this paper, the alignment of noisy high-resolution radar signals using the maximum position method is studied. The relationship between the shift estimation and the signal-to-noise ratio is considered. As a result, two analytical expressions are obtained that approximate the root-mean-square error of the difference in the shift estimation with and without noise. These two expressions allow us to improve the understanding of the sensitivity to noise of the Maximum Position alignment method. - Reference

Predicted Detection Performance of MIMO Radar

It has been shown that multiple-input multiple-output (MIMO) radar systems can improve target detection performance significantly by exploiting the spatial diversity gain. We introduce the system model in which the radar target is composed of a finite number of small scatterers and derive the formula to evaluate the theoretical probability of detection for the system having an arbitrary array-target configuration. The results can be used to predict the detection performance of the actual MIMO radar without time-consuming simulations. - Reference

Radar Revisited (review of "Radar Handbook, 3rd ed." by Merrill Skolnik) [Book Reviews]

This is the third edition of an established handbook, edited by one of the most-recognized names in the field of radar technology. The volume is a compilation of 26 chapters, authored by individuals with a thorough command of, and incredible credentials in, the topics of their chapters. Most chapters have a large number of figures (up to several dozen) and extensive bibliographies. Chapters range from fairly quantitative and mathematical ones to cursory and descriptive ones. Some sections of the handbook represent a concise and readable summary of the state-of-the-art of knowledge on their topics; others are a sketchy collection of remarks for which it is difficult to identify the benefits to be derived by the reader. There is little coordination between chapters where similar topics may be discussed, and a lack of any cross-referencing. There are also weaknesses in the index, as well. While the older, classical radar topics receive much attention, the book overlooks newer areas such as coverage of automotive radars. This volume will appeal to the generalists with interest in the conventional radar subjects, and to others as a starting point for locating sources with more detailed information. - Reference

Measurements of the Transmission Loss of a Radome at Different Rain Intensities

Results on the transmission loss of a dry and a wet C-band weather radar radome at different rain intensities are presented. Two methods were used in the study, both carried out under laboratory conditions. In the first method, the complex permittivity of a dry radome is measured and the transmission loss calculated. To analyze the transmission loss of a wet radome, the thickness of a continuous water layer on the surface of a radome at different rain intensities and the complex permittivity of water are calculated. In the second method, the transmission loss is measured as a free space transmission measurement with a 1.3-m² piece of a radome panel. The piece is measured as dry and as doused by a rain system designed for the measurements. The measurements are performed with a dirty, cleaned, and waxed radome to examine the effects of maintenance measures with an old radome on the transmission loss. Because the transmission loss as a function of rain intensity is measured with a small piece of radome, a method is developed to scale the free space measurements for a complete 6.7-m-diameter radome with equal dielectric properties. Results of the one-way transmission loss of a dry radome with the permittivity and free space measurements are in a good agreement (0.34 and 0.35 dB, respectively). According to the analysis, a continuous water layer on a radome has a significant influence on the transmission loss. A 3-dB two-way transmission loss caused by a dirty radome is observed at a rain intensity of 15.1 mm h⁻¹. Waxing gives promising results in reducing the wet radome loss because the waxing prevents the formation of a continuous water layer on the surface of the radome.- Reference

A Study on Optimum Tilt Angle for Wind Estimation Using Indian MST Radar

The effect of tilt angle on horizontal wind estimation is studied using Indian mesosphere–stratosphere–troposphere (MST) radar located at Gadanki (13.45°N, 79.18°E). It operates in Doppler beam swinging (DBS) mode with a beamwidth of 3°. Horizontal winds are computed for different tilt angles from 3° to 15° with an increment of 3° from a height range of 3.6–18 km. The effective beam pointing angle (θ_eff) is calculated to determine the effect of aspect sensitivity on the determination of horizontal wind components. For different tilt angles radar-derived winds are compared with simultaneous GPS sonde wind measurements, which were launched from a nearby site. The first method utilizes direct comparison of radar-derived winds with those of GPS sondes using the actual beam pointing angle; the second method uses the effective beam pointing angle derived from the ratios of two oblique beams. For this study a variety of statistics were explored in terms of standard deviation, correlation coefficient, and percentage error. From the results it is observed that in agreement with previous studies, the effective beam pointing angle deviates from the actual beam pointing angle, which results in the underestimation of horizontal wind components, and also when tilt angle is close to zenith and far from zenith, the estimation of horizontal winds is found to be far from true values at different heights. Radar wind estimation has better agreement with GPS sonde measurement when the off-zenith angle is around 10°. It is also found that correction to the actual beam pointing angle provides 3%–6% improved agreement between the radar and GPS wind measurements. -Reference

Sequential Along-Track Integration for Early Detection of Moving Targets

This paper concerns the joint multiframe sequential target detection and track estimation in early-warning radar surveillance systems. The rationale for applying sequential procedures in such a scenario is that they promise a sensitivity increase of the sensor or, alternatively, a reduction in the time needed to take a decision. Unlike previous works on sequential radar detection, the attention is not restricted to stationary targets, namely position changes during the illumination period are allowed. Starting from previous sequential rules, different truncated sequential strategies are proposed and assessed: they are aimed at orienting the sensor resources towards either the detection or the track estimation or the position estimation. Bounds on the performances of the proposed procedures in terms of the system parameters are derived and computational complexity is examined. Also, numerical experiments are provided to elicit the interplay between sensor-target parameters and system performances, and to quantify the gain with respect to other fixed-sample-size procedures. - Reference

Signal Synthesis and Receiver Design for MIMO Radar Imaging

Multiple-input–multiple-output (MIMO) radar is an emerging technology that has significant potential for advancing the state-of-the-art of modern radar. When orthogonal waveforms are transmitted, with $M+N$ ($N$ transmit and $M$ receive) antennas, an $MN$-element filled virtual array can be obtained. To successfully utilize such an array for high-resolution MIMO radar imaging, constant-modulus transmit signal synthesis and optimal receive filter design play critical roles. We present in this paper a computationally attractive cyclic optimization algorithm for the synthesis of constant-modulus transmit signals with good auto- and cross-correlation properties. Then we go on to discuss the use of an instrumental variables approach to design receive filters that can be used to minimize the impact of scatterers in nearby range bins on the received signals from the range bin of interest (the so-called range compression problem). Finally, we present a number of numerical examples to demonstrate the effectiveness of the proposed approaches.- Reference