Digital Beam Forming in Radar

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Digital Beam Forming in Radar

milstar: Improvements for Air-Surveillance Radar Merrill Skolnik Systems Directorate Naval Research Laboratory Washington, D. C. 20375 http://dasl.mem.drexel.edu/Hing/Improvements%20for%20Air-surveillance%20radar.pdf L band, from 1215 to 1400 MHz, has been a popular frequency for long-range air-surveillance radar. There is also a near-by band, extending from 850 to 942 MHz, in which radar is authorized to operate. The U. S. Navy's ANEPS-49 uses this band. The initial motivation for pursuing the Senrad concept was to develop and demonstrate a radar that would be less vulnerable to electronic countermeasures than a conventional radar. For this reason, we chose to design Senrad to operate within the frequency range from 850 to 1400 MHz, a relative bandwidth of about 50% A radar, of course, is not normally allowed to operate without restrictions over such a wide bandwidth since there are other important military and civilian electromagnetic services that occupy this band. Senrad operated simultaneously within the 1215-1400 MHz band and the 850-942 MHz band to demonstrate capabilities not available with conventional narrow- band air-surveillance radars systems. ---------------------- Naval Research Laboratory Systems Aspects of Digital Beam Forming Ubiquitous Radar MERRILL SKOLNIK Systems Directorate June 28, http://www.dtic.mil/cgi-bin/GetTRDoc?AD=ADA403877&Location=U2&doc=GetTRDoc.pdf ----------------------------------- smotri gl. 2.13 M.Skolnik ,Radar izdanie 2008 goda http://www.scribd.com/doc/49249408/0071485473-Radar-Handbook3rd 2.13 Dynamic Range and A/D convesion cosiderations ----------------------------------- Dynamic Range and Stability requirement 4.24 ADC in Doppler radar http://www.scribd.com/doc/49249408/0071485473-Radar-Handbook3rd ...The most stressing dynamic range requirement is due to main beam clutter ,when searching for small low flying target ------------------------------------------- example 4.15 C/N 53 db na wisote RLS 1000 fut/300 metrow trebuetsja 12 bit dlja 63 db -------------------------------- 5.12 Glawa 5 Merrril Skolnik 2008 goda MULTIFUNCTIONAL RADAR SYSTEMS FOR FIGHTER AIRCRAFT 1.Real beam map 0.5 -10 mgz 2.Doppler beam sharp 5-25 mgz 3. SAR 10 -500 mgz 4.A-S range 1-50 mgz 5.PVU 1-10 mgz 6.TF/TA 3-15 mgz 7.Sea surface search 0.2 -500 mgz 8.Inverse SAR 5-100 mgz 9. GMTI 0.5-15 mgz 10.Fixed target track 1-50 mgz 11.GMTT 0.5 -15 mgz 12.Sea Surface track 0.2-10 mgz 13.Hi power Jam 1-100 mgz 14.CAl/A.G.C 1-500 mgz 15A-S data link 0.5-250 mgz -------------------------------------

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milstar: Stoimost 16 -bitnix AZP AD9467 s SFDR 90 dBFS i snr 74 dbc by Fin 300 mhz = okolo 100 $ Stoimost samogo deschewogo 12 -bintongo 1 gsps ADS 5400 = 775 $ wse 12 bitnie imejut priemrno 56-57 dbc SNR na 1 ghz i64-66 dBFS SFDR http://www.ti.com/ww/en/analog/dataconverters/rf_sampling_adc.shtml http://www.msc-ge.com/de/produkte/elekom/linear/e2v/453-www.html http://www.msc-ge.com/de/6982-www/version/default/part/AttachmentData/data/EV12AS200ZPY_prel_April11.pdf?language=en lutschij 10 bit ,3gsps po publikazii ,ne serijnij SiC ,S-band 3 GS/s S-Band 10 Bit ADC and 12 Bit DAC on SiGeC Technology http://see.conference-services.net/resources/253/1452/pdf/RADAR2009_0293.pdf Soobrazenija pri razrabotke 10 bit 2.2 gsps folding interpolating ADc http://convergencepromotions.com/atmel/v_6/pdf/v_6_pg-43-48.pdf 7.3 GS/s S-Band 10 Bit ADC and 12 Bit DAC on SiGeC Technology http://see.conference-services.net/resources/253/1452/pdf/RADAR2009_0293.pdf

milstar: Potential Military Applications Air defense. Much of the previous discussion in this report related to the airdefense application. In addition to having a considerably reduced radiated peak power that lowers the probability of intercept, the ubiquitous radar can simultaneously search at long ranges with a low data rate, search at a higher data rate for low-altitude targets that pop-up at short range, control weapons to an intercept with a high data rate, acquire targets at any range much faster, and perform burnthrough and/or noncooperative target recognition with a long duration observation. Some air defense systems that employ multifunction phased array radars have only modest doppler processing because of the limited time they can dwell in any particular direction. Therefore, they can have difficulty in detecting moving targets in land or weather clutter. This can be a very serious limitation to military air defense. The reason for this lack of doppler capability is that good doppler processing requires a long time-on-target (or dwell time). As mentioned previously, a multifunction phased array radar for air defense does not always have the luxury of a long time-on-target because its many functions are time shared. An important advantage of a ubiquitous radar is that it can have a much longer time-on-target since its many functions are accomplished in parallel rather than one at a time. HF over-the-horizon (OTH) radar. The U. S. Navy ROTHR33 (relocatable over-the-horizon radar), developed in the late 1980s, already employs digital beam forming. It has 16 contiguous receiving beams covering a wide sector in azimuth and a wide-beam transmitting antenna covering the same angular 24 sector. This was an early application of DBF. Digital beam forming is easier to accomplish at HF than at microwave frequencies since HF OTH radar has much narrower signal bandwidths than does a microwave radar. ROTHR, however, cannot perform simultaneous multiple functions since its sixteen receiving beams and the single transmitting beam are stepped together in azimuth over eight sectors to provide 60 degrees of azimuth coverage. It should be relatively straight forward to now increase the number of receiving beams to include its entire coverage area. An HF OTH radar can detect aircraft, ships, ballistic missiles, and can provide the wind speed and direction over the ocean. Each of these requires a different dwell time and a different revisit time. For example, an OTH radar has to dwell for about one to three seconds to detect aircraft. The revisit time is from 10 to 20 s. Ship detection requires long dwell times of from several tens of seconds to about two minutes, but the revisit time can be one hour. Thus a conventional OTH radar that detects ships cannot simultaneously detect aircraft. An HF OTH ubiquitous radar, on the other hand, can simultaneously detect aircraft, ships, and ballistic missiles, and ocean winds. It might be noted that HF OTH radar can readily recognize helicopter targets by the harmonics introduced by the blade frequency, an important need for observing the battlefield. Ships have large radar echoes at HF, but they are of slow speed so their doppler shifted echo can be close to the doppler shifted echo from the moving sea. OTH radars for the detection of ships therefore require large antennas (over a mile long in some current OTH radars) in order to reduce the amount of sea clutter with which the target must complete. The long time of observation possible with a ubiquitous radar (since ships do not change course as rapidly as do aircraft) can result in narrow doppler filters, which might reduce the need for a large antenna. Likewise a cruise missile is less likely to perform maneuvers than a manned aircraft so its detection might be enhanced by the long-term integration offered by a ubiquitous radar. The HF OTH radar is a good candidate for a ubiquitous radar. The required technology is easier to achieve than at microwaves, there are multiple functions that would benefit from simultaneous operation, and the current OTH radars already have digital beam forming. Battlefield radar. Here it is assumed that the radar is on the ground. The multiple functions that might be performed by a single ubiquitous battlefield radar include: - Short range air surveillance and engagement of fixed-wing aircraft, helos, and battlefield UAVs. - NCTR of helicopters based on blade signature. - Mortar and artillery detection location, and direction of counter-fire. - Personnel and ground vehicle surveillance. - Moderate range air surveillance to obtain the "air picture" needed for situational awareness and air-traffic control. The first four of the above are generally of short range and might be obtained with one ubiquitous radar mounted on HMMWVs. It is not now obvious that general air surveillance (the fifth function listed above) should be included with the other four, or whether a separate longer range radar would be better. Airborne air-surveillance (AEW and AWACS). The chief benefit of a ubiquitous radar for airborne air-surveillance is low probability of intercept. (This assumes a wide operational bandwidth and a high duty cycle waveform.) Since these radars perform important military missions it should be expected that a determined adversary would want to negate their effectiveness. An ARM designed for such radars should be expected. Thus the benefits offered by a ubiquitous radar for low probability of intercept ought to be of value for this application. Airborne missile warning. LPI would be the chief reason for employing the ubiquitous concept. http://www.dtic.mil/cgi-bin/GetTRDoc?AD=ADA403877&Location=U2&doc=GetTRDoc.pdf

milstar: Navy's AMDR program focuses on digital beamforming technology Competition for the Navy's Air and Missile Defense Radar program is ramping up, and development of the S-band digital beamforming technology is emerging as the focus. Lockheed Martin said digital beamforming has advantages over analog beamforming. At the Naval Sea Systems Command testing site at Wallops Island, Va., S-band digital beamforming technology was demonstrated, Navsea officials confirmed

milstar: Raytheon Air and Missile Defense Radar Modules Excel During Testing by Staff Writers Tewksbury, MA (SPX) Sep 20, 2011 http://www.spacewar.com/reports/Raytheon_Air_and_Missile_Defense_Radar_Modules_Excel_During_Testing_999.html AMDR provides unprecedented capabilities for the Navy, beginning with the Arleigh Burke-class destroyers. It fills a critical gap in the joint forces' integrated air and missile defense capability, enabling highly effective missile defenses to be deployed in a flexible manner wherever needed. The radar suite consists of an S-band radar, X-band radar and radar suite controller. Raytheon's transmit/receive (T/R) modules for the U.S. Navy's Air and Missile Defense Radar (AMDR) program have passed a significant developmental testing milestone. Raytheon's Gallium Nitride modules exceeded Navy-specified requirements for extended, measured performance, demonstrating no degradation after more than 1,000 hours of testing. Currently working Phase II of the AMDR program, Raytheon is developing a technology demonstrator for the system's S-band radar and radar suite controller. During the radio frequency operating life testing, the modules demonstrated consistent power output across multiple channels. The more than 1,000-hour Radio Frequency Operating Life test was a self-imposed early milestone for Raytheon. "The threats that AMDR is designed to counter require leap-ahead technology that Raytheon is ready to deliver," said Raytheon Integrated Defense Systems' Kevin Peppe, vice president of Seapower Capability Systems. "We are seeing our Gallium Nitride (GaN) modules exceed the program's performance requirements, which ensures that the Navy will get the capability and reliability they need for this sophisticated radar system at an affordable cost." AMDR provides unprecedented capabilities for the Navy, beginning with the Arleigh Burke-class destroyers. It fills a critical gap in the joint forces' integrated air and missile defense capability, enabling highly effective missile defenses to be deployed in a flexible manner wherever needed. The radar suite consists of an S-band radar, X-band radar and radar suite controller. The system is fully scalable, enabling the radar to be sized according to mission need and to be installed on ships of varying size as necessary to meet the Navy's current and future mission requirements. The radar's digital beamforming capability enables it to perform multiple simultaneous missions, ---------------------------------------------------------------------------------------------------------- a critical feature that makes the system affordable and operationally effective for the Navy. Raytheon's skill and experience working with large-scale active phased-array radars spans the frequency spectrum from UHF to X/Ku-band and dates back to the Cobra Judy and Upgraded Early Warning Radar programs, continuing today with the advanced Dual Band Radar, AN/TPY-2 and Cobra Judy Replacement programs. The knowledge and experience gained from these programs will ensure that the AMDR S- and X-band radars operate in coordination across a variety of operational environments. The company has a long heritage of developing and producing some of the world's most capable air and missile defense radars, which positions it well for the AMDR competition. Additionally, Raytheon has produced more than 1.8 million AESA (active electronically scanned array) T/R modules to date and has decades of experience working with adaptive beamforming technologies. Raytheon is also a leading provider of high-performance GaN technology. Work on the AMDR program is performed at Integrated Defense Systems' Headquarters, Tewksbury, Mass.; at the Surveillance and Sensors Center, Sudbury, Mass.; at the Seapower Capability Center, Portsmouth, R.I.; and at the Integrated Air Defense Center, Andover, Mass. Raytheon has partnered with General Dynamics Advanced Information Systems and naval architect Gibbs and Cox in the concept and technology development of this next-generation radar solution. Learn more about AMDR here as well as Raytheon's radar heritage and leading-edge technologies. Related Links

milstar: Radar Digital Beam-Former Utilizing FPGA Based COTS Processors Edward J. Monastra Lockheed Martin Maritime Systems & Sensors edward.j.monastra@lmco.com, John E. Fontana Lockheed Martin Maritime Systems & Sensors john.e.fontana@lmco.com http://www.ll.mit.edu/HPEC/agendas/proc06/Day2/09_Fontana_Abstract.pdf Lockheed Martin has implemented a demonstration system to perform Real Time Digital Beam- Former Front End functions to serve as a risk reduction activity for a Digital Array Radar.

milstar: Northrop Grumman Develops Phased Array Radar with Digital Beam-Forming Sensing Technology Published on September 15, 2011 at 6:05 AM By Andy Choi Northrop Grumman in collaboration with CEA Technologies recently demonstrated the CEAFAR, a multi-functional active electronically scanned array (AESA) S-Band radar best suited for use in naval vessels irrespective of size, that includes offshore patrol craft, destroyers and cruisers. Northrop CEAFAR The CEAFAR is a phased array radar which incorporates state-of-the-art digital beam-forming. Fully scalable in terms of size, power and frequency, the radar system is customizable depending on the technical and operational requirements. The CEAFAR’s unique design allows each sensor to be tuned and adjusted individually. Using digital beam-forming (DBF) sensor technology, ------------------------------------------------------------ the CEAFAR can be fitted to existing as well as new vessels and can be configured for use in various threat scenarios as well as operating environments. The use of the radar helps extend the operational lifespan of the vessel as well as amplify the platforms’ mission capability. The Vice President,Operation of the Naval and Marine Systems Division at Northrop Grumman, Paul Sullivan explained that the scalability offered by the lightweight radar system offers unparalleled help to the warfighter. During the demonstration, carried out at the Undersea Systems facility located at Annapolis, CEA Technologies used a dual face unit to display the various capabilities and applications the radar system can provide to the armed forces. An Ethernet connection and power supply was required to control the two CEAFAR faces of the self-contained demonstration unit. Additionally Northrop Grumman’s NG Con and Integrated Combat Management System was integrated with the CEAFAR to showcase the system’s flexibility in terms of target detection by showcasing various threat scenarios with both controlled and uncontrolled maritime and air targets. Source: http://www.northropgrumman.com

milstar: http://www.es.northropgrumman.com/solutions/ceafar/ CEAFAR Active Phased Array Radar CEAFAR is an active, S-band, multi-function, phased array radar that is fully scalable in frequency, size and power based on the number and type of tiles in each face. This fully digital radar system incorporates advanced digital beam-forming and is user-configurable depending on operational and technical requirements. CEAFAR is a unique radar solution that allows each of the sensor elements to be individually tuned and adjusted. The system is extremely lightweight, and requires relatively modest cooling and power. CEAFAR is a fully digital beam-forming sensor that can be dynamically configured to meet a range of operating environments and threat scenarios. It can be fitted to both new build vessels and vessels already in service, to extend their operational lifespan and increase the range of missions capable of being performed by these platforms. Related Solutions AN/SPQ-9B Anti-Ship Missile Defense (ASMD) http://www.es.northropgrumman.com/solutions/spq9b/index.html AN/SPQ-9B Anti-Ship Missile Defense (ASMD) The AN/SPQ-9B is a multimode X-band pulse Doppler radar that detects all known and projected sea skimming missiles. News Releases Northrop Grumman and CEA Demonstrate Scalable CEAFAR Next-Generation Phased Array Sensor System ANNAPOLIS, Md. – Sept. 13, 2011 – Northrop Grumman Corporation (NYSE:NOC) and partner CEA Technologies Pty Limited successfully conducted a demonstration of CEAFAR, a scalable and tailorable S-Band Active Electronically Scanned Array (AESA) multi-function radar suitable for naval vessels as small as offshore patrol craft and as large as destroyers and cruisers. CEAFAR is an active, S-band, multi-function, phased array radar that is fully scalable in frequency, size and power based on the number and type of tiles in each face. This fully digital radar system incorporates advanced digital beam-forming and is user-configurable depending on operational and technical requirements. CEAFAR is a unique radar solution that allows each of the sensor elements to be individually tuned and adjusted. The system is extremely lightweight, and requires relatively modest cooling and power. CEAFAR is a fully digital beam-forming sensor that can be dynamically configured to meet a range of operating environments and threat scenarios. It can be fitted to both new build vessels and vessels already in service, to extend their operational lifespan and increase the range of missions capable of being performed by these platforms. "This type of scalability and tailoring is unparalleled in the radar domain, and represents a true capability advantage to the warfighter – at a fraction of the price of current demonstrated or fielded competitor radars," said Paul Sullivan, vice president of Operations for Northrop Grumman's Naval and Marine Systems Division. "Today's demonstration provided an opportunity to evaluate key attributes of the CEAFAR system and its potential application to our armed forces." During the tests conducted at Northrop Grumman's Undersea Systems business unit in Annapolis, CEA utilized its Dual Face Demonstration unit to showcase a broad range of applications and capabilities afforded by CEAFAR to representatives from the U. S., Australian and various other international armed forces. The self-contained Dual Face Demonstration unit consists of two CEAFAR faces requiring only power and an Ethernet connection to control the system. To enhance the demonstration, the CEAFAR radar was successfully integrated with Northrop Grumman's Integrated Combat Management System (ICMS) and NG Con, a mobile command and control system. Several threat scenarios demonstrating controlled and uncontrolled air and maritime targets were used to depict the flexibility of the system in all aspects of target detection. The Dual Face Demonstration unit was developed in support of the CEA Technologies phased array radar system recently fitted to the Royal Australian Navy's (RAN) ANZAC Class Frigate HMAS Perth, as part of the ANZAC Class Anti-Ship Missile Defense (ASMD) Upgrade Program. This program included the installation of six CEAFAR S-band AESA radar faces and four CEAMOUNT X-band active phased array illumination faces, each providing full 360-degree radar coverage. The installation onboard Perth was successfully completed in late 2010, with sea trials commencing shortly thereafter and culminating with a successful Evolved SeaSparrow Missile (ESSM) firing in May 2011. Following this, an early operational assessment was conducted on the new phased array radar system at the U.S. Navy's Pacific Missile Range Facility (PMRF) in June 2011. CEA Technologies, a partner of Northrop Grumman, developed and supplied the CEAFAR Demonstration Unit. CEA Technologies is one of Australia's leading military electronic systems and radar companies which specializes in the design, development and manufacture of advanced radar and communications solutions for civilian and military applications. Please visit www.cea.com.au for more information. Northrop Grumman is a leading global security company providing innovative systems, products and solutions in aerospace, electronics, information systems, and technical services to government and commercial customers worldwide. Please visit www.northropgrumman.com for more information. CONTACT: Fernando Catta-Preta Northrop Grumman +1 (434) 242-9283 fernando.catta-preta@ngc.com Sandra Lumsden CEA Technologies Pty Limited +61 407 236 532 sandra.lumsden@cea.com.au http://www.es.northropgrumman.com/solutions/ceafar/

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milstar: A simple block diagram of a digital beamforming(DBF) radar is showninFig.1. Ateachelementofthereceivingarraythereisare- ceiver front end that heterodynes the received signal to a frequency at which an A D converter operates. Once the signals from each an- tenna element are digitized and converted to a number, they can be reused many times for many different purposes without a reduction in the signal-to-noise ratio. This makes digital beamfonning much more attractive and usehl than analog beamfonning. 19 http://vko.forum24.ru/?1-3-0-00000205-000-0-0-1420709446

milstar: https://archive.org/stream/DTIC_ADC000914/DTIC_ADC000914_djvu.txt Abstract: The generic characteristics and performance of an experimental long-range air-surveillance radar, known at the Naval Research Laboratory as Senrad, is described. Its distinguishing feature is that it can operate with simultaneous transmissions over a very wide bandwidth-from 850 to 1400 MHz. The technology and type of experimental radar equipment employed are discussed and examples are given of its performance capabilities obtained by means of very wideband operation. The unusually wide bandwidth of this radar allows 1) improved detection and tracking performance because of the absence of the nulls that are common in the antenna elevation radiation-pattern of a single-frequency radar; 2) moving target indication (MTI) without loss of targets due to blind speeds and without the need for multiple PRFs (pulse repetition frequencies); 3) accurate height finding with a fan-beam radar by taking advantage of the multipath time difference as a function of target height; 4) a form of limited target recognition based on high range-resolution; and 5) a reduction of the effectiveness of electronic countermeasures that can seriously degrade more narrowband radars. Published in: IEEE Transactions on Aerospace and Electronic Systems ( Volume: 37 , Issue: 4 , Oct 2001 ) https://ieeexplore.ieee.org/document/976957?tp=&arnumber=976957&isnumber=21073&tag=1

milstar: At the higher frequencies (such as S band), there is more room in the spectrum for wideband operation, and resolution in the angle and range dimensions usually can be better than at the lower frequencies. Radars at the higher frequencies, on the other hand, generally cost more to achieve the same range performance as at lower frequencies; rain can seriously reduce target detection capability; and it is more difficult to achieve good MTI performance. https://ieeexplore.ieee.org/document/976957?tp=&arnumber=976957&isnumber=21073&tag=1 In considering the choice of frequency for the Senrad air-surveillance radar, we wanted to employ as much bandwidth as practical. Bandwidth is an important resource for radar since it represents information as well as allowing flexibility for radars. It was decided that the radar should operate simultaneously at both Land Lu bands, covering from 850 to 1400 MHz In addition to operating in two bands with simultaneous frequency diversity, the radar is capable of changing its frequency on a pulse-to-pulse basis (frequency agility) when Doppler processing is not needed. When multiple pulses must all be at the same frequency in order to perform Doppler processing, frequency agility is on a waveform-to-waveform basis. 2. Benefits of Wideband Operation The capabilities that are possible because of the use of multiple frequencies over an extremely wide bandwidth include the following. 1) Good automatic detection and track (ADT) because of the absence of fades (loss of signal). The deep interference nulls in the elevation coverage that result from surface-multipath reflection with a single narrowband signal are greatly reduced with the use of wideband frequency diversity. In addition to increasing the ability to detect targets, it makes ADT more reliable because there is no large loss of echo signal due to the target being in a deep null of the antenna multipath pattern. 2) Better MTI. Loss of echo signal because of MTI blind speeds is effectively eliminated by frequency diversity, without the need for multiple staggered pulse repetition frequencies. 3) Enhanced target cross section. The combined echo signals from a multiple-frequency radar is not likely to experience the very low values that can occur when a slowly fluctuating target is viewed with only a single frequency [9]. (This is similar to converting a Swerling case 1 cross section model to a Swerling case 2). 4) ECCM (electronic counter-countermeasures). Proper operation over a wide bandwidth forces a noise jammer to cover the entire band. Consequently, there is a reduction of the jammer power density the radar has to face compared with what it would be if all the jammer power were concentrated into a narrow bandwidth. 5) High range resolution. This allows height finding based on multipath, as well as providing a form of target recognition based on the target's range profile.

milstar: The use of two transmitters, rather than a single transmitter, to cover the 50% bandwidth offers a more technically feasible system with greater experimental flexibility and important operational advantages. Two transmitters allow simultaneous transmission at two widely separated frequencies, something not as practical with a single transmitter. A single wideband transmitter generally has to radiate multiple frequencies sequentially rather than simultaneously. Simultaneous operation was important in the Senrad concept since it makes the countermeasures threat easier to handle. Two separate radar transmitters (and receivers) also have the advantage of increased reliability since such a radar can perform as a conventional radar in case only one of the two sub-bands is operable. It was also envisioned that for naval applications, a small ship needing a long-range air-surveillance radar might use a smaller version of the radar that operated in only one of the two sub-bands. Larger ships would employ both sub-bands while smaller ships might have either the upper or the lower sub-band. Using only one sub-band on smaller ships would still force jammers to cover the entire band since both sub-bands would likely be found within a naval task force.

milstar: 4. Transmitter The traveling wave tube (TWT) and the solid-state amplifier were considered suitable for this application since both are quite capable of the required bandwidth and both allow good MTI (detection of moving targets in clutter). Initially, it seemed possible to use a single TWT transmitter to cover the entire 50% band. This, however, would have required a special tube development, something usually too expensive for R&D budgets. It was also considered that solid-state modules might be used to cover the entire band, either as a separate transmitter or with the modules located on a rotating array antenna—one module to a radiating element. This option might be more viable today, but it was not chosen at the time because of high cost; and it would require special development. Putting the solid-state transmitter on the antenna also increases the weight on the antenna, makes cooling more arduous, places more of a burden on maintenance, and makes it difficult to achieve very low sidelobe antennas. Thus, we chose to configure the transmitter with two TWTs: one to cover the lower frequencies (Lu band) and the other to cover the standard L band. There was already a suitable operational TWT available (Raytheon QKWI671A) for the upper sub-band from 1215 to 1400 MHz, which was being used in other radar systems. It was a grid-pulsed, liquid-cooled, ring-bar TWT with an integral solenoid for focusing. The tube had a gain of 50 dB, which permitted the use of a low-power solid-state driver. At the lower sub-band, a frequency-scaled version of the upper sub-band TWT was developed, and was known as the QKW1818. Test data showed that this tube was capable of operating from 850 to 1300 MHz. Both tubes had similar characteristics. Their peak power output was nominally 160 kW and their average power could be as high as 10 kW. In the experimental Senrad system, the tubes were operated at about half of their average power so as to reduce cost and risk. The power supply for the experimental radar was a surplus dual-tube life-test station, modified for these purposes.

milstar: By using two transmitters, a separate duplexer could be employed at each sub-band. High-power duplexers to cover the entire band from 850 to 1400 MHz did not exist at the time, so a major and risky development to obtain a suitable duplexer would have had to be undertaken if a single wideband system were used. A broadband, high-power diplexer was designed to combine the outputs of the two transmitters to feed a single antenna. 5. Antenna The experimental system utilized two different types of mechanically rotating antennas. One was a conventional parabolic reflector and the other was a low-sidelobe array antenna. A photograph of the two antennas on the roof of the Radar Division building at the NRL Chesapeake Bay Field Site is shown in Fig. 2. They are mounted back-to-back for experimental convenience. (Only one antenna would be used in an operational system.) The particular parabolic-reflector antenna employed in this experimental equipment was the antenna from the developmental model of the Navy's AN/SPS-50, an L-band cousin of the Lu-band AN/SPS-49. A broadband double-ridged waveguide feed covering the entire 850–1400 MHz frequency band was designed and built. The antenna was 24 ft wide by 6.5 ft high and it radiated horizontal polarization. It had an azimuth beamwidth of 3° at 900 MHz and 2.3° at 1300 MHz. The elevation coverage extended to 30 deg with cosecant-squared shaping, but with 3 dB enhancement of the gain above an elevation angle of 20°. Its peak sidelobe was −22 dB and gain was 27.2 dB at 900 MHz and 29.8 dB at 1300 MHz.

milstar: The parabolic reflector was used for the early experiments, but later in the program a low-sidelobe antenna was developed for Senrad by Westinghouse (now Northrop Grumman). It consisted of 16 rows of 36 dipole radiators each, and was 24 by 7.5 ft with an azimuth beamwidth from 3.8 to 2.8° depending on frequency. The elevation coverage was cosecant-squared up to 30°. The gain was nominally 28.5 dB. Its peak sidelobe was designed to be −40 dB. This sidelobe level might not seem “bold,” but it should be remembered that the antenna was of relatively low gain compared with other low-sidelobe antennas. The lower the gain the more difficult it is to reduce the sidelobes to low levels. The vertical polarization of the low-sidelobe antenna helped in making comparisons of the effect of polarization with respect to the horizontally polarized reflector antenna. The antenna rotation rate was 15 rpm (4 s revisit time), which is much faster than the 5 or 6 rpm common with long-range civil air-traffic control radars.

milstar: 7. Communications via Radar Although it was not a direct result of the wide bandwidth available in Senrad, the radar was also used as a test bed to demonstrate the advantages of using a radar to communicate to nearby radars. Communication between netted radars that observe the same coverage offers advantages for more reliable detection and more accurate tracking. This can occur within the radars of a naval task force or the air-defense radars of large ground forces. Conventional military communications links for command and control can be used to transfer radar data among radars, but radar data might not always have sufficient priority over such links to insure timely transfer of target information from one radar to another. Using the radar itself as the communications transmitter, however, allows the rapid transfer of information among the netted radars. Furthermore, high-power and high transmitting antenna gain make this communications link much less vulnerable to hostile jamming. Only processed radar data, not the raw radar output, is communicated. Processed data is of relatively low information bandwidth compared with raw radar data. Since a radar pulse generally supports much greater bandwidth than the bandwidth required to transmit processed data, only a small portion of the radar's signal bandwidth need be used for transmitting radar information. The receiver at the other end of the communications link is a separate omni-directional antenna, permitting information to be communicated effectively whenever the radar antenna illuminates a nearby radar. For naval applications, the radars to be netted by communications generally will be within the line of sight of one another. The high power of the transmitted signal, however, will likely allow some propagation beyond the geometric line of sight. =========== https://ieeexplore.ieee.org/document/976957/metrics#metrics

milstar: 3. High-Resolution Operation Conventional air-surveillance radars typically have pulsewidths of one or a few microseconds, which result in range resolutions of several hundreds of meters. This is usually satisfactory for accomplishing most air-surveillance-radar tasks. The wide bandwidth of Senrad in both the upper and lower sub-bands, however, offers capabilities not available with the narrow bandwidths typical of conventional surveillance radars. The use of wideband radar waveforms for high range-resolution is well known as a method for reducing the amount of distributed rain-clutter and surface-clutter echoes with which the target echo has to compete. If there is sufficient resolution to separate the direct target-echo from the surface-reflected target-echo, Fig. 8, there will be no fading of the target echo signals due to multipath nulls in the elevation antenna pattern. Both of the above capabilities (clutter reduction and separation of multipath) can enhance detection. A high-resolution waveform in Senrad was not used for increasing the probability of detection in clutter during surveillance, but to gather additional information on targets that had already been detected. In particular, the wide bandwidth was used to obtain 1) target height by measuring the time delay between multipath echoes, and 2) by performing a degree of limited target recognition (sometimes called perceptual class recognition) based on the target's profile in the range coordinate. Both of these tasks were performed with Senrad using a linear-FM Stretch pulse-compression waveform. Figure 8

milstar: Fig. 3 illustrates the long-range surveillance pulses interspersed with the 3-pulse MTI waveforms for one of the two sub-bands. With a 15 rpm antenna rotation rate, the time taken for the half-power points of the parabolic reflector antenna beam to scan by a point target was approximately 25.6 ms at the highest frequency of almost 1400 MHz, and 33.3 ms at the lowest frequency of 850 MHz. The duration of the waveform shown in Fig. 3 was 24.8 ms. Thus the complete sequence of pulses shown in this figure was able to illuminate a target even at the highest radar frequency where the antenna beamwidth was smallest. As a minimum, therefore, each target was illuminated by four long-range surveillance waveforms and four MTI waveforms in each sub-band, and each could be at a different frequency. The three MTI pulses, however, had to be at the same frequency for doppler processing to be obtained. This is unavoidable and can make the radar more vulnerable to ECM. Senrad, therefore, could operate with up to eight different frequencies radiated within the higher frequency sub-band during the time on target, and more than eight at the lower sub-band. Operation of a radar over a wide frequency range forces a jammer to dilute its radiated power-density by spreading the total energy over a very wide band. 3. Rain and Chaff Wayform In the presence of wind-blown rain or chaff, doppler processing must be able to filter the moving volumetric clutter as well as the stationary surface clutter. A sequence of 14 pulses was originally considered for this waveform with processing being performed by two three-pulse cancelers in cascade. One three-pulse canceler had its doppler rejection notch centered on the velocity of the surface clutter (sea or land). The other three-pulse canceler had its doppler rejection notch centered on the average velocity of the volumetric clutter (rain or chaff). This was replaced by a ten-pulse waveform with 30 μs pulsewidths to eliminate both surface and volume clutter similar to that which is done in the Moving Target Detector [10]. A three-pulse canceler with binomial weighting was followed by an eight-pulse doppler filter bank which used an eight-point fast Fourier transform (FFT) with a log-CFAR (constant false alarm rate) normalizer [11] at the output of each filter. The sidelobes of the doppler filter bank were −29 dB. The basic unambiguous range of this waveform was approximately 80 nmi, so that a range ambiguity could occur for long-range targets. A shift in the PRF between the first ten-pulse group and the second ten-pulse group permitted resolution of the range ambiguity between the first and second 80 nmi intervals. Alternate groups of ten pulses were transmitted on different frequencies. As with the clear-sky waveform, simultaneous transmissions were made in both sub-bands so that the rain and chaff waveform radiated on at least four frequencies during the time on target. Range-extent gates (which look for extended echoes in more than two adjacent range resolution cells) were used in conjunction with the FFT doppler filter-bank to eliminate range-extended land, sea, or rain clutter, as well as chaff echoes. A blanker loop was closed around the doppler processor to remove low-velocity clutter echoes and large fixed-clutter residues which were not sufficiently extended in range to be removed by the range-extent gates and were sufficiently large so as to exceed the attenuation of the first three-pulse MTI canceler.

milstar: 5. Antenna The experimental system utilized two different types of mechanically rotating antennas. One was a conventional parabolic reflector and the other was a low-sidelobe array antenna. A photograph of the two antennas on the roof of the Radar Division building at the NRL Chesapeake Bay Field Site is shown in Fig. 2. They are mounted back-to-back for experimental convenience. (Only one antenna would be used in an operational system.) ========================================================== https://ieeexplore.ieee.org/document/976957/metrics#metrics

milstar: https://web.archive.org/web/20141212012332/http://www.navsea.navy.mil/nswc/dahlgren/Leading%20Edge/Sensors/03_Development.pdf

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