Моноимпульсная (многоканальная )радиолокация

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Моноимпульсная (многоканальная )радиолокация

milstar: Моноимпульсная радиолокация Перевод Моноимпульсная радиолокация (от Моно... и Импульс метод измерения радиолокационных станцией (РЛС) угловых координат объекта, основанный на определении угловой ошибки положения её антенны, направленной на объект, по принятому одиночному (отражённому или переизлучённому объектом) импульсному сигналу. М. р. используется в т. н. моноимпульсных РЛС сопровождения. Основное преимущество этого метода перед другими радиолокационными методами, основанными на обработке непрерывных или нескольких последовательно принимаемых импульсных сигналов (см. Радиолокация), заключается в более высокой точности измерений (ошибки снижаются до десятых долей угловой минуты). Это является следствием нечувствительности моноимпульсных РЛС к флуктуациям амплитуды принятых сигналов. Однако реализация М. р. связана с дополнительным усложнением приёмного тракта РЛС — с необходимостью использования нескольких приёмных каналов (в связи с чем этот метод получил также название многоканального). http://dic.academic.ru/dic.nsf/bse/110392/%D0%9C%D0%BE%D0%BD%D0%BE%D0%B8%D0%BC%D0%BF%D1%83%D0%BB%D1%8C%D1%81%D0%BD%D0%B0%D1%8F The Millimeter Wave Radar (MMW) is a dual frequency (Ka- and W-Band) monopulse tracking radar. ############################################################## http://www.smdc.army.mil/KWAJ/RangeInst/MMW.html It is characterized by high range and Doppler resolution, high sensitivity, precise pointing and tracking, waveform flexibility, and a high degree of computer control for real-time operation and signal processing. The MMW has a signal bandwidth of 2 GHz yielding a range resolution of 0.014 meters. The Doppler resolution at 35 GHz is 0.214 m/sec. The recording window is 37.5 meters. A larger recording window is available by reducing the pulse bandwidth to 1000 MHz or 500 MHz. For targets that do not require signature waveforms, narrowband pulses of 6 and 12 MHz bandwidth are available. MMW System Characteristics Frequency: Ka-Band, W-Band Waveforms: interlaced Ka- and W-Band, Wideband and Narrowband pulse trains PRF: 50-2000 Pulsewidth: 50 µsec Modulation: Linear FM Chirp Bandwidth : 6 & 12 MHz, NB 500, 1000, 2000 MHz, WB

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milstar: History Monopulse radar was extremely "high tech" when it was first introduced by Robert M. Page in 1943 in a Naval Research Laboratory experiment. As a result, it was very expensive, labor-intensive due to complexity, and less reliable. It was only used when extreme accuracy was needed that justified the cost. Early uses included the Nike Ajax missile, which demanded very high accuracy, or for tracking radars used for measuring various rocket launches. An early monopulse radar development, in 1958, was the AN/FPS-16, on which NRL and RCA collaborated. The earliest version, XN-1, utilised a metal plate lens. The second version XN-2 used a conventional 3.65 meter [12 ft] parabolic antenna, and was the version which went to production. These radars played an important part in the Mercury, Gemini, and early Apollo missions, being deployed in Bermuda, Tannarive, and Australia, among other places for that purpose. The IRACQ [Increased Range ACQuisition] modification was installed on certain of these installations; certainly the one located at Woomera, Australia was so modified. One of the larger installations first appeared in the 1970s as the US Navy's AN/SPY-1 radar used on the Aegis Combat System, ######################################################### and MK-74 radar used used on Tartar Guided Missile Fire Control System and research.[1] The cost and complexity of implementing monopulse tracking was reduced and reliability increased when digital signal processing became available after the 1970s, and the technology is today found in most modern tracking radars, and in many types of disposable ordnance like missiles. http://en.wikipedia.org/wiki/Monopulse_radar

milstar: The AN-FPQ 6 radar was built by RCA and was, effectively, a development of the AN-FPS 16. The Q6, as it was known by those who worked on it, was an amplitude comparison monopulse C-band radar, with a 2.8 MW peak klystron transmitter tunable from 5.4 to 5.8 GHZ, which had a 9 meter parabolic antenna, having 52 dB gain, a 0.6 degree beam width, utilizing a Cassegrainian feed with a five horn monopulse comparator. This radar had an unambiguous maximum range of 215 or 32,768 nautical miles (60,686 km), and employed uncooled parametric amplifiers with a system noise temperature of 440 K, [a noise figure of 4 dB]. A major features of the radar was its maximum unambiguous range of 32,768 nautical miles (60,686 km) despite a pulse repetition frequency [PRF]of some hundreds of pulses per second http://en.wikipedia.org/wiki/AN/FPQ-6 The AN/FPQ-6 is a fixed, land-based C-band radar system used for long-range, small-target tracking. The AN/FPQ-6 Instrumentation Radar located at the NASA Kennedy Space Center was the principal C-Band tracking radar system for Apollo program. RCA’s Missile and Surface Radar Division developed the FPQ-6 skin tracking C-Band radar as a successor to the AN/FPS-16 radar set. The AN/FPQ-6 can provide continuous spherical coordinate information at ranges of 32,000 nautical miles (59,000 kilometers) with an accuracy of plus and minus 6 ft (1.8 m). The AN/FPS-16 has range limited to 500 nmi (930 kilometers) with an accuracy of 15 feet (5 m), although it could be modified to a maximum range of 5,000 nmi (9,300 kilometers). The AN/FPQ-6 radar employed a 2.8 megawatt peak power (4.8 kilowatt average), broad banded (5400–5900 MHz) transmitter with a frequency stability of 1Ч108. The 8.8 meter diameter parabolic antenna, using a Cassegrain antenna feed, had a 0.4° beamwidth and a gain of 51 dB. Its monopulse, 5 horn feed system permitted the reference and error antenna patterns to have their gains ##################################################################### independently established as well as the slope of the error patterns optimized while supplying target return signals to the receiving system with a minimum of insertion loss. The three channel signal outputs of the antenna feed system were supplied directly to the receiving system without undergoing any additional loss-inducing signal manipulation with bandwidths optimized for the specified pulse widths of 0.5, 0.75, 1.0 and 2.4 microseconds and the receiver noise figure of 7.5 dB was improved to 3.5 dB through the addition of closed-cycle parametric RF amplifiers. This system ensured a dynamic range in excess of 120 dB.

milstar: Monopulse Radar http://www.nrl.navy.mil/accomplishments/systems/monopulse-radar/ In 1943, NRL developed monopulse radar, now the basis for all modern tracking and missile control radars. The monopulse technique was first applied to the Nike-Ajax missile system, which at the time was the nation's continental air defense system. Monopulse radar eventually led to the development of the AN/FPS-16, the first high-precision monopulse instrumentation radar. In 1958, this radar was used to guide the launchings of the first U.S. space satellites at Cape Canaveral. Monopulse radar is still the most widely used technique for military tracking radar because of its high accuracy and relative immunity to electronic countermeasures that degrade other tracking methods.

milstar: http://www.radartutorial.eu/06.antennas/an17.en.html Monopulse gives much better target azimuth measurements than the estimating of the angular position shown in figure 1. It can operate at a much lower interrogation rate to benefit others in the environment. Monopulse systems usually contain enhanced processing to give better quality target code information. A single pulse is sufficiently for monopulse bearing measurement (hence the use of the term monopulse). The elements in linear antenna array are divided into two halves. These two separate antennae arrays are placed symmetrically in the focal plane on each side of the axis of the radar antenna (this often called boresight axis). In transmission (Tx) mode, both antennae arrays will be fed in phase and the radiation pattern is represented by the ice blue area, which is called the Σ or Sum -diagram. (shown in the Figure as blue graph and pattern) In reception (Rx) mode an additional receiving way is possible. From the received signals of both separate antenna arrays, it is possible to calculate Σ (like the transmitted Sum -diagram) and the difference ΔAz, the so called Delta azimuth- diagram. The antenna pattern is given by the red and green area on the same figure. Both signals are then compared as a reply processor function and their difference is used to estimate the azimuth of the target more exactly. The angle between the axis of the antenna (boresight axis) and the direction of the target is also known as OBA-value (Off-Boresight Angle). The elevation angle is also measured at 3D radars as a third coordinate. Well, the procedure is used twice now. Here the antenna is derived in addition in an upper half and a lower half. The second difference channel (ΔEl) is called „Delta Elevation” now. II +ΔEl -ΔAz I +ΔEl+ΔAz III -ΔEl -ΔAz IV -ΔEl+ΔAz Figure 5: the four quadrants of a monopulse antenna The Monopulse antenna is divided up into four quadrants now: The following signals are formed from the received signals of these four quadrants: Sum - signal Σ ( I + II + III + IV ) Difference - signal ΔAz ( I + IV ) - ( II + III ) Difference - signal ΔEl ( I + II ) - ( III + IV ) The · Auxiliary Signal Ω also shall to complete the picture be mentioned, although this one isn't tied to the monopulse antenna. This channel to the compensation of side lobes always has practically its own small antenna and has a very wide antenna diagram and also serves for the reconnaissance of active jamming. All these signals need an own receiver channel. Well, modern 3D- radar sets have at least four parallel receiver- channels. ################################################

milstar: Леонов А.И., Фомичев К.И. - Моноимпульсная радиолокация [1984, PDF, RUS] http://rutracker.org/forum/viewtopic.php?t=3973460 http://www.twirpx.com/file/486718/

milstar: Phase-Comparison Monopulse Analysis Leonov and Fomichev [13] give an analysis of glint for phase-comparison monopulse systems that they also apply to cross-eye jamming. This analysis gives the same results as the linear-fit analysis showing that cross-eye jamming affects both amplitude- and phase-comparison monopulse radars. This analysis is similar to the extended analysis described in Section 4.2.1, but the results differ, mainly because Leonov and Fomichev do not consider the retrodirective implementation of cross-eye jamming. Furthermore, Leonov and Fomichev introduce a number of assumptions that limit the accuracy of their models in order to obtain agreement with other results. Finally, Leonov and Fomichev also make no attempt to generalise these results to other types of monopulse radar, instead opting to use the linear-fit analysis for amplitude-comparison monopulse systems. http://upetd.up.ac.za/thesis/available/etd-06122010-215639/unrestricted/thesis.pdf

milstar: Introductory Remarks The use of a generalised phase-comparison monopulse antenna as a model for any mono- pulse antenna is considered in this chapter. This is done as a prelude to analysing a cross-eye jamming scenario in Chapter 4 to demonstrate the wide validity of that analy- sis. The work described in this chapter forms the basis of a submitted journal paper [1].1 A monopulse radar uses two antenna beams, the sum- and difference-channel beams. The sum-channel beam has a peak in the radar’s boresight direction and is used for transmission, target detection and angle-error normalisation. The difference-channel beam has a null in the radar’s boresight direction and is used to form an error signal determined by the angular tracking error [13,15,17,22,30,31]. The sum- and difference- channel beams can be formed in a number of ways, including: • amplitude-comparison monopulse systems using the sum and difference of two squinted beams [13,15,17,22,30,31], • phase-comparison monopulse systems using the sum and difference of two beams with offset phase centres [13,15,17,22,30,31], • phased arrays which form the sum- and difference-channel beams directly [13,17, 30,69], and • combinations of these approaches (e.g. the five-horn feed forms the sum-channel beam directly while forming the difference-channel beams using the amplitude- comparison approach) [30,31]. Of these, phase-comparison is the most common [26]. While there are significant differ- ences in the design and practical implementation of each of these monopulse systems, they all form a sum-channel beam (peak on boresight) and a difference-channel beam (null on boresight), so all monopulse systems work in the same way. Sherman [30] has shown the equivalence of the antenna patterns in the amplitude- and phase-comparison cases, but acknowledges that his analysis considers antenna pat- terns that “have a peculiar, asymmetrical shape and are not likely to have practical application” and “are likely to have unusual shapes” [30]. The equivalence of a general monopulse antenna and a generalised phase-comparison monopulse antenna near boresight is proved in Section 3.2. The use of a generalised phase-comparison monopulse antenna to approximate measured monopulse antenna pat- terns is considered in Section 3.3. Concluding remarks are provided in Section 3.4. 1Portions of this chapter are reprinted, with permission, from [1]. ⃝c 2009 IEEE. http://upetd.up.ac.za/thesis/available/etd-06122010-215639/unrestricted/thesis.pdf

milstar: 3.3 Results and Discussion The use of a generalised phase-comparison antenna to model any type of monopulse antenna is demonstrated in this section by approximating the measured patterns of two monopulse antennas. The AN/FPQ-6 radar is an C-Band monopulse tracking radar whose antenna consists of a five-horn Cassegrain feed and a 29-foot reflector dish [30,31,70]. The fact that a five-horn feed is used is ideal for demonstrating the principles described above because the feed structures for the sum and difference channels are different. The QCS15.5-17N(D1587) is a monopulse antenna manufactured by Q-par Angus Ltd and operates from 15.5 to 17 GHz. The antenna has a four-horn Cassegrain feed and a 1.2-m reflector [71]. The four-horn feed is widely used to construct amplitude- comparison monopulse antennas making this a useful test case. Measured and approximated the sum- and difference-channel patterns, and mono- pulse errors are shown in Figures 3.1 and 3.2 based on plots of the sum- and difference- channel antenna patterns of an AN/FPQ-6 radar [70] and a Q-par Angus Ltd QCS15.5- 17N(D1587) antenna [71]. The indicated angle cannot be calculated because this would require a knowledge of how the radar processes its signals, and this information is not available. The origins of the curves in Figures 3.1 and 3.2 are described below. In all cases, the monopulse error on boresight was determined from the measured values at ±0.1◦ for the AN/FPQ-6 radar and at ±0.15◦ for the Q-par Angus Ltd antenna. If additional parameters were available, the minimax error value in (3.18) was minimised over the range 0.1◦ ≤ |θ| ≤ 0.5◦ for the AN/FPQ-6 radar and over the range 0.15◦ ≤ |θ| ≤ 1◦ for the Q-par Angus Ltd antenna.

milstar: M.Skolnik Radar http://www.turma-aguia.com/davi/skolnik/Skolnik_chapter_18.pdf 18.3 MONOPULSE(SIMULTANEOUSLOBING) The susceptibility of scanning and lobing techniques to echo amplitude fluctua- tions was the major reason for developing a tracking radar that provides simul- taneously all the necessary lobes for angle-error sensing. The output from the lobes may be compared simultaneously on a single pulse, eliminating any effect of time change of the echo amplitude. The technique was initially called simulta- neous lobing, which was descriptive of the original designs. Later the term monopulse was used, referring to the ability to obtain complete angle error infor- mation on a single pulse. It has become the commonly used name for this track- ing technique. The original monopulse trackers suffered in antenna efficiency and complexity of microwave components since waveguide signal-combining circuitry was a relatively new art. These problems were overcome, and monopulse radar with off-the-shelf components can readily outperform scanning and lobing systems. The monopulse technique also has an inherent capability for high-precision angle measurement be- cause its feed structure is rigidly mounted with no movingparts. This has made pos- sible the development of pencil-beam tracking radars that meet missile-range instrumentation-radar requirements of 0.003° angle-tracking precision. This chapter is devoted to tracking radar, but monopulse is used in other sys- tems including homing devices, direction finders, and some search radars. How- ever, most of the basic principles and limitations of monopulse apply for all ap- plications. A more general coverage is found in Refs. 3 and 4.

milstar: Amplitude-Comparison Monopulse. A method for visualizing the operation of an amplitude-comparison monopulse receiver is to consider the echo signal at the focal plane of an antenna.5 The echo is focused to a "spot" having a cross-section shape approximately of the form J1(X)IX for circular apertures, where J1(X) is the first-order Bessel function. The spot is centered in the focal plane when the target is on the antenna axis and moves off center when the target moves off axis. The antenna feed is located at the focal point to receive maximum energy from a target on axis. An amplitude-comparison monopulse feed is designed to sense any lateral dis- placement of the spot from the center of the focal plane. A monopulse feed using the four-horn square, for example, would be centered at the focal point. It pro- vides a symmetry so that when the spot is centered equal energy falls on each of the four horns. However, if the target moves off axis, causing the spot to shift, there is an unbalance of energy in the horns. The radar senses the target displace- ment by comparing the amplitude of the echo signal excited in each of the horns. This is accomplished by use of microwave hybrids to subtract outputs of pairs of horns, providing a sensitive device that gives signal output when there is an un- balance caused by the target being off axis. The RF circuitry for a conventional four-horn square (Fig. 18.8) subtracts the output of the left pair from the output of the right pair to sense any unbalance in the azimuth direction. It also subtracts the output of the top pair from the output of the bottom pair to sense any unbal- ance in the elevation direction. The Fig. 18.8 comparator is the circuitry which performs the addition and sub- traction of the feedhorn outputs to obtain the monopulse sum and difference sig- nals. It is illustrated with hybrid-T or magic-T waveguide devices. These are four- port devices which, in basic form, have the inputs and outputs located at right angles to each other. However, the magic Ts have been developed in convenient "folded" configurations for very compact comparator packages. The perfor- mance of these and other similar four-port devices is described in Ref. 3, Chap. 4. The subtracter outputs are called difference signals, which are zero when the target is on axis, increasing in amplitude with increasing displacement of the tar- get from the antenna axis. The difference signals also change 180° in phase from one side of center to the other. The sum of all four horn outputs provides a ref- erence signal to allow angle-tracking sensitivity (volts per degree error) even though the target echo signal varies over a large dynamic range. AGC is neces- sary to keep the gain of the angle-tracking loops constant for stable automatic angle tracking. Figure 18.9 is a block diagram of a typical monopulse radar. The sum signal, elevation difference signal, and azimuth difference signal are each converted to intermediate frequency (IF), using a common local oscillator to maintain relative phase at IF. The IF sum-signal output is detected and provides the video input to the range tracker. The range tracker determines the time of arrival of the desired target echo and provides gate pulses which turn on portions of the radar receiver only during the brief period when the desired target echo is expected. The gated video is used to generate the dc voltage proportional to the magnitude of the 2 signal or ISIfor the AGC of all three IF amplifier channels. The AGC maintains constant angle-trackingsensitivity(volts per degree error) even though the target echo signal varies over a large dynamic range by controlling gain or dividing by I2l. AGC is necessary to keep the gain of the angle-tracking loops constant for stable automatic angle tracking. Some monopulse systems, such as the two-channel monopulse, can provide instantaneous AGC or normalizingas described later in this section. The sum signal at the IF output also provides a reference signal to phase de- tectors which derive angle-tracking-error voltages from the difference signal.

milstar: The phase detectors are essentially a dot-product device producing the output voltage ISl IAI A e=Wv~\cos* or *= acose where e = angle-error-detector output voltage l£l = magnitude of sum signal IAl = magnitude of difference signal 6 = phase angle between sum and difference signals The dot-product error detector is only one of a wide variety of monopulse angle error detectors described in Ref. 3, Chap. 7. Normally, 6 is either 0° or 180° when the radar is properly adjusted, and the only purpose of the phase-sensitive characteristic of the detector is to provide a plus or minus polarity corresponding to 0 = 0° and 0 = 180°, respectively, giving direction sense to the angle-error-detector output. In a pulsed tracking radar the angle-error-detector output is bipolar video; that is, it is a video pulse with an amplitude proportional to the angle error and whose polarity (positive or negative) corresponds to the direction of the error. This video is typically processed by a boxcar circuit which charges a capacitor to the peak video-pulse voltage and holds the charge until the next pulse, at which time the capacitor is discharged and recharged to the new pulse level. With moderate low-pass filtering, this gives a dc error voltage output employed by the servo am- plifiers to correct the antenna position. The three-channel amplitude-comparison monopulse tracking radar is the most commonly used monopulse system. The three signals may sometimes be com- bined in other ways to allow use of a two-channel or even a single-channel IF system as described later in this section. Monopulse-Antenna Feed Techniques. Monopulse-radar feeds may have any of a large variety of configurations. For two-angle tracking such as azimuth and elevation, the feeds may include three or more apertures.6 Single apertures are also employed by using higher-order waveguide modes to extract angle- error-sensing difference signals. There are many tradeoffs in feed design because optimum sum and difference signals, low sidelobe levels, omnipolarization capa- bility, and simplicity cannot all be fully satisfied simultaneously. The term sim- plicity refers not only to cost saving but also to the use of noncomplex circuitry which is necessary to provide a broadband system with good boresight stability to meet precision-tracking requirements. (Boresight is the electrical axis of the antenna or the angular location of a signal source within the antenna beam at which the angle-error-detector outputs go through zero.) Some of the typical monopulse feeds are described to show the basic relations involved in optimizing the various performance factors and how the more impor- tant factors can be optimized by a feed configuration but at the price of lower performance in other areas. Many new techniques have been added since the original four-horn square feed in order to provide good or excellent performance in all desired feed characteristics in a well-designed monopulse radar. The original four-horn square monopulse feed is inefficient since the optimum feed size in the plane of angle measurement for the difference signals is approx- imately twice the optimum size for the sum signal.7 Consequently, an interme- diate size is typically used with a signif- icant compromise for both sum and dif- ference signals. The optimumfour-horn square feed, which is subject to this compromise, is described in Ref. 3 as based on minimizing the angle error caused by receiver thermal noise. How- ever, if sidelobes are a prime consider- ation, a somewhat different feed size may be desired. The limitation of the four-horn square feed is that the sum- and difference-signal E fields cannot be con- SUM AZIMUTH DIFFERENCE trolled independently. If independent control could be provided, the ideal would be approximately as described in Fig. 18.10 with twice the dimension for the dif- ference signals in the plane of error sensing than that for the sum signal.7 A technique used by the MIT Lincoln Laboratory to approach the ideal was the 12-horn feed (Fig. 18.11). The overall feed, as illustrated, is divided into small parts and the microwave circuitry selects the portions necessary for the sum and difference signals to approach the ideal. One disadvantage is that this feed re- quires a very complex microwave circuit. Also, the divided four-horn portions of the feed are each four element arrays which generate large feed sidelobes in the H plane because of the double-peak E field. Another consideration is that the 12- horn feed is not practical for focal-point-fed parabolas or reflectarrays because of its size. A focal-point feed is usually small to produce a broad pattern and must be compact to avoid blockage of the antenna aperture. In some cases the small size required is below waveguide cutoff, and dielectric loading becomes neces- sary to avoid cutoff. A more practical approach to monopulse-antenna feed design uses higher- order waveguide modes rather than multiple horns for independent control of sum- and difference-signal E fields. This allows much greater simplicity and flex- ibility. A triple-mode two-horn feed used by RCA7'8 retracts the /s-plane septa to allow both the TE10 and TE30 modes to be excited and propagate in the double- width septumless region as illustrated in Fig. 18.12. At the septum the double- humped E field is represented by the combined TE10 and TE30 modes subtracting at the center and adding at the TE30-mode outer peaks. However, since the two modes propagate at different velocities, a point is reached farther down the double-width guide where the two modes add in the center and subtract at the outer humps of the TE30 mode. The result is a sum-signal E field concentrated toward the center of the feed aperture. This shaping of the sum-signal E field is accomplished independently of the difference-signal E field. The difference signal is two TE10-mode signals arriving at the septum of Fig. 18.12 out of phase. At the septum it becomes the TE20 mode, which propagates to the horn aperture and uses the full width of the horn as desired. The TE20 mode has zero E field in the center of the waveguide where the septum is located and is unaffected by the septum. The AN/FPS-16 radar feed used two retracted septum horns illustrated in Fig. 18.13. The TE20-mode signals are added for the //-plane difference signal, the combined TE10 and TE30 modes are added for the sum signal, and they are sub- tracted for the E-plane difference signal. Since this is a focal-point feed, it is small in size (wavelengths) and RF currents tend to flow around the top and bottom

milstar: A technique used by the MIT Lincoln Laboratory to approach the ideal was the 12-horn feed (Fig. 18.11). ############################################################### The overall feed, as illustrated, is divided into small parts and the microwave circuitry selects the portions necessary for the sum and difference signals to approach the ideal. One disadvantage is that this feed re- quires a very complex microwave circuit. Also, the divided four-horn portions of the feed are each four element arrays which generate large feed sidelobes in the H plane because of the double-peak E field. Another consideration is that the 12- horn feed is not practical for focal-point-fed parabolas or reflectarrays because of its size. A focal-point feed is usually small to produce a broad pattern and must be compact to avoid blockage of the antenna aperture. In some cases the small size required is below waveguide cutoff, and dielectric loading becomes neces- sary to avoid cutoff. http://www.turma-aguia.com/davi/skolnik/Skolnik_chapter_18.pdf

milstar: However, the five-horn feed is a pracical choice between complexity and efficiency. It has been used in several instrumentation radars including the AN/FPQ-6, AN/FPQ-10, AN/TPQ-18, and AN/MPS-369'10 and in the AN/TPQ-27 tactical precision-tracking radar.11 Multiband monopulse feed configurations are practical and in use in several systems. A simple example is a combined X-band and Ka-band monopulse pa- raboloid antenna radar. Separate conventional feeds are used for each band, with the Ka-band feed as a Cassegrain feed and the X-band feed at the focal point.15 The Cassegrain subdish is a hyperbolic-shaped grid of wires reflective to parallel polarization and transparent to orthogonal polarization. It is oriented to be trans- parent to the X-band focal-point feed behind it and reflective to the orthogonally polarized Ka-band feed extending from the vertex of the paraboloid. Monopulse feed horns at different microwave frequencies can also be com- bined with horns interlaced. The multiband feed clusters will sacrifice efficiency but can satisfy multiband requirements in a single antenna.

milstar: SystemsAspectsofDigitalBeamFormingUbiquitousRadarMERRILLSKOLNIKSystemsDirectorat NavalResearchLaboratory https://pdfs.semanticscholar.org/2cf7/6259bfcfeff6cc013278024f050f42892f48.pdf

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