DE2821401A1 - PROCEDURE AND EQUIPMENT FOR RADAR IMPACT SIGNAL SUPPRESSION - Google Patents

Description

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description

The amplitude properties of radar echoes depend on radar and geometric parameters as well as on the physical properties of the objects from which the echoes originate. In particular, the echo properties depend also depends on the polarization, both of the one used for transmission and for polarization used for reception.

The radar cross-section G * is a useful quantity for determining the strength of the echo. This size is defined as "

p *

where the power density at the target ρ, the power density at the radar station p ^r and the distance to the target R.

The expression βΓ _β is used to denote the radar cross section (RCS) for the transmit polarization A and the receive polarization B. If, for example, the symbol χ denotes a linear polarization in any direction and y denotes a polarization perpendicular to χ, then there is O " the radar cross-section RCS for the transmission of any linear polarization and the reception of a linear polarization perpendicular to the transmitted one. Because of the reciprocity, d" = ö "*. It is here

xy yx

also noted that the received signal power is proportional to cf if all other factors are equal.

The reflective properties of an object depend depends on various factors, including the upper

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surface shape, size, material, orientation, as well as the frequency and polarization of the radar signals. The shape and orientation of the object can cause waves to be re-radiated with a polarization different from the polarization incident on the object, ie 6 ^ _n ^ 0. Such shapes are said to produce depolarization. Most large objects that have smooth surfaces, be they metallic or dielectric, do not cause depolarization. As a result, there are many interesting targets that produce less depolarization than is mostly caused by land and sea areas.

The use of the depolarization effects of opacities or interference to discriminate between the interfering signal and a target is discussed in several patents been. Means for differentiating between target echoes and interference echoes based on the transmission of a linear polarized wave and the reception of that polarization and a polarization perpendicular to them in U.S. Patent 2,508,571 and U.S. Patent Nos. 3,566,403 and 3,849,780 and 3,918,059. A differentiating device between target echoes and interference echoes in which a circularly polarized wave sent and both left and right circularly polarized echoes are received, are in the US patents 3,403,397 and 3,614,787 and 3,755,810.

As described in the book "Radar Reflectivity of Land and Sea" by M.W. Long, published in 1975 by D.C. Heath and Company, Lexington, Massachusetts, p. 338 et seq., There are annoying target-like sea echoes called spikes and are only slightly depolarized, i.e. these echoes consist almost entirely of only one polarization. Hence are the double-polarized radar systems explained in the above publications for suppressing this type

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Cloudiness or disturbance ineffective.

There are also two patents which explain devices in which different parameters, here discriminants can be used to reduce the effects of sea echoes. In the US patent 3,893,117 two pulse lengths and two beam widths are used and U.S. Patent 4,008,472 suggests the use two polarizations and two carrier wavelengths. There are facilities for comparing the video amplitudes for a value mentioned operationally here of a discriminant with another value of the same discriminant intended. Means are also provided for switching off the receiver outputs when the ratio the video amplitude is beyond a given value, whereby the receiver output is switched through when the ratio is between the two specified values. As such, these suggestions are limiting and thus disadvantageous, as the ratios for the glitches assume almost any value and with speeds can vary, which can be 200 Hz or more for the sea spikes. This means that the Interfering signals will very often be present in any radar resolution cell used. Note that fundamental Differences between the gate devices explained in the last-mentioned printed publications and those Facilities exist to improve the suppression of spurious signals, antenna sidelobes and interference used by external sources. There are also devices equipped with an antenna, which the Use pulse length as discriminant, whereas other embodiments according to the patents mentioned use the Require use of two antennas. We, iter limit the facilities explained in the cited patents the signal processing device to those,

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which is either the video output of a receiver or another receiver or the sum of the outputs of the process both recipients.

The devices explained in the above-mentioned documents use the wavelength as a discriminant and do not reveal that the frequencies must be kept close to one another, so that two video signals received at the same time are the same or almost the same for a target. Furthermore, these devices use separate transmitters without maintaining a frequency difference and two antennas for the carrier wavelengths A. ₁ and λ The antennas are constructed identically with the exception that they are matched _{to the carrier wavelengths Λ and λ 2.}

In contrast, the invention distinguishes targets from interfering signals by using different discriminants. One Discriminant is a radar parameter for which two "values" called "operators" are received differently Carry video signals. For example, the two discriminants can receive polarization and Be transmit carrier frequency. The operators include special polarizations, transmission carrier frequencies, transmission pulse lengths, Antenna directions and antenna beam widths.

Novel features of the invention include the following:

A. A comparator compares a first received video signal with a second received video signal and gives an output only when both video signals are of substantial magnitude and when the relative Size of the first received video signal to the size of the second received video signal gives a ratio within a predetermined ratio range. Notice

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that the comparator used in the latter patents provides a radar signal output, if one of the two received video signals is substantial and the other received video signal is zero is because the gates are used in parallel. Thus, the comparator according to the invention allows an improved one Suppression of interference signals (clutters), antenna sidelobes and interference with external Sources.

B. An improved signal processing device responds to the output of a comparator and speaks does not respond to a received video signal in any other way.

C. An improved noise canceller compares more than two video signals received at the same time.

D. The setup only requires one antenna to use the polarization, frequency and beam width as Discriminants.

E. It is a means of using the direction of the antenna beam as a discriminant for extraction an improved interference signal suppression provided.

F. The use of small carrier signal differences

as a discriminant for improved interference signal suppression and target selection is created according to the invention. the Frequency differences are typically 10 MHz or less, so the video signals at the same time Reception for interfering signals are no longer related, but related to interesting targets, i.e. stay correlated.

G. It is sent with circular polarization, and there will be two linear polarizations at the same time

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receive what metallic surfaces, in particular metallic double planes with improved security recognizable makes, whereby diplomatic navigation buoys can be determined with greater certainty.

The invention is explained in detail below with reference to the embodiments shown in the accompanying drawings described. Show it:

Fig. 1 is a block diagram of a preferred embodiment of the invention;

Figure 2 is a block diagram of a first alternative embodiment of a signal conditioning device;

3 is a block diagram of a second embodiment of a signal conditioning device;

4 is a block diagram of a third alternative for a signal conditioning device;

5 is a block diagram of a fourth alternative of a signal conditioning device;

Figure 6 is a block diagram of a preferred embodiment of two used in series Gates which form a simple comparator;

Figure 7 is a block diagram of a preferred embodiment of cascaded Comparators;

Figure 8 is a block diagram of a preferred embodiment of the invention having a Comparator, which consists of comparators connected in cascade;

9 is a block diagram of a sixth alternative for a signal conditioning device;

Fig. 10 is a block diagram of a seventh alternative for a signal conditioning device;

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11 shows a block diagram for an eighth alternative a signal conditioning device; and

Fin. 12 is a block diagram of a ninth alternative for a signal conditioning device.

According to FIG. 1, the antenna arrangement 10 and the radar transceiver 11 are arranged in such a way that receiver video output signals depend on different operators (values) of a discriminant. The discriminants are polarization, carrier frequency, pulse length, beam width and direction of antenna alignment. For example, the video device 1 shown as block 12 can respond to the operator transmit / receive polarization pair P ₁ and the video device 2 shown as block 14 to the operator transmit / receive polarization pair P-.

The amplitudes of the video devices 1 and 2 are compared simultaneously in the comparator 16 and it is a gate signal for further signal processing is obtained on the basis of the relative amplitude. With others In words, a comparator output 18 is only generated when the ratio of the amplitudes from the video device 1 and the video device 2 is within a predetermined ratio range.

By using at least three operators, three or more video signals can be used for signal processing can be obtained on the basis of ratios. Fig. Shows a preferred embodiment in which the Amplitudes of four received video signals are compared by a comparator 72. On the basis of various A comparator signal 65 is obtained for the further signal processing of relative sizes.

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The gate signals 18 and 65 can be used directly as radar outputs; they can also be further processed and used as radar outputs; or they can also be used in the processing of other signals Role-play.

As mentioned earlier, the strength of the radar echo depends of an object depends on both the transmit polarizations and the receive polarizations. The term "polarization pair" serves to describe the two polarizations. For example, a special polarization pair is a horizontal (H) transmit polarization and a vertical (V) reception polarization and is called HV for short. There is a first aspect of the invention in that the ratio of the echo strengths for two polarization pairs on the shape, size, orientation of the echo generator as well as on the substance of which the echo generator is made.

Some polarization properties of targets are explained in the already mentioned book "Radar Reflectivity of Land and Sea", and special polarization properties which facilitate understanding of the invention are given here. H, V, L and R designate a horizontal, vertical, left-circular and right-circular polarization. Because of the reciprocity of the transmission and reception paths in air, the following applies: oT_ _T = <31 ₇ ", & Z _T =

JtiV VrI JKLf

^ iD ^{= 0} TJtIf ⁰ TrV ⁼ & r \ Ti etc. It should also be made clear

IiK Kn VJLj i-iV

be that when H and V polarizations are transmitted simultaneously, the received signal strengths in H and V will generally depend on the relative phase of the two transmitted waves. However, if eTT " _T = dT _T " = 0

xlV VJn

this relative phase does not affect the strengths of the H and V polarized echoes.

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The following abbreviations are used for simplification:

A >> B means that A is at least 10 times B Ä «5B means that A is approximately equal to B. A ^ B means that A is seldom equal to B.

There can be many artificial targets for which the polarization properties are the same as those of a large, are smooth, metallic surfaces, for which the following typically applies:

Some natural surfaces can be considered great smooth dielectric surfaces are characterized. The swell or swell is such an example. These Surfaces cause only a slight depolarization and <3T "is usually equal to or greater than The following applies to these surfaces

The polarization properties of rain can often be characterized by those of a cloud of spheres will. For a sphere and for metal, three-sided corner reflectors, the following applies:

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The reflective properties of metallic double planes (two-sided corners used on navigation buoys) are:

⁰ HII ^{= 0} VV ° VH ^ ° ' ⁰ VH ^ ⁰ HH

where c5 ^ _H Φ oC _v if E represents the irregular polarizations for which the H and V components are equal.

/ -2

The orientation of the edge of the double plane affects some polarities, even if they are in one Plane is perpendicular to the radar line of sight. Then hang

and d ^ y depend on the orientation,

however, <5Z ", ö" l! - _T , o * 7 "and 6ΓΓ _{ΤΤ are} independent

Kn KV JjH LiV

from the orientation.

Certain aircraft have polarization properties such as large, smooth, metallic surfaces plus metallic cal Di surfaces as follows:

⁰ VV * ⁰ VH

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Extensive land and lake areas usually behave like a mixture of irregularly oriented ones infinitesimal dipoles and smooth non-metallic Surfaces as follows:

The above notation, for example ο * φ

HH

indicates that the different radar cross-sections for clutter signals are relatively seldom the same. With others In other words, for the example given, the amplitude of the HH echo is seldom the same as that of the W echo. Both these amplitudes usually fluctuate for targets as well as clutter signals. However, the ratio varies these amplitudes are wider and faster for clutter signals as well as for artificial targets.

As already noted, the amplitude range for a clutter signal is large. Furthermore, it usually fluctuates Echo for one polarization independent of that for another polarization. Hence the amplitude ratio of the two video signals from each radar resolution cell are essentially zero to very large large values fluctuate. The clutter echo varies rapidly because it is the composite result of the echo summation is made up of many individual scattering sources with phases that are opposite to the relative positions of the scattering sources are sensitive. Fluctuation rates are usually determined by a continuum of frequencies with a

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Half power bandwidth represented by the transmission wavelength depends. For example, this bandwidth for the sea is typically 50 to 100 Hz for a 3 cm Wavelength.

Sometimes there are echoes that are exceptionally strong relative to the composite echo from other scattering locations. Such Echoes can be generated by a dielectric surface that is smooth and large in relation to the radar wavelength. For one such wave usually occurs slight depolarization of the echo and the echo amplitude for the HH polarization will equal or exceed W polarization. For example, sea spikes are discussed in the book "Radar Reflectivity of Land and Sea ", a particularly annoying type of clutter signals (interference signals), which have several properties similar to the goal.

The amplitude ratio of the two signals is used as the basis for deciding whether the echo signals should be used as targets are to be treated or not and thereby also for the decision about those echo signals that are rejected should be. This ratio can change very quickly for targets and for clutters, but that is the range the ratio values are usually much larger for clutters than for targets. The difference in the probability distribution the ratio is essential to the invention. In other words, a reinforcement of the goals relative to the clutter is achieved by a signal processing device by removing differences in the frequencies the occurrence of echoes with different reception polarization ratios can be exploited. By choice On the one hand, broad general classifications for targets are achieved by certain ratio bands for processing and clutter signals on the other hand.

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The invention can be used to discriminate between broad classes of artificial targets such as buildings, streets, Corner reflectors and ships. It is further possible to choose between broad classes of natural Destinations such as rain, water masses, and land masses, as well as properties of the lake surface such as to make the swell, the swell, foam crowns, wave fronts, wind surfaces and river boundaries visible. Therefore As used herein, the word "target" includes both artificial and natural targets.

When using the polarization as a discriminant, a comparator is used that determines the amplitudes of two or compares several signals, each of which has a significant size and is derived from different send / Receiving polarization pairs results, so that an output depending on a ratio of the properties mentioned is obtained to indicate the presence of a target echo. At least two different polarizations serve for the four signals: first transmission signals, first reception signals, second transmission signals and second reception signals. The first and second received signals result at least two signal amplitudes of significant magnitude. The comparator compares an output based on the relative Size of the two received signals is based, and this output is used for further signal processing or is processed further. Therefore, the invention uses selected polarizations to simultaneously generate two video signals Create essential size goals and compare those sizes. If the ratio of this Sizes is within a preselected range, a gate signal is used to trigger the processing of the Signals generated as target signals. ,

Thus, FIG. 1 shows a block diagram of a preferred embodiment of the invention. The antenna device

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and the radar transceiver 11 are arranged so that Receiver video output signals are generated by the Target echo strength for at least two different polarizations are dependent. For example, the as Block 12 shown video device 1 on the transmission and reception of a horizontal polarization and the Video device 2 shown as block 14 respond to the transmission and reception of the vertical polarization. It is of crucial importance that the amplitudes of the video devices 1 and 2 are each from essential size and that each is based on an echo strength for different polarization pairs (first transmit / receive signals and second transmit / receive signals) responds. Neither do the transmit polarizations nor the receive polarizations have to be which are assigned to the video device 1 or the video device 2 must be the same. At least However, one of the polarizations must be, for example the transmission polarization for video device 1, reception polarization for video device 1, transmit polarization for video device 2 or receive polarization for Video device 2 may be different from the other three polarizations used.

The amplitudes from the video devices 1 and 2 are compared in the comparator 16 and on the basis of a relative amplitude received a gate signal 18 for further signal processing. In other words, the Video 1 and Video 2 signals, each of a substantial size, are compared and preselected based on A gate signal 18 is obtained for the amplitude ratios for these signals. The selected relationships are related by comparator 16 and others standing devices, such as the video; device 1 and 2, the radar transceiver 11 and the antenna device as well as the radar target properties were created.

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The gate signal 18 can be used directly as a radar output, it can be processed further and as a a radar output can be used, or it can be used in processing other radar transceiver outputs, such as those from the video device 1 and video device 2 are used. Take for an explanation indicate that the target of interest is a sphere and that the polarizations have been chosen as described above and assume further that the radar parameters are chosen to match the amplitudes of the video equipment 1 and 2 are the same for a sphere. Assume that the comparator 16 is set to receive a gate signal is obtained from the comparator 16 only when the Video devices 1 and 2 are such that the ratio is close to unity. In these circumstances and with others suitably selected polarizations, a gate signal would rarely be triggered by an echo from land or sea. Therefore, spheres and other targets with the preselected polarization properties would be displayed as targets and other echoes were suppressed.

The comparator 16 could of course have more than one ratio band or address a range of ratios than that indicated above being "about one" became. Therefore, a gate signal can be created to provide a target selection option based on preselected Polarization ratios based.

The embodiments of the invention can be included in the range the radar technology known components can be realized. The antenna can be of the reflector type with irradiation (lighting) by a dual linear polarization feeder, which is aimed at maximum reception of a horizontally polarized wave is aligned with a feed output, reducing the reception of the vertical

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Polarization is maximized for the other output. It is noted here that most types of land and sea clutter relative to the target echo will be satisfactory can be suppressed even if other feeder alignment angles are used. Here, however the special use of the reception of horizontal and vertical polarizations to process sea spikes and other echoes.

A single antenna can be used to transmit and receive a wide variety of polarizations of a dual polarization device called the dual or multiple polarization coupler will. Details of such couplers for linear and circular polarization are in the article "Dual-Mode Coupler "by R.C. Johnson et al, which is described in U.S. Pat IEEE Transactions on Microwave Theory and Techniques, Vol. MTT-15, 1967, pages 651-652. Alternatively can have different polarizations by using a separate antenna for each polarization can be obtained.

"Receiving polarization 1" is called the echo wave polarization defined to which the amplitude of the video device is responsive; Video device 2 is similarly proportional to "receiving polarization 2". The abbreviations H, V, L and R are used to denote horizontal, vertical, left-circular and right-circular polarization.

Figures 2, 3, and 14 give examples of signal conditioning in a signal conditioning device 15 from Fig. 1, which the outputs on the video EJinrichtung 1 and Video device 2 supply. In Fig. 2, the power

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of the transmitter 25 in a hybrid connection 24 divided so that the same H and V signals are emitted via the H and V antenna. Duplexers 21 and 22 are provided so that return signals via the H and V antennas 20 can be received. In this configuration, “receiving polarization 1” means H and “receiving polarization 2” then means V. There are applications for which the relative phase 0 is insignificant. However, the device indicated by 23 in the block diagram can adjust the phase between the transmitted signals so that when 0 equals 90 °, the transmitted wave is circularly polarized. There is an important advantage for the transmission of the circular polarization when H and V polarizations are received, since (SZ. _XT = o "^" = o "T" = ö * T _X7

Kn. KV i-iii LiV

for a metallic di-plane is independent of the edge orientation. For this choice of polarizations will be therefore the amplitude ratio of the Video 1 and Video 2 signals do not change with the inclination of the Di plane .

According to FIG. 3, the antenna 30 emits a circular polarization and receives left and right circular polarizations. The relative phase angle, 0, is shown with block 32 is selected so that after combining the received signals in the hybrid connection 34 the Result signals are such that the "reception video 1" is an H and the "reception video 2" is a V. The ones in the Fig. 2 and 3 illustrated configurations are exemplary of the device that meets the basic requirements for the conditions, so that the targets are amplified with respect to the clutter signals.

FIG. 4 shows a method that is alternative to FIG. 3. In the devices according to FIGS. 3 and 4, the receives Antenna 30 the signals L and R. As already noted,

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In the device according to FIG. 3, the inputs for the receivers 35 and 36 are proportional to H and V. In Fig. 4 are signals of intermediate frequency that are proportional to L and R, reinforced in units 44 and 45 and with a suitable phase of hybrid connection 47 so that the inputs to units 48 and 49 are proportional to H and V. Note that the Devices according to FIGS. 2, 3 and 4 each show embodiments of the signal conditioning device 15 for which the Video 1 and Video 2 signals are proportional to the echo strengths for the H and V polarizations are. Therefore, the receive polarizations for each of these embodiments are H and V, although the Antenna 30 according to the devices shown in FIGS. 3 and 4 is an L and an R antenna.

The performance of a preferred embodiment of the invention in which the relative strengths of Video 1 and Video 2 are compared when HH and W polarizations are used, is explained below. By definition, HH means that only H is sent and only H is received while W means that only V is transmitted and V is received. Therefore, strictly speaking, HH and W echoes can cannot be obtained at the same time, but in practice they can be obtained by sending and receiving H and then through Sending and receiving of V can be obtained within time intervals that are short compared to the important ones Fluctuation speeds of the echoes.

Assume that the transmit and receive polarization between H and V increases on the basis of area scanning Area scanning is switched, i.e. for area scanning the transmit and receive polarizations are H. (Video 1) and shortly thereafter for another area scan, the transmit and receive polarizations are V (Video 2).

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The echo signals can then be used as a function using a conventional radar memory and delay technology of the area for Video 1 can be received and stored, and then compared with those for Video 2. if after the transmitter range scan frequency is sufficiently high, one can practically compare the echo strength from Transmit Η-Receive H with the echo strength for Transmit V-Receive V, and this can be done for each radar resolution cell are executed.

There are numerous possible polarization combinations using the inventive concept and by interconnection either the transmission polarization or the reception polarization or both polarizations can be obtained can. Examples of the wave switching modes are shown in Table 1 below.

TABLE 1. Switching modes

Send- number of Reception polarization recipient polarization fixed 1 switched fixed 2 switched switched 1 fixed switched 1 switched switched 2 switched

Further advantages of interconnecting the transmission polarization will now be explained, the invention with circular Polarization is used.

Circular polarization is used to reduce the echo from rain relative to the echo from certain targets, mainly from Aircraft, used. Experience shows that when the circular reception polarization has the same meaning

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like the circular transmission polarization, the echo from rain is reduced more than that from airplanes. The reason for this becomes clear when one remembers that the ratios O ^ / <^ _R and ⁰ TrZ ⁰ Tt for rain, but for an aircraft the ratios are on average much smaller than for rain.

To the mentioned advantages of circular polarization to use it, assume that a circular polarization is sent and a video 1 signal is present after reception. For the next area scan, assume that the other circular polarization is transmitted and as a Video 2 signal Will be received. Realize that the rain echo is relative to the echo of the airplane and certain other targets in the video 1 and 2 signals have been reduced because one signal is echoed by the LL and the other was obtained from the RR echo. However, the LL echo and the RR echo are not identical for all destinations. As already mentioned, the video 1 signals can be recorded as a function of the area using radar memory and delay technology can be received and stored and then compared with those of the Video 2 signals. In this way, land and sea interference signals are also suppressed because the gate signal from the comparator for an aircraft is more frequent is obtained as for land and sea clutter signals because the amplitude ratios for the Video 1 and Video 2 signals for an aircraft over a smaller area change than for extensive land or sea areas. Therefore, the Video 1 and Video 2 contain signals, respectively Signals for which the rain echo has been suppressed relative to the echo of the aircraft and similar targets, and the gate signal is obtained more often for an aircraft than for land and sea clutter signals because of the ratio from ^ r / ^ l to more areas for interfering signals changes than for an airplane.

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An important feature of the invention for suppression of clutter signals is to use a predetermined ratio band or bands corresponding to those of a desired target that is used to process the received signals for the radar output is activated. Since the ratios for clutter signals usually change over large areas, the are much larger than those for goals, this feature automatically reduces the percentage of Clutter signals contained in the radar output.

Another feature of the invention for suppressing the clutter signals is that two transmit / receive polarization pairs be transmitted, which can be chosen so that the echo of non-depolarizing Objects is suppressed. One such example are the spikes generated by the swell, for which the echo amplitude for the HH polarization is equal to or greater than that for the VV polarization. Based on the Reflective properties of water is used for rough seas without Wave crests (swells) the HH echo power usually exceeds that for VV by less than a factor of 2, and the HH echo power will seldom be greater than 10 times a W echo power. For the circuit implementation should be kept in mind that for a smooth dielectric surface the strength of the RH (or LH, HL, HR) echo relative to the strength of the RV (or LV, VL, VR) echo equal to The strength of the HH echo is relative to the strength of the W echo.

Frequency response

For a fixed frequency radar signal, the strength of the echo fluctuates due to changes in orientation and in the relative positions of the objects, within

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a radar resolution cell. A change in the radar frequency also leads to a change in the strength of the echo, and therefore, rapid frequency changes (frequency response) are occasionally used to amplify the echo fluctuation rate used. In the book "Radar Design Principles" by F.E. Nathanson, published by the McGraw-Hill Book Company, New York, 1969, mentions certain advantages of the frequency response. By taking advantage of the Frequency response, the clutter signal can be displayed more uniformly and at a level that is weaker than that of the strong clutter signals that occur occasionally. Furthermore, the probability of a target echo strength of equal to or approximately equal to zero can be significantly reduced by utilizing the frequency response. The properties of the frequency response can therefore also be used to advantage within the scope of the invention.

Frequency comparisons

This section describes embodiments of the invention, the two or more transmit carrier frequencies for Use clutter signal suppression and target classification. Effects of the frequency changes in the radar echo are described in the aforementioned book by F.E. Nathanson explained.

A main idea of the invention is that the amplitudes of two echoes are statistically independent of a target and are therefore not predictable if the echoes are for two transmission carrier frequencies that differ by at least / \ f "

(D

where c is the speed of light and L is the effective target length.

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From theory and practice it follows that the echoes from a large number of distributed targets (scattering sites) such as raindrops, are uncorrelated (independent) if the difference in the carrier frequency (\ f. Equation corresponds if L equals the radial extent measured longitudinally Therefore, if the scatter sites fill the radar resolution cell, then the effective length L is equal to the length in the area of the radar resolution cell, since the area resolution for a pulse radar is cT / 2 , where £ is the pulse length, Af equals the term 1 / T '»if the clutter signal source fills the radar resolution cell.

The echo amplifier for a single sphere is insensitive to small changes in frequency. Therefore the effective length L approximately equal to zero. However, L is for a cluster signal for many such irregularly distributed Spheres equal to the smallest of the following: The cluster length (measured along the radar beam) or cf / 2.

For an artificial target that does not contain a large number of separate scatter sites, L can be considerably smaller as the spatial length measured along the radar beam. For the analysis given here, it is estimated that the echo amplitudes for two carrier frequencies are almost the same (fixed target orientation assumed), provided that the difference between the carrier frequencies is less than

zo I _p '

where L is the spatial length of the target measured in the direction of the radar beam.

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According to the invention, a gate signal that the processing Allowed by signals as target signals, # generated only when the relative size of the two video signals out of the two transmission frequencies remains within a predetermined ratio range. In other words, for Reception of the channels with the same gain, video signals are processed as if they originated from a target, only if the relative size of the video signals is close to one within a ratio band; otherwise the signals will not reach the radar output. Therefore, the transmission frequencies are chosen so that the due echo generated by sources extending over a large area is rejected at a higher percentage than the echo of desired goals.

In the preferred embodiment of the invention shown in Fig. 1, the antenna device 10 and the radar transceiver 11 are arranged so that receiver video output signals respond to a target echo strength for different carrier frequencies. For example, the video device 1 shown as block 12 can respond to the sending and receiving of a carrier frequency f... And the video device 2 shown as block 14 can respond to sending and receiving a carrier frequency f ". Imagine here that f ^ and f _{2 can} each represent a group of transmission frequencies. For example, f. In other words, the Video 2 signals may respond to the same transmit frequencies that the Video 1 signals generate, except that they are delayed by one transmitter interpulse period. For this example, two video signals are received simultaneously from blocks 12 and 14 and are speaking

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each to a different transmission frequency. The delay required to obtain the Video 2 signals can be can be achieved with conventional radar memory and delay technology.

The amplitudes of the video 1 and video 2 signals are compared simultaneously in the comparator 16 and depending on the relative amplitude, a gate signal 18 is generated for further signal processing. In other words, the Video 1 and Video 2 amplitudes are compared and if the amplitude ratio is within a given one A gate signal 18 is generated. The selected ratio is made by the comparator 16 as well as other related components such as the Video 1 and Video 2 circuits, the radar transceiver 11 and the antenna arrangement 10.

There are many combinations (codes) that can be used for changes (differences) in the transmission frequency. Such coding in the amount of frequency change (difference) can be used to amplify the targets based on the effective length L. For example, assume that half the frequency differences are of a relatively small value of, such that (a) the corresponding video amplitudes within each resolution cell for clutter signals are decorrelated, and (b) the corresponding video amplitudes for all of interest Goals are highly correlated. Assume further that half of the frequency differences are Af , where Af is greater than of, and where 4f is chosen such that (c) the corresponding video amplitudes for large targets, e.g. ships, are decorrelated on average; ) the corresponding video amplitudes for small targets, e.g. buoys, are highly correlated. In the specified

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Example would be a comparator signal (a) for an interfering signal seldom produced, (b) produced only about half the time for ships, and (c) for Buoys are generated almost all of the time.

The preceding discussion was based on the comparison of video signals resulting from sending only one at a time Carrier frequency resulted. Alternatively, the video 1 signals and video 2 signals can also be transmitted through the simultaneous Sending two pulses with different carrier frequencies and receiving echoes for them at the same time both broadcasts are received. The required frequency changes can of course be made by changing the frequency of one or more transmitters. Fig. 5 illustrates an embodiment in which two Carrier frequencies are sent simultaneously.

In the embodiment according to FIG. 5, a variable-frequency transmitter 25 generates an output with a frequency f * which is different for each successive range scans. This output is divided into two parts by the hybrid connection 24. An output signal of the frequency f ₁ reaches the antenna arrangement 10 via the duplexer 21, and an output signal of the frequency f ~ i, which is generated by the frequency converter 50, reaches the antenna arrangement 10 through the duplexer 22. Thus, the antenna device 10 emits two signals with the carrier frequencies f .. and f ₂ from. It is understood that in the f in Fig. Embodiment of the invention shown in Figure 5 .. and f ₂ by a specified by the frequency converter 50 constant amount are different and therefore, f ₁ and f ₂ are respectively for successive area scans by the frequenzveränderliehen transmitter 25. to be changed.

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The radar echoes generated for the frequencies f .. and for the frequencies f _o are received by the antenna arrangement. The reception frequencies f .. reach the f ₁ -Empfanger 26 so that the dependent video signals of the echoes obtained at those frequencies to the Video 1 output 12 via the duplexer 21 and are detected and processed. The signals which are dependent on the echoes with the frequencies f 1 are received at the video 2 output 14 after reaching the f 1 receiver 27 via duplexers 22 from the antenna device 10. Thus, for each area, the video 1 signals and the video 2 signals are obtained simultaneously. It can be seen that the signals recorded simultaneously in this way can be processed further as explained above with a comparator 16 and a signal processor 17 as shown in FIG.

Assume that the difference between the frequency f ~ and the frequency f ₁ is at least Äf in equation (1) for

I C *

a given echo source. Then the size of the Video 1 signal relative to the size of the Video 2 signal is unpredictable. Without a target or radar movement, without a change in f _1, the following f ... echo and the following f n echo would be unchanged. It therefore follows that the transmitter output 25 with the frequency f .. by at least A f in equation (1) must change in order to ensure that the relative sizes of the video 1 and video 2 signals over a large percentage differentiate any time interval.

Some features of the embodiments shown in FIG. 5 will now be explained using a numerical example explained. Assume the transmitter pulse length is 1 microsecond and assume that the Turbidity or the clutter spread across many radar resolution cells. Then it follows from the already mentioned literature

L. _& (clutter) = 150 m.

809884/0623

Assume effective lengths L of 5 m and 0.5 m for the targets. Hence the frequency changes that for SijC production of uncorrelated echo amplitudes required are the following:

(Clutter) = 1 MHz (5 m target) = 30 MHz (0.5 m target) = 300 MHz.

Assume that there is no target or radar platform movement and that f ^ differs from f .. by 3 MHz. Then the Video 1 and Video 2 amplitudes will always be approximately the same for both targets and will be unpredictable for the interfering signal. If the changes in transmitter frequency f .. are at least 1 MHz between pulses, the percentage of time during which the gate pulses are generated by the jamming comparator will be small in relation to the percentage for the targets. If the changes in f were 30 MHz, the Video 1 pulses would be uncorrelated (same goes for Video 2 pulses) for the 5 m target, but correlated for the 0.5 m target. Even if f2 minus f .. = 3 MHz, the video 1 and video 2 target pulses received at the same time would be nearly the same. It follows from the consideration made here that the target selection can be achieved by a suitable choice of the frequencies to be used.

It has now become clear that a main feature of the invention is the use of a predetermined frequency band in combination with suitable carrier frequency differences. This feature reduces the percentage Share of interfering signals in processing.

809884/0623

Use of other discriminants

The use of different polarizations and different frequencies was (a) for extraction of Video 1 and Video 2 signals for which the amplitude ratio for spurious signals fluctuates to a large extent, and (b) is described for a ratio that is due to the Target fluctuations is less large than for interfering signals, described.

Another method for (a) and (b) is to process the Video 1 and Video 2 signals themselves, which generated by the echo from different resolution cells will. For example, video 1 signal for transmission pulses of a first length and video 2 signal for pulses a different length can be obtained. Then the video 1 signal can be compared to the video 2 signal using radar memory and delay means will. In this way, the relative size of two signals from different but overlapping signals can be achieved Dissolution cells are obtained. Thus, an echo from a target can be contained in both cells is to be processed as the target echo at the radar output. Another method of comparing different ones however, there is overlapping resolution cells Comparison of the video 1 echo for beam width 1 and video 2 echoes for beam width 2. Obviously, different Combinations of beam widths and pulse lengths can be used.

Different but overlapping beam directions of the directional antennas can be used to obtain different Video 1 and Video 2 signals can be obtained. For example, assume that the beam is in azimuth is continuously scanned. Then because of the

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282HQ1

Radar storage and delay technology, the echo signals from one beam direction with the echo from another Beam direction can be compared. Then, with suitable time delays, the target echo can be used for comparison purposes received and compared for different main directions will.

The device of FIG. 2 is based on other methods in which the video 1 signals and video 2 signals respond to different main directions of the antennas. Assume that the antenna device 20 is supported by a replaced those with two main feeders, which are offset from the reflector axis, so that the antenna beam main directions for the two feeders (dipoles) are different. When receiving, the video 1 signals are then and video 2 signals depending on different antenna main directions. The two feeders (dipoles) can be of the same or different polarizations. Assume that the feeders (dipoles) for the H- and V polarizations are provided and they suppress spikes. Then the phase shifter be adjusted so that the polarization at the tip of the transmission beam is circular. When feeders (dipoles) the same polarization are used, the phase shifter device 23 can be set so that the transmission beam is maximized.

As previously described in connection with FIG. 5, pulses of the same length with carrier frequencies f ₁ and fy are transmitted simultaneously. Assume that the output pulses of the frequency converter 50 are abbreviated by a high-speed switch or an attenuator operated by the transmitter 25. Such a switch or muffler can be between the

809884/0623

Frequency converter 50 and the duplexer 22 are switched on. Then the video 1 signal and the video 2 signal would be ' depending on different transmitter pulse lengths.

The device of FIG. 5 also illustrates a method according to which the video 1 signals and video 2 signals respond to different antenna beam widths. Let us assume that the two connections of the antenna device represent two primary feeders which irradiate a reflector in such a way that the beam widths for f ... and f "are different. Then video 1 signal and video 2 signal respond to different antenna beam widths.

FIG. 5 now explains the simultaneous use of frequency differences to suppress rain echoes and polarization differences to suppress sea spikes. Both wear discriminatory measures for reducing a homogeneous sea interference signal or a homogeneous turbidity caused by sea. Assume that the antenna device 10 is replaced by the H and V antenna 20 from FIG. Now speaks Video 1 signal to the transmit / receive horizontal polarization for carrier frequency for and video 2 signal on transmit / receive vertical polar isation for carrier frequency f .. an. Note that the polarization pairs use HH and VV at the same time since different carrier frequencies are used at the same time.

Signal processing

The embodiment of the invention shown in FIG. 6 has the comparator 16 from FIG. 1. A ₁ and A ~ represent output amplifiers for video 1 and video 2, which are designated by 12 and 14 in FIG. For the comparator from Fig. 6, the gates 1 and 2 are denoted by 55 and 56 and connected in series so that the comparator

809884/0623

output 18 only occurs when both gate 55 and gate 56 allow a signal to pass. To explain the operating behavior of the comparator from FIG. 6, assume that gate 1 passes a signal 57 when A _{1 is} greater than 0.8A ₂ and gate 2 only passes a signal 18 when (1) signal 57 is present and (2) if A _{1 is} less than 1.25A „. Then a comparator output 18 only occurs when A. is greater than 0.8A _? and is less than 1.25A ₂ . Note that the gate alone acts as a comparator for which a comparator signal is generated when A _{1 is} greater than 0.8A_. In this case the signal 57 from FIG. 6 would be used as the comparator output.

The operation of the signal processor 17 is not limited to any particular signal processing technique. For example the comparator 16 can generate a train of equal amplitude pulses when the ratio of Amplitudes of the video signals 1 and 2 is within a predetermined range. Those impulses can then can be processed further in the signal processor, or, alternatively or in combination, the video 1 and Output video 2 signals for further processing.

Processing the comparator pulses instead of the Video 1 or Video 2 signals can sometimes be beneficial. In this case, all can be processed Signals, whether they come from a target or from a random source, are of the same amplitude regardless be from the area. This eliminates the need to process extremely wide ranges of signal amplitude, as a result, for example, no echo amplitude for a given target is a strong function of area is. Another advantage of processing comparator pulses of the same amplitude is that the

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2-82H01

Clutter impulses are never larger than the impulses from a target even if the actual clutter echo or clouding echo will be much larger than the target echo should.

A useful method of signal processing is based on the fact that gate pulses are more frequent for targets than generated for clutter signals. Therefore, the gate pulses can be continuously fed to an integrator in the signal processor 17 are supplied and a threshold value circuit after the integrator can be chosen so that the echo of the desired destinations is displayed and the clutter is rejected.

Several coding methods are available for changes in the transmission frequency to suppress turbidity (clutter signals) which provides a target classification based on the effective target length along the radar beam. It is clear that the methods by using more complicated codes as well as by using them at the same time can be expanded further by more than two transmission frequencies.

Cascade of comparator outputs

The previous description was based on the comparison of two received video signals with a comparator. Alternatively, three or more operators can be used to receive three or more different ones Video signals, and any pair of such Video signals can be compared with another comparator. Then each comparator can be converted into a Cascade according to FIG. 7 are switched on. The arrangement of FIG. 7 appears in FIG. 8 simply as

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2-82HQ1

Comparator 72. FIGS. 9-12 show preferred embodiments of the signal conditioning device for creating four received video signals, called video 1 to 4 for short and which have amplitudes A ₁ to A.

In Fig. 7, A. to A represent the amplitudes of the received video signals compared _{in the comparators C 1} to C _fi. Comparator C ₁ supplies an output signal 60 when the ratio of the amplitudes A ₁ and A _{2 is} in a predetermined ratio range. Comparator C ″ generates a signal 61 when signal 60 is present and when the ratio of the amplitudes A ″ and A _{3 is} within a predetermined ratio range. Similarly, comparator C i generates a signal 62 when signal 61 is present and when the ratio of the amplitudes A ₁ and A is within a predetermined range of ratios. It can be seen from this, finally, that the comparator C, - generates an output signal 65 only when the signal 64 is present and the ratio of the amplitudes A, and A, is within a predetermined ratio range. In other words, the comparator C _fi has an output which is only present when all of the various ratios of A ^, A «, A ^ and A- are within the specified ratio ranges.

FIG. 8 explains the use of comparators connected together to form cascades according to FIG. 7. Recall that A ₁ through A represent the amplitudes of four different received video signals. These amplitudes are compared simultaneously in comparator 72, which in reality contains a cascade of comparators. On the basis of the various

809884/0623

relative amplitudes A ₁ to A, the gate signal 65 may or may not be obtained. The gate signal 65 can be viewed and processed directly as a radar output, or it can be used in the processing of other radar transmit / receive outputs, such as the four received video signals with amplitudes A ₁ to A-.

In the device from FIG. 9, the four operators are the carrier frequencies f .. to f4, which are transmitted simultaneously and generated by means of a four-frequency transmitter 83a in which the differences between the frequencies are recorded. This transmitter can be set up by using a transmitter operating at frequency f. And three frequency converters for the frequencies f ~, f ₃ and f. The four carrier frequencies are received by the four receivers 85 to 88 separately.

According to FIG. 10, the operators are four antenna main directions, like that in the area of the monopulse radar practiced and in the book "Radar Handbook" by M.I. Skolnik published by the McGraw-Hill Book Company, New York, 1970. The power from the transmitter 83 is divided equally and the phases are with corrected by the power splitter and the phase corrector 90 so that a transmission beam from the antenna 80a is obtained, as known from the monopulse radar is. When receiving, there are four reception beams, one for each feeder (dipole) and therefore four received video signals 89a to 89d are obtained.

Referring to Figure 11, the operators are two carrier frequencies and two polarizations. The H and V polarizations are sent and received with the antenna 80b.

809884/0623

Two transmission carrier frequencies f ... and f "are generated simultaneously by a two-frequency transmitter 83b, in which the difference between the frequencies f ₁ and f" is recorded. The transmitter can be set up by using a transmitter at frequency f "and a frequency converter to generate the frequency f". Recall that the video 1 signal is responsive to the H polarization and frequency f- at 89a, the video 2 signal is responsive to the H polarization and frequency f 'at 89b, the video 3 signal is responsive to the polarization at 89c V and the frequency f .. responds, and that finally the signal Video 4 at 89d responds to the polarization V and the frequency f ₂ . The phase shift network 92 allows circular transmission polarizations for the frequencies f ^ and f ₂ · It can be seen that the antenna 80b for H and V can be replaced by an antenna in which two dipoles (feeders) are substituted for one polarization for different antenna main directions can be. The phase shifter network 92 can then be set in such a way that there is one transmit beam direction, although there are two receive beam directions. It should also be noted that the two antenna dipoles can have different beam widths, which enables the use of two antenna beam widths as operators.

In Figure 12 the operators are two polarizations and two antenna beam principal directions. There are two Antenna feeders (dipoles) 90a, 90b are provided, one each for H and V polarization. These feeders can irradiate a reflector, so that two antenna beam directions are available when receiving. Phase shift networks 92a and 92t »are provided so that the transmit polarizations from both feeders 90a and 90b on the one hand right-circular and on the other hand left-circular

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282U01

are. The transmitter 83 generates power which is equally divided by the hybrid connection 91c and the transmission power is once again equally divided by the hybrid connections 91a and 91b. Hence takes each feeder 90a and 90b has the same transmission power. By suitable choice of phase shift 0, with phase shift network 92c results in a transmission antenna beam main direction and the transmission polarization is either be right-circular or left-circular. At reception If there are two antenna beam directions available, one is from the feeder 1.90a and the other from the feeder 2.90b recorded. Note also that the H and V polarizations are picked up by each antenna feeder and be received. Four receivers 85a to 85d thus become four received video signals Video 1 to used, which are labeled 89a to 89d. It can be seen that the signal 89a, that is to say video 1, has the H polarization and addresses a first major direction; the video 2 signal 89b speaks to the Η polarization and that first Main direction to; Video 3 signal 89c speaks to the Η polarization and the second main direction and video 4 signal 89d speaks to the V polarization and the second Main direction.

Interference and sidelobe suppression

The described embodiments of the invention have certain advantages of interference suppression and improved effective antenna characteristics. Assume that the facility operates with radar output is obtained only when Video 1 signal and Video 2 signal are almost the same. Then a must Signal coming from outside and being processed as a target has almost the same amplitudes for video signals Generate 1 and 2.

The ability to generate an improved effective antenna spectrum arises because of the Invention the comparison of echoes of different polarizations and different antenna diagrams suggests that are present for each polarization. For example, if the antenna is for one polarization has a very narrow main lobe and if for the other polarization the antenna has very weak side lobes has, the resulting directional distribution of the device can be such that it has a very has a narrow main direction and very weak side directions.

The embodiments of the invention can per se in the prior art known components can be realized. For improved dynamic recipient areas logarithmic amplifiers can be used. Alternatively, linear amplifiers can also be used. Appropriate comparators, integrators and delay devices are also available.

The invention proposes a device for suppressing radar opacity and for target classification the at least two signals of significant magnitude, which are made up of transmit / receive pairs of different combinations and polarizations are received, and wherein a signal based on the amplitude ratio of the received signals is generated. The signal processing uses the differences in the Echoes for different polarizations and has a device in which these differences in the Echoes caused by differences in the transmit carrier frequency, Pulse length, antenna beam width and main beam direction are used. Sender and receiver with variable transmit and receive frequencies to be used.

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2B2HQ1

Overall, a device for suppressing radar opacity or radar jamming signals and for target classification was created that compares two or more video signals. Various signal conditioning and processing devices are used to improve the echo differences between targets and the opacity causing interference signals caused by differences in polarization, carrier frequency, pulse length, Antenna beam width and antenna main direction. Signals are considered to be coming from a destination processed when the ratio of the video amplitudes is within a ratio band and signals are processed suppressed as interfering signals when the conditions are not are within the ratio bands specified for the objectives. The invention thus creates a method to suppress interference signals caused by rain, Land or sea can be generated.

While the foregoing description is accurate in explaining the accompanying figures, it is clear that numerous Connections of the circuit components shown in the figures and easily recognizable not expressis verbis are included in the description. In this respect, the drawings are compared to the description independent means of disclosure of the invention.

809884/0623

Claims (11)

Maurice Wayne Long, 1036 Somerset Drive, North West, Atlanta, Georgia (V.St.A.) Method and device for radar interference signal suppression Expectations MJ method for suppressing radar interference signals, at the at least two operators enabling discrimination and at least two received video signals so formed so that each of the received video signals is responsive to at least one of the operators; that the received video signals are compared in pairs and an output is provided if each of the received video signals has substantial size and the aspect ratio of each pair of received video signals within is within a predetermined range of ratios; and in which the output to the target display is processed further. 2. Device for radar interference signal suppression, preferably for performing the method according to claim 1, HZ / il / ig 809884 / 0S23 ORWBfNAL INSPECTED 282UQ1 characterized by a first device (11) to create at least two operators that enable discrimination; by signal transmitter (12, 14), which emit at least two received video signals so that each received video signal on addresses at least one of the operators; by a comparison device (16) in which the sizes of the received video signals are compared in pairs and an output is generated when each of the received Video signals of substantial size and the aspect ratio of each pair of received video signals is within a predetermined ratio range; as well as by one on the generated output responsive processing means (17) for displaying a target. 3. Device according to claim 2, characterized in that the carrier frequencies are selected as operators. 4. Device according to claim 2 or 3, characterized in that that the transmission pulse lengths are selected as operators. 5. Device according to one of claims 2 to 4, characterized in that the antenna beam widths as operators are chosen. 6. Device according to one of claims 2 to 5, characterized in that the polarization directions as operators of the transmitted and received radar signals are selected. 7. Device according to one of claims 2 to 6, characterized in that an antenna device (10, 20, 30) is provided, which sends radar signals and receives. 809884/0623 282 UOI 8. Device according to one of claims 2 to 7, characterized in that the signal generators _{generate at least i} two video signals so that at least one of the video signals is responsive to each of the operators; and in that the comparator (16) compares the received video signals in one or more pairs and provides an output if the magnitudes of the signals or of the pairs are within a predetermined range of ratios. 9. Device according to one of claims 2 to 8, characterized by a first device for Generation of a first transmit / receive polarization pair is provided; through a second facility for generating a second transmit-receive polarization pair; by a third device for supply a first received video signal responsive to the first transceiver polarization pair, fourth means generating a second received video signal responsive to the second transmit receive polarization pair and further wherein the comparator (16) is responsive to the first received video signal compares with the second received video signal and only provides an output if the two Video signals are of substantial magnitude and when the relative magnitude of the first received Video signal to the size of the second received video signal has a ratio which is in a predetermined Ratio range is; and by a processing device (17) which is based on the output responds from the comparator and indicates the presence of a target and suppresses an interference signal. 10. Device according to claim 8, characterized in that that for the first device either the transmit polarization or the receive polarization 809884/0623 -A- 282U0 circular and the other polarization is horizontal; that for the second device either the Transmit or receive polarization is circular and the other polarization is vertical is; that the comparator generates an output signal when the relative size of the first received Video signal to the size of the second received video signal within a predetermined Ratio range is. 11. Device according to one of Claims 9 or ] Q, characterized in that the r r.ite device generates a first transmit / receive polaris> i pair of lions for which the receive polarization is not orthogonal to the transmit polarization; Un <l that the second device generates a second send, eiapf angspolarisationspaar, for which the receive polarization is not orthogonal to the ikir ^ lepolarization. 809884/0823