EP2830156B1 - Waveguide radiator, group antenna radiator and synthetic aperture radar radiator - Google Patents

Description

The invention relates to a waveguide radiator with a slotted waveguide with a plurality of slots mounted in the waveguide. The invention further relates to a group antenna radiator and a synthetic aperture radar system.

Waveguide radiators or array antenna radiators (also referred to in the literature as radiators or subarrays) are used, for example, in phased array antennas of synthetic aperture radar (SAR) systems with single and dual polarization. So far, so-called microstrip patch antennas or slotted waveguide antennas are used as emitters.

Microstrip patch antennas have high electrical losses and their electrical feed network is not efficient in longer radiator lengths than about seven wavelengths feasible (in the X-band about 20 cm). In the case of an active antenna with distributed generation of the RF transmission power through so-called T / R modules (transmitting / receiving modules), the problem arises of dissipating the heat of the active modules, which are mounted on the back of the radiators, to the front.

The slotted waveguide antennas, however, are limited by their electrically resonant behavior in the achievable relative bandwidth (<5%). In addition, they require a high manufacturing accuracy and are very expensive to produce as dual polarized group radiators. Concepts used in the prior art include waveguides with inner lands and longitudinal slots for vertical polarization, and rectangular waveguides with skewed wires and transverse slots for horizontal polarization. Here are Also, the necessary transitions of the connected coaxial cable in the waveguide problematic.

From the DE 10 2006 057 144 A1 and the associated family member WO 2008/064655 A1 , a waveguide radiator is known which comprises a slotted waveguide in which an additional inner conductor, a so-called barline, is mounted. This inner conductor is polarization-dependent specially shaped to excite all slots of the waveguide in phase. In contrast to conventional slotted waveguides, the propagation modes are no longer dispersive but correspond to those in coaxial lines, ie TEM modes. This can increase the bandwidth. In addition, the cross-sections of the waveguide can be significantly reduced in size, since there is no lower limit frequency (so-called cutoff) in TEM modes. The coupling can be done by a direct coaxial transition, which is mechanically very easy to implement, for example, by commercially available SMA chassis sockets.

From Römer, Christian: "Slotted waveguide in phased array antennas". Karlsruhe: IHE, 2008 (Research Reports from the Institute for High Frequency Technology and Electronics of the University of Karlsruhe, 55). 159 S. - Zugl.: Karlsruhe, Univ., Diss., 2008, another waveguide radiator is known which comprises a slotted waveguide in which an additional inner conductor is disposed on a dielectric material. The height of the dielectric material is used to optimize the electrical conductance for the waveguide radiator.

Out Yamaguchi, Satoshi et al. "Inclined Slot Array Antennas on a Rectangular Coaxial Line", Antennas and Propagation, Proceedings of the 5th European Conference on, IEEE, April 11, 2011, pp. 1036-1040 Also known is a waveguide radiator comprising a slotted waveguide in which an additional inner conductor is disposed on a dielectric material.

Other generic waveguide radiators are from the US 2,914,766 A and the US 4,409,595 A known.

It is an object of the invention to provide a waveguide radiator, which is functionally and / or structurally improved. The waveguide radiator should be broadband, efficient and inexpensive to produce, so that from this a planar array antenna can be built, the u.a. can be used in space or airborne synthetic aperture radar (SAR) systems.

This object is achieved by a waveguide radiator according to the features of claim 1, a group antenna radiator according to the features of claim 9 and a synthetic aperture radar system according to the features of claim 13.

Advantageous embodiments will be apparent from the dependent claims.

This object is achieved by a waveguide radiator comprising a slotted waveguide having a plurality of transverse or longitudinal slots mounted in the waveguide. If the waveguide has transverse slots, the direction of the emitted polarization of the waveguide corresponds to the longitudinal direction of the waveguide. If the slotted waveguide has longitudinal slots, the direction of the emitted polarization of the waveguide corresponds to the transverse direction of the waveguide. Depending on the orientation of the slots, thus either horizontally or vertically polarized waves can be radiated. The additional inner conductor mounted in the waveguide is such that the distance between adjacent slots along the waveguide corresponds to exactly one wavelength of a traveling wave to provide in-phase excitation, thereby providing a traveling wave principle and all slots of the waveguide can be excited in phase. For attachment of the inner conductor, a layer of dielectric material is mounted in the waveguide, on the upper side of which the inner conductor is mounted, for example by gluing. According to the height varies July 14, 2015 the dielectric material along the waveguide at least in sections, whereby the amplitude assignment of the slots along the waveguide can be influenced.

Due to the interior conductor of the slotted waveguide (so-called Barline), a dispersion-free, transversely electrically magnetic propagation mode is supported (TEM mode). The inner conductor is polarization-dependent specially shaped to stimulate either longitudinal or transverse slots can. The proposed waveguide radiator is distinguished from that in the DE 10 2006 057 144 A1 described waveguide radiators through a significantly higher bandwidth.

The height or thickness of the dielectric layer is not uniform along the waveguide, but has an individually shaped height profile. Due to the height profile and the shape of the inner conductor, the amplitude and phase of the electric field strength in the slots along the waveguide can be selectively influenced, so that any aperture can be realized, for example, to suppress secondary maxima in the antenna pattern below a predetermined value. In the same way, it is also possible to achieve a homogeneous amplitude and phase coverage along the waveguide, for example in order to maximize the antenna gain and to minimize the half-width.

Each slot of the waveguide radiator can have individual geometric dimensions. It is understood, however, that the waveguide radiator has either only longitudinal or transverse slots.

The special shape of the inner conductor is composed of repeating sections of similar geometry along the waveguide. The length of these sections is identical to the spacing of adjacent slots along the waveguide. The additional inner conductor may be formed from, in particular alternately arranged, straight and winding conductor sections.

One feature of the standing wave resonant feed is an additional quarter wave transformer located in each of the repeating sections. This quarter-wave transformer is realized by a taper of the inner conductor, i. a reduction of the conductor width. The length of this taper or conductor width reduction is preferably chosen so that it corresponds to an electrical path length of exactly one quarter of a line wavelength. The reduction of the conductor width causes an increase of the characteristic impedance along the tapered portion. The thus realized quarter-wave transformers compensate for the reflection points that would otherwise result at these positions.

The inner conductor may have in the region of the ends of the waveguide a straight section as an open stub.

While in the DE 10 2006 057 144 A1 described emitter uses a supply with a standing wave, comes in the waveguide according to the invention, a so-called. Wanderwellenspeisung used.

A coupling of a signal can take place in the middle of the waveguide radiator through a galvanically coupled coaxial transition, in which the inner conductor a connected coaxial cable (eg via SMA, SMP connection) is connected directly to the feed point of the inner conductor. The outer conductor of the connected coaxial cable is connected directly to the wall of the waveguide.

The feed point may be slightly offset in the transverse direction, thus allowing the transition to a mounted on the back of the radiator board at a suitable location.

In a slotted waveguide with transverse slots, the feed point of the waveguide with respect to the geometric center of the waveguide may be displaced in the longitudinal direction. The displacement may be about 6 to 7 mm in a specific implementation, depending on the wavelength or frequency of the signal to be generated.

In a further embodiment of a slotted waveguide with transverse slots, the feed point of the waveguide can be arranged in the waveguide such that the electrical phase position at the positions of all slits is identical at center frequency.

In a slotted waveguide with longitudinal slots, the additional inner conductor has a feed point which is arranged in the longitudinal direction of the slotted waveguide in the geometric center. It may further be provided that the slotted waveguide is formed with the additional inner conductor mirror-symmetrical about the feed point.

Overall, it is achieved that the fed at the feed point of the radiator shaft in the center of the radiator can propagate reflection-free up to the ends of the inner conductor.

The invention has the advantage that, in contrast to the resonant power supply, significantly higher bandwidths can be realized. The in the DE 10 2006 057 144 A1 mentioned advantages to conventional slotted waveguides are all preserved without compromising, such as no dispersion, size reduction of the cross section, no lower limit frequency, robustness to manufacturing tolerances, greater possible radiator lengths, low production costs, short production times, unproblematic transition to coaxial cable, high power feedable, low ohmic Losses, high cross-polar suppression.

The development of the waveguide radiator, in particular the determination of the exact geometric dimensions of the inner conductor and the slots is carried out by means of electromagnetic simulation method. As an approximation, the behavior of the radiator described here can also be described by network models with suitable equivalent circuit diagrams. These models are usually used in a first step in order to optimize the sizes of the elements present in the equivalent circuit diagram. In the second step, these quantities are then translated into suitable geometric parameters. Commercially available software packages can be used for this, which use full-wave analysis to calculate the electromagnetic behavior of the actual geometry (3D models).

An array antenna radiator according to the invention comprises one or more slotted waveguides with transverse slots and one or more slotted waveguides with longitudinal slits of the type described above. The slotted waveguides may be juxtaposed transversely in one configuration, alternately a waveguide with transverse slits and a waveguide Waveguide with longitudinal slots next to each other. In this case, the waveguides, ie all waveguides, preferably have an identical length.

The waveguides with transverse slots can be offset upwards relative to the waveguides with longitudinal slots, so that a step-like structure of the array antenna radiator is given. At the top is that side of a respective waveguide radiator, on which the waveguides have the slots.

A synthetic aperture radar system, particularly a high resolution synthetic aperture radar system, comprises at least one array antenna radiator of the type described above.

Fig. 1

eine Darstellung eines erfindungsgemäßen Hohlleiter-Strahlers mit transversalen Schlitzen;

Fig. 2

einen Höhenverlauf einer im Inneren des Hohlleiters aus Fig. 1 angeordneten dielektrischen Schicht;

Fig. 3

eine Darstellung der Form des Innenleiters (Barline) in dem Hohlleiter-Strahler mit transversalen Schlitzen aus Fig. 1;

Fig. 4

eine vergrößerte Darstellung des mittleren Bereichs des Innenleiters aus Fig. 3;

Fig. 5

eine vergrößerte Darstellung des Bereichs der Enden des Innenleiters aus Fig. 3;

Fig. 6

eine Darstellung eines erfindungsgemäßen Hohlleiter-Strahlers mit longitudinalen Schlitzen;

Fig. 7

einen Höhenverlauf einer im Inneren des Hohlleiters aus Fig. 6 angeordneten dielektrischen Schicht;

Fig. 8

eine Darstellung der Form des Innenleiters (Barline) in dem Hohlleiter-Strahler mit longitudinalen Schlitzen aus Fig. 6;

Fig. 9

eine vergrößerte Darstellung des mittleren Bereich des Innenleiters aus Fig. 8;

Fig. 10

eine vergrößerte Darstellung des Bereichs der Enden des Innenleiters aus Fig. 8;

Fig. 11

einen dual polarisierten Gruppenantennen-Strahler aus einer Kombination von Hohlleitern mit transversalen Schlitzen und Hohlleitern mit longitudinalen Schlitzen;

Fig. 12

eine graphische Darstellung der insgesamt im Strahler auftretenden elektrischen Verluste in dB gegenüber einer idealen Apertur gleicher Größe;

Fig. 13

eine graphische Darstellung der Anpassung in dB;

Fig. 14

eine graphische Darstellung der Abstrahlungseigenschaften in dB (Antennendiagramm) eines Strahlers mit Wanderwellenspeisung; und

Fig. 15

eine graphische Darstellung der Abstrahlungseigenschaften in dB (Antennendiagramm) eines Strahlers mit resonanter Speisung und stehender Welle.

The invention will be explained in more detail below with reference to exemplary embodiments in the drawing. Show it:

Fig. 1

a representation of a waveguide radiator according to the invention with transverse slots;

Fig. 2

a height profile of a inside of the waveguide Fig. 1 arranged dielectric layer;

Fig. 3

a representation of the shape of the inner conductor (Barline) in the waveguide radiator with transverse slots Fig. 1 ;

Fig. 4

an enlarged view of the central region of the inner conductor Fig. 3 ;

Fig. 5

an enlarged view of the region of the ends of the inner conductor Fig. 3 ;

Fig. 6

an illustration of a waveguide radiator according to the invention with longitudinal slots;

Fig. 7

a height profile of a inside of the waveguide Fig. 6 arranged dielectric layer;

Fig. 8

a representation of the shape of the inner conductor (Barline) in the waveguide radiator with longitudinal slots Fig. 6 ;

Fig. 9

an enlarged view of the central region of the inner conductor Fig. 8 ;

Fig. 10

an enlarged view of the region of the ends of the inner conductor Fig. 8 ;

Fig. 11

a dual polarized array antenna radiator of a combination of waveguides with transverse slots and waveguides with longitudinal slots;

Fig. 12

a graphical representation of the total occurring in the radiator electrical losses in dB compared to an ideal aperture of the same size;

Fig. 13

a graphic representation of the adjustment in dB;

Fig. 14

a graphical representation of the radiation properties in dB (antenna diagram) of a radiator with traveling wave supply; and

Fig. 15

a graphical representation of the radiation properties in dB (antenna diagram) of a resonant power source with stationary wave.

The absolute values and dimensions given below are only exemplary values and do not represent a restriction of the invention to such dimensions. The illustrations show the invention only schematically and in particular are not to be regarded as true to scale.

The structure of a waveguide radiator according to the invention (short: radiator) with a slotted waveguide (hereinafter referred to as waveguide 10, 30) and an inner conductor 14, 34 arranged in the waveguide 10, 30 will be described below. It is between slotted waveguides 10, 30 with transverse slots 12 (FIG. Fig. 1 ) and longitudinal slots 32 (FIG. Fig. 6 ), in which the shape of the inner conductor 14 and 34 used differs. The exact configuration of the inner conductor 14 for the waveguide 10 with transverse slots 12 is in the Fig. 3 to 5 shown. The exact configuration of the inner conductor 34 for the waveguide 30 with longitudinal slots 32 is in the Fig. 8 to 10 shown.

The geometrical dimensions given below refer to an exemplary embodiment in the X-band at a center frequency of 9.6 GHz. The radiator described here can be readily designed for deviating center frequencies. The size dimensions in this case scale over the ratio of the respective wavelengths.

The waveguides 10, 30 are formed from conventional rectangular waveguides, in the transverse slots 12 and longitudinal slots 32 are introduced. The interior of the waveguides 10, 30 is filled with a dielectric material. The dielectric layer 24, 44 is in the Fig. 2 and 7 shown. While prior art radiators have a constant layer thickness, the dielectric layers 24, 44 of the invention have a variable height in the longitudinal extent of the waveguide.

The choice of the material used for the dielectric layer is determined by its electrical properties, namely the dielectric constant and the loss angle. The dielectric constant influences the propagation velocity of the traveling wave traveling on the inner conductor (shortening factor). The distance between adjacent slots along the waveguide corresponds to exactly one wavelength of the traveling wave in order to achieve an in-phase excitation. In addition, the slot spacing is smaller than a free space wavelength in order to avoid unwanted secondary maxima (so-called grating praise). Typically, the slot pitch is in the range of 0.5 to 0.9 times a free space wavelength. This results in the value of the dielectric constant, which is thus typically in the range from 1.2 to 3.0. The loss angle should be as small as possible in order to keep the dielectric losses as low as possible, for a suitable material the value should be smaller than 1 × 10 ^-3 .

The thickness of the dielectric layer 24, 44 along the waveguide has a characteristic profile. The height at the positions of the slots 12, 32 determines the proportion of the decoupled power of the traveling wave. A larger height results in a stronger decoupling, a lower level correspondingly reversed.

That in the Fig. 2 and 7 In this case, the thickness of the dielectric layer 24, 44 increases to the outer ends of the respective waveguide 10, 30, because of the decreasing power of the traveling wave an ever higher relative proportion must be disconnected.

Another commonality of the two variants, as will become apparent from the following description, that the inner conductor 14, 34 sections with reduced conductor width 18 and 38 (see. Fig. 4 and 8th ) exhibit. These act as transformation lines and prevent the occurrence of reflections (standing waves) on the line.

In the following, the features of the waveguide with transverse slots and the waveguide with longitudinal slots are described separately:

Waveguide with transverse slots

Fig. 1 shows a waveguide 10 with transverse slots 12. The shape of the inner conductor 14 in the waveguide 10 with the transverse slots 12 is in Fig. 3 shown. The positions of the slots are in Fig. 3 indicated by arrows The middle area, which includes a feed point 16, is in Fig. 4 shown enlarged. The feed point 16 is offset relative to the geometric center in the longitudinal direction by approximately 6 mm. This displacement causes a phase difference of 180 ° of the outgoing from the feed point 16 traveling wave in the right and left part of the waveguide 10. In this way, an in-phase excitation of the slots results both in the right and in the left part of the waveguide 10th

The inner conductor 14 begins immediately at the feed point 16 with sections 18 (transformation lines) with reduced conductor width. These are used to transform the characteristic impedance of the connected and not shown here coaxial cable of typically 50 ohms. The further course of the inner conductor 14 to the ends of the waveguide 10 consists of straight sections 18 with reduced conductor width and tortuous sections 20. The straight sections thus act as transformation lines. The twisting of the remaining portions 20 causes a delay of the propagation velocity of the traveling wave in the longitudinal direction of the waveguide 10. A stronger expression of the distortion causes a greater delay and vice versa. Hereby, the phase difference between adjacent slots 12 can be set to exactly 360 °.

The slots 12 are cut transversely into the outer wall of the waveguide 10. They protrude into the side walls with a cutting depth of about 4mm. The width of the slots 12 is about 2-3mm. The slots 12 have resonant behavior, the resonance frequency coincides with the center frequency of the radiator.

The outermost slot 12A at the ends of the waveguide 10 with the underlying portion 22 of the inner conductor 14 has a peculiarity. According to the state of the art, the ends of the traveling waveguide are often resistively terminated in traveling-wave-principle radiators. This leads to undesirable losses, since the power remaining at the end of the line is dissipated in a resistor. In the concept presented here of a traveling wave radiator with homogeneous excitation of all slots, the power remaining at the end of the line is radiated completely over the outermost slot, whereby additional losses are avoided. For this purpose, the height profile of the dielectric layer is designed such that the power remaining at the outermost slot 12A corresponds to the power coupled out at the remaining slots, whereby a homogeneous coverage of all slots 12, 12A is achieved while maintaining this boundary condition. Fig. 5 this shows an enlarged view of the region of the ends of the inner conductor Fig. 3 , wherein the unclip, open line termination can be seen with the section 22, which supports the described properties.

Waveguide with longitudinal slots

Fig. 6 shows a waveguide 30 with longitudinal slots. The shape of the inner conductor 34 in a waveguide with longitudinal slots 30 is shown in FIG Fig. 8 shown. The central area containing the feed point 36 is in Fig. 9 shown enlarged. The feed point 36 is seen in the longitudinal direction in the geometric center. Displacement in the longitudinal direction, as in a waveguide with transverse slots 10, is not necessary in this case symmetrical construction of the right and left half of the waveguide 30, an in phase excitation of the slots 32 can be achieved.

The inner conductor 34 begins immediately at the feed point 36 with transformation lines with reduced conductor width. These are used to transform to the characteristic impedance of the connected coaxial cable of typically 50 ohms. The further course of the inner conductor 34 to the ends of the waveguide consists of straight sections 38 and winding sections 40. The tortuous shape of the sections 40 is designed so that the inner conductor extends at the middle positions of the slots 32 in the transverse direction. This is necessary for a coupling of the longitudinal slots 32, since for this purpose a flow of the induced current in the transverse direction must be present on the wall of the waveguide 30. The position of the slots is in Fig. 8 indicated by arrows.

The tortuous shape of the sections 40 additionally causes a delay of the propagation velocity of the traveling wave in the longitudinal direction of the waveguide. A stronger expression of the tortuous shape causes a greater delay and vice versa. This allows the phase difference between adjacent slots to be set to exactly 360 °.

The slits 32 are cut longitudinally (longitudinally) into the outer wall of the waveguide 30. The slots 32 have a length of approximately half the free space wavelength. The exact length can vary slightly from slot to slot. The width of the slots is about 2 mm. The slots have resonant behavior, the resonance frequency coincides with the center frequency of the radiator.

The outermost slot 32A at the ends of the waveguide 30 with the underlying portion 42 of the inner conductor 42 has a peculiarity. According to the prior art in emitter with traveling wave principle often the ends the traveling wave line resistive completed. This leads to undesirable losses, since the power remaining at the end of the line is dissipated in a resistor. In the concept of a traveling wave radiator with homogeneous excitation of all slots 32 presented here, the power remaining at the end of the line is radiated completely over the outermost slot 32A, whereby additional losses are avoided. For this purpose, the height profile of the dielectric layer 44 is designed in such a way that the power remaining at the outermost slot 32A corresponds to the power coupled to the remaining slots 32, so that a homogeneous coverage of all the slots 32, 32A can be achieved in compliance with this boundary condition. Fig. 10 shows an enlarged view of the region of the ends of the inner conductor Fig. 8 , Evident is the unsound, open line termination with the section 42 of the inner conductor 34, which supports the described properties.

Dual polarized emitter group

By combining a waveguide 10 with transverse slots with a waveguide 30 with longitudinal slots, dual polarized radiator groups 60 can be realized in a simple manner. Since the widths of the waveguides can be greatly reduced with the emitter concept described here (up to a quarter of the wavelength), dual-polarized, electronically controllable array antennas with a very large swivel range can be realized (> ± 60 °).

Fig. 11 shows the construction of a dual polarized radiator group 60 (group antenna radiator). It consists of a combination of alternately a slotted waveguide 10 with transverse slots 12 and a waveguide 30 with longitudinal slots 32. The waveguides 10 with transverse slots 12 are about 7 mm to 8 mm in relation to the waveguides 30 with longitudinal slots 12 offset upwards, so that a step-like structure is formed.

The proposed waveguide radiator is distinguished from the well-known from the prior art waveguide radiators by a significantly higher bandwidth. This is in the FIGS. 12 to 15 exemplified for a radiator of length 250mm for the X-band.

Fig. 12 shows a representation of the total occurring in the radiator electrical losses in dB compared to an ideal aperture of the same size. The solid line curve represents traveling wave power source losses, the dashed line curve represents resonant standing wave power losses.

Fig. 13 shows a representation of the adjustment in dB, wherein the solid line curve to a radiator with traveling wave feed and the dashed line curve is assigned to a radiator with resonant feed (standing wave).

Fig. 14 shows a plot of the radiation characteristics in dB (antenna diagram) of a radiator with traveling wave feed, where the dashed line curve shows the antenna pattern at 8.7 GHz, the solid line curve the antenna diagram at 9.6 GHz (center frequency) and the dotted line curve the antenna diagram at 10.5GHz show.

Fig. 15 Finally, Fig. 12 shows a plot of the radiation characteristics in dB (antenna diagram) of a resonant power source with a standing wave, where the dashed line curve shows the antenna pattern at 8.7GHz, the solid line curve the antenna pattern at 9.6GHz (center frequency) and the curve with dotted line show the antenna diagram at 10.5GHz.

LIST OF REFERENCE NUMBERS

10

Slotted waveguide with transverse slots

12

transverse slot

12A

transverse slot at the end of the waveguide

14

Inner conductor of the waveguide with transverse slots

16

Feed point of waveguide with transverse slots

18

Transformation line section of the inner conductor (waveguide with transverse slots)

20

wound section of the inner conductor (waveguide with transverse slots)

22

End section of the inner conductor with open stub line (waveguide with transverse slots)

24

dielectric layer of the waveguide with transverse slots

30

Slotted waveguide with longitudinal slots

32

longitudinal slot

32A

longitudinal slot at the end of the waveguide

34

Inner conductor of the waveguide with longitudinal slots

36

Feed point of waveguide with longitudinal slots

38

Transformation line section of the inner conductor (waveguide with longitudinal slots)

40

wound section of the inner conductor (waveguide with longitudinal slots)

42

End section of the inner conductor with open stub line (waveguide with longitudinal slots)

44

dielectric layer of the waveguide with longitudinal slots

60

Dual polarized emitter group

Claims (13)

1. A waveguide radiator, comprising

   - a slotted waveguide (10; 30) having a plurality of transversal or longitudinal slots (12; 32) provided in the waveguide (10; 30); and

   - an additional inner conductor (14; 34) arranged in the waveguide (10; 30), wherein the additional inner conductor (14; 34) comprises conductor sections (18, 20; 38, 40) which, with respect to a remaining line, have a reduced conductor width, wherein the length of the conductor width reduction is selected, such that it corresponds to an electrical path length of exactly the quarter of a line wavelength, in such a manner that a result is a feed of the slots according to a travelling wave principle, and wherein a spacing between adjacent slots (12, 32) along the waveguide corresponds exactly to a wavelength of a travelling wave to achieve an excitation with identical phase;

   - wherein the slotted waveguide (10; 30) is partially filled with a dielectric material (24; 44) on which the additional inner conductor (14; 34) is arranged;

   characterized in that a height of the dielectric material (24; 44) along the waveguide (10; 30) varies at least in certain sections in order to influence an amplitude occupancy of the slots (12; 32) along the waveguide (10; 30).
2. The waveguide radiator according to claim 1, characterized in that the additional inner conductor (14; 34) is formed from, in particular alternately arranged, straight and twisted conductor sections (18, 20; 38, 40).
3. The waveguide radiator according to any one of the foregoing claims, characterized in that the additional inner conductor (14; 34) is composed of repetitive line sections (18, 20; 38, 40) along the slotted waveguide (10; 30), wherein a length of the repetitive line sections (18, 20; 38, 40) is identical to a spacing of adjacent slots (12; 32) along the waveguide.
4. The waveguide radiator according to any one of the foregoing claims, characterized in that the inner conductor (14; 34) has a straight section as open stub (22; 42) in a region of the ends of the waveguide (10; 30).
5. The waveguide radiator according to any one of claims 1 to 4, characterized in that the slotted waveguide (10) has transversal slots (12), and wherein a feed point (16) of the waveguide (10) is shifted with respect to a geometric center of the waveguide in a longitudinal direction.
6. The waveguide radiator according to claim 5, characterized in that the feed point (16) of the waveguide (10) is shifted with respect to the geometric center of the waveguide in the longitudinal direction in such a manner that an electric phase at positions of all slots (12) is identical at center frequency.
7. The waveguide radiator according to any one of claims 1 to 4, characterized in that the slotted waveguide (30) has longitudinal slots (32), and wherein the additional inner conductor (34) has a feed point (36) which, in a longitudinal direction of the slotted waveguide (30), is arranged in a geometric center.
8. The waveguide radiator of claim 7, characterized in that the slotted waveguide (30) with the additional inner conductor (34) is formed mirror-symmetrically around the feed point (36).
9. An array antenna radiator, comprising one or more slotted waveguides (10) having transversal slots (12) according to any one of claims 1 to 6 and one or more slotted waveguides (30) having longitudinal slots (32) according to any one of claims 1 to 4, 7 or 8.
10. The array antenna radiator according to claim 9, characterized in that the slotted waveguides (10; 30) are arranged side-by-side in a transverse direction, wherein a waveguide (10) having transversal slots (12) and a waveguide (30) having longitudinal slots (32) lie alternately next to one another.
11. The array antenna radiator according to claim 9, characterized in that the waveguides (10; 30) have identical lengths.
12. The array antenna radiator according to any one of claims 9 to 11, characterized in that the waveguides (10) having transversal slots (12) are offset upwards with respect to the waveguides (30) having longitudinal slots (32) to form a step-like structure of the array antenna radiator.
13. A synthetic aperture radar system, in particular a high-resolution synthetic aperture radar system, comprising an array antenna radiator (60) according to any one of claims 9 to 12.

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