Waveguide radiator, array antenna radiator and synthetic aperture radar system

Abstract

A waveguide radiator includes a slotted waveguide with a plurality of transverse or longitudinal slots provided in the waveguide and an additional inner conductor provided in the waveguide. The inner conductor is formed, depending on the alignment of the slots in such a manner that the result is a feed according to the traveling wave principle, wherein all slots of the waveguide can be excited with identical phase.

Claims

1. A waveguide radiator, comprising a slotted waveguide having a plurality of longitudinal slots provided in the slotted waveguide; and an additional inner conductor arranged in the slotted waveguide, wherein the additional inner conductor is configured, depending on the alignment of the slots, in such a manner that a result is a feed according to the traveling wave principle, wherein all slots of the waveguide are excited with identical phase, wherein the slotted waveguide is partially filled with a dielectric material on which the additional inner conductor is arranged, and wherein the additional inner conductor comprises more than two straight conductor sections, which are spaced apart from each other by respective twisted sections, and which, with respect to the twisted sections, have a reduced conductor width and act as transformation lines, wherein a height of the dielectric material longitudinally along the waveguide varies at least in certain sections, thereby influencing an amplitude occupancy of the slots along the waveguide such that power remaining at an outermost slot of the plurality of longitudinal slots corresponds to power coupled at a remaining of the plurality of longitudinal slots, wherein the additional inner conductor has a feed point which, in a longitudinal direction of the slotted waveguide, is arranged in a geometric center, and wherein the slotted waveguide with the additional inner conductor is formed mirror-symmetrically around the feed point.

2. The waveguide radiator of claim 1, wherein the additional inner conductor is formed from alternately arranged straight and twisted conductor sections.

3. The waveguide radiator of claim 1, wherein the additional inner conductor is composed of repetitive line sections along the slotted waveguide, wherein a length of the repetitive line sections is identical to a spacing of adjacent slots along the slotted waveguide.

4. The waveguide radiator of claim 1, wherein the additional inner conductor has a straight section as open stub in a region of ends of the slotted waveguide.

5. The waveguide radiator of claim 1, wherein the slotted waveguide has transverse slots, and wherein a feed point of the slotted waveguide is shifted with respect to a geometric center of the slotted waveguide in a longitudinal direction.

6. The waveguide radiator of claim 1, wherein the slotted waveguide has transverse slots, and wherein a feed point of the slotted waveguide is arranged in the slotted waveguide in such a manner that an electric phase at positions of all slots is identical at center frequency.

7. An array antenna radiator, comprising: one or more first slotted waveguides, including: a plurality of transverse slots provided in the first slotted waveguides; and an additional first inner conductor arranged in the first slotted waveguides, wherein the additional first inner conductor is configured, depending on alignment of the transverse slots, in such a manner that a result is a feed according to the traveling wave principle, wherein all transverse slots of the one or more first waveguides are excited with identical phase; and one or more second slotted waveguides, including: a plurality of longitudinal slots provided in the second slotted waveguides; and an additional second inner conductor arranged in the second slotted waveguides, wherein the additional second inner conductor is configured, depending on alignment of the longitudinal slots, in such a manner that a result is a feed according to the traveling wave principle, wherein all longitudinal slots of the one or more second waveguides are excited with identical phase, wherein the first and second slotted waveguides are each partially filled with a dielectric material on which the respective additional inner conductor is arranged, wherein a height of the dielectric material longitudinally along the respective waveguide varies at least in certain sections, thereby influencing an amplitude occupancy of the slots along the respective waveguide such that power remaining at an outermost slot of the plurality of respective transversal or longitudinal slots corresponds to power coupled at a remaining of the plurality of respective transversal or longitudinal slots, wherein each of the additional first and second inner conductors comprises more than two conductor sections which are spaced apart from each other by respective intermediate sections and which, with respect to the intermediate sections, have a reduced conductor width and act as transformation lines, wherein each additional inner conductor has a feed point which, in a longitudinal direction of the respective slotted waveguide, is arranged in a geometric center, and wherein each slotted waveguide with the respective additional inner conductor is formed mirror-symmetrically around the feed point.

8. The array antenna radiator of claim 7, wherein the one or more first and second slotted waveguides are arranged side-by-side in a transverse direction, wherein a waveguide having transverse slots and a waveguide having longitudinal slots lie alternately next to one another.

9. The array antenna radiator of claim 7, wherein the one or more first and second slotted waveguides have identical lengths.

10. The array antenna radiator of 7, wherein the one or more first waveguides are offset upwards with respect to the one or more second waveguides to form a step-like structure of the array antenna radiator.

11. A high-resolution synthetic aperture radar system, comprising: an array antenna radiator, which comprises: one or more first slotted waveguides, including: a plurality of transverse slots provided in the first slotted waveguides; and an additional first inner conductor arranged in the first slotted waveguides, wherein the additional first inner conductor is configured, depending on alignment of the transverse slots, in such a manner that a result is a feed according to the traveling wave principle, wherein all transverse slots of the one or more first waveguides are excited with identical phase; and one or more second slotted waveguides, including: a plurality of longitudinal slots provided in the second slotted waveguides; and an additional second inner conductor arranged in the second slotted waveguides, wherein the additional second inner conductor is configured, depending on alignment of the longitudinal slots, in such a manner that a result is a feed according to the traveling wave principle, wherein all longitudinal slots of the one or more second waveguides are excited with identical phase, wherein the first and second slotted waveguides are each partially filled with a dielectric material on which the respective additional inner conductor is arranged, wherein a height of the dielectric material longitudinally along the respective waveguide varies at least in certain sections, thereby influencing an amplitude occupancy of the slots along the waveguide such that power remaining at an outermost slot of the plurality of respective transversal or longitudinal slots corresponds to power coupled at a remaining of the plurality of transversal or longitudinal slots, wherein each of the additional first and second inner conductors comprises more than two conductor sections which are spaced apart from each other by respective intermediate sections and which, with respect to the intermediate sections, have a reduced conductor width and act as transformation lines, wherein each additional inner conductor has a feed point which, in a longitudinal direction of the respective slotted waveguide, is arranged in a geometric center, and wherein each slotted waveguide with the respective additional inner conductor is formed mirror-symmetrically around the feed point.

Description

BRIEF DESCRIPTION OF THE INVENTION

(1) The invention is explained in greater detail below by means of exemplary embodiments in the drawing. In the figures:

(2) FIG. 1 shows an illustration of the waveguide radiator according to the invention having transverse slots;

(3) FIG. 2 shows a height profile of a dielectric layer arranged inside the waveguide from FIG. 1;

(4) FIG. 3 shows an illustration of the shape of the inner conductor (barline) in the waveguide having transverse slots from FIG. 1;

(5) FIG. 4 shows an enlarged illustration of the central region of the inner conductor from FIG. 3;

(6) FIG. 5 shows an enlarged illustration of the region of the ends of the inner conductor from FIG. 3;

(7) FIG. 6 shows an illustration of a waveguide radiator according to the invention having longitudinal slots;

(8) FIG. 7 shows a height profile of a dielectric layer arranged inside the waveguide from FIG. 6;

(9) FIG. 8 shows an illustration of the shape of the inner conductor (barline) in the waveguide radiator having longitudinal slots from FIG. 6;

(10) FIG. 9 shows an enlarged illustration of the central region of the inner conductor from FIG. 8;

(11) FIG. 10 shows an enlarged illustration of the region of the ends of the inner conductor from FIG. 8;

(12) FIG. 11 shows a dual-polarized array antenna radiator from a combination of waveguides having transverse slots and waveguides having longitudinal slots;

(13) FIG. 12 shows a graphical representation of the overall losses in dB occurring in the radiator compared to an ideal aperture of the same size;

(14) FIG. 13 shows a graphical representation of the adaptation in dB;

(15) FIG. 14 shows a graphical representation of the radiation properties in dB (antenna radiation pattern) of a radiator with traveling wave feed; and

(16) FIG. 15 shows a graphical representation of the radiation properties in dB (antenna radiation pattern) of a radiator with resonant feed and standing wave.

(17) The absolute values and dimensions indicated below are merely exemplary values and do not limit the invention in any way to such dimensions. The illustrations show the invention only schematically and are in particular not to be considered as being true to scale.

DETAILED DESCRIPTION

(18) Hereinafter, the structure of the waveguide radiator (in short: radiator) according to the invention comprising a slotted waveguide (hereinafter designated as waveguide 10, 30) and an inner conductor 14, 34 arranged in the wave guide 10, 30 is described. A differentiation is made here between slotted waveguides 10, 30 having transverse slots 12 (FIG. 1) and longitudinal slots (32) (FIG. 6), in which the shape of the inner conductors 14 and 34 used is different. The exact configuration of the inner conductor 34 for the waveguide 30 having transverse slots 32 is illustrated in the FIGS. 8 to 10.

(19) The geometric dimensions indicated below relate to an exemplary embodiment in the X-band at a center frequency of 9.6 GHz. The radiator described here can readily also be designed for different center frequencies. In this case, the dimensions are scaled via the ratio of the corresponding wavelengths.

(20) The waveguides 10, 30 are formed from conventional rectangular waveguides in which transverse slots 12 or longitudinal slots 32 are provided. The inside of the waveguide 10, 30 is filled with a dielectric material. The dielectric layer 24, 44 is illustrated in the FIGS. 2 and 7. While radiators according to the prior art have a constant layer thickness, the dielectric layers 24, 44 of the invention have a variable height or thickness in the longitudinal extent of the waveguide.

(21) The selection of the material used for the dielectric layer is determined by the electrical properties thereof, namely the relative permittivity and the loss angle. The relative permittivity influences the propagation speed of the traveling wave running on the inner conductor (velocity factor). The spacing between adjacent slots along the waveguide for achieving excitation with identical phase corresponds exactly to one wavelength of the traveling wave. Moreover, the slot spacing is smaller than a free-space wavelength in order to avoid undesirable side lobes (so-called grating lobes). Typically, the slot spacing lies in the range of the 0.5-fold to 0.9-fold of a free-space wavelength. As a result, the value of the relative permittivity is obtained, which therefore typically lies in the range of from 1.2 to 3.0. The loss angle should be as small as possible in order to keep the dielectric loss as small as possible; for a suitable material, the value should be less than 1.Math.10.sup.3.

(22) 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 portion of the coupled-out power of the traveling wave. A greater height results in more intense coupling out and vice versa in the case of a lower height.

(23) The example illustrated in the FIGS. 2 and 7 shows the case of a homogenous excitation of all slots 12, 32. The thickness of the dielectric layer 24, 44 increases in this case towards the outer ends of the respective waveguide 10, 30 since a steadily increasing relative proportion has to be coupled out from the decreasing power of the traveling wave.

(24) As is apparent from the following description, another commonality of the two variants is that the inner conductor 14, 34 has sub-sections with reduced conductor width 18 and 38 (cf. FIGS. 4 and 8). They act as transformation lines and prevent the occurrence of reflections (standing wave) on the line.

(25) Hereinafter, the features of the waveguide having transverse slots and of the waveguide having longitudinal slots are described separately:

(26) Waveguide Having Transverse Slots

(27) FIG. 1 shows a waveguide 10 having transverse slots 12. The shape of the inner conductor 14 in the waveguide 10 having transverse slots 12 is illustrated in FIG. 3. The positions of the slots are indicated in FIG. 3 by arrows. The central region that includes a feed point 16 is illustrated enlarged in FIG. 4. The feed point 16 is shifted with respect to the geometric center by approximately 6 mm in the longitudinal direction. This shift effects a phase difference of 180 of the traveling wave extending from the feed point into the right and left parts of the waveguide 10. In this manner, excitation with identical phase of the slots in the right as well as the left part of the waveguide 10 is obtained.

(28) The inner conductor 14 begins directly at the feed point 16 with sections 18 (transformation lines) with reduced conductor width. They serve for transformation to the characteristic wave impedance of the connected coaxial cables of typically 50 Ohm, which are not illustrated here in detail. The further course of the inner conductor 14 towards the ends of the waveguide 10 consists of straight sections 18 with reduced conductor width and twisted sections 20. The straight sections thus act as transformation lines. The twisting of the remaining sections 20 effects a delay in the propagation speed of the traveling wave in the longitudinal direction of the waveguide 10. A higher degree of twisting results in a greater delay and vice versa. Through this, the phase difference between adjacent slots 12 can be set to exactly 360.

(29) The slots 12 are cut in the transverse direction into the outer wall of the waveguide 10. They protrude into the lateral walls with a cutting depth of approximately 4 mm. The width of the slots 12 is approximately 2-3 mm. The slots 12 exhibit a resonant behavior; the resonant frequency coincides with the center frequency of the radiator.

(30) The outermost slot 12A at the ends of the waveguide 10 with the section 22 of the waveguide 10 located therebelow shows a particular feature. According to the prior art, the ends of the traveling wave lines are often terminated resistively. This results in undesirable losses since the power remaining at the end of the line is dissipated in a resistor. In the concept introduced here of a traveling wave radiator with homogenous excitation of all slots, power remaining at the end of the line is completely radiated via the outermost slot, as a result of which additional losses are avoided. For this purpose, the height profile of the dielectric layer is designed such that power remaining at the outermost slot 12A corresponds to the power coupled out at the remaining slots, so that by adhering to this boundary condition, homogenous occupancy of all slots 12, 12A is achieved. In this connection, FIG. 5 shows an enlarged illustration of the region of the ends of the inner conductor from FIG. 3, wherein the non-twisted open line end with the section 22 can be seen, which supports the described properties.

(31) Waveguide Having Longitudinal Slots

(32) FIG. 6 shows a waveguide 30 having longitudinal slots. The shape of the inner conductor 34 in a waveguide having longitudinal slots 30 is illustrated in FIG. 8. The central region that includes the feed point 36 is illustrated enlarged in FIG. 9. Viewed in the longitudinal direction, the feed point 36 is located in the geometrical center. Shifting in the longitudinal direction, as in the case of a waveguide having transverse slots, is not required in this case since excitation of the slots 32 with identical phase can be achieved by the symmetric structure of the right and left halves of the waveguide 30.

(33) The inner conductor 34 begins directly at the feed point 36 with transformation lines of reduced conductor width. They serve for transformation to the characteristic wave impedance of the connected coaxial cable of typically 50 Ohm. The further course of the inner conductor 34 to the ends of the waveguide consists of straight sections 38 and twisted sections 40. The twisted shape of the sections 40 is embodied in such a manner that the inner conductor runs in the transverse direction at the central positions of the slots 32. This is necessary for coupling the longitudinal slots 32, because for this, a flow of the induced current in the transverse direction has to be present on the wall of the waveguide 30. The position of the slots in FIG. 8 is indicated by arrows.

(34) The twisted shape of the sections 40 effects in addition a delay of the propagation speed of the traveling wave in the longitudinal direction of the waveguide. A more twisted shape effects a greater delay and vice versa. Through this, the phase difference between adjacent slots can be set to exactly 360.

(35) The slots 32 are out in the longitudinal direction into the outer wall of the waveguide 30. The slots 32 have a length of approximately half of the free-space wavelength. The exact length can vary slightly from slot to slot. The width of the slots is approximately 2 mm. The slots exhibit resonant behavior; the resonant frequency coincides with the center frequency of the radiator.

(36) The outermost slot 32A at the ends of the waveguide 30 with the section 42 of the inner conductor 42 located therebelow shows a particular feature. According to the prior art, the ends of the traveling wave line are often resistively terminated in radiators using the traveling wave principle. This results in undesirable losses since the power remaining at the end of the line is dissipated in a resistor. In the concept introduced here of a traveling wave radiator with homogenous excitation of all slots 32, power remaining at the end of the line is completely radiated via the outermost slot 32A, as a result of which additional losses are avoided. For this purpose, the height profile of the dielectric layer 44 is designed such that power remaining at the outermost slot 32A corresponds to the power coupled out at the remaining slots 32, so that by adhering to this boundary condition, homogenous occupancy of all slots 32, 32A can be achieved. FIG. 10 shows an enlarged illustration of the region of the ends of the inner conductor from FIG. 8. The non-twisted open line end with the section 42 of the inner conductor 34, which supports the described properties, can be seen.

(37) Dual-Polarized Radiator Array

(38) By combining a waveguide 10 having transverse slots with a waveguide 30 having longitudinal slots, dual-polarized radiator arrays 60 can be implemented in a simple manner. Since the widths of the waveguides can be greatly reduced (up to a fourth of the wavelength) with the radiator concept described here, dual-polarized electronically controllable array antennas with very large pivoting range (>60) can be implemented.

(39) FIG. 11 shows the structure of a dual-polarized radiator array 60 (array antenna radiator). It consists of a composition of a slotted waveguides 10 having transverse slots 12 that alternate in each case with waveguides 30 having longitudinal slots 32. The waveguides 10 having transverse slots 12 are offset upwards with respect to the waveguides 30 having longitudinal slots 12 by approximately 7 mm to 8 mm so that a step-like structure is created.

(40) Compared to the waveguide radiators known from the prior art, the proposed waveguide radiator is characterized by a bandwidth that is significantly increased again. This is illustrated by way of example in the FIGS. 12 to 15 for a radiator of the length 250 mm for the X-band.

(41) FIG. 12 shows an illustration of the overall electrical losses in dB occurring in the radiator compared to an ideal aperture of the same size. The curve drawn with a solid line represents losses of the radiator with traveling wave feed, and the curve drawn with a dashed line represents losses at resonant feed with standing wave.

(42) FIG. 13 shows an illustration of the adaptation in dB, wherein the curve with solid line is to be associated with a radiator with traveling wave feed and the curve with dashed line is to be associated with a radiator with resonant feed (standing wave).

(43) FIG. 14 shows an illustration of the radiation properties in dB (antenna radiation pattern) of a radiator with traveling wave feed, wherein the curve with the dashed line shows the antenna radiation pattern at 8.7 GHz, the curve with the solid line shows the antenna pattern at 9.6 GHz (center frequency) and the curve with the dotted line shows the antenna radiation pattern at 10.5 GHz.

(44) FIG. 15 finally shows at illustration of the radiation properties in dB (antenna radiation pattern) of a radiator with resonant feed and standing wave, wherein the curve with the dashed line shows the antenna radiation pattern at 8.7 GHz, the curve with the solid line shows the antenna radiation pattern at 9.6 GHz (center frequency) and the curve with the dotted line shows the antenna radiation pattern at 10.5 GHz.

(45) The foregoing disclosure has been set forth merely to illustrate the invention and is not intended to be limiting. Since modifications of the disclosed embodiments incorporating the spirit and substance of the invention may occur to persons skilled in the art, the invention should be construed to include everything within the scope of the appended claims and equivalents thereof.

REFERENCE LIST

(46) 10 slotted waveguide having transverse slots 12 transverse slot 12A transverse slot at the end of the waveguide 14 inner conductor of the waveguide having transverse slots 16 feed point of the waveguide having transverse slots 18 transformation line section of the inner conductor (waveguide having transverse slots) 20 twisted sub-section of the inner conductor (waveguide having transverse slots) 22 end section of the inner conductor with open stub (waveguide having transverse slots) 24 dielectric layer of the waveguide having transverse slots 30 slotted waveguide having longitudinal slots 32 longitudinal slot 32A longitudinal slot at the end of the waveguide 34 inner conductor of the waveguide having longitudinal slots 36 feed point of the waveguide having longitudinal slots 38 transformation line section of the inner conductor (waveguide having longitudinal slots) 40 twisted sub-section of the inner conductor (waveguide having longitudinal slots) 42 end section of the inner conductor with open stub (waveguide with longitudinal slots) 44 dielectric layer of the waveguide having longitudinal slots 60 dual-polarized radiator array