Folding reflective array antenna using novel planar feed source

Abstract

The utility model discloses a folded reflective array antenna using a novel planar feed source, which comprises a polarization torsion reflective array, a polarization grid, a plurality of nylon columns and the novel planar feed source used for transmitting linearly polarized waves, and the novel planar feed source is coplanar with the polarization torsion reflective array. The polarized torsional reflection array comprises a plurality of polarized torsional reflection units arranged in a square array, each unit comprises a metal layer, a first dielectric substrate and a first metal floor which are sequentially arranged from top to bottom, the metal layer is etched on the upper surface of the first dielectric substrate and is of a double-crack square ring stacked structure, and the first metal floor is of a double-crack square ring stacked structure. The double-crack square ring superposition type metal patch comprises a first crack square ring metal patch and a second crack square ring metal patch, openings of the first crack square ring metal patch and the second crack square ring metal patch are oppositely superposed to form a square closed structure in the center, and meanwhile, right-angle W-shaped structures symmetrically extend out of opposite angles of the square closed structure. Compared with the existing pyramid horn feed folding reflective array antenna, the folding reflective array antenna has the advantages that the compactness of the antenna is greatly improved, the profile of the antenna is reduced, and the folding reflective array antenna has the characteristics of wide band and high aperture efficiency and shows good application prospect.

Description

TECHNICAL FIELD

[0001] The utility model belongs to the technical field of reflecting array antenna, especially a folding reflecting array antenna using novel plane feed source. BACKGROUND

[0002] High gain array antenna is an important component in most radars and long distance communication systems. Among them, the reflecting array antenna is widely concerned due to its light weight, small size, easy processing and planar structure. However, most of the traditional reflecting array antennas have high profile, which is not conducive to practical application in limited space height. Therefore, in order to reduce the profile of the reflecting array antenna, the folding reflecting array antenna emerges as the times require, which integrates the feed source and the reflecting surface in the same plane on the basis of the traditional reflecting array, uses the reflecting unit with polarization twist function and adjustable phase, and combines the polarization grid with polarization selection characteristics, which can effectively reduce the profile of the reflecting array antenna. In recent years, domestic and foreign scholars have proposed several folding reflecting array antennas, for example, a folding reflecting array antenna based on double square meander-line ring type subwavelength reflecting unit is designed in the paper "Broadband Reflectarray Antenna Using Subwavelength Elements Based on Double Square Meander-Line Rings". A folding reflecting array antenna based on split square ring structure reflecting unit is designed in the paper "Broadband Folded Reflectarray Antenna Using Single-Layer Cross-Polarization Conversion Subwavelength Elements". A wideband high gain circularly polarized folding reflecting array antenna is designed in the paper "A Wideband Circularly Polarized Folded Reflectarray Antenna With Linearly Polarized Feed".

[0003] In addition, the traditional folded reflectarray antenna feed uses a horn antenna, which often has a high profile. In order to further reduce the profile height of the planar reflectarray antenna, the profile height of the feed can be greatly reduced by using a planar feed, so that the folded reflectarray antenna can be applied to more demanding scenarios in terms of space height. For example, a high-gain folded reflectarray antenna using a planar feed is proposed in the paper "Wideband Folded Reflectarray With Integrated Single-Layer Differential Slot Feed". The proposed folded reflectarray antenna is composed of a top polarized grid and a bottom sub-wavelength unit reflectarray integrated with a planar feed. The measurement results show that the impedance bandwidth of the antenna is 27.9%, and the 3-dB gain bandwidth is 21.6%. Therefore, it has certain practical significance and application value to research and design a folded reflectarray antenna using a new type of planar feed. Utility model content

[0004] The utility model discloses to the technical problems existing in the prior art, provide a kind of folded reflectarray antenna using new type of planar feed.

[0005] The technical solution for achieving the utility model is as follows: a folded reflectarray antenna using a new type of planar feed, comprising a polarization twist reflectarray, a polarization grid and a plurality of nylon columns, the polarization grid is placed above the polarization twist reflectarray, and the two are supported and fixed by the nylon columns, characterized by further comprising a new type of planar feed for transmitting linearly polarized waves, which is installed at the center position of the upper surface of the polarization twist reflectarray;The polarization twist reflectarray includes a plurality of polarization twist reflection units arranged in a square array, the polarization twist reflection unit includes a metal layer, a first dielectric substrate and a first metal ground plate arranged in order from top to bottom, the metal layer is etched on the upper surface of the first dielectric substrate, and is a double-slit square ring superposition structure, the double-slit square ring superposition structure includes a first slit square ring metal patch and a second slit square ring metal patch, and the two are oppositely opened and superimposed in the center to form a square closed structure, while a straight angle type "W" structure is extended at the diagonal of the square closed structure;The center hole of the polarization twist reflectarray is connected with the new type of planar feed to realize integrated design;The polarization grid includes a second dielectric substrate and a plurality of metal strips with the same width arranged on the second dielectric substrate, and the spacing between adjacent two metal strips is equal.

[0006] Further, the novel planar feed source comprises a second metal floor and a V-shaped groove metal patch arranged above the second metal floor, and a third dielectric substrate is arranged between the second metal floor and the V-shaped groove metal patch; the V-shaped groove metal patch is a metal patch with a V-shaped groove in the center, and the V-shaped groove is a V-shaped groove structure with the bottom top corner of the V-shaped groove cut off along the horizontal direction; a coordinate system o-xyz is established with the horizontal left-right direction as the x-axis and the vertical direction as the z-axis, and the bottom edge of the V-shaped groove is arranged along the x-axis direction, and the slot opening is symmetrical about the y-axis, and the slot opening direction is along the positive direction of the y-axis.

[0007] Further, the second metal floor, the third dielectric substrate and the V-shaped groove metal patch are all rectangular structures, and the adjacent edges of the rectangular structures are arranged along the x-axis and y-axis directions, respectively.

[0008] Further, the first dielectric substrate and the first metal floor are both rectangular structures.

[0009] Further, the length l2 of the metal patch of the two outer sides of the "W" type structure can be adjusted to realize the change of the reflection phase of the polarization twist reflection unit.

[0010] Further, when the polarization twist reflection unit performs phase compensation, the continuous phase change of 0-360° is realized by performing the horizontal mirror image operation.

[0011] Further, the distance between the polarization twist reflection units is P=0.3λ, wherein λ is the free space wavelength corresponding to the center frequency.

[0012] Further, the thickness of the first dielectric substrate and the third dielectric substrate is 0.067λ, and the thickness of the second dielectric substrate is 0.033λ, wherein λ is the free space wavelength corresponding to the center frequency.

[0013] Further, the polarization grid is located directly above the polarization twist reflection array.

[0014] Further, the polarization twist reflection array and the polarization grid are the same size and the center projections coincide.

[0015] Compared with the prior art, the utility model has the following advantages:

[0016] (1) The double-split square ring superposition type reflection unit proposed in the utility model can change the polarization characteristics of electromagnetic waves and can better realize 90° polarization twist of incident waves.

[0017] (2) The double-split square ring superposition type reflection unit proposed in the utility model realizes the continuous phase change of 0-360° through the mirror image mode. While ensuring the reflection performance, the height of the profile is reduced as much as possible, and the requirement of low profile is better met.

[0018] (3) The novel plane feed source provided in the utility model has the advantages of low profile, lightness, integration and integration compared with the traditional corner horn feed source, and has good application prospect.

[0019] (4) The polarization grid provided in the utility model has excellent electromagnetic wave polarization selection characteristics, and in the working frequency band, the polarization grid totally reflects the polarization wave parallel to it and has good transmission performance on the polarization wave vertical to it.

[0020] (5) Compared with the existing traditional reflective array antenna, the utility model greatly reduces the profile of the antenna.

[0021] The utility model will be further described in detail below in combination with the drawings. DRAWINGS

[0022] Figure 1 It is a three-dimensional schematic view of the folded reflective array antenna using the novel plane feed source in an embodiment.

[0023] Figure 2 It is a side view of the folded reflective array antenna using the novel plane feed source in an embodiment.

[0024] Figure 3 It is a three-dimensional schematic view of the novel plane feed source in an embodiment.

[0025] Figure 4 It is a schematic view of the polarization twist reflection unit of the folded reflective array antenna using the novel plane feed source in an embodiment.

[0026] Figure 5 It is a side view of the polarization twist reflection unit of the folded reflective array antenna using the novel plane feed source in an embodiment.

[0027] Figure 6 It is a three-dimensional schematic view of the polarization grid of the folded reflective array antenna using the novel plane feed source in an embodiment.

[0028] Figure 7 It is a side view of the polarization grid of the folded reflective array antenna using the novel plane feed source in an embodiment.

[0029] Figure 8 It is a top view of the novel plane feed source of the folded reflective array antenna using the novel plane feed source in an embodiment.

[0030] Figure 9 It is a side view of the novel plane feed source of the folded reflective array antenna using the novel plane feed source in an embodiment.

[0031] Figure 10Reflection amplitude and phase curves of the dual-split square loop stacked reflector element of the folded reflectarray antenna using the new planar feed in an embodiment at the design center frequency of 10 GHz in two different states, before and after the mirror.

[0032] Figure 11 Reflection amplitude and transmission amplitude curves of the polarization grid of the folded reflectarray antenna using the new planar feed in an embodiment in the design frequency range of 8-12 GHz.

[0033] Figure 12 Simulation S 11 curves of the new planar feed of the folded reflectarray antenna using the new planar feed in an embodiment.

[0034] Figure 13 E-plane radiation patterns simulated and measured at the center frequency of 10 GHz of the folded reflectarray antenna using the new planar feed in an embodiment.

[0035] Figure 14 H-plane radiation patterns simulated and measured at the center frequency of 10 GHz of the folded reflectarray antenna using the new planar feed in an embodiment.

[0036] Figure 15 E-plane radiation patterns simulated and measured at different frequencies of the folded reflectarray antenna using the new planar feed in an embodiment.

[0037] Figure 16 H-plane radiation patterns simulated and measured at different frequencies of the folded reflectarray antenna using the new planar feed in an embodiment.

[0038] Figure 17 Antenna gain and aperture efficiency versus frequency curves simulated and measured at the design frequency range of 8-12 GHz of the folded reflectarray antenna using the new planar feed in an embodiment. DETAILED DESCRIPTION

[0039] In order to make the purpose, technical scheme and advantages of the present application clearer, the present application will be further described in detail below in combination with the drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present application and not to limit the present application.

[0040] It should be noted that if the embodiment of the present application involves directional indications (such as up, down, left, right, front, back, etc.), the directional indications are only used to explain the relative position relationship, movement condition, etc. between the components in a certain specific posture (as shown in the drawings), if the specific posture changes, the directional indications will also change accordingly.

[0041] In addition, if the description of "first", "second" and the like is involved in the embodiments of the present application, the description of "first", "second" and the like is only for the purpose of description, and cannot be understood as indicating or implying the relative importance of the indicated technical features or implicitly indicating the number of the indicated technical features. Therefore, the features limited by "first", "second" can be explicitly or implicitly included at least one of the features. In addition, the technical solutions of each embodiment can be combined with each other, but it must be based on the realization of ordinary skilled in the art, when the combination of technical solutions appears contradictory or unachievable, it should be considered that the combination of technical solutions does not exist, and is not within the protection scope required by the present application.

[0042] In one embodiment, in combination Figures 1 to 9 , a folded reflectarray antenna using a new type of planar feed source is provided, comprising a polarization twist reflectarray 2, a polarization grid 3 placed above the polarization twist reflectarray 2, and a plurality of nylon columns 4 supporting and fixing the two, characterized in that it further comprises a new type of planar feed source 1 for transmitting linearly polarized waves, which is installed at the center position of the upper surface of the polarization twist reflectarray 2; the polarization twist reflectarray 2 comprises a plurality of polarization twist reflecting units 5 arranged in a square array, the polarization twist reflecting unit 5 comprises a metal layer 7, a first dielectric substrate 8 and a first metal ground plate 9 arranged in order from top to bottom, the metal layer 7 is etched on the upper surface of the first dielectric substrate 8, which is a double-split square ring superposition structure, the double-split square ring superposition structure comprises a first split square ring metal patch and a second split square ring metal patch, the two are oppositely opened and superimposed in the center to form a square closed structure, and at the same time, a "W" type structure of right angle type is extended at the diagonal of the square closed structure; the center hole of the polarization twist reflectarray 2 is connected with the new type of planar feed source 1 to realize integrated design; the polarization grid 3 comprises a second dielectric substrate 11 and a plurality of metal strips 10 with the same width arranged on the second dielectric substrate 11, and the spacing between adjacent two metal strips 10 is equal.

[0043] The antenna of the present application can reduce the profile height of the traditional reflectarray antenna by one half, and realize good gain bandwidth and aperture efficiency.

[0044] Further, in one of the embodiments, the novel planar feed source 1 comprises a second metal floor 12 and a V-shaped groove metal patch 14 arranged above the second metal floor 12, and a third dielectric substrate 13 is arranged between the second metal floor 12 and the V-shaped groove metal patch 14; the V-shaped groove metal patch 14 is a metal patch with a V-shaped groove in the center, and the V-shaped groove is a V-shaped groove structure with the "V-shaped" bottom corner cut off along the horizontal direction; a coordinate system o-xyz is established with the horizontal left-right direction as the x-axis and the vertical direction as the z-axis, and the bottom edge of the V-shaped groove is arranged along the x-axis direction, and the slot opening is symmetrical about the y-axis, and the slot opening direction is along the positive direction of the y-axis.

[0045] Preferably, in some embodiments, the second metal floor 12, the third dielectric substrate 13, and the V-shaped groove metal patch 14 are all rectangular structures, and the adjacent edges of the rectangular structures are arranged along the x-axis and y-axis directions, respectively.

[0046] Here, the use of the V-shaped groove metal patch not only ensures a high gain of the feed source, but also lays a good foundation for the integrated design with the polarization twist reflection array.

[0047] Preferably, in some embodiments, the metal layer 7, the first dielectric substrate 8, and the first metal floor 9 are all rectangular structures.

[0048] Further, in one of the embodiments, the length l2 of the metal patch on the two outer sides of the "W" type structure is adjustable, which is used to realize the reflection phase change of the polarization twist reflection unit 5.

[0049] Preferably, in some embodiments, the length l2 is in the range of [0.1mm, 3.5mm].

[0050] Further, in one of the embodiments, when the polarization twist reflection unit 5 performs phase compensation, a horizontal mirror image operation is performed to realize a continuous phase change of 0-360°.

[0051] Here, the polarization twist reflection unit 5 includes two working states, and state B is mirror image of state A, and the relationship is determined by the phase distribution of the array surface. According to the normalized phase range, 0-180° uses state A, and 180°-360° uses state B, and the two can be combined to synthesize a phase range of 360 degrees.

[0052] Preferably, in some embodiments, the distance between the polarization twist reflection units 5 is P=0.3λ, where λ is the free space wavelength corresponding to the center frequency.

[0053] Preferably, in some embodiments, the thickness of the first dielectric substrate 8 and the third dielectric substrate 13 is 0.067λ, and the thickness of the second dielectric substrate 11 is 0.033λ, where λ is the free space wavelength corresponding to the center frequency.

[0054] Preferably, in some embodiments, the polarization grid 3 is located directly above the polarization twisted reflective array 2.

[0055] Preferably, in some embodiments, the polarization twisted reflective array 2 and the polarization grid 3 are the same size and have overlapping center projections.

[0056] The folded reflective array antenna using the novel planar feed source has a novel structure, good performance, and a very low profile compared with a traditional horn.

[0057] As a specific example, in one embodiment, the utility model is further verified in detail.

[0058] The folded reflective array antenna using the novel planar feed source in this embodiment includes a novel planar feed source 1, a reflective array 2, a polarization twisted reflective array 3, and a plurality of nylon columns 4. The novel planar feed source 1 is placed on the upper surface center of the polarization twisted reflective array 3, the polarization grid 3 is placed above the polarization twisted reflective array 2, and the two are supported and fixed by the nylon columns 4; the polarization twisted reflective array 2 is composed of 718 polarization twisted reflective units 5, the polarization twisted reflective unit 5 includes a metal layer 7, a first dielectric substrate 8, and a first metal ground plate 9 arranged in order from top to bottom, a double-slit square ring superposition type metal patch is etched on the metal layer 7, the double-slit square ring superposition type metal patch includes a first slit square ring metal patch and a second slit square ring metal patch, the two are oppositely overlapped to form a square closed structure in the center, and a straight angle type "W" structure is extended at the diagonal of the square closed structure; the polarization grid 3 is composed of a plurality of metal strips with the same width, and the spacing between adjacent two metal strips is equal. In order to facilitate installation and fixation, the polarization twisted reflective array 2 and the polarization grid 3 are appropriately expanded in size and have the same size after expansion, and the diameter is 261 mm, and the height of the nylon column 4 between the polarization twisted reflective array 2 and the polarization grid 3 is 79 mm.

[0059] In this embodiment, in combination with Figure 4 and Figure 5 , the spacing P between the polarization twisted reflective units 5 is 9 mm, that is, 0.3λ, where λ is the free space wavelength corresponding to 10 GHz. The thickness H of the first dielectric substrate 8 is 2 mm, the side length l1 of the square slit square ring metal patch is 5.9 mm, the distance g from the unit center to one side of the square slit ring metal patch is 2.2 mm, the width l0 of the square slit ring metal patch is 0.8 mm, and the length l2 of the metal patch of the two outer sides in the "W" structure is 0.1-3.5 mm.

[0060] Combining Figure 8 and Figure 9 , the parameters of the new planar feed 1: the length a of the V-shaped groove metal patch is 16 mm, the width b is 8 mm, the thickness H1 of the third dielectric substrate is 2 mm, the width w1 of the V-shaped groove bottom edge is 6.2 mm, the width w0 of the V-shaped groove side edge is 0.8 mm, the length l of the V-shaped groove side edge is 7.2 mm, and the V-shaped groove bevel angle θ is 95°.

[0061] As can be seen from Figure 6 , Figure 7 and Figure 11 , the polarization grid 3 includes a second dielectric substrate and a plurality of metal strips with a width of 0.5 mm, the spacing between the metal strips is 0.5 mm, the thickness of the polarization grid is 0.5 mm, and the thickness of the second dielectric substrate is 1 mm. In the working frequency band, when the incident wave is x-polarized, the reflection amplitude of the polarization grid is about 0 dB, and the transmission amplitude is about -65 dB, which means that the x-polarized wave parallel to the strip cannot be transmitted from the grid and will be completely reflected by the grid; when the incident wave is y-polarized, the reflection amplitude of the polarization grid is about -14 dB, and the transmission amplitude of the polarization grid is almost 0 dB, which indicates that the polarization grid has good transmission performance for y-polarized waves perpendicular to it.

[0062] As can be seen from Figure 10 , the polarization twist reflection unit 5 has a 360° reflection phase range and an amplitude close to 0 dB in the 8-12 GHz working frequency band when l2 changes.

[0063] As can be seen from Figure 12 , the new planar feed 1 has an S 11 value lower than -10 dB in the 9.4-10.6 GHz frequency band, indicating that the feed has good matching performance and can work stably in the designed frequency range.

[0064] As can be seen from Figure 13 and Figure 14 , the simulation and measurement of the E-plane and H-plane of the folded reflectarray antenna using the new planar feed are basically coincident at 10 GHz. The main lobe directions of the E-plane and H-plane are both at 0°, which is consistent with the design. The measured side lobe level and cross-polarization level of the E-plane are -17.7 dB and -31.4 dB, respectively, and those of the H-plane are -15.0 dB and -28.9 dB, respectively.

[0065] As can be seen from Figure 15 and Figure 16It can be seen that the radiation characteristics of the folded reflectarray antenna using the new planar feed source are also ideal at different frequencies, and the E-plane and H-plane side lobe average is lower than-15dB, and the cross polarization average is lower than-20dB.

[0066] By Figure 17 It can be seen that the measurement results of the folded reflectarray antenna using the new planar feed source show that the gain at 10GHz is 24.77dBi, and the maximum aperture efficiency is 38.26%. At the same time, the folded reflectarray antenna can realize a 3-dB gain bandwidth of 25.0%.

[0067] In summary, compared with the existing conventional reflectarray antenna, the profile of the antenna is greatly reduced, and the profile is only 2.75λ, and λ is the free space wavelength corresponding to 10GHz. The double-slit square ring superposition type reflecting unit proposed in the utility model can change the polarization characteristics of electromagnetic waves, and can better realize 90° polarization twist of incident waves, and can realize continuous phase change of 0-360° through mirror image mode. While ensuring the reflection performance, the height of the profile is as low as possible, and the low profile requirement is better met. The new planar feed source proposed in the utility model has the advantages of low profile, light weight, integration and integration compared with the traditional corner horn feed source. The polarization grid has excellent electromagnetic wave polarization selection characteristics, and in the working frequency band, the polarization grid fully reflects the polarization wave parallel to it, and has good transmission performance for the polarization wave perpendicular to it.

[0068] The basic principles, main features and advantages of the utility model are shown and described above. It should be understood by those skilled in the art that the utility model is not limited by the above examples, and the above examples and descriptions in the specification are only to illustrate the principles of the utility model, and any modification, equivalent replacement, improvement, etc. within the spirit and principles of the utility model should be included in the protection scope of the utility model.

Claims

1. A folded reflectarray antenna using a new type of planar feed, comprising a polarization twisted reflectarray (2), a polarization grid (3) placed above the polarization twisted reflectarray (2) and supported by nylon columns (4) between them, characterized in that, Also included is a new type of planar feed source (1) for transmitting linearly polarized waves, which is installed at the center position of the upper surface of the polarization twist reflection array (2); the polarization twist reflection array (2) comprises a plurality of polarization twist reflection units (5) arranged in a square array, the polarization twist reflection unit (5) comprises a metal layer (7), a first dielectric substrate (8) and a first metal ground plane (9) arranged in order from top to bottom, the metal layer (7) is etched on the upper surface of the first dielectric substrate (8), and is a double-split square ring superposition type structure, the double-split square ring superposition type structure comprises a first split square ring metal patch and a second split square ring metal patch, both of which are oppositely opened and superimposed in the center to form a square closed structure, while a straight angle type "W" structure is extended at the diagonal of the square closed structure; the polarization twist reflection array (2) is connected with the new type of planar feed source (1) to realize integrated design; the polarization grid (3) comprises a second dielectric substrate (11) and a plurality of metal strips (10) with the same width arranged on the second dielectric substrate (11), and the spacing between adjacent two metal strips (10) is equal.

2. The folded reflectarray antenna using a novel planar feed of claim 1, wherein, The new type of planar feed source (1) comprises a second metal ground plane (12) and a V-shaped groove metal patch (14) arranged above the second metal ground plane (12), and a third dielectric substrate (13) is arranged between the two; the V-shaped groove metal patch (14) is a metal patch with a V-shaped groove in the center, and the V-shaped groove is a V-shaped groove structure with the bottom corner of the "V shape" cut off along the horizontal direction; a coordinate system o-xyz is established with the horizontal left-right direction as the x-axis and the vertical direction as the z-axis, the bottom edge of the V-shaped groove is arranged along the x-axis direction, the slot is symmetric about the y-axis, and the slot direction is along the positive direction of the y-axis.

3. The folded reflectarray antenna using novel planar feeds of claim 2, wherein, The second metal ground plane (12), the third dielectric substrate (13) and the V-shaped groove metal patch (14) are all rectangular structures, and the adjacent edges of the rectangular structures are arranged along the x-axis and y-axis directions, respectively.

4. The folded reflectarray antenna using novel planar feeds of claim 1, wherein, The first dielectric substrate (8) and the first metal ground plane (9) are both rectangular structures.

5. The folded reflectarray antenna using novel planar feeds of claim 1, wherein, The length l2 of the metal patch of the two outer sides of the "W" structure can be adjusted to realize the change of the reflection phase of the polarization twist reflection unit (5).

6. The folded reflectarray antenna using novel planar feeds of claim 5, wherein, When the polarization twist reflection unit (5) performs phase compensation, a horizontal mirror image operation is performed to realize a continuous phase change of 0-360°.

7. The folded reflectarray antenna using novel planar feeds of claim 1, wherein, The spacing between the polarization twist reflection units (5) is P=0.3λ, where λ is the free space wavelength corresponding to the center frequency.

8. The folded reflectarray antenna using novel planar feeds of claim 1, wherein, The thickness of the first dielectric substrate (8) and the third dielectric substrate (13) is 0.067λ, and the thickness of the second dielectric substrate (11) is 0.033λ, where λ is the free space wavelength corresponding to the center frequency.

9. The folded reflectarray antenna using novel planar feeds of claim 1, wherein, The polarization grid (3) is located directly above the polarization twist reflection array (2).

10. The folded reflectarray antenna using novel planar feeds of claim 9, wherein, The polarization twist reflection array (2) and the polarization grid (3) are the same size and the center projections coincide.

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