A non-dispersive Cassegrain antenna

Abstract

The present invention discloses a non-dispersive Cassegrain antenna, comprising: a non-dispersive polarization selective metasurface at the top layer, a polarization flip metasurface at the bottom layer, and a feed antenna embedded in the center of the polarization flip metasurface; the non-dispersive polarization selective metasurface is divided into a plurality of regional units according to the phase dispersion velocity, and the phase of each unit at a different position satisfies the phase compensation of converting a spherical wave into a plane wave by adjusting the tilt angle and the metal opening angle in each unit. The non-dispersive Cassegrain antenna disclosed by the present invention can maintain the antenna gain stability.

Description

Technical Field

[0001] The present invention relates to the technical field of antennas, in particular to a non-dispersive Cassegrain antenna. Background Art

[0002] Antennas, as devices that radiate or receive electromagnetic waves into space, have had a significant impact on people's lives since their invention, and are widely used in various fields such as wireless communications, radar detection, navigation, remote sensing, and electronic countermeasures. With the widespread application of antennas in these fields, different types of systems are in urgent need of matching high-performance antennas, especially high-gain antennas to enhance long-distance communication capabilities, and miniaturized antennas for easy integration.

[0003] As a common high-gain antenna, reflectarray antenna has the advantages of low cost and simple structure, but its high profile disadvantage makes it unable to meet the requirements of high integration on advanced equipment such as radars and satellites. In order to solve the high profile problem, a folded Cassegrain antenna was proposed. However, the non-dispersive polarization selective metasurface (1) in the existing folded Cassegrain reflector antenna is restricted by the inherent dispersion characteristics. When the operating frequency shifts from the center frequency, it is difficult for the non-dispersive polarization selective metasurface (1) to convert the spherical wave radiated by the feed source into a plane wave after phase compensation, resulting in a decrease in antenna gain.

[0004] In the prior art, the invention patent with the patent publication number CN117096614A discloses a large frequency ratio dual-frequency dual-polarization common aperture antenna, including an upper metasurface and a lower substrate with an integrated dual-frequency composite feeding structure; the upper metasurface is composed of a periodic metasurface composed of multiple metasurface units, and metal plates are respectively provided on the upper and lower surfaces of the lower substrate, and a dual-frequency composite feeding structure is provided in the middle of the upper surface of the lower substrate. The distance between the lower substrate and the upper metasurface is L, and a virtual feed source is provided at a distance of 2L below the dual-frequency composite feeding structure. At low frequencies, since the cavity height meets the resonance condition, the electromagnetic waves transmitted out each time are superimposed in phase to form a high-gain beam in the far field. At high frequencies, the left-handed circularly polarized wave reaching the metasurface forms a high-gain beam in the far field after phase compensation and polarization conversion. However, in the prior art, the phase cannot change with the frequency, and the operating frequency is analyzed when it is at the center frequency. Summary of the invention

[0005] The technical problem to be solved by the present invention is to solve the problem that a non-dispersive polarization selective metasurface (1) in a folded Cassegrain reflector antenna is restricted by inherent dispersion characteristics. When the operating frequency deviates from the center frequency point, the non-dispersive polarization selective metasurface (1) is difficult to convert the spherical wave radiated by the feed source into a plane wave after phase compensation, thereby causing a decrease in antenna gain.

[0006] In order to solve the above technical problems, the present invention provides the following technical solutions:

[0007] A non-dispersive Cassegrain antenna comprises: a non-dispersive polarization selective metasurface (1) located at a top layer, a polarization flip metasurface (3) located at a bottom layer, and a feed antenna (2) embedded in the center of the polarization flip metasurface (3); the non-dispersive polarization selective metasurface (1) is divided into a plurality of regional units according to the phase dispersion velocity, and the phase of each unit at a different position satisfies the phase compensation of converting a spherical wave into a plane wave by adjusting the tilt angle (β) and the metal opening angle (α) in each unit.

[0008] In one embodiment of the present invention, the plurality of regional units include a first unit, a second unit and a third unit, which are used to realize total reflection of x-polarized electromagnetic waves, transmit y-polarized electromagnetic waves, and adjust the phase of the transmitted waves.

[0009] In one embodiment of the present invention, the first unit, the second unit and the third unit are a hierarchical structure; wherein the hierarchical structure of the first unit includes: the first layer is metal grating 1, the second layer is dielectric substrate 1, the third layer is double open circular ring, the fourth layer is dielectric substrate 2, the fifth layer is metal grating 2, the sixth layer is isolation layer, and the seventh layer is split square groove metal.

[0010] In one embodiment of the present invention, the hierarchical structure of the second unit is based on the first unit and an eighth isolation layer 1 and a ninth split square groove metal 1 are added.

[0011] In one embodiment of the present invention, the hierarchical structure of the third unit is added with a tenth isolation layer 2 and an eleventh split square groove metal 2 on the basis of the second unit.

[0012] In one embodiment of the present invention, the second metal grating is placed vertically to the first metal grating.

[0013] In one embodiment of the present invention, the double-opening circular ring is placed at an angle.

[0014] In one embodiment of the present invention, the feed antenna (2) radiates x-polarized electromagnetic waves, and the x-polarized electromagnetic waves are incident on the non-dispersive polarization selective metasurface (1). The non-dispersive polarization selective metasurface (1) can reflect the x-polarized electromagnetic waves along the mirror surface and maintain the chirality. The reflected x-polarized electromagnetic waves are polarized on the polarization reversal metasurface (3) at the bottom to generate y-polarized electromagnetic waves, which are then propagated toward the top non-dispersive polarization selective metasurface (1) again, converting the spherical waves into plane waves.

[0015] In one embodiment of the present invention, the spherical wavefront is converted into a plane wavefront, and the (m, n)th unit phase on the non-dispersive polarization selective metasurface (1) satisfies:

[0016]

[0017] In the formula, is the phase of the (m,n)th unit, π is the circumference of a circle, λ0 is the free space wavelength corresponding to the center frequency, (x mn ,y mn ,z mn ) is the position of the (m,n)th unit, and F0 is the focal length.

[0018] In one embodiment of the present invention, the feed antenna (2) is a linearly polarized antenna or a waveguide port.

[0019] Compared with the prior art, the beneficial effect of the present invention is that the present invention uses units whose phase dispersion changes with frequency to form a polarization-selective metasurface, thereby satisfying the amplitude and phase dispersion requirements of converting the spherical waves radiated by the feed source into plane waves within a broadband range, and finally realizing a non-dispersive folded Cassegrain antenna. Due to the introduction of the non-dispersive polarization-selective metasurface 1, the path of the electromagnetic wave radiated by the feed antenna to the reflective array is folded, and the electromagnetic wave is reflected to the non-dispersive polarization-selective metasurface through the reflective array, so the antenna profile can be reduced to 1 / 3.

[0020] In order to convert the spherical wave emitted by the feed source into a plane wave, a phase compensation needs to be performed on the non-dispersive polarization selective metasurface. The unit of the non-dispersive polarization selective metasurface in the present invention is composed of a part that realizes the polarization selective grating and a split square slot part, the former is used to control the phase characteristics, and the latter is used to control the dispersion. By cascading them, the phase and dispersion of the unit can be controlled independently, and any phase dispersion curve can be designed as needed. The non-dispersive polarization selective metasurface can be used to compensate the spherical wave generated by the feed antenna into a plane wave within a broadband range, thereby maintaining the gain stability of the antenna. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 The figure is a schematic diagram of the structure of a non-dispersive Cassegrain antenna according to an embodiment of the present invention.

[0022] Figure 2 This is a schematic diagram of the principle of a non-dispersive folded Cassegrain antenna according to an embodiment of the present invention.

[0023] Figure 3(a) to Figure 3(c) A schematic diagram of the unit structure of a non-dispersive polarization selective metasurface according to an embodiment of the present invention.

[0024] Figure 4(a) to Figure 4(d) Schematic diagram of the unit metal layer structure of the non-dispersive polarization selective metasurface according to an embodiment of the present invention.

[0025] Figure 5Schematic diagram of compensation phase distribution according to an embodiment of the present invention.

[0026] Figure 6 A schematic diagram of the amplitude and phase curves of the non-dispersive polarization selective metasurface unit structure of an embodiment of the present invention.

[0027] Figure 7 Schematic diagram of the compensation phase variation with frequency at 9-13 GHz according to an embodiment of the present invention.

[0028] Figure 8 Schematic diagram of phase dispersion curves of three units of the non-dispersive polarization selective metasurface according to an embodiment of the present invention.

[0029] Fig. 9 Schematic diagram of three unit distributions and actual structures of the non-dispersive polarization selection metasurface according to an embodiment of the present invention.

[0030] Fig.10 It is a schematic diagram of the structure of the feed antenna and a schematic diagram of its S parameter curve according to an embodiment of the present invention.

[0031] Fig.11 It is a schematic diagram of the unit structure in the polarization reversal metasurface of an embodiment of the present invention and a schematic diagram of the actual structure of the polarization reversal metasurface.

[0032] Fig.12 Schematic diagram of antenna S parameter curve and gain curve according to an embodiment of the present invention. DETAILED DESCRIPTION

[0033] In order to facilitate those skilled in the art to understand the technical solution of the present invention, the technical solution of the present invention is further described in conjunction with the accompanying drawings of the specification.

[0034] The terms "first" and "second" are used for descriptive purposes only and should not be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of the features. In the description of this application, the meaning of "plurality" is two or more, unless otherwise clearly and specifically defined.

[0035] See also Figure 1 and Figure 2 As shown, the present invention discloses a non-dispersive Cassegrain antenna, comprising: a non-dispersive polarization selective metasurface 1 located at the top layer, a polarization flip metasurface 3 located at the bottom, and a feed antenna 2 embedded in the center of the polarization flip metasurface 3. The non-dispersive polarization selective metasurface 1 is divided into a plurality of regional units according to the phase dispersion velocity, and the phase of each unit at a different position satisfies the phase compensation of converting a spherical wave into a plane wave by adjusting the tilt angle β and the metal opening angle α in each unit.

[0036] In this embodiment, the feed antenna 2 is used to generate an X-polarized electromagnetic wave, and the non-dispersive polarization-selective metasurface 1 is used to reflect the X-polarized electromagnetic wave and transmit the Y-polarized electromagnetic wave and convert it into an X-polarized electromagnetic wave. In addition, the non-dispersive polarization-selective metasurface 1 can also be used to adjust the phase of the transmitted wave. The polarization flip metasurface 3 is used to flip the incident X-polarized electromagnetic wave into a Y-polarized electromagnetic wave.

[0037] Specifically, the non-dispersive polarization selective metasurface 1 has multiple regional units, including the first unit, the second unit and the third unit in this embodiment, which have different numbers of layers, but are not limited to three layers, and can also be 2, 3, 4...N layers, which can achieve total reflection of x-polarized electromagnetic waves, transmit y-polarized electromagnetic waves, and adjust the phase of the transmitted waves. The feed antenna 2 is a tangent polarized antenna or a waveguide port, for example, a microstrip antenna or a patch antenna.

[0038] In this embodiment, the feed antenna 2 radiates x-polarized electromagnetic waves, and the x-polarized electromagnetic waves are incident on the non-dispersive polarization-selective metasurface 1. The non-dispersive polarization-selective metasurface 1 can reflect the x-polarized electromagnetic waves along the mirror surface and maintain the chirality. The reflected x-polarized electromagnetic waves are polarized on the polarization-reversed metasurface 3 at the bottom, generating y-polarized electromagnetic waves that propagate toward the non-dispersive polarization-selective metasurface 1 on the top layer again, converting the spherical waves into plane waves. Since the non-dispersive polarization-selective metasurface 1 is transmissive to the y-polarized electromagnetic waves and can achieve phase compensation, a plane wave is finally generated. The whole process involves two reflections, so the virtual focus of the folded Cassegrain antenna is located below the bottom polarization-reversed metasurface. The total path length from the wave source to the free space is:

[0039] P total =P1+P2+P3;

[0040] Since all reflections are mirror reflections, P1 = P2 = P3. Therefore, the cross-sectional height H between the top non-dispersive polarization selective metasurface 1 and the bottom polarization flip metasurface 3 can be reduced to one third of the focal length f.

[0041] In this embodiment, the present invention utilizes units whose phase dispersion varies with frequency to form a polarization selective metasurface, thereby satisfying the amplitude and phase dispersion requirements of converting the spherical waves radiated by the feed source into plane waves within a broadband range, and ultimately realizing a non-dispersive folded Cassegrain antenna.

[0042] Due to the introduction of the non-dispersive polarization selective metasurface 1, the path of the electromagnetic wave radiated by the feed antenna 2 to the reflective array is folded, and the electromagnetic wave is reflected by the reflective array to the non-dispersive polarization selective metasurface 1, so the antenna profile can be reduced to 1 / 3. In order to convert the spherical wave emitted by the feed source into a plane wave, a phase compensation is required on the non-dispersive polarization selective metasurface. The total phase of each unit on the non-dispersive polarization selective metasurface can be expressed as φ all (r,f)=φ t (r,f)+φ m (r,f), where φ t (r,f) represents the phase dispersion accumulated when electromagnetic waves propagate in free space, φ m (r, f) represents the phase dispersion generated by the metasurface. Since the distances from the feed antenna 2 to each unit of the non-dispersive polarization selective metasurface are different, the phase that needs to be compensated also changes with frequency.

[0043] In order to ensure the high efficiency and broadband of the dispersion-controlled metasurface, it is necessary to control the phase dispersion generated by the metasurface in a broadband range so that it becomes a function of frequency. The unit of the non-dispersive polarization-selective metasurface in the present invention is composed of a part that realizes the polarization-selective grating and a split square slot part, the former is used to control the phase characteristics, and the latter is used to control the dispersion. By cascading them, the phase and dispersion of the unit can be controlled independently, and any phase dispersion curve can be designed as needed. The non-dispersive polarization-selective metasurface can be used to compensate the spherical wave generated by the feed antenna into a plane wave in a broadband range, thereby maintaining the gain stability of the antenna.

[0044] For details, please refer to Figure 3(a) to Figure 3(c) as well as Figure 4(a) to Figure 4(d) As shown, in this embodiment, the first unit, the second unit and the third unit are hierarchical structures. Among them, the hierarchical structure of the first unit includes: the first layer is a metal grating 1 composed of metal sheets, the second layer is a dielectric substrate 1, the relative power saving constant of the dielectric substrate 1 is 2.65, and the loss tangent is 0.003, specifically, for example, it is an F4B dielectric substrate. The third layer is 4 double open circular rings placed obliquely and connected in the middle, the fourth layer is a dielectric substrate 2, for example, it is also an F4B dielectric substrate, the fifth layer is a metal grating 2, which is placed vertically with the metal grating 1, the sixth layer is an isolation layer, for example, PH-52 foam, whose dielectric constant is 1.05 and the loss tangent is 0.001, and the seventh layer is a split square groove metal, as shown in Figure 3 (a).

[0045] In this embodiment, the second unit has a 9-layer structure, and an eighth isolation layer 1 and a ninth split square groove metal 1 are added to the first unit. The isolation layer 1 is PH-52 foam, as shown in FIG3(b).

[0046] The second unit has an 11-layer structure, with the tenth isolation layer 2 and the eleventh split square groove metal 2 added to the second unit. The isolation layer 2 is PH-52 foam, as shown in FIG3(c).

[0047] In this embodiment, in the first unit, the second unit and the third unit, the period of each unit is p=13mm. In the first layer, the width of the metal sheet of the metal grating one is a=25.97mm, and the interval between the gratings is g=7.66mm. In the third layer, the metal bandwidth of the double open circular ring is w=0.5mm. Changing the inclination angle β of the open ring and the retained metal angle α can adjust the phase of the transmitted wave. In the fifth layer, the metal grating two is perpendicular to the metal grating one, but has the same size. In the seventh layer, the outer side length of the split square groove of the split square groove metal is d1=12.97mm, the inner side length of the split square groove is d2=7.5mm, and the split square groove interval is w2=1mm.

[0048] In this embodiment, the focal length of the antenna is selected as F0 = 150 mm, the antenna profile H = F0 / 3 = 50 mm, and the entire non-dispersive polarization selective metasurface 1 is circular with a radius of 117 mm, corresponding to 9 unit period lengths. In order to convert the spherical wavefront into a plane wavefront, the (m, n)th unit phase on the non-dispersive polarization selective metasurface 1 should satisfy:

[0049]

[0050] In the formula, is the phase of the (m,n)th unit, π is the circumference of a circle, λ0 is the free space wavelength corresponding to the center frequency, (x mn ,y mn ,z mn ) is the position of the (m,n)th unit, and F0 is the focal length. At the center frequency, the calculated phase distribution of the spherical wave converted to a plane wave is as follows: Figure 5 In order to achieve phase compensation, the tilt angle β of the double-open ring in the third layer and the reserved metal angle α can be changed to achieve phase adjustment. Figure 6 It can be seen that by adjusting the tilt angle of the rotating opening ring, the transmission phase control range exceeds 360° while maintaining a relatively high transmission amplitude.

[0051] In one embodiment of the present invention, Figure 7 The required phase change of a 9-circle unit in a non-dispersive polarization selective metasurface when the frequency increases from 9 GHz to 13 GHz is given. Figure 8The dispersion curves of the three units from 9GHz to 13GHz show that the phase dispersion speed of the first unit is slow, the phase dispersion speed of the third unit is fast, and the phase dispersion speed of the second unit is between the two. Therefore, the non-dispersive polarization selective metasurface 1 can be divided into three regions according to the phase dispersion speed, and the three units can be used to achieve phase compensation respectively. The specific unit type distribution and the actual structure of the non-dispersive polarization selective metasurface can be seen in Fig. 9 .

[0052] See also Fig.10 As shown, in this embodiment, the feed antenna 2 used in the present invention is a patch antenna. However, it is not limited to this form. Any antenna that can generate linearly polarized waves can be used as an excitation source. The feed antenna is within the frequency band of 9 GHz to 13 GHz. 11 |<-15dB, achieving good broadband matching.

[0053] See also Fig.11 As shown, in this embodiment, the entire unit of the polarization reversal metasurface 3 is composed of two metal layers and one dielectric layer, as shown in FIG. Fig.11 As shown in (a), the unit period is p2=8.8mm, the top layer is a strip metal with a length of l=9mm and a width of w3=1mm. The medium is an F4B dielectric substrate with a relative dielectric constant of 2.65, a loss tangent of 0.003, a thickness of ha=4mm, and the bottom layer is a metal ground. Fig.11 (b) shows the reflection coefficient of the unit for the conversion of x-polarized incident electromagnetic wave into y-polarized incident wave. It can be seen that in the range of 9-13GHz, the reflection coefficient remains above -0.4dB. Fig.11 (c) shows the actual structure diagram of the polarization reversal metasurface.

[0054] See also Fig.12 As shown, in this embodiment, the S parameter curve and gain curve of the entire non-dispersive Cassegrain antenna are given. Fig.12 (a) shows that the S11 of the antenna remains below -10 dB in the frequency band of 9-13 GHz, indicating that the antenna is well matched. Fig.12 (b) shows a gain comparison diagram of a non-dispersive Cassegrain antenna and a traditional dispersive folded Cassegrain antenna. It can be seen that the non-dispersive folded Cassegrain antenna proposed in the present invention still maintains a relatively high gain when it deviates from the center frequency.

[0055] It is obvious to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above, and that the present invention can be implemented in other specific forms without departing from the spirit or essential features of the present invention. Therefore, the embodiments should be regarded as exemplary and non-limiting from any point of view, and the scope of the present invention is defined by the appended claims rather than the above description, and it is intended that all changes falling within the meaning and scope of the equivalent elements of the claims are included in the present invention, and any reference numerals in the claims should not be regarded as limiting the claims involved.

[0056] The above-described embodiments merely represent implementation methods of the invention. The protection scope of the present invention is not limited to the above-described embodiments. For those skilled in the art, several modifications and improvements may be made without departing from the concept of the present invention, which all belong to the protection scope of the present invention.

Claims

1. A non-dispersive Cassegrain antenna, characterized in that: include: A non-dispersive polarization selective metasurface (1) located at the top layer, a polarization flip metasurface (3) located at the bottom layer, and a feed antenna (2) embedded in the center of the polarization flip metasurface (3); the non-dispersive polarization selective metasurface (1) is divided into a plurality of regional units according to the phase dispersion velocity, and the phase of each unit at a different position satisfies the phase compensation of converting a spherical wave into a plane wave by adjusting the tilt angle (β) and the metal opening angle (α) in each unit; The plurality of regional units include a first unit, a second unit and a third unit; and the non-dispersive polarization selective metasurface (1) is respectively the first unit, the second unit and the third unit from the center to the periphery; The first unit, the second unit and the third unit are hierarchical structures; The hierarchical structure of the first unit includes: the first layer is metal grating 1, the second layer is dielectric substrate 1, the third layer is double-opening circular ring, the fourth layer is dielectric substrate 2, the fifth layer is metal grating 2, the sixth layer is isolation layer, and the seventh layer is split square groove metal; The hierarchical structure of the second unit is based on the first unit and adds an eighth isolation layer one and a ninth split square groove metal one; The hierarchical structure of the third unit is based on the second unit and includes a tenth isolation layer 2 and an eleventh split square groove metal 2; And the dispersion speeds of the first unit, the second unit, and the third unit increase sequentially.

2. The non-dispersive Cassegrain antenna according to claim 1, characterized in that: The multiple regional units are used to achieve total reflection of x-polarized electromagnetic waves, transmit y-polarized electromagnetic waves, and can adjust the phase of the transmitted waves.

3. The non-dispersive Cassegrain antenna according to claim 1, characterized in that: The second metal grating is placed vertically to the first metal grating.

4. The non-dispersive Cassegrain antenna according to claim 1, characterized in that: The double-opening circular rings are placed obliquely.

5. The non-dispersive Cassegrain antenna according to claim 1, characterized in that: The feed antenna (2) radiates x-polarized electromagnetic waves, and the x-polarized electromagnetic waves are incident on the non-dispersive polarization selective metasurface (1). The non-dispersive polarization selective metasurface (1) can reflect the x-polarized electromagnetic waves along the mirror surface and maintain the chirality. The reflected x-polarized electromagnetic waves undergo polarization conversion on the polarization reversal metasurface (3) at the bottom, generating y-polarized electromagnetic waves that propagate toward the non-dispersive polarization selective metasurface (1) at the top layer again, thereby converting the spherical waves into plane waves.

6. The non-dispersive Cassegrain antenna according to claim 2, characterized in that: in, The spherical wavefront is converted into a plane wavefront, and the phase of the (m, n)th unit on the non-dispersive polarization selective metasurface (1) satisfies: In the formula, is the phase of the (m,n)th unit, π is the circumference of a circle, λ0 is the free space wavelength corresponding to the center frequency, (x mn ,y mn ,z mn ) is the position of the (m,n)th unit, and F0 is the focal length.

7. The non-dispersive Cassegrain antenna according to claim 1, characterized in that: The feed antenna (2) is a linear polarization antenna or a waveguide port.

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