Folding Cassegrain antenna

Abstract

The invention relates to the technical field of antennas, and discloses a folding Cassegrain antenna, a polarization flipping focusing metasurface is located below a frequency-polarization adjustable metasurface, and the distance between the polarization flipping focusing metasurface and the frequency-polarization adjustable metasurface is half of the focal length of the polarization flipping focusing metasurface; the linear polarization feed source is located at the focus of the polarization overturning focusing metasurface and used for radiating y polarization waves; the frequency-polarization adjustable metasurface comprises a plurality of polarization rotation units which are arranged periodically, and each polarization rotation unit comprises a flexible substrate located on the upper layer, two single-opening resonance rings which are etched on the flexible substrate and are opposite in opening direction, and a metal grating located on the lower layer. By folding the flexible substrate, the polarization rotation unit forms a left-handed or right-handed chiral structure, and the technical effects of reconfigurable switching of x-polarized waves, left-handed circularly-polarized waves and right-handed circularly-polarized waves and adjustable central working frequency of the folding Cassegrain antenna can be achieved.

Description

Technical Field

[0001] The present application relates to the field of antenna technology, and in particular to a folded Cassegrain antenna. Background Art

[0002] Radar antenna systems have expanded from military aviation to fields such as navigation, deep space exploration, meteorological monitoring, satellite communications, and radio astronomy, enjoying a wide range of applications. As the most commonly used radar antenna, the reflector antenna has a relatively simple mechanical structure and is lighter than other horn antennas. It possesses excellent electromagnetic properties, high gain, high aperture efficiency, and no chromatic aberration. However, traditional reflector antennas suffer from the disadvantages of a large focal ratio and redundant longitudinal dimensions, which limits their applicability in space-constrained scenarios such as airborne platforms and low-orbit satellites. To overcome the issues of large focal ratio and large physical space, related technologies have proposed the folded Cassegrain antenna. By introducing a sub-reflector to compress the optical path length, the axial dimension has been successfully reduced by approximately 50%. However, after manufacturing, the polarization characteristics (linear or circular polarization) and center operating frequency of existing Cassegrain antennas are fixed and cannot be dynamically adjusted. This has become a key technical bottleneck restricting the development of high-performance folded Cassegrain antennas. Summary of the Invention

[0003] The present application provides a folded Cassegrain antenna, which solves the technical problems of fixed polarization characteristics and unadjustable central operating frequency of related antennas, and achieves the technical effects of reconfigurable switching of linear polarization, left-hand circular polarization, and right-hand circular polarization and adjustable central operating frequency.

[0004] In order to achieve the above objectives, the main technical solutions adopted in this application include:

[0005] In a first aspect, an embodiment of the present application provides a folded Cassegrain antenna, which includes a frequency-polarization tunable metasurface, a polarization flip focusing metasurface, and a linear polarization feed source, wherein the polarization flip focusing metasurface is located below the frequency-polarization tunable metasurface, and the distance between the polarization flip focusing metasurface and the frequency-polarization tunable metasurface is half the focal length of the polarization flip focusing metasurface; the polarization flip focusing metasurface is used to convert the y-polarization wave into the x-polarization wave and reflect it, and to perform 360-degree wavefront phase control on the reflected x-polarization wave to achieve focusing; the linear polarization feed source is located above the polarization flip focusing metasurface. at the focus of the y-polarization tunable metasurface, for radiating y-polarized waves; the frequency-polarization tunable metasurface includes a plurality of periodically arranged polarization rotation units, each of which includes a flexible substrate located on an upper layer and two single open resonant rings etched on the flexible substrate with opposite opening directions, and a metal grating located on a lower layer, wherein the periodic direction of the metal grating is along the x-axis, and the scribed direction of the metal grating is along the y-axis, for total reflection of the y-polarized wave. By folding the flexible substrate, the polarization rotation unit forms a left-handed or right-handed chiral structure, thereby realizing reconfigurable switching among x-polarized waves, left-handed circularly polarized waves, and right-handed circularly polarized waves, and the central operating frequency of the folded Cassegrain antenna is adjustable.

[0006] The folded Cassegrain antenna provided in an embodiment of the present application includes a frequency-polarization tunable metasurface, a polarization flip focusing metasurface, and a linear polarization feed; the polarization flip focusing metasurface is located below the frequency-polarization tunable metasurface, and the distance between the polarization flip focusing metasurface and the frequency-polarization tunable metasurface is half the focal length of the polarization flip focusing metasurface; the linear polarization feed is located at the focus of the polarization flip focusing metasurface and is used to radiate y-polarized waves; wherein the frequency-polarization tunable metasurface includes a plurality of periodically arranged polarization rotation units, the polarization rotation unit including a flexible substrate located on an upper layer and a single open resonant ring with two openings in opposite directions etched on the flexible substrate, and a metal grating located on a lower layer, and the flexible substrate is folded so that the polarization rotation unit forms a left-handed or right-handed chiral structure, thereby realizing reconfigurable switching of x-polarized waves, left-handed circularly polarized waves, and right-handed circularly polarized waves, and the center operating frequency of the folded Cassegrain antenna is adjustable.

[0007] Optionally, a center line connecting the two single open resonant rings in the polarization rotation unit is parallel to the x-axis direction, the opening direction of the single open resonant ring is along the y-axis, and the folding axis of the flexible substrate is along the y-axis and located between the two single open resonant rings; when the flexible substrate is in a planar state, the polarization rotation unit is used for high transmission of x-polarized waves; when the flexible substrate is folded in the negative direction of the z-axis, the polarization rotation unit forms a left-handed chiral structure for converting the x-polarized wave into left-handed circularly polarized wave radiation; when the flexible substrate is folded in the positive direction of the z-axis, the polarization rotation unit forms a right-handed chiral structure for converting the x-polarized wave into right-handed circularly polarized wave radiation.

[0008] Optionally, when the flexible substrate is in a folded state, the center operating frequency of the folded Cassegrain antenna is adjustable by adjusting the folding angle of the plane where the two single open resonant rings are located, wherein the absolute value range of the folding angle is 104-136 degrees, and the control range of the center operating frequency is 8.4-9.6 GHz.

[0009] Optionally, the larger the absolute value of the folding angle is, the smaller the central operating frequency is.

[0010] Optionally, the distance between the polarization flip focusing metasurface and the frequency-polarization tunable metasurface is set to 77 mm, and the frequency-polarization tunable metasurface is composed of 13×25 polarization rotation units, wherein 13 and 25 are the number of units of the polarization rotation unit along the x-axis and y-axis directions, respectively; the length of the polarization rotation unit along the x-axis direction is 16.8 mm, and the length along the y-axis direction is 9 mm; the thickness of the flexible substrate is 0.025 mm, and the relative dielectric constant is 3.5; the single open resonant ring is a metal square ring with a length and width of 8 mm, an opening width of the single open resonant ring is 1.1 mm, and an arm width is 1 mm.

[0011] Optionally, the period of the metal grating is 1.52 mm and the duty cycle is 50%; when the incident angle of the y-polarized wave is 0-60 degrees and the frequency range is 6-12 GHz, the reflection coefficient of the metal grating is above 0.9.

[0012] Optionally, the polarization flip focusing metasurface is provided with a plurality of metasurface units arranged in a parabolic phase, and the metasurface unit includes a double-open resonant ring located on the upper layer and a metal layer located on the lower layer, wherein the metal layer on the lower layer is used to achieve total reflection, and the rotation angle and opening size of the double-open resonant ring are adjusted to achieve 360-degree control of the wavefront phase.

[0013] Optionally, the rotation angle of the double-open resonant ring is set to ±45 degrees, and the opening size of the double-open resonant ring is in the range of 20-84 degrees.

[0014] Optionally, the polarization flip focusing metasurface is provided with a plurality of metasurface units arranged in a parabolic phase, including: calculating the compensation phase required at different positions of the polarization flip focusing metasurface according to a phase compensation method; and placing a metasurface unit with a corresponding compensation phase at each position of the polarization flip focusing metasurface.

[0015] Optionally, in the frequency range of 7.5-12 GHz, the cross-polarization reflection coefficient of the polarization flip focusing metasurface is greater than 0.85. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] In order to more clearly illustrate the specific implementation methods of the present application or the technical solutions in the prior art, the following is a brief introduction to the drawings required for use in the specific implementation methods or the description of the prior art. Obviously, the drawings described below are some implementation methods of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without any creative work.

[0017] Figure 1 A schematic structural diagram of a folded Cassegrain antenna provided in an embodiment of the present application;

[0018] Figure 2 A schematic structural diagram of a polarization rotation unit provided in an embodiment of the present application;

[0019] Figure 3 A schematic diagram of a folded Cassegrain antenna radiating x-polarized waves provided in an embodiment of the present application;

[0020] Figure 4 A schematic diagram of the structure of a folded flexible substrate provided in an embodiment of the present application;

[0021] Figure 5 A schematic diagram of a folded Cassegrain antenna radiating left-handed circularly polarized waves provided in an embodiment of the present application;

[0022] Figure 6 A schematic diagram of the structure of a folded flexible substrate provided in an embodiment of the present application;

[0023] Figure 7 A schematic diagram of a folded Cassegrain antenna radiating right-handed circularly polarized waves provided in an embodiment of the present application;

[0024] Figure 8 The transmission spectrum of the polarization rotation unit provided in the embodiment of the present application;

[0025] Figure 9The transmission spectrum of the polarization rotation unit provided in the embodiment of the present application;

[0026] Figure 10 The transmission spectrum of the polarization rotation unit provided in the embodiment of the present application;

[0027] Figure 11 A reflection spectrum of the polarization rotation unit provided in an embodiment of the present application;

[0028] Figure 12 This is a graph showing the axial ratio-frequency characteristics of the polarization rotation unit provided in an embodiment of the present application;

[0029] Figure 13 A schematic structural diagram of a metasurface unit provided in an embodiment of the present application;

[0030] Figure 14 A wavefront phase control diagram of the metasurface unit provided in an embodiment of the present application;

[0031] Figure 15 A reflection spectrum of the metasurface unit provided in an embodiment of the present application;

[0032] Figure 16 Phase control diagram of the metasurface unit provided in the embodiment of the present application;

[0033] Figure 17 A compensation phase distribution diagram of the polarization reversal focusing metasurface provided in an embodiment of the present application;

[0034] FIG18( a ) is a perspective schematic diagram of a linearly polarized ME pole antenna provided in an embodiment of the present application;

[0035] FIG18( b ) is a plan view of a linearly polarized ME pole antenna provided in an embodiment of the present application;

[0036] Figure 19 The S11 parameter and gain performance curve of the linearly polarized ME pole antenna provided in the embodiment of the present application;

[0037] Figure 20 Provide a radiation pattern of a linearly polarized ME pole antenna for an embodiment of the present application;

[0038] Figure 21-23 S11 parameter diagram of the folded Cassegrain antenna provided in an embodiment of the present application;

[0039] Figure 24 The gain spectrum of the folded Cassegrain antenna provided in an embodiment of the present application in the unfolded state;

[0040] Figure 25-26 A gain-axial ratio parameter diagram of the folded Cassegrain antenna provided in an embodiment of the present application in the folded state;

[0041] Figure 27-28 The radiation pattern of the folded Cassegrain antenna provided in an embodiment of the present application in an unfolded state;

[0042] Figures 29-32 The radiation pattern of the folded Cassegrain antenna provided in an embodiment of the present application in the folded state. DETAILED DESCRIPTION

[0043] To make the purpose, technical solutions, and advantages of the embodiments of the present application more clear, the technical solutions in the embodiments of the present application will be clearly and completely described below in conjunction with the drawings in the embodiments of the present application. Obviously, the described embodiments are part of the embodiments of the present application, not all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without making creative efforts shall fall within the scope of protection of this application.

[0044] Radar antenna systems have expanded from military aviation to fields such as navigation, deep space exploration, meteorological monitoring, satellite communications, and radio astronomy, enjoying a wide range of applications. Reflector antennas, the most commonly used type of radar antenna, have a relatively simple mechanical structure and are lighter than other horn antennas. They possess excellent electromagnetic properties, high gain, high aperture efficiency, and no chromatic aberration. However, traditional reflector antennas suffer from the disadvantages of a large focal ratio and redundant longitudinal dimensions, limiting their applicability in space-constrained scenarios such as airborne platforms and low-orbit satellites. To overcome the technical challenges of large focal ratios and large physical space, related technologies have proposed folded Cassegrain antennas. By introducing a sub-reflector to compress the optical path length, the axial dimension has been successfully reduced by approximately 50%. However, after manufacturing, the polarization characteristics (linear or circular polarization) and center operating frequency of existing folded Cassegrain antennas are fixed, making dynamic adjustment impossible. This has become a key technical bottleneck restricting the development of high-performance folded Cassegrain antennas.

[0045] The embodiment of the present application proposes a folded Cassegrain antenna, which is a deformed antenna of a reflector antenna with an operating frequency designed to be 8-12 GHz. The reflection of the linearly polarized feed source is 360-degree phase-controlled and focused by the polarization conversion focusing metasurface on the lower surface, and selective transmission is performed by the frequency-polarization tunable metasurface on the upper surface. It can realize reconfigurable switching of linearly polarized waves, left-handed circularly polarized waves, and right-handed circularly polarized waves, and the center operating frequency of the folded Cassegrain antenna can be adjusted, while achieving the technical effect of high gain.

[0046] Please refer to Figure 1 , Figure 1 A schematic diagram of the structure of the folded Cassegrain antenna provided in an embodiment of the present application is shown in FIG. Figure 1As shown, the folded Cassegrain antenna includes a frequency-polarization tunable metasurface, a polarization flip focusing metasurface and a linear polarization feed, wherein the polarization flip focusing metasurface is located below the frequency-polarization tunable metasurface, and the distance between the polarization flip focusing metasurface and the frequency-polarization tunable metasurface is half of the focal length of the polarization flip focusing metasurface; the polarization flip focusing metasurface is used to convert the y-polarization wave into the x-polarization wave and reflect it, and to perform 360-degree control on the wavefront phase of the reflected x-polarization wave to achieve focusing; the linear polarization feed is located at the focus of the polarization flip focusing metasurface and is used to radiate the y-polarization wave. The frequency-polarization tunable metasurface includes a plurality of periodically arranged polarization rotation units, each of which includes a flexible substrate located on an upper layer and two single open resonant rings etched on the flexible substrate with opposite opening directions, and a metal grating located on a lower layer. The periodic direction of the metal grating is along the x-axis, and the scribed lines of the metal grating are along the y-axis for total reflection of the y-polarized wave. By folding the flexible substrate, the polarization rotation unit forms a left-handed or right-handed chiral structure, thereby realizing reconfigurable switching among the x-polarized wave, the left-handed circularly polarized wave, and the right-handed circularly polarized wave, and the center operating frequency of the folded Cassegrain antenna is adjustable.

[0047] When the flexible substrate is in a planar state, the frequency-polarization tunable metasurface is used to achieve total reflection of y-polarized waves and high transmission of x-polarized waves. When the flexible substrate is in a planar state, the flexible substrate is parallel to the underlying metal grating, and the folded Cassegrain antenna can radiate x-polarized waves. The flexible substrate is folded in the positive or negative z-axis direction. When the flexible substrate is folded, the polarization rotation units form left-handed or right-handed chiral structures, thereby radiating left-handed or right-handed circularly polarized waves. By changing the folding angle of the flexible substrate, that is, when it is in a circularly polarized state, the center operating frequency of the folded Cassegrain antenna can be adjusted. By folding the flexible substrate, reconfigurable switching between x-polarized waves, left-handed circularly polarized waves, and right-handed circularly polarized waves can be achieved. The frequency-polarization tunable metasurface comprises multiple periodically arranged polarization rotation units. For example, the frequency-polarization tunable metasurface consists of m×n polarization rotation units, where m and n are the number of units along the x-axis and y-axis, respectively.

[0048] Among them, please refer to Figure 2 , Figure 2 This is a schematic diagram of the structure of the polarization rotation unit provided in the embodiment of the present application. Figure 2As shown, the polarization rotation unit consists of a two-layer structure. The upper layer includes a flexible substrate and a pair of single split resonant rings etched on the flexible substrate, while the lower layer includes a metal grating. The polarization rotation unit has periods of px and py along the x-axis and y-axis, respectively. The pair of single split resonant rings in the upper layer are identical in shape, with their openings oriented in opposite directions, along the positive and negative y-axis, respectively. The single split resonant rings are made of metal and etched onto the flexible substrate using printed circuit board (PCB) technology. The single split resonant rings on the flexible substrate can be folded along the flexible substrate. The single split resonant ring can be a metal rectangular ring with a length of lx and a width of ly, respectively. The metal arm width of the single split resonant ring is w, and the opening width is g. The metal grating has a periodic direction along the x-axis, a period of pt, and a duty cycle of 50%. The metal grating is used to achieve total reflection of y-polarized waves.

[0049] The polarization-flip focusing metasurface is located below the frequency-polarization tunable metasurface, and the distance between the two is half of the focal length of the polarization-flip focusing metasurface, which is used to ensure that the electromagnetic wave radiation radiated by the antenna is highly directional. The polarization-flip focusing metasurface can achieve a focusing function while realizing cross-polarization reflection. Specifically, cross-polarization reflection refers to converting the y-polarized wave into an x-polarized wave and reflecting it; achieving focusing refers to controlling the wavefront phase of the cross-polarized reflected wave (i.e., the reflected x-polarized wave) 360 degrees, that is, achieving 360-degree wavefront phase full coverage in the working frequency band, and the radiation phase is dispersion-free.

[0050] The linearly polarized feed is located at the center of the polarization-flipping focusing metasurface, with its top surface flush with the metasurface. The y-polarized wave radiated by the linearly polarized feed is totally reflected by the frequency-polarization tunable metasurface. The polarization direction of the y-polarized wave is then converted and reflected by the polarization-flipping focusing metasurface. The cross-polarized reflected wave is then focused through 360-degree phase control. The cross-polarized reflected wave (the reflected x-polarized wave) is selectively transmitted through the frequency-polarization tunable metasurface, enabling reconfigurable switching between x-polarized, left-hand circularly polarized, and right-hand circularly polarized waves, as well as adjustable center operating frequency of the folded Cassegrain antenna.

[0051] The linearly polarized feed source may be a linearly polarized ME pole antenna for radiating y-polarized waves. The linearly polarized ME pole antenna is excited by a standard coaxial feed line.

[0052] In some embodiments, a center line connecting the two single open resonant rings in the polarization rotation unit is parallel to the x-axis, the opening direction of the single open resonant ring is along the y-axis, and the folding axis of the flexible substrate is along the y-axis and located between the two single open resonant rings; when the flexible substrate is in a planar state, the polarization rotation unit is used for high transmission of x-polarized waves; when the flexible substrate is folded in the negative direction of the z-axis, the polarization rotation unit forms a left-handed chiral structure for converting the x-polarized wave into left-handed circularly polarized wave radiation; when the flexible substrate is folded in the positive direction of the z-axis, the polarization rotation unit forms a right-handed chiral structure for converting the x-polarized wave into right-handed circularly polarized wave radiation.

[0053] When the flexible substrate is flat, plastic bolts are used at its four corners to secure it to the metal grating, ensuring that the plane of the flexible substrate is parallel to the plane of the metal grating. A specified distance, such as 6 mm, is maintained between the two planes to enhance the reflectivity of Y-polarized waves. When the flexible substrate is folded, it can be placed directly on the metal grating.

[0054] The two single split resonant rings within the polarization rotation unit are oriented in opposite directions, along the positive and negative y-axis, respectively. When the flexible substrate is folded, the folding axis is parallel to the y-axis, and the planes of the two split resonant rings form a folding angle. If the flexible substrate is folded toward the negative z-axis, left-handed circularly polarized waves are radiated; if the flexible substrate is folded toward the positive z-axis, right-handed circularly polarized waves are radiated. If the flexible substrate is unfolded, with the plane of the flexible substrate parallel to the plane of the metal grating, x-polarized waves are radiated.

[0055] In some embodiments, when the flexible substrate is in a folded state, the center operating frequency of the folded Cassegrain antenna is adjustable by adjusting the folding angle of the plane where the two single open resonant rings are located, wherein the absolute value range of the folding angle is 104-136 degrees, and the control range of the center operating frequency is 8.4 GHz to 9.6 GHz.

[0056] Please refer to Figure 3 , Figure 3 A schematic diagram of the folded Cassegrain antenna radiating x-polarized waves provided in an embodiment of the present application is shown in FIG. Figure 3 As shown in , when the flexible substrate is in the unfolded state, the plane of the flexible substrate is parallel to the plane of the metal grating, and the folded Cassegrain antenna realizes x-polarized wave radiation. Figure 4 , Figure 4 A schematic diagram of the structure of a folded flexible substrate provided in an embodiment of the present application. Figure 5 A schematic diagram of a folded Cassegrain antenna radiating left-handed circularly polarized waves provided in an embodiment of the present application is shown in FIG. Figure 4 、 Figure 5 As shown in the figure, when the flexible substrate is folded in the negative direction of the z-axis, the folding angle is set to negative, and the folded Cassegrain antenna realizes left-handed circularly polarized wave radiation. Figure 6 , Figure 6 A schematic diagram of the structure of a folded flexible substrate provided in an embodiment of the present application. Figure 7 A schematic diagram of a folded Cassegrain antenna radiating right-handed circularly polarized waves provided in an embodiment of the present application is shown in FIG. Figure 7 As shown, when the flexible substrate is folded in the positive z-axis direction, the folding angle is set to positive, and the folded Cassegrain antenna achieves right-handed circularly polarized wave radiation. The folded Cassegrain antenna provided in the embodiments of the present application can achieve reconfigurable switching between x-polarized waves, left-handed circularly polarized waves, and right-handed circularly polarized waves, simply by adjusting the size of the folding angle and the positive and negative angle changes. It also achieves the technical effect of adjustable center operating frequency of the folded Cassegrain antenna.

[0057] In some embodiments, the distance between the polarization flip focusing metasurface and the frequency-polarization tunable metasurface is set to 77 mm; the frequency-polarization tunable metasurface is composed of 13×25 polarization rotation units, wherein 13 and 25 are the number of units of the polarization rotation unit along the x-axis and y-axis directions, respectively; Figure 2 As shown, the length px of the polarization rotation unit along the x-axis direction is 16.8 mm, and the length py along the y-axis direction is 9 mm; the thickness of the flexible substrate is 0.025 mm, and the relative dielectric constant is 3.5; the single open resonant ring is a square ring with a length lx and a width ly both of 8 mm, an opening width g of the single open resonant ring is 1.1 mm, and a metal arm width w is 1 mm.

[0058] In some embodiments, as Figure 2 As shown, the period of the metal grating is 1.52 mm and the duty cycle is 50%; the metal grating is etched on an F4B substrate with a relative dielectric constant of 2.65 and a thickness d of 2 mm.

[0059] like Figure 2 As shown, the angle between the plane where the single-port resonant ring is located and the xy plane is set to θ, and the folding angle between the planes where the two single-port resonant rings are located can be expressed as 180°-2θ. Figure 8 , Figure 8 This is the transmission spectrum of the polarization rotation unit provided in the embodiment of the present application. Figure 8 As shown, in the unfolded state, the transmission coefficient of the x-polarized wave is t xx In the 6.1-10.9GHz frequency range, the transmission rate is greater than -1dB, indicating that the polarization rotation unit can achieve high transmission of x-polarized waves. Figure 9 , Figure 9 This is the transmission spectrum of the polarization rotation unit provided in the embodiment of the present application. Figure 9 As shown, when folded into a left-handed chiral structure, that is, enantiomer A, the folding angle is set to negative, and the polarization rotation unit can realize left-handed circularly polarized wave radiation. Taking θ as -30 degrees as an example, the x-polarized wave is converted into a left-handed circularly polarized wave, and the transmission coefficient t Lx The frequency range of greater than -0.5dB is 8.3-9.25GHz. Figure 10 , Figure 10 This is the transmission spectrum of the polarization rotation unit provided in the embodiment of the present application. Figure 10 As shown, when folded to the right-handed chiral structure, that is, enantiomer B, the folding angle is set to positive, and the polarization rotation unit can realize the radiation of right-handed circularly polarized waves. Taking θ as 30 degrees as an example, the x-polarized wave is converted to the right-handed circularly polarized wave, and the transmission coefficient t Rx The frequency range of greater than -0.5dB is 8.3-9.25GHz. Figure 11 , Figure 11 The reflection spectrum of the polarization rotation unit provided in the embodiment of the present application is as follows: Figure 11 As shown in the figure, when the incident angle of the y-polarized wave is 0-60 degrees and the frequency range is 6-12 GHz, the reflection coefficient R of the polarization rotation unit is yy Above 0.9.

[0060] In some embodiments, the larger the absolute value of the folding angle is, the smaller the central operating frequency is.

[0061] When the flexible substrate is in the folded state, the center operating frequency of the folded Cassegrain antenna can be adjusted by adjusting the folding angle. Take the right-handed chiral structure enantiomer B as an example, at different folding angles, θ is 22 degrees, 30 degrees, and 38 degrees respectively. Please refer to Figure 12 , Figure 12 This is a graph showing the axial ratio-frequency characteristics of the polarization rotation unit provided in the embodiment of the present application. Figure 12 As shown, the center operating frequency in the range of axial ratio less than 3dB can be adjusted from 8.4GHz to 9.6GHz.

[0062] It can be seen from this that the polarization rotation unit provided in this application can effectively reflect y-polarized waves, and can reconfigure and switch x-polarized waves into x-polarized waves or left-hand circularly polarized waves or right-hand circularly polarized waves, and realize the regulation of the center operating frequency. The operating frequency band of the above simulation results meets the antenna design requirements.

[0063] In some embodiments, the polarization flip focusing metasurface is provided with a plurality of metasurface units arranged in a parabolic phase, and the metasurface unit includes a double-open resonant ring located on the upper layer and a metal layer located on the lower layer, wherein the lower metal layer is used to achieve total reflection, and the rotation angle and opening size of the double-open resonant ring are adjusted to achieve 360-degree control of the wavefront phase.

[0064] Among them, the polarization flip focusing metasurface is used to perform polarization deflection on the y-polarized wave excited by the linear polarization feed source, convert it into an x-polarized wave and reflect it (cross-polarization reflection). The polarization flip focusing metasurface is also used to achieve 360-degree wavefront phase control of the cross-polarized reflected wave to achieve the focusing function. The polarization flip focusing metasurface includes multiple metasurface units. Please refer to Figure 13 , Figure 13 This is a schematic diagram of the structure of the metasurface unit provided in the embodiment of the present application. Figure 13 As shown in the figure, the metasurface unit consists of a two-layer structure. The bottom layer is a metal layer for achieving total reflection, and the upper layer is a double-open resonant ring. The dielectric layer is between the upper double-open resonant ring and the bottom metal layer. By adjusting the rotation angle β and the opening size α, 360-degree wavefront phase coverage can be achieved in the operating frequency band. Arranging metasurface units with different transmission phases according to the parabolic phase can achieve a focusing function, and the output is a plane wave. By adjusting the opening size α, the interaction path of the cross-polarized reflected wave can be adjusted, thereby changing the phase of the cross-polarized reflected wave.

[0065] Specifically, in the polarization flip focusing metasurface, the number of metasurface units is 25×25, with 25 metasurface units along the x-axis and 25 along the y-axis. The period pu of the metasurface unit is 8.5 mm, and the double-open resonant ring is in the shape of a double-open circular ring with an outer radius R out is 3.75mm, the inner radius of the ring R in The double open resonant ring is also provided with a bridging metal strip passing through the center of the ring, with a metal patch on each side of the bridging metal strip. The length au of the metal patch is 3.8 mm, and the width du of the metal patch is 1.25 mm.

[0066] In some embodiments, the rotation angle of the double split resonant ring is ±45 degrees, and the size of the split resonant ring is in the range of 20-84 degrees.

[0067] In some embodiments, in the frequency range of 7.5-12 GHz, the cross-polarization reflection coefficient of the polarization-flipping focusing metasurface is greater than 0.85.

[0068] Specifically, such as Figure 13 As shown, a bridging metal strip is provided in the double-open resonant ring in the metasurface unit. The angle between the length direction of the bridging metal strip and the x-axis direction is the rotation angle β of the double-open resonant ring. The line between the double openings is perpendicular to the length direction of the bridging metal strip. Figure 14 , Figure 14 This is a wavefront phase control diagram of the metasurface unit provided in the embodiment of the present application. Figure 14As shown in the figure, the operating frequency is 8.95GHz, the rotation angle β is set to ±45 degrees, and the opening size α of the double split resonant ring changes from 20 degrees to 84 degrees, the wavefront phase change can cover 360 degrees. Please refer to Figure 15 , Figure 15 This is the reflection spectrum of the metasurface unit provided in the embodiment of the present application. Figure 15 As shown, the metasurface unit provided in the embodiment of the present application has broadband characteristics and can operate in the 7.5-12 GHz frequency band. Figure 15 As shown, the cross-polarization reflection coefficient R xy All are greater than 0.85. Figure 16 , Figure 16 This is a phase control diagram of the metasurface unit provided in the embodiment of the present application. Figure 16 As shown, the radiation phase is dispersion-free and the controllable phase can cover 360 degrees.

[0069] In some embodiments, the polarization flip focusing metasurface is provided with a plurality of metasurface units arranged in a parabolic phase, including: calculating the compensation phase required at different positions of the polarization flip focusing metasurface according to a phase compensation method; and placing a metasurface unit with a corresponding compensation phase at each position of the polarization flip focusing metasurface.

[0070] Among them, in order to achieve the focusing function, in addition to having a metasurface unit that can achieve 360-degree phase control, it is also necessary to use the phase compensation method to determine the compensation phase at different positions. First, determine the focal length 2×H of the focused polarization flip focusing metasurface, set the central operating frequency to 9GHz, and then calculate the compensation phase required at different positions of the metasurface unit according to the following phase compensation formula

[0071]

[0072] In the above formula, Indicates the compensation phase required for electromagnetic wave focusing; x mn 、y mn represents the relative position of the metasurface unit, and λ0 is the wavelength at the central operating frequency f0.

[0073] From the above formula, we can see that the compensation phase It is closely related to the central operating frequency f0. According to the phase distribution calculated by the above formula, the metasurface units with corresponding reflection phases are arranged at the corresponding positions of the polarization flip focusing metasurface. Figure 17 , Figure 17 This is the compensation phase distribution diagram of the polarization reversal focusing metasurface provided in the embodiment of the present application. Figure 17As shown in Figure 2, the polarization-flipping focusing metasurface can achieve focusing when a linear polarization wave is incident vertically. By designing a polarization-flipping focusing metasurface to compensate for path phase differences, a parabolic phase arrangement can be used to achieve plane wave focusing.

[0074] In some embodiments, please refer to Figures 18(a) and 18(b). Figure 18(a) is a schematic perspective view of a linearly polarized ME pole antenna provided in an embodiment of the present application, and Figure 18(b) is a schematic plan view of a linearly polarized ME pole antenna provided in an embodiment of the present application. As shown in Figures 18(a) and 18(b), the linearly polarized ME pole antenna includes a bottom metal layer, four metal patches on the top layer, and a rectangular metal sheet in the middle. The bottom metal layer is connected to the four metal patches on the top layer through vias; the rectangular metal sheet in the middle is connected to the center of the coaxial line through metal vias.

[0075] In order to achieve higher antenna radiation efficiency in the 8-10GHz frequency band, the parameters of the linearly polarized ME pole antenna can be set as follows: the length and width of the upper metal patch are ax = 6.2mm, ay = 6.2mm, and there are notches on the sides of each metal patch. The length and width of the notches are gx = 0.2mm and gy = 0.2mm, respectively, which can achieve better matching of S parameters. The length and width of the rectangular metal piece are la = 7.4mm, lb = 2mm, respectively. The diameter of the coaxial via is r1 = 1.6mm. The upper surface of the linearly polarized ME pole antenna is coplanar with the polarization-flipping focusing metasurface. In order to integrate the linearly polarized ME pole antenna with the polarization-flipping focusing metasurface, the dielectric layer between the double open resonant ring on the upper layer of the metasurface unit and the metal layer on the bottom layer is consistent with the dielectric layer of the linearly polarized ME pole antenna. The thickness of the dielectric layer is set to 4mm, and the dielectric layer is F4B with a relative dielectric constant of 2.65. Please refer to Figure 19 , Figure 19 The S11 parameter and gain performance curve of the linearly polarized ME pole antenna provided in the embodiment of the present application is as follows: Figure 19 As shown in the figure, S11 is less than -14dB in the 8GHz-10 GHz range, indicating that the linearly polarized ME pole antenna has high radiation efficiency; the gain is around 7dBi in the 8GHz-10 GHz frequency band. Figure 20 , Figure 20 The radiation pattern of the linearly polarized ME pole antenna is provided in the embodiment of the present application, such as Figure 20 As shown, the embodiment of the present application selects three frequency points of 8 GHz, 9 GHz and 10 GHz, and the simulation results show that all three frequency points have good radiation direction performance.

[0076] In some embodiments, CST is used to simulate the radiation performance of the folded Cassegrain antenna in the unfolded state and four folded states, that is, θ is set to 0°, ±22°, and ±30° respectively. Figure 21-23 , Figure 21-23 This is a diagram of the S11 parameters of the folded Cassegrain antenna provided in an embodiment of the present application. Figure 24 The gain spectrum of the folded Cassegrain antenna provided in the embodiment of the present application in the unfolded state is shown in FIG. Figure 25-26 This is a gain-axial ratio parameter diagram of the folded Cassegrain antenna provided in an embodiment of the present application in the folded state. Figures 27-28 This is the radiation pattern of the unfolded folded Cassegrain antenna provided in an embodiment of the present application. In the unfolded state, i.e., when θ is 0°, the frequency band in which S11 is less than -10dB is 7.62-10.34GHz, and the gain is greater than 20.2dBi, enabling x-polarized wave radiation.

[0077] Figure 29-30 The radiation pattern of the folded Cassegrain antenna provided in the embodiment of the present application in the folded state. When in the folded state, that is, when θ is -22° and -30° respectively, the frequency band with an axial ratio less than 3dB is adjusted from 9.65-9.9GHz to 8.7-9.2GHz, the gain is greater than 19.3dBi and 21.6dBi respectively, and the center operating frequencies are 9.8GHz and 8.95GHz respectively. The radiation patterns are as follows: Figure 30 and Figure 29 As shown, left-hand circularly polarized wave radiation is achieved.

[0078] Figure 31-Figure 32 The radiation pattern of the folded Cassegrain antenna in the folded state provided in the embodiment of the present application. Figure 31-Figure 32 As shown in the figure, in the folded state, when θ is 22° and 30° respectively, the frequency band with a ratio less than 3dB is adjusted from 9.65-9.9GHz to 8.7-9.2GHz, the gain is greater than 19.3dBi and 21.6dBi respectively, the central operating frequencies are 9.8GHz and 8.95GHz respectively, and the radiation patterns are as follows: Figure 32 and Figure 31 As shown, right-hand circularly polarized wave radiation is achieved.

[0079] The folded Cassegrain antenna provided in an embodiment of the present application includes a frequency-polarization tunable metasurface, a polarization flip focusing metasurface, and a linear polarization feed; the polarization flip focusing metasurface is located below the frequency-polarization tunable metasurface, and the distance between the polarization flip focusing metasurface and the frequency-polarization tunable metasurface is half the focal length of the polarization flip focusing metasurface; the linear polarization feed is located at the focus of the polarization flip focusing metasurface and is used to radiate y-polarized waves; wherein the frequency-polarization tunable metasurface includes a plurality of periodically arranged polarization rotation units, the polarization rotation unit including a flexible substrate located on an upper layer and a single open resonant ring with two openings in opposite directions etched on the flexible substrate, and a metal grating located on a lower layer, and the flexible substrate is folded so that the polarization rotation unit forms a left-handed or right-handed chiral structure, thereby realizing reconfigurable switching of x-polarized waves, left-handed circularly polarized waves, and right-handed circularly polarized waves, and the center operating frequency of the folded Cassegrain antenna is adjustable.

[0080] It should also be noted that the terms "comprises," "includes," or any other variations thereof are intended to encompass non-exclusive inclusion, such that a process, method, commodity, or apparatus comprising a series of elements includes not only those elements but also other elements not explicitly listed, or elements inherent to such process, method, commodity, or apparatus. In the absence of further limitations, an element defined by the phrase "comprising a ..." does not preclude the presence of other identical elements in the process, method, commodity, or apparatus comprising the element.

[0081] The various embodiments in this specification are described in a progressive manner, and the same or similar parts between the various embodiments can be referred to each other. Each embodiment focuses on the differences from other embodiments.

[0082] The foregoing is merely an embodiment of the present application and is not intended to limit the present application. For those skilled in the art, the present application may have various changes and variations. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of the present application should all be included within the scope of the claims of the present application.

[0083] Although the embodiments of the present application have been described with reference to the accompanying drawings, those skilled in the art may make various modifications and variations without departing from the spirit and scope of the present application, and such modifications and variations shall fall within the scope defined by the appended claims.

Claims

1. A folded Cassegrain antenna, characterized in that: The folded Cassegrain antenna includes a frequency-polarization tunable metasurface, a polarization flip focusing metasurface, and a linear polarization feed. The polarization flip focusing metasurface is located below the frequency-polarization tunable metasurface, and the distance between the polarization flip focusing metasurface and the frequency-polarization tunable metasurface is half the focal length of the polarization flip focusing metasurface. The polarization flip focusing metasurface is used to convert the y-polarized wave into the x-polarized wave and reflect it, and to perform 360-degree control on the wavefront phase of the reflected x-polarized wave to achieve focusing. The linear polarization feed is located at the focus of the polarization flip focusing metasurface and is used to radiate the y-polarized wave. The frequency-polarization tunable metasurface includes multiple periodically arranged polarization rotation units, each of which includes a flexible substrate located on the upper layer, two single open resonant rings etched on the flexible substrate with opposite opening directions, and a metal grating located on the lower layer. The periodic direction of the metal grating is along the x-axis, and the scribed lines of the metal grating are along the y-axis, which is used to fully reflect the y-polarized wave. By folding the flexible substrate, the polarization rotation unit forms a left-handed or right-handed chiral structure, thereby realizing reconfigurable switching between x-polarized waves, left-handed circularly polarized waves, and right-handed circularly polarized waves, and adjusting the central operating frequency of the folded Cassegrain antenna.

2. The folded Cassegrain antenna according to claim 1, wherein: The center line connecting the two single open resonant rings in the polarization rotation unit is parallel to the x-axis direction, the opening direction of the single open resonant ring is along the y-axis, and the folding axis of the flexible substrate is along the y-axis and located between the two single open resonant rings. When the flexible substrate is in a planar state, the polarization rotation unit is used to highly transmit the x-polarized wave. When the flexible substrate is folded in the negative direction of the z-axis, the polarization rotation unit forms a left-handed chiral structure for converting the x-polarized wave into left-handed circularly polarized wave radiation. When the flexible substrate is folded in the positive direction of the z-axis, the polarization rotation unit forms a right-handed chiral structure for converting the x-polarized wave into right-handed circularly polarized wave radiation.

3. The folded Cassegrain antenna according to claim 2, wherein: When the flexible substrate is in a folded state, the center operating frequency of the folded Cassegrain antenna is adjustable by adjusting the folding angle of the plane where the two single open resonant rings are located, wherein the absolute value range of the folding angle is 104-136 degrees, and the control range of the center operating frequency is 8.4-9.6 GHz.

4. The folded Cassegrain antenna according to claim 3, wherein: The larger the absolute value of the folding angle is, the smaller the central operating frequency is.

5. The folded Cassegrain antenna according to any one of claims 1 to 4, characterized in that: The distance between the polarization flip focusing metasurface and the frequency-polarization tunable metasurface is set to 77 mm. The frequency-polarization tunable metasurface is composed of 13×25 polarization rotation units, wherein 13 and 25 are the number of units of the polarization rotation unit along the x-axis and y-axis directions, respectively; the length of the polarization rotation unit along the x-axis direction is 16.8 mm, and the length along the y-axis direction is 9 mm; the thickness of the flexible substrate is 0.025 mm, and the relative dielectric constant is 3.5; the single open resonant ring is a metal square ring with a length and width of 8 mm. The opening width of the single open resonant ring is 1.1 mm, and the arm width is 1 mm.

6. The folded Cassegrain antenna according to claim 5, characterized in that: The period of the metal grating is 1.52 mm and the duty cycle is 50%. When the incident angle of the y-polarized wave is 0-60 degrees and the frequency range is 6-12 GHz, the reflection coefficient of the metal grating is above 0.

9.

7. The folded Cassegrain antenna according to claim 1, wherein: The polarization flip focusing metasurface is provided with a plurality of metasurface units arranged in a parabolic phase, and the metasurface units include a double-open resonant ring located on the upper layer and a metal layer located on the lower layer, wherein the metal layer on the lower layer is used to achieve total reflection, and the 360-degree control of the wavefront phase is achieved by adjusting the rotation angle and opening size of the double-open resonant ring.

8. The folded Cassegrain antenna according to claim 7, characterized in that: The rotation angle of the double-open resonant ring is set to ±45 degrees, and the opening size of the double-open resonant ring ranges from 20 to 84 degrees.

9. The folded Cassegrain antenna according to claim 7, wherein: The polarization reversal focusing metasurface is provided with a plurality of metasurface units arranged in a parabolic phase, including: Calculating the compensation phase required at different positions of the polarization flip focusing metasurface according to the phase compensation method; A metasurface unit corresponding to the compensation phase is placed at each position of the polarization flip focusing metasurface.

10. The folded Cassegrain antenna according to any one of claims 7 to 9, characterized in that: In the frequency range of 7.5-12 GHz, the cross-polarization reflection coefficient of the polarization flip focusing metasurface is greater than 0.85.

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