Flexible combined multi-functional wideband metasurface antenna for synthetic aperture radar

Abstract

The embodiment of the present disclosure discloses a flexible combined multifunctional broadband metasurface antenna for synthetic aperture radar, which comprises, from inside to outside, a core metasurface antenna located at the center and a peripheral metasurface located at the periphery, and the core metasurface antenna and the peripheral metasurface are connected through a U-shaped slot plug structure, wherein the core metasurface antenna and the peripheral metasurface can be replaced according to different application scenarios. The present disclosure has the characteristics of simple and reliable modular structure and flexible configuration according to task requirements; it meets the requirements of high-precision multiple transmission modes and corresponding amplitude-phase consistent multiple polarization reception of synthetic aperture radar, effectively increases the working bandwidth of the core antenna under low profile, reduces the radar scattering area of the antenna, optimizes the antenna radiation pattern and reduces the mutual coupling characteristics, further improves the imaging performance of the synthetic aperture radar, and reduces the signal-to-interference ratio of the synthetic aperture radar system.

Description

Technical Field

[0001] This disclosure relates to the field of synthetic aperture radar technology, and more specifically to a flexible, modular, multifunctional broadband metasurface antenna for synthetic aperture radar. Background Technology

[0002] Synthetic Aperture Radar (SAR) is evolving towards multi-polarization, high resolution, wide swath, multi-spectral, and multi-mode capabilities. The radar antenna is a crucial component of a SAR system, determining its performance. Its beam shape and scanning capability affect the SAR's range and azimuth resolution, imaging ambiguity, system sensitivity, and mapping bandwidth. With advancements in radar science and technology, the design of synthetic aperture radar antennas also faces new challenges.

[0003] Currently, waveguide slot array antennas are widely used in SAR systems due to their low cost, ease of fabrication, high precision, compact structure, high gain, and easy control of aperture distribution. Examples include the antennas of the SIR-C SAR satellite, jointly designed and manufactured by NASA and Ball Aerospace, and the antennas of the Radarsat-II SAR satellite, designed and developed by the German Aerospace Center (DLR) and Donneau. However, with the development of high-resolution wide-swath technology, SAR systems require wider operating bandwidths, significantly increasing the complexity of waveguide slot array antenna structures, manufacturing difficulty, and cost. Furthermore, the development of new concepts such as multi-band, multi-polarization, variable viewing angle and variable beamwidth, and miniaturized ultra-lightweight inflatable SAR arrays demands more compact, integrated, solid-state, and easily iteratively debuggable modular antennas. Moreover, in increasingly complex electromagnetic environments, improving the signal-to-noise ratio of SAR systems, reducing their radar cross-section, and enhancing the stealth and security of SAR imaging systems through antenna design have become increasingly important issues.

[0004] In summary, proposing a flexible, multifunctional, and easily iteratively debuggable broadband antenna based on existing SAR system antennas, while addressing the requirements of multifunctionality, compact integration, and easy iterative debugging, is a significant problem. Summary of the Invention

[0005] This disclosure provides a flexible, modular, multifunctional broadband metasurface antenna for synthetic aperture radar.

[0006] In a first aspect, this disclosure provides a flexible, modular, multifunctional broadband metasurface antenna for synthetic aperture radar, characterized in that: from the inside out, it includes: a core metasurface antenna located at the center and a peripheral metasurface located around the periphery, the core metasurface antenna and the peripheral metasurface being connected by a U-shaped slot plug-in structure, wherein the core metasurface antenna and the peripheral metasurface with different structures can be replaced according to different application scenarios.

[0007] Furthermore, the core metasurface antenna operates in the X-band and is compactly stacked from two 1mm thick dielectric substrates, a metasurface antenna layer, a microstrip feed layer, and a metal ground layer. The two dielectric substrates are respectively disposed between the metasurface antenna layer and the microstrip feed layer, and between the microstrip feed layer and the metal ground layer, with no air gaps between the different layers. The metasurface antenna layer is provided with square chamfered radiating patch units arranged in a 3×3 equally spaced rectangular grid. The microstrip feed layer is provided with two inductively coupled side-fed microstrip lines, each of which is connected to one signal input port, and the phase difference between the input signals of the two side-fed microstrip lines connected to the signal input ports is 90 degrees. The metal ground layer is disposed on the bottom side of the lower dielectric substrate.

[0008] Furthermore, the peripheral metasurface is composed of 3×3 passive type I cell arrays with the same orientation arranged in a horizontal plane, with a gap of 2.9-3.1 mm between adjacent arrays. The arrangement direction of the passive type I cell array is along the vertical or horizontal direction in the horizontal plane, and its overall layout is obtained through topology optimization, presenting a random arrangement pattern.

[0009] Furthermore, the passive Type I cell array includes a radiating metal layer, a single-layer dielectric substrate layer, and a metal ground layer arranged sequentially from top to bottom, with an overall thickness of 3.8 mm and no air gaps between different layers.

[0010] Furthermore, the radiating metal layer of the passive type I unit array is composed of type I metal strips located at the center of the metasurface unit, with a length of 6.3 mm and a width of 3.6 mm. The spacing between two adjacent type I metal strips is 5.9-7.1 mm. At the upper and lower ends of the type I metal strips, there are rectangular metal tuning branches of the same length and width, symmetrically distributed about the center of the passive type I unit array unit. The spacing between two adjacent type I metal strip tuning branches is 0.4-0.6 mm. The single-layer dielectric substrate is a homogeneous dielectric plate without metallized vias and has a relative permittivity of 2-4.5. The metal ground layer is a homogeneous metal plate without etched gaps.

[0011] Furthermore, the peripheral metasurface is formed by digitally controlled PIN diode metasurface units arranged cyclically in a horizontal plane. The gap between adjacent PIN diode metasurface units is 2.0-2.2 mm. The arrangement direction of the PIN diode metasurface units is along the vertical direction in the horizontal plane. The number of rows and columns is the same. The overall layout is a square with a width of 280 mm.

[0012] Furthermore, the digitally controlled PIN diode metasurface unit includes, from top to bottom, a top radiating metal layer, a single-layer dielectric substrate layer, a bottom metal ground layer, and two metallized vias, with an overall thickness of only 3.8 mm and no air gaps between different layers.

[0013] Furthermore, the top radiating metal layer of the digitally controlled PIN diode metasurface unit is composed of two radiators symmetrically distributed at the center, with open circuits at the ends. Simultaneously, an RF PIN diode is used at the center of the PIN diode metasurface unit to connect the two symmetrical radiators. The single-layer substrate is a homogeneous dielectric plate with two metallized vias connecting the L-shaped metal strip to the bottom metal ground. The metallized vias are symmetrical about the RF switch, and the voltage controls the on / off state of the RF switch through the metallized vias. The relative permittivity is 2-4.5. The bottom metal ground layer is a homogeneous metal plate with metal gaps etched along the RF switch placement direction at the center of the unit. These metal gaps divide the bottom metal ground layer into two parts, ensuring good on / off switching of the RF switch when a DC bias voltage is applied.

[0014] Furthermore, each radiator of the top radiating metal layer is composed of two L-shaped metal strips connected together. The first type of L-shaped metal strip is rotate symmetrically connected about the RF switch, with a top width of 1.9-2.2 mm and a longitudinal length of 3.6-4.4 mm. The second type of L-shaped metal strip has an open end and the other end is connected to the end of the first type of L-shaped metal strip. It is rotate symmetrically distributed about the RF switch, with a top width of 2.6-3.0 mm and a longitudinal length of 5.0-5.6 mm. The longitudinal gap between the two types of metal strips is 0.26-0.27 mm, and the transverse gap is 0.25-0.75 mm.

[0015] Furthermore, the range of the metal gap etched in the bottom metal layer is 0.16-0.18 mm, and the metal layers on both sides of the metal gap also serve as electrodes connected to the positive and negative terminals of the external driving power supply, respectively.

[0016] Furthermore, the U-shaped slot insertion structure includes a U-shaped protrusion located at the center of the cross-section of the core metasurface antenna and a U-shaped groove on the outer metasurface at the center of the cross-section. The U-shaped protrusion and the U-shaped groove have the same thickness, which is 1 / 3 of the overall thickness of 1.3 mm. The length of the U-shaped protrusion is 6 mm and the depth of the U-shaped groove is 5.8 mm to achieve an interference fit.

[0017] The technical solutions provided in this disclosure may have the following beneficial effects:

[0018] This disclosure presents a flexible, modular, multi-functional broadband metasurface antenna for synthetic aperture radar (SAR) and its corresponding physical configuration. At 9.6 GHz, its overall low profile is only 0.06λ0. The flexibly configurable core metasurface antenna and peripheral metasurface of this invention can provide a variety of functions. For example, when configured with a passive, topology-optimized, sequentially coded I-shaped peripheral metasurface, the overall radar cross-section of the antenna is significantly reduced by 90% within the operating bandwidth of the core antenna without introducing external energy, thus improving the stealth and security of the SAR imaging system. When configured with a digitally controlled PIN diode peripheral metasurface, the operating bandwidth of the core antenna is extended to 28.9% (8.35 GHz - 11.7 GHz), the polarization axial ratio is optimized to 19.5% (8.35 GHz - 10.16 GHz), and the normal gain is increased to over 9.56 dBi. This disclosed embodiment firstly optimizes and innovates the antenna structure in the synthetic aperture radar (SAR) transmit / receive modes, featuring a simple, reliable, modular structure that can be flexibly configured according to mission requirements. Secondly, it meets the requirements of SAR for high-precision multiple transmission modes and corresponding amplitude-phase consistent multi-polarization reception. At a low profile, it effectively increases the operating bandwidth of the core antenna, optimizes the antenna radiation pattern, and reduces mutual coupling characteristics, further improving the imaging performance of the SAR and reducing the signal-to-interference ratio (SIR) of the SAR system. Alternatively, by reducing the overall radar cross-section of the antenna, it greatly improves the stealth and security of the imaging system, providing a foundation for further miniaturization and stealth SAR radar. It achieves various performance targets and has good practical application value.

[0019] It should be understood that the above general description and the following detailed description are exemplary and explanatory only, and are not intended to limit this disclosure. Attached Figure Description

[0020] Other features, objects, and advantages of this disclosure will become more apparent from the following detailed description of non-limiting embodiments, taken in conjunction with the accompanying drawings. In the drawings:

[0021] Figure 1A schematic diagram of the overall structure of a flexible modular multifunctional broadband metasurface antenna for synthetic aperture radar and its corresponding physical configuration structure according to an embodiment of the present disclosure is shown.

[0022] Figure 2 A schematic diagram of the reflection phase change curve of a passive type I metasurface unit according to an embodiment of the present disclosure is shown.

[0023] Figure 3 A schematic diagram of the radar cross-section variation curve of a combined antenna with a passive, topology-optimized, sequenced I-shaped coded peripheral metasurface configured according to an embodiment of the present disclosure is shown.

[0024] Figure 4 A schematic diagram of the reflection phase change curve of a PIN diode metasurface unit according to an embodiment of the present disclosure is shown.

[0025] Figures 5A-5B A schematic diagram of the S-parameters versus frequency and a directional diagram of a combined antenna with a digitally controlled PIN diode peripheral metasurface according to an embodiment of the present disclosure are shown. Detailed Implementation

[0026] In the following, exemplary embodiments of the present disclosure will be described in detail with reference to the accompanying drawings to enable those skilled in the art to readily implement them. Furthermore, for clarity, portions unrelated to the description of the exemplary embodiments have been omitted from the drawings.

[0027] In this disclosure, it should be understood that terms such as “comprising” or “having” are intended to indicate the presence of features, figures, steps, behaviors, components, parts or combinations thereof disclosed in this specification, and do not preclude the possibility of the presence or addition of one or more other features, figures, steps, behaviors, components, parts or combinations thereof.

[0028] It should also be noted that, unless otherwise specified, the embodiments and features described in this disclosure can be combined with each other. This disclosure will now be described in detail with reference to the accompanying drawings and embodiments.

[0029] Based on the background technology, this invention addresses the needs of synthetic aperture radar (SAR) antennas for multifunctionality, compact integration, and easy iterative debugging. It proposes a flexible, modular, multifunctional broadband metasurface antenna for SAR. This antenna, from the inside out, comprises a core metasurface antenna at the center and peripheral metasurfaces at the periphery. The core and peripheral metasurfaces are connected via a U-shaped slot plug-in structure. It has a low profile, is easy to manufacture, has a compact structure, and is flexible and adjustable. It features a wide operating bandwidth, excellent antenna pattern, multiple polarization modes, low mutual coupling characteristics, and a low radar cross-section, making it better suited for various SAR scenarios.

[0030] To achieve the above objectives, the technical solution of this invention is as follows: a flexible, modular, multifunctional broadband metasurface antenna for synthetic aperture radar (SAR). To meet the requirements of small antenna size and low profile thickness in SAR systems, the overall thickness of this antenna is approximately 3.8 mm. It consists of a high-performance broadband core metasurface antenna compactly connected via a U-slot plug-in structure and a flexibly configurable peripheral metasurface providing various additional functions. The core metasurface antenna and the peripheral metasurface can be replaced with different structures according to different application scenarios.

[0031] Figure 1 A schematic diagram of the overall structure of a flexible, modular, multifunctional broadband metasurface antenna for synthetic aperture radar according to an embodiment of this disclosure is shown. Figure 1 As shown, this broadband metasurface antenna is used for detection by synthetic aperture radar. The core metasurface microstrip patch antenna operates in the X-band and is composed of three metal layers (metasurface antenna layer, microstrip feed layer, and metal ground layer) and two Rogers dielectric substrates with a thickness of 1 mm stacked between them, with no air gaps between the different layers.

[0032] In some embodiments, the core metasurface antenna 1 operates in the X-band and is compactly stacked from two Rogers dielectric substrates with a thickness of 1 mm, a metasurface antenna layer, a microstrip feed layer, and a metal ground layer. One of the two Rogers dielectric substrates is disposed between the metasurface antenna layer and the microstrip feed layer, and between the microstrip feed layer and the metal ground layer, with no air gap between the different layers. The metasurface antenna layer is provided with square chamfered radiating patch units arranged in a 3×3 equally spaced rectangular grid. Two side-fed microstrip lines 2 with inductive coupling excitation are disposed on the microstrip feed layer, each microstrip line being connected to a signal input port with a phase difference of 90 degrees between the input signals. The metal ground layer is disposed on the bottom side of the lower Rogers dielectric substrate.

[0033] In some embodiments, the peripheral metasurface 3 can be formed by 3×3 passive I-type unit arrays with the same orientation arranged in a horizontal plane, with a gap of 2.9-3.1 mm between adjacent arrays. The arrangement direction of the I-type unit array is along the vertical or horizontal direction in the horizontal plane, and its overall layout is obtained through topology optimization, presenting a certain random arrangement pattern macroscopically.

[0034] In some embodiments, the passive Type I metasurface unit includes a radiating metal layer 6, a single-layer Rogers dielectric substrate layer 7, and a metal ground layer 8 arranged sequentially from top to bottom, with an overall thickness of only 3.8 mm and no air gaps between different layers.

[0035] In some embodiments, the radiating metal layer of the passive Type I metasurface unit is composed of Type I metal strips located at the center of the metasurface unit, with a length of 6.3 mm and a width of 3.6 mm. The spacing between two adjacent Type I metal strips is 5.9-7.1 mm. At the upper and lower ends of the Type I metal strips, there are rectangular metal tuning branches of the same length and width, symmetrically distributed about the center of the unit. The spacing between two adjacent Type I metal strip tuning branches is 0.4-0.6 mm. The single-layer Rogers substrate layer is a homogeneous dielectric plate without metallized vias and has a relative permittivity of 2-4.5. The metal ground layer is a homogeneous metal plate without etched gaps.

[0036] In some embodiments, the U-shaped slot plug-in structure can quickly install and replace different core metasurface antennas and peripheral metasurfaces according to the needs of different application scenarios, such as a phase-shifting switch PIN diode metasurface digitally controlled by a programmable gate array (FPGA), thus realizing the modularity and multi-functionality requirements of the synthetic aperture radar antenna system.

[0037] The outer metasurface 3 can also be formed by digitally controlled PIN diode metasurface units arranged cyclically in the horizontal plane. The gap between adjacent units is 2.0-2.2mm. The arrangement direction of the PIN diode metasurface units is along the vertical direction in the horizontal plane. The number of rows and columns is the same. The overall layout is a square with a width of 280mm.

[0038] The digitally controlled PIN diode metasurface unit consists of, from top to bottom, a top radiating metal layer 9, a single-layer Rogers dielectric substrate layer 10, a bottom metal ground layer 11, and two metallized vias 12 and 13. The overall thickness is only 3.8 mm, and there are no air gaps between different layers.

[0039] The top radiating metal layer of the digitally controlled PIN diode metasurface unit consists of two radiators symmetrically distributed at the center, with open ends. An RF PIN diode 14 connects the two symmetrical radiators at the center of the unit. The single-layer Rogers substrate is a homogeneous dielectric plate with two metallized vias that electrically connect the L-shaped metal strip to the bottom metal ground. The metallized vias are symmetrical about the RF switch, and the voltage controls the on / off state of the RF switch through the metallized vias. The relative permittivity is 2-4.5. The bottom metal ground layer is a homogeneous metal plate. A metal gap 17 is etched at the center of the unit along the direction of the RF switch placement. This metal gap divides the bottom metal ground into two parts, ensuring good on / off switching of the RF switch when a DC bias voltage is applied.

[0040] Each radiator in the top radiating metal layer is composed of two L-shaped metal strips connected together. The first type of L-shaped metal strip 15 is rotate symmetrically connected about the RF switch, with a top width of 1.9-2.2 mm and a longitudinal length of 3.6-4.4 mm. The second type of L-shaped metal strip 16 is open at one end and connected to the end of the first type of L-shaped metal strip at the other end. It is rotate symmetrically distributed about the RF switch, with a top width of 2.6-3.0 mm and a longitudinal length of 5.0-5.6 mm. The longitudinal gap between the two types of metal strips is 0.26-0.27 mm, and the transverse gap is 0.25-0.75 mm.

[0041] The range of the metal gaps etched in the bottom metal layer is 0.16-0.18mm. At the same time, the metal ground on both sides of the gap also serves as electrodes, which are connected to the positive and negative terminals of the external driving power supply, respectively.

[0042] The two U-shaped slot plug-in structures 4 and 5 include a U-shaped protrusion at the center of the cross-section of the core metasurface antenna and a U-shaped groove on the outer metasurface at the center of the cross-section. They have the same thickness, which is 1 / 3 of the overall thickness of 1.3 mm. The length of the protrusion is 6 mm and the depth of the U-shaped groove is 5.8 mm to achieve an interference fit.

[0043] In some embodiments, to improve impedance matching characteristics and enhance antenna performance to meet the needs of synthetic aperture radar systems, the spacing of the 3×3 equally spaced rectangular unit grids and the shape and size of the square radiating patches on the metasurface antenna layer are analyzed and improved using characteristic mode theory. Notably, a portion of each small square radiating patch is cut off at its four corners, which effectively suppresses higher-order modes that degrade according to characteristic mode theory.

[0044] In some embodiments, based on the characteristic that the current direction is along the edge of the radiating element patch in the characteristic mode theory, the present invention employs a side-fed inductive coupling excitation method in the microstrip feed layer. This feed structure can effectively excite the two main characteristic modes that play a supporting role in the characteristic mode theory, and achieves a wide operating bandwidth, wide beam and high gain characteristics while maintaining good dual circular polarization characteristics, thus meeting the requirements of synthetic aperture radar imaging.

[0045] This disclosure presents a flexible, modular, multi-functional broadband metasurface antenna for synthetic aperture radar (SAR) and its corresponding physical configuration. At 9.6 GHz, its overall low profile is only 0.06λ0. The flexibly configurable core metasurface antenna and peripheral metasurface of this invention can provide a variety of functions. For example, when configured with a passive, topology-optimized, sequentially coded I-shaped peripheral metasurface, the overall radar cross-section of the antenna is significantly reduced by 90% within the operating bandwidth of the core antenna without introducing external energy, thus improving the stealth and security of the SAR imaging system. When configured with a digitally controlled PIN diode peripheral metasurface, the operating bandwidth of the core antenna is extended to 28.9% (8.35 GHz - 11.7 GHz), the polarization axial ratio is optimized to 19.5% (8.35 GHz - 10.16 GHz), and the normal gain is increased to over 9.56 dBi. This disclosed embodiment firstly optimizes and innovates the antenna structure in the synthetic aperture radar (SAR) transmit / receive modes, featuring a simple, reliable, modular structure that can be flexibly configured according to mission requirements. Secondly, it meets the requirements of SAR for high-precision multiple transmission modes and corresponding amplitude-phase consistent multi-polarization reception. At a low profile, it effectively increases the operating bandwidth of the core antenna, optimizes the antenna radiation pattern, and reduces mutual coupling characteristics, further improving the imaging performance of the SAR and reducing the signal-to-interference ratio (SIR) of the SAR system. Alternatively, by reducing the overall radar cross-section of the antenna, it greatly improves the stealth and security of the imaging system, providing a foundation for further miniaturization and stealth SAR radar. It achieves various performance targets and has good practical application value.

[0046] In some embodiments, the present invention configures a passive, topology-optimized, sequenced I-shaped encoded peripheral metasurface. Experiments have shown that... Figure 1 The electromagnetic waves reflected by horizontally arranged I-shaped coded metasurface units differ by 180° from those reflected by vertically arranged I-shaped coded metasurface units. This result is shown in... Figure 2 Next, a 3×3 submatrix topological stochastic optimization algorithm was used to obtain a 15×27 I-shaped coded metasurface element array sequence capable of uniformly scattering incident electromagnetic waves to directions deviating from the main lobe. Without introducing additional energy or affecting the performance of the core metasurface antenna, the radar cross-section of the antenna in this embodiment was reduced by 9.2 dB within its operating frequency band. Figure 3 As shown, this effectively improves the electromagnetic stealth characteristics and security of synthetic aperture radar imaging systems.

[0047] In some embodiments, the present invention is configured as follows Figure 1 The diagram shows a 30×30 digitally controlled metasurface for PIN diodes. Controlled by a pre-set programmable gate array, the PIN diodes are sequentially turned on or off. The reflection phase of each individual PIN diode metasurface unit differs by 180° within the 7.2GHz-10.6GHz range. Figure 4 As shown in Figure 5, based on the principle of the Electromagnetic Band Gap Surface (EBG Surface), the core metasurface antenna and the surrounding PIN diodes in this embodiment form a three-dimensional electromagnetic periodic structure. Its specific arrangement can prevent / assist the propagation of electromagnetic waves at all angles of arrival and in all polarization states within a specified frequency band. Therefore, the radiation characteristics of the antenna in this embodiment can be adjusted and optimized in real time, as shown in Figure 5. In this embodiment, the overall normal 3dB circular polarization axial ratio bandwidth of the antenna is extended to 28.9% (8.35GHz-11.7GHz), the polarization axial ratio is increased to 19.5% (8.35-10.16GHz), the normal gain is increased to greater than 9.56dBi, the radiation pattern is optimized, and the mutual coupling characteristics are reduced, which further improves the imaging performance and signal-to-noise ratio of the synthetic aperture radar.

[0048] In some embodiments, the present invention is configured as follows Figure 1 The U-shaped slot insertion structure shown includes a U-shaped protrusion at the center of the cross-section of the core metasurface antenna and a U-shaped groove on the outer metasurface at the center of the cross-section. Both have the same thickness, 1.3 mm (1 / 3 of the overall thickness). The protrusion is 6 mm long, and the groove is 5.8 mm deep. Experiments have shown that this dimensional configuration effectively achieves an interference fit, ensuring reliable assembly of the core metasurface antenna and the outer metasurface, and meeting the modular requirements of the synthetic aperture radar system antenna without increasing the overall thickness.

[0049] In some embodiments, Figure 1 The dimensional parameters of the metasurface antenna are shown in Table 1 below:

[0050] Table 1

[0051] parameter n <![CDATA[m1]]> <![CDATA[m2]]> p W k j value 3.6 6.3 5.1 24 240 1.3 3.8 parameter <![CDATA[W1]]> <![CDATA[W2]]> a <![CDATA[l1]]> <![CDATA[l2]]> h U value 2.80 2.10 7.04 5.30 4.00 3.80 280

[0052] In Table 1, the outer length m1 and inner length m2 of the passive Type I metal strip are 6.3 mm and 5.1 mm, respectively, and its width n is 3.6 mm. The width p of the 3×3 passive Type I element array with the same orientation is 24 mm. W = 240 mm represents the width of the passive Type I element array. The thickness j of the core metasurface antenna and the thickness j of the U-shaped protrusion at the center of the cross-section are 3.8 mm and 1.3 mm, respectively. The width U of the digitally controlled PIN diode metasurface array is 280 mm, and the overall thickness is only h = 3.8 mm. The width a of the metasurface unit of the digitally controlled PIN diode is 7.04 mm. The top width of the first type of L-shaped metal strip is W1 = 2.80 mm and the longitudinal length l1 is 5.30 mm. The top width of the second type of L-shaped metal strip is W2 = 2.10 mm and the longitudinal length l2 is 4.00 mm. The longitudinal gap between the two types of metal strips is 0.26-0.27 mm and the transverse gap is 0.25-0.75 mm.

[0053] The above description is merely a preferred embodiment of this disclosure and an explanation of the technical principles employed. Those skilled in the art should understand that the scope of the invention involved in this disclosure is not limited to technical solutions formed by specific combinations of the above-described technical features, but should also cover other technical solutions formed by arbitrary combinations of the above-described technical features or their equivalents without departing from the inventive concept. For example, technical solutions formed by substituting the above-described features with (but not limited to) technical features disclosed in this disclosure that have similar functions.

Claims

1. A flexible, modular, multi-functional broadband metasurface antenna for synthetic aperture radar, characterized in that: From the inside out, it includes: The core metasurface antenna is located at the center and the peripheral metasurface is located around the perimeter. The core metasurface antenna and the peripheral metasurface are connected by a U-shaped slot plug-in structure. The core metasurface antenna and the peripheral metasurface can be replaced with different structures according to different application scenarios. The core metasurface antenna operates in the X-band and is compactly stacked from two 1mm thick dielectric substrates, a metasurface antenna layer, a microstrip feed layer, and a metal ground layer. The two dielectric substrates are positioned between the metasurface antenna layer and the microstrip feed layer, and between the microstrip feed layer and the metal ground layer, with no air gaps between the layers. The metasurface antenna layer has square, chamfered-corner radiating patch elements arranged in a 3×3 equally spaced rectangular grid. The microstrip feed layer has two inductively coupled side-fed microstrip lines, each connected to a signal input port, with a 90-degree phase difference between the input signals at the two connected ports. The metal ground layer is located on the bottom side of the lower dielectric substrate. The outer metasurface is composed of 3×3 passive type I cell arrays with the same orientation arranged in a horizontal plane, with a gap of 2.9-3.1 mm between adjacent arrays. The arrangement direction of the passive type I cell array is along the vertical or horizontal direction in the horizontal plane, and its overall layout is obtained through topology optimization, presenting a random arrangement pattern.

2. The flexible, modular, multi-functional broadband metasurface antenna for synthetic aperture radar as described in claim 1, characterized in that: The passive Type I unit array includes a radiating metal layer, a single-layer dielectric substrate layer and a metal ground layer arranged sequentially from top to bottom, with an overall thickness of 3.8 mm and no air gaps between different layers.

3. The flexible, modular, multifunctional broadband metasurface antenna for synthetic aperture radar as described in claim 2, characterized in that: The radiating metal layer of the passive type I unit array consists of type I metal strips located at the center of the metasurface unit, with a length of 6.3 mm and a width of 3.6 mm. The spacing between two adjacent type I metal strips is 5.9-7.1 mm. At the upper and lower ends of the type I metal strips, there are rectangular metal tuning branches of the same length and width, symmetrically distributed about the center of the passive type I unit array unit. The spacing between two adjacent type I metal strip tuning branches is 0.4-0.6 mm. The single-layer dielectric substrate is a homogeneous dielectric plate without metallized vias and has a relative permittivity of 2-4.

5. The metal ground layer is a homogeneous metal plate without etched gaps.

4. The flexible, modular, multi-functional broadband metasurface antenna for synthetic aperture radar as described in claim 1, characterized in that: The peripheral metasurface is formed by digitally controlled PIN diode metasurface units arranged cyclically in a horizontal plane. The gap between adjacent PIN diode metasurface units is 2.0-2.2 mm. The arrangement direction of the PIN diode metasurface units is vertical in the horizontal plane. The number of rows and columns is the same. The overall layout is a square with a width of 280 mm.

5. The flexible, modular, multifunctional broadband metasurface antenna for synthetic aperture radar as described in claim 4, characterized in that: The digitally controlled PIN diode metasurface unit includes, from top to bottom, a top radiating metal layer, a single-layer dielectric substrate layer, a bottom metal ground layer, and two metallized vias, with an overall thickness of only 3.8 mm and no air gaps between different layers.

6. The flexible, modular, multifunctional broadband metasurface antenna for synthetic aperture radar as described in claim 5, characterized in that: The top radiating metal layer of the digitally controlled PIN diode metasurface unit consists of two radiators symmetrically distributed at the center, with open circuits at the ends. An RF PIN diode connects the two symmetrical radiators at the center of the PIN diode metasurface unit. The single-layer dielectric substrate is a homogeneous dielectric plate with two metallized vias connecting an L-shaped metal strip to the bottom metal ground. The metallized vias are symmetrical about the RF switch, and the voltage controls the on / off state of the RF switch through the metallized vias. The relative permittivity is 2-4.

5. The bottom metal ground layer is a homogeneous metal plate with metal gaps etched along the RF switch placement direction at the center of the unit. These metal gaps divide the bottom metal ground layer into two parts, ensuring good on / off switching of the RF switch when a DC bias voltage is applied.

7. A flexible, modular, multi-functional broadband metasurface antenna for synthetic aperture radar as described in claim 6, characterized in that: Each radiator of the top-layer radiating metal layer is composed of two L-shaped metal strips connected together. The first type of L-shaped metal strip is rotate symmetrically connected about the RF switch, with a top width of 1.9-2.2 mm and a longitudinal length of 3.6-4.4 mm. The second type of L-shaped metal strip has an open end and the other end is connected to the end of the first type of L-shaped metal strip. It is rotate symmetrically distributed about the RF switch, with a top width of 2.6-3.0 mm and a longitudinal length of 5.0-5.6 mm. The longitudinal gap between the two types of metal strips is 0.26-0.27 mm, and the transverse gap is 0.25-0.75 mm.

8. A flexible, modular, multi-functional broadband metasurface antenna for synthetic aperture radar as described in claim 6 or 7, characterized in that: The range of the metal gap etched in the bottom metal layer is 0.16-0.18 mm. At the same time, the metal layers on both sides of the metal gap also serve as electrodes connected to the positive and negative terminals of the external driving power supply, respectively.

9. A flexible, modular, multifunctional broadband metasurface antenna for synthetic aperture radar as described in claim 1, characterized in that: The U-shaped slot plug-in structure includes a U-shaped protrusion at the center of the cross-section of the core metasurface antenna and a U-shaped groove on the outer metasurface at the center of the cross-section. The U-shaped protrusion and the U-shaped groove have the same thickness, which is 1 / 3 of the overall thickness, 1.3 mm. The length of the U-shaped protrusion is 6 mm and the depth of the U-shaped groove is 5.8 mm to achieve an interference fit.

Images