Low-profile-based fully-polarized wide-angular-domain near-far-field wave beam two-dimensional adjustable holographic metasurface and regulation and control method

Abstract

The invention provides a low-profile-based fully-polarized wide-angular-domain near-far field wave beam two-dimensional adjustable holographic metasurface and a regulation and control method, the metasurface comprises a top metal plate, the top metal plate is provided with a T-shaped coupling structure array, the T-shaped coupling structure array comprises a plurality of novel coupling units, and the novel coupling units are arranged on the top metal plate. And radio frequency switches are arranged in the vertical direction and the horizontal direction of each novel coupling unit and are used for controlling coupling radiation. The FPGA control circuit and the direct feed network are arranged on the lower layer of the second dielectric substrate, and the direct feed network applies different direct current bias voltages to the center of each novel coupling unit so as to control the on or off of the radio frequency switch. The invention has the advantages of simple structure and low cost, can easily realize the multi-polarization wave beam at any direction of a far / near field, realizes the scanning of the wave beam at a pitch angle and an azimuth angle, and can achieve the scanning of a far-field pen-shaped wave beam at a large angle of + / -70 degrees and the scanning of a near-field Bessel wave beam at a large angle of + / -60 degrees.

Description

Technical Field

[0001] The present invention belongs to the technical field of holographic metasurface antennas, and in particular relates to a two-dimensional adjustable holographic metasurface based on low-profile, fully polarized, wide-angle, near- and far-field beams, and a control method. Background Art

[0002] The holographic principle in the microwave field comes from the principle of optical imaging. When the object light and the reference light meet on a holographic recording medium (such as a holographic plate or photosensitive film), an interference pattern is formed. This interference pattern records the phase and amplitude information of the object. The pattern formed by interference is saved on the recording medium. When the hologram is illuminated with reference light, the reference beam is redirected and diffracted through the hologram. This process causes the light waves to re-form the original object.

[0003] In order to promote the holographic technology in the microwave field, scientists have been trying to use the surface impedance of the printed circuit board structure to record the target wave information in the early 21st century. When the reference wave irradiates the impedance surface, it will invert the pre-designed target wave. Therefore, the holographic antenna can easily realize the target beam with different deflection angles, but because the surface impedance is not reconfigurable, it does not have scanning capabilities.

[0004] O. Yurduseven et al. proposed a reconfigurable holographic metasurface antenna based on a slot two-dimensional array leaky wave structure in the literature, which realized two-dimensional beam scanning (O. Yruduseven and DR Smith, "Dual-Polarization Printed Holographic Multibeam Metasurface Antenna" in IEEE Antennas and Wireless Propagation Letters, vol. 16, pp. 2738-2741, 2017). However, no corresponding feeding structure was given, making it difficult to directly apply it to actual scenarios.

[0005] Application number CN202311528193.3, invention name Antenna unit with complementary open resonant rings, antenna and beam scanning method, discloses an antenna unit with complementary open resonant rings, antenna and beam scanning method, including a copper metal floor, a substrate integrated waveguide dielectric substrate, a microstrip line etched with a CSRR structure and a liquid crystal layer arranged in sequence from bottom to top; the substrate integrated waveguide dielectric substrate is used as a transmission structure; the substrate integrated waveguide dielectric substrate is formed by directly adding two rows of metal columns in the middle of the dielectric substrate in the microstrip line transmission structure; the middle part of the microline etched with a CSRR structure, the CSRR structure is composed of two metal slot rings with opposite openings and different sizes. The antenna composed of the antenna unit can realize the low profile, small volume, high gain, and wide-angle beam scanning function of the antenna in the Ka band; and can also realize multi-beam scanning.

[0006] The antenna unit, antenna and beam scanning method with complementary open resonant rings are one-dimensional liquid crystal reconfigurable antennas based on holographic theory, with microstrip lines and liquid crystal layers etched with CSRR structures; substrate-integrated waveguide dielectric substrates are used as transmission structures; substrate-integrated waveguide dielectric substrates are formed by directly adding two rows of metal columns in the middle of the dielectric substrate in the microstrip line transmission structure to form +30° and 0°, -10° and +10°, -30° and +30°, -30° and +50° beam pointing patterns. The problems are: high cost and complex system, large volume and weight; and planar reflective array and transmission array antennas require additional spatial illumination sources, and the system profile is high, which increases the difficulty of system integration. Summary of the invention

[0007] The purpose of the present invention is to solve the defects of the above-mentioned prior art and to provide a two-dimensional adjustable holographic metasurface and a control method based on a low-profile, fully polarized, wide-angle, far- and near-field beams. The antenna is based on binary holographic theory and can realize all-round two-dimensional, fully polarized, wide-angle, far / near-field beam scanning, and has a simple structure and low cost.

[0008] The present invention adopts the following technical solution:

[0009] A two-dimensional adjustable holographic metasurface based on low-profile, fully polarized, wide-angle, near- and far-field beams includes a metal plate, a dielectric substrate, a radio frequency feeding structure, and a direct current feeding network. The first metal plate is located on the upper surface of the first dielectric substrate, the second metal plate is located on the lower surface of the first dielectric substrate, the second dielectric substrate is located on the lower surface of the second metal plate, the direct current feeding network is located on the lower surface of the second dielectric substrate, the radio frequency feeding structure is an SMA connector, the metal shell of the SMA connector passes through the second dielectric substrate and the second metal plate, and is connected to the second metal plate, and the inner core probe of the SMA connector passes through the second dielectric substrate, the second metal plate, the first dielectric substrate, and the first metal plate.

[0010] The T-shaped coupling structure array is etched on the first metal plate for leaky wave radiation, and the T-shaped coupling structure array includes a plurality of novel coupling units that are symmetrical all around. An annular gap with the inner core probe of the SMA connector as the origin is etched on the first metal plate, and the novel coupling units are distributed around the annular gap.

[0011] Furthermore, the novel coupling unit is loaded with a radio frequency switch in the vertical direction and the horizontal direction respectively.

[0012] Furthermore, an outer portion of the first metal plate is grounded.

[0013] Furthermore, the length of the novel coupling unit is less than or equal to half the guided wavelength, the width is less than or equal to one sixth of the guided wavelength, and the spacing between two adjacent novel coupling units along the long side is less than or equal to 0.6 times the guided wavelength.

[0014] Furthermore, the novel coupling unit also includes a metal via, which penetrates the first dielectric substrate, the second metal plate and the second dielectric substrate, one end of which is connected to the central part of the first metal plate, and the other end is connected to the FPGA control circuit and the DC feed network. The RF switch is connected to the outer contour and the inner contour of the novel coupling unit respectively. The T-shaped coupling structure array includes a 21*21 novel coupling unit, the outer contour of the novel coupling unit is the negative pole, and the inner contour is the positive pole.

[0015] Furthermore, the FPGA control circuit and the DC feeding network can apply different DC bias voltages to the positive electrode of each RF switch to control the on or off of the RF switch.

[0016] Furthermore, the difference between the inner diameter of the annular gap and the diameter of the inner core probe is 0.1 mm-0.4 mm, preferably 0.2 mm.

[0017] Furthermore, the radio frequency switch is a PIN diode.

[0018] Furthermore, the thickness of the first dielectric substrate and the second dielectric substrate are both less than a quarter of the waveguide wavelength, and the width is approximately ten times the waveguide wavelength.

[0019] The control method based on a two-dimensional adjustable holographic metasurface with low-profile, fully polarized, wide-angle, near- and far-field beams includes the following steps:

[0020] Step 1. Write the plane wave function expression Ψ of the target wave in free space according to the beam azimuth and elevation angles and polarization type of the desired far / near field target wave obj The cylindrical magnetic field generated by the SMA in the parallel plate waveguide is used as the reference wave Ψ ref ,From the interference theory, it can be concluded that the interference information is the superposition state of phase and amplitude obtained by the target beam and the reference beam interfering on the metasurface aperture;

[0021] Step 2. The reference wave is fed by the embedded central SMA, which causes the center of the obtained beam to be concave. To avoid this, a 180° phase difference is introduced between the upper and lower half planes of the interference field.

[0022] Step 3. Set a certain threshold s and use the threshold to determine the normalized interference field Ψ inf Distribute the elements in the matrix to obtain two binary matrices in the vertical / horizontal direction;

[0023] Step 4. In order to simplify the antenna feeding structure, the RF switches in the vertical and horizontal directions are designed to be regulated simultaneously. By performing logical judgment on the common parts of the vertical binary matrix and the horizontal binary matrix, the common parts are eliminated from the first two matrices, and the multi-polarization function is realized by retaining the common parts.

[0024] Step 5. If the target wave beam direction (elevation angle or azimuth angle) changes, repeat steps 1 to 4 above.

[0025] Furthermore, step 3 also includes further binarization of the two-dimensional matrix, and the binarization threshold s is 0.5-0.9.

[0026] Beneficial effects of the present invention:

[0027] The low-profile, fully polarized, wide-angle, near- and far-field beam-based two-dimensional adjustable holographic metasurface provided by the present invention has the advantages of simple structure, lower profile and low cost compared to existing planar phased array antennas.

[0028] The novel coupling unit structure of the present invention is based on the binary radiation holographic theory, and can easily realize arbitrarily directed fully polarized wide-angle far / near field beams, as well as beam scanning in elevation and azimuth angles.

[0029] The present invention is based on a low-profile, fully polarized, wide-angle, near- and far-field beam, two-dimensionally adjustable holographic metasurface. Compared with a two-dimensional slot antenna, the present invention has the advantages of convenient control, easy addition of diodes, and processing feasibility. Compared with the existing FP resonant cavity antenna, the present invention has the advantages of a larger scanning range, and can achieve a far-field pencil beam with a large angle of ±70° scanning, and a near-field Bessel beam with a large angle of ±60° scanning.

[0030] The present invention sets a novel coupling unit array on the top metal plate, and sets a radio frequency switch in each array unit in the vertical direction and the horizontal direction for coupling radiation. Different DC bias voltages are applied to the center of each unit by using an FPGA control circuit and a DC feed network set on the upper surface of the bottom dielectric substrate to control the conduction or disconnection of the radio frequency switch. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 A side view of the holographic metasurface.

[0032] Figure 2 A top view of the second metal plate of the holographic metasurface.

[0033] Figure 3 A three-dimensional schematic diagram of the gap unit structure of the holographic metasurface.

[0034] Figure 4 A three-dimensional schematic diagram of the overall structure of the holographic metasurface.

[0035] Figure 5 This is the simulation result of the far-field pencil beam pattern of the holographic metasurface.

[0036] Figure 6 This is the near-field Bessel beam simulation result of the holographic metasurface.

[0037] Figure 7 Schematic diagram of the structure of the new coupling array.

[0038] Figure 8 for Figure 4 An enlarged schematic diagram of .

[0039] In the figure: 1-first metal plate, 2-first dielectric substrate, 3-second metal plate, 4-second dielectric substrate, 5-RF feeding structure, 6-DC feeding network, 101-annular gap, 103-RF switch, 501-metal shell of SMA connector, 502-inner core probe of SMA connector. DETAILED DESCRIPTION

[0040] In order to make the purpose, technical solution and advantages of the present invention clearer, the technical solution of the present invention is described clearly and completely below. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0041] Example

[0042] like Figure 1 , Figure 2 , Figure 3As shown, the two-dimensional adjustable holographic metasurface based on low-profile, fully polarized, wide-angle, near- and far-field beams of the present invention includes a first metal plate 1, a second metal plate 3, an RF feeding structure 5, and a DC feeding network 6. The first metal plate 1 is located on the upper surface of the first dielectric substrate 2, the second metal plate 3 is located on the lower surface of the first dielectric substrate 2, and the second dielectric substrate 4 is located on the lower surface of the second metal plate 3. The RF feeding structure 5 is an SMA connector (Sub-Miniature-A), the metal shell of the SMA connector passes through the second dielectric substrate 4 and the second metal plate 3, and is connected to the second metal plate 3, and the inner core probe 502 of the SMA connector passes through the second dielectric substrate 4, the second metal plate 3, the first dielectric substrate 2, and the first metal plate 1. The DC feeding network 6 is located on the lower surface of the second dielectric substrate 4.

[0043] like Figure 8 As shown, a gap is etched with the connection point between the first metal plate 1 and the inner core probe 502 of the SMA connector as the center, forming an annular gap 101 with the inner core probe 502 of the SMA connector as the center. Figure 3 As shown, a T-shaped coupling structure array is etched on the first metal plate 1. The T-shaped coupling structure array is distributed around the annular gap 101. The difference between the inner diameter of the annular gap 101 and the inner diameter of the inner core probe 502 of the SMA connector is 0.1mm-0.4mm, preferably 0.2mm.

[0044] like Figure 3 , Figure 4 As shown, the T-shaped coupling structure array is composed of a plurality of new coupling units that are symmetrical all around. Two RF switches 103 are loaded on each new coupling unit, which are respectively located in the horizontal and vertical directions. In this embodiment, the RF switches use PIN diodes.

[0045] like Figure 7 As shown, in order to conveniently represent the internal structure, the vertical length of the metal via is highlighted in the new coupling unit. The metal via runs through the first dielectric substrate 2, the second metal plate 3 and the second dielectric substrate 4. One end is connected to the central part of the first metal plate 1, and the other end is connected to the FPGA control circuit and the DC feeding network 6.

[0046] like Figure 7 As shown, the two ends of the RF switch 103 are connected to the outer contour and the inner contour of the new coupling unit. The T-shaped coupling structure array includes 21*21 new coupling units, the outer contour of the new coupling unit is the negative pole, and the inner contour is the positive pole. Using the FPGA control circuit and the DC feed network 6 arranged on the lower surface of the second layer of the dielectric substrate 4, different DC bias voltages can be applied to the positive pole of each RF switch 103 to control the conduction or disconnection of the RF switch 103.

[0047] The dielectric substrate described in this embodiment (including the first dielectric substrate 2 and the second dielectric substrate 4) is made of F4B plate, with a relative dielectric constant of 2.65 and an area of ​​230.36mm×230.36mm, wherein the thickness of the first dielectric substrate 2 is 3mm, and the thickness of the second dielectric substrate 4 is 1.52mm. The frequency of the electromagnetic wave is 8GHz. The length of each new coupling unit in the T-shaped coupling structure array is 0.29 waveguide wavelengths (the waveguide wavelength is the wavelength in free space divided by the relative dielectric constant of the medium under the square root), which is about 10.97mm, and the number of matrices is 21×21.

[0048] Each of the novel coupling units integrates two PIN diodes, which are respectively located in the vertical / horizontal direction. When a forward bias voltage is applied to the diode, the diode is in the "on" state, and the coupling unit is "cut off" from it. The gap there is equivalent to two gaps with a length of λ / 4, so the resonant frequency of the gap is 2f0, and no effective radiation is generated at the set frequency f0; when a reverse bias voltage is applied or no bias voltage is applied, the diode is in the "off" state, and the gap there is still a gap with a length of λ / 2, and the resonant frequency is f0, generating radiation, such as Figure 3 , Figure 4 shown.

[0049] In addition, the present invention also provides a control method based on a two-dimensional adjustable holographic metasurface with low-profile fully polarized wide-angle near- and far-field beams, including:

[0050] The holographic principle is used to calculate the interference field strength formed by the interference of the reference wave and the target wave to determine whether the PIN diode at each gap is turned on. The cylindrical magnetic field generated by the SMA in the parallel plate waveguide is used as the reference wave Ψ ref , can be described by the first kind of Hankel function.

[0051] Among them A Hankel is the reference amplitude. The target beam is reproduced on the metasurface aperture. The condition for reproducing the target beam is to stimulate the interference information again with the reference wave. From the interference theory, it can be concluded that the interference information is the superposition state of phase and amplitude obtained by the interference of the target beam and the reference beam on the metasurface aperture.

[0052] Therefore, the final expression of the interference field strength is found to be the double-line part of the above equation is the target wave Ψ tar Multiply by the reference wave Ψ ref As long as we excite the reference wave Ψ again ref , which happens to be the target wave Ψ tar Multiply by a positive A (amplitude, default is 1). To display the target wave Ψ in more detail tar The reconstruction process first transforms the target wave Ψ tar and the reference wave Ψ refThe amplitude and phase information are replaced.

[0053]

[0054] Where X / Y is polarization in different directions. After logical deduction, it can be seen that the change law of the interference pattern is the cosine function of the phase difference between the reference wave and the target wave. This cosine function is the key information of the interference pattern we need. It should be noted that the reference wave is fed by the embedded central SMA point, which will cause the center of the obtained light beam to be concave. In order to avoid this situation, it is necessary to introduce a phase difference of 180° between the upper and lower halves of the interference field. The design unit has two states, ON and OFF, and the interference field distribution matrix of the continuous phase needs to be normalized and binary algorithm is performed. A certain threshold s is set, and the normalized interference field Ψ is judged by the threshold. inf Distribute the elements in a matrix to obtain a binary matrix.

[0055] After normalization, each element of the two-dimensional matrix is ​​between 0 and 1. The two-dimensional matrix is ​​further binarized: the binarization threshold s is set to 0.7, and for each element, when the element value is greater than or equal to the threshold, the element value is set to 1, otherwise it is set to 0 (wherein, the selection of the binarization threshold can be selected according to the antenna gain and beam pointing accuracy required by the experiment. If it is found that the gain of the antenna in a certain direction is too low, the threshold can be adjusted to increase the radiation gaps and thus improve the gain). The matrix is ​​fed back to the control circuit, and the control circuit applies corresponding DC bias voltages to all PIN diode switches according to the matrix information: if the matrix element value corresponding to a certain gap unit is 1, no bias voltage is applied to the PIN diode of the gap, so that the diode is turned on; otherwise, a forward bias voltage is applied to the PIN diode of the gap, so that it is turned off.

[0056] The far-field radiation direction of the metasurface of the present invention in all directions when working at 8 GHz is as follows: Figure 5 As shown in the figure: the scanning results of full polarization 0°, 30°, 45° and maximum deflection angle, which reflects the two-dimensional controllability of the beam. The maximum deflection angle of the beam on the pitch plane can reach 70°. The simulation software used is CST Microwave Studio 2022. Figure 6 As shown, the scanning results of the near-field Bessel beam at full polarization of 0°, 30°, 45° and the maximum deflection angle reflect the two-dimensional controllable capability of the beam.

[0057] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some of the technical features therein. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. Based on a low-profile, fully polarized, wide-angle, near- and far-field beam-forming two-dimensionally adjustable holographic metasurface, it is characterized by , including a metal plate, a dielectric substrate, an RF feeding structure, and a DC feeding network. The first metal plate is located on the upper surface of the first dielectric substrate, the second metal plate is located on the lower surface of the first dielectric substrate, the second dielectric substrate is located on the lower surface of the second metal plate, and the DC feeding network is located on the lower surface of the second dielectric substrate. The RF feeding structure is an SMA connector. The metal shell of the SMA connector passes through the second dielectric substrate and the second metal plate, and is connected to the second metal plate. The inner core probe of the SMA connector passes through the second dielectric substrate, the second metal plate, the first dielectric substrate, and the first metal plate. A T-shaped coupling structure array is etched on the first metal plate. The T-shaped coupling structure array includes a plurality of new coupling units that are symmetrical all around. An annular gap with the inner core probe of the SMA connector as the origin is etched on the first metal plate. The new coupling units are distributed around the annular gap. The new coupling units are loaded with an RF switch in the vertical direction and the horizontal direction respectively.

2. The two-dimensional adjustable holographic metasurface based on low-profile fully polarized wide-angle near- and far-field beams according to claim 1 is characterized in that: The length of the novel coupling unit is less than or equal to half the guided wavelength, the width is less than or equal to one sixth of the guided wavelength, and the spacing between two adjacent novel coupling units along the long side is less than or equal to 0.6 times the guided wavelength.

3. The two-dimensional adjustable holographic metasurface based on low-profile fully polarized wide-angle near- and far-field beams according to claim 1 is characterized in that: The new coupling unit also includes a metal via, which passes through the first dielectric substrate, the second metal plate and the second dielectric substrate, one end of which is connected to the central part of the first metal plate, and the other end is connected to the FPGA control circuit and the DC feeding network. The RF switch is respectively connected to the outer contour and inner contour of the new coupling unit. The T-shaped coupling structure array includes 21*21 new coupling units, the outer contour of the new coupling unit is the negative pole, and the inner contour is the positive pole.

4. The two-dimensional adjustable holographic metasurface based on low-profile fully polarized wide-angle near- and far-field beams according to claim 3 is characterized in that: The FPGA control circuit and the DC feeding network can apply different DC bias voltages to the positive electrode of each RF switch to control the on or off of the RF switch.

5. The two-dimensional adjustable holographic metasurface based on low-profile fully polarized wide-angle near- and far-field beams according to claim 1 is characterized in that: The outer side of the first metal plate is grounded.

6. The two-dimensional adjustable holographic metasurface based on low-profile fully polarized wide-angle near- and far-field beams according to claim 1 is characterized in that: The difference between the inner diameter of the annular gap and the diameter of the inner core probe is 0.1 mm-0.4 mm.

7. The two-dimensional adjustable holographic metasurface based on low-profile fully polarized wide-angle near- and far-field beams according to claim 1 is characterized in that: The RF switch is a PIN diode.

8. The two-dimensional adjustable holographic metasurface based on low-profile fully polarized wide-angle near- and far-field beams according to claim 1 is characterized in that: The thickness of the first dielectric substrate and the second dielectric substrate are both less than a quarter of the waveguide wavelength, and the width is ten times the waveguide wavelength.

9. A control method based on a two-dimensional adjustable holographic metasurface with low-profile, fully polarized, wide-angle, near- and far-field beams, characterized in that: The following steps are involved: Step 1. Write the plane wave function expression Ψ of the target wave in free space according to the beam azimuth and elevation angles and polarization type of the desired far / near field target wave obj , the cylindrical magnetic field generated by the SMA in the parallel plate waveguide is used as the reference wave Ψ ref ,From the interference theory, it can be concluded that the interference information is the superposition state of phase and amplitude obtained by the target beam and the reference beam interfering on the metasurface aperture; Step 2. The reference wave is fed by the embedded central SMA, which causes the center of the obtained beam to be concave, and it is necessary to introduce a 180° phase difference between the upper and lower half planes of the interference field; Step 3. Set a certain threshold s and use the threshold to determine the normalized interference field Ψ inf Distribute the elements in the matrix to obtain two binary matrices in the vertical / horizontal direction; Step 4. The RF switch in the vertical / horizontal direction is designed to be controlled simultaneously. By performing logical judgment on the common parts of the vertical binary matrix and the horizontal binary matrix, the common parts of the first two matrices are eliminated and the common parts are retained, thus realizing the multi-polarization function. Step 5. If the target wave beam direction changes, repeat steps 1 to 4 above.

10. The method according to claim 9, characterized in that Step 3 also includes further binarization of the binary matrix, wherein the binarization threshold s is set to a value of 0.5-0.9.

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