Metasurface testing device and PB phase testing method

Abstract

The application provides a metasurface testing device and a PB phase testing method, the testing device comprising: a first coaxial waveguide converter, a second coaxial waveguide converter, an orthogonal mode coupler, a polarizer, a reflection waveguide and a vector network analyzer (VNA), the coaxial ends of the two coaxial waveguide converters are connected with the vector network analyzer, and the waveguide ends are connected with the orthogonal mode coupler; the orthogonal mode coupler, the polarizer and the reflection waveguide are sequentially connected; the reflection waveguide has a reflection surface for reflecting an incident circularly polarized wave; when the metasurface testing device is loaded with a measured structure, a reflection signal S11 is measured. The application realizes PB (Pancharatnam-Berry) phase testing by collecting the amplitude and phase of the polarization conversion reflected beam through the testing device. The PB phase testing method of the testing device can quickly and accurately obtain the PB phase of the measured structure.

Description

Technical Field

[0001] This invention proposes a metasurface testing device and a PB phase testing method, which relates to the field of metasurface unit structure performance testing, and particularly to a metasurface unit structure PB phase testing device and method. Background Technology

[0002] Metasurfaces, through their specific unit cell structures and novel physical properties, can confine and manipulate electromagnetic waves at the subwavelength scale. They have also attracted widespread attention from the scientific and industrial communities due to their advantages such as low loss, low profile, and ease of design and fabrication. With the continuous development of metasurfaces, the design of unit cell structures has evolved from simple to complex, and the functions they can perform have diversified capabilities. This determines the diversity and complexity of the performance requirements and evaluation standards for these metasurfaces. Accurately measuring the performance of these metasurfaces is therefore an important task.

[0003] Current analyses of metasurface properties primarily focus on full-mode testing of the entire metasurface. While this method can accurately and completely reveal all metasurface properties, full-mode sample fabrication is costly and time-consuming. Polarization is a crucial property of electromagnetic waves, and its manipulation is widely applied in communication and detection. A review of published literature reveals that testing the polarization conversion characteristics of metasurfaces is typically performed using far-field transmission and reception methods, which places high demands on the testing system and incurs significant costs. Therefore, full-size metasurface performance testing is not an ideal choice; a more efficient testing scheme with lower fabrication and testing costs is needed. Summary of the Invention

[0004] To address the above issues, this invention proposes a metasurface testing device and a Pancharatnam-Berry (PB) phase testing method. This device can quickly and accurately obtain the PB phase of metasurface unit structures by measuring them at different rotation angles, thereby revealing the geometric phase control capability of the unit structure. The PB phase is a geometric phase related to the polarization or polarization of electromagnetic waves; that is, the PB phase based on subwavelength unit structures allows for more flexible control of electromagnetic waves.

[0005] The technical solution adopted by this invention to solve its technical problem is as follows:

[0006] A metasurface testing apparatus includes: a first coaxial waveguide transducer, a second coaxial waveguide transducer, an orthogonal mode coupler, a polarizer, a reflecting waveguide, and a vector network analyzer (VNA). The coaxial ends of the two coaxial waveguide transducers are connected to the VNA, and the waveguide ends are connected to the orthogonal mode coupler. The orthogonal mode coupler, polarizer, and reflecting waveguide are connected in sequence. The reflecting waveguide has a reflecting surface for reflecting incident circularly polarized waves. When the metasurface testing apparatus is loaded with the structure under test, the reflected signal S11 is measured: the first coaxial waveguide transducer radiates a linearly polarized wave with the same polarization direction as the aforementioned linearly polarized wave. The wave passes through the orthogonal mode coupler, the polarizer, and the reflecting waveguide in sequence. After being reflected by the reflecting surface of the reflecting waveguide and the structure under test, the wave passes through the polarizer and the orthogonal mode coupler again. The reflected wave, polarized by the structure under test, is received by the first coaxial waveguide transducer, and the corresponding reflected signal S11 is displayed on the VNA.

[0007] Furthermore, the testing device includes a motor capable of driving the structure under test to rotate.

[0008] Furthermore, the polarizer is a circular polarizer, the reflecting waveguide is a reflecting square waveguide, and a square-to-circular transition waveguide is used to connect the two.

[0009] Furthermore, the first coaxial waveguide converter, the second coaxial waveguide converter, the orthogonal mode coupler, the polarizer, and the reflecting waveguide are fixedly or detachably connected.

[0010] Furthermore, the structure under test can be a single metasurface unit structure or an array of N×M metasurface unit structures, where N and M are positive integers.

[0011] The present invention also proposes the following technical solutions:

[0012] A PB phase testing method based on the metasurface testing device described above includes:

[0013] 1) The reflected signal S11 was measured, specifically including:

[0014] When the structure under test is loaded, the first coaxial waveguide converter radiates a linearly polarized wave with the same polarization direction as described above. This wave is converted into a circularly polarized wave by the polarizer through the orthogonal mode coupler. The circularly polarized wave enters the reflecting waveguide and is reflected by the reflecting surface and the structure. The circularly polarized incident wave that is polarized by the structure is converted into a circularly polarized reflected wave with the same rotation direction as the incident wave. The circularly polarized incident wave that is not polarized by the structure is converted into a circularly polarized reflected wave with the opposite rotation direction to the incident wave. The two circularly polarized reflected waves are converted into linearly polarized waves with two orthogonal directions by the polarizer. These are separated by the orthogonal mode coupler and the reflected waves are received by the two coaxial waveguide converters respectively. The reflected wave that is polarized by the structure is received by the first coaxial waveguide converter, i.e., the reflected signal S11.

[0015] 2) Rotate the structure under test by an angle θ; automatically collect the phase information of S11 corresponding to different angles θ;

[0016] 3) Select any frequency point within the measured frequency band range and plot the coordinate diagram of θ and phase information.

[0017] The testing device described in this invention can customize the waveguide structure size according to the size of the structure under test and the operating frequency range.

[0018] Furthermore, the linearly polarized wave radiated by the first coaxial waveguide converter can be a linearly polarized wave with H polarization, V polarization, or other polarization directions.

[0019] Compared with the prior art, the beneficial effects of this invention are as follows: using this testing device to test metasurface unit structures does not require far-field testing equipment, the structure is compact, and it can effectively reduce the processing and testing costs required for the full-size metasurface polarization characteristic testing process, thereby improving the efficiency of testing work. Attached Figure Description

[0020] Figure 1 This is a schematic diagram of the structure of the present invention;

[0021] Figure 2 The structure under test used in the examples of this invention;

[0022] Figure 3 This is a comparison diagram of the polarization conversion test of the tested structure and the theoretical results in an example of this invention;

[0023] Figure 4 This is a comparison diagram of the PB phase test and theoretical results of the tested structure in this invention example.

[0024] Figure label:

[0025] 1-First coaxial waveguide converter, 2-Second coaxial waveguide converter, 3-Orthogonal mode coupler, 4-Polarizer, 5-Square-circular transition waveguide, 6-Reflection waveguide, 7-Structure under test. Detailed Implementation

[0026] The present invention will now be described in detail with reference to the accompanying drawings and specific embodiments. However, the scope of protection of the present invention is not limited to the following embodiments, but should include all contents of the claims.

[0027] like Figure 1As shown, a metasurface testing device includes: a first coaxial waveguide converter 1, a second coaxial waveguide converter 2, an orthogonal mode coupler 3, a polarizer 4, a reflecting waveguide 6, and a vector network analyzer (VNA). The two coaxial waveguide converters 1 and 2 are used to transmit and receive orthogonally linearly polarized waves. The coaxial ends of the two coaxial waveguide converters are connected to the vector network analyzer to transmit signals to it, and the waveguide ends are connected to the orthogonal mode coupler 3. The orthogonal mode coupler 3 can separate or synthesize orthogonally linearly polarized waves. The orthogonal mode coupler 3, the polarizer 4, and the reflecting waveguide 6 are connected sequentially. The first coaxial waveguide converter 1, the second coaxial waveguide converter 2, the orthogonal mode coupler 3, the polarizer 4, and the reflecting waveguide 6 can be fixedly connected or detachably connected; the connection method does not affect the functionality. In this embodiment, they are connected sequentially by screws. The polarizer 4 can convert incident linearly polarized waves into circularly polarized waves and also convert reflected circularly polarized waves into linearly polarized waves. The reflecting waveguide 6 has a reflecting surface for reflecting incident circularly polarized waves. In this embodiment, for ease of explanation, the system is arranged horizontally; in actual applications, the system can be positioned vertically or in other orientations. Those skilled in the art can customize the waveguide structure dimensions according to the size of the structure under test and the operating frequency range.

[0028] In this embodiment, the first coaxial waveguide converter 1 and the second coaxial waveguide converter 2 are selected as model HD-100WCAS, the orthogonal mode coupler 3 is selected as model HD-100CWOMT23.825T3, the polarizer 4 is selected as model HD-23.825CWPST1, and the reflecting waveguide 6 is selected as model HD-20X20WSST1. Furthermore, since the selected polarizer 4 has a circular cross-section and the reflecting waveguide 6 has a square cross-section, a [specific model] is selected here to connect the two devices. The square-to-circular transition waveguide 5, designated HD-20X20RCA23.825T1, has its circular waveguide port connected to the circular polarizer 4 and its square waveguide port connected to the reflecting square waveguide 6. If the two devices have the same cross-sectional shape, they can be directly connected without selecting other devices. Furthermore, this example only illustrates the model selected in this embodiment; those skilled in the art can select coaxial waveguide converters, orthogonal mode couplers, circular polarizers, square-to-circular transition waveguides, and reflecting square waveguides according to actual conditions. During testing, the structure under test can be a single metasurface unit structure, such as... Figure 2 As shown; it can also be an array composed of multiple metasurface unit structures, such as N×N or N×M. Figure 2 The array shown consists of metasurface unit structures, where N and M are positive integers. During testing, it can be... Figure 2 The metasurface unit structure shown is assembled into Figure 1Position 7. The structure under test is a rectangular patch with length l and width w. In this embodiment, the values ​​are l = 18 mm and w = 5 mm. The material is stainless steel, and the patch thickness is 1 mm. The distance between the patch and the reflective surface is 7.5 mm. The metasurface unit structure can also be made of a dielectric material. The measurement principle of this measuring device is independent of the material of the metasurface unit structure and can be used to test the circular polarization conversion efficiency of metasurface unit structures made of any material. In order to measure the PB phase of the metasurface unit structure, in this embodiment, a motor is used to drive the metasurface unit structure fixed on the motor shaft to rotate. The motor can change the rotation angle θ of the structure under test. In actual use, as long as the structure under test or the aforementioned testing device can rotate relative to each other, the PB phase can be measured. There are no restrictions on the specific structure that generates relative rotation.

[0029] The polarization conversion efficiency test method of this test device is as follows: including the following steps:

[0030] 1) Obtaining the reference signal: Without the metasurface unit structure, the normalized reflected signal S21 is measured. Here, S21 represents the signal emitted by the first coaxial waveguide converter 1 and received by the second coaxial waveguide converter 2. Similarly, S11 represents the signal emitted by the first coaxial waveguide converter 1 and received by the first coaxial waveguide converter 1. For ease of distinction, this step's S21 is labeled S21-1. Within the electromagnetic wave frequency band output by the first coaxial waveguide converter 1, the amplitude value of the reflected signal S21 is calibrated by direct calibration to characterize the ratio of the input linearly polarized wave energy to the output linearly polarized wave energy of the first coaxial waveguide converter 1. The electromagnetic wave transmission and reception process is as follows: The first coaxial waveguide converter 1 radiates an H-polarized wave, which enters the polarizer 4 through the common port of the orthogonal mode coupler 3 and is converted into a circularly polarized wave. The circularly polarized wave passes through the square-circular transition waveguide 5 and enters the reflection waveguide 6. At this time, the circularly polarized wave entering the reflection waveguide 6 is reflected by the reflecting surface. At the same time, due to half-wave loss, the incident wave is polarized by the reflection waveguide 6 and converted into an orthogonal circularly polarized reflected wave. The orthogonal circularly polarized reflected wave is converted into V-polarization again through the polarizer 4. After being separated by the orthogonal mode coupler 3, it is received by the second coaxial waveguide converter 2 and the signal S21-1 is displayed on the vector network analyzer. The amplitude value of S21-1 is then calibrated by operating the vector network analyzer. After calibration, the value is approximately 1. The specific calibration method is a conventional method used by those skilled in the art and will not be described in detail here.

[0031] 2) Load the structure under test. The structure under test is loaded in front of the reflective surface, and the reflected signal S21-2 is measured. The electromagnetic wave transmission and reception process is as follows: The first coaxial waveguide converter 1 radiates a polarized wave with the same polarization as in step 1), which is an H-polarized wave in this embodiment. It enters the polarizer through the orthogonal mode coupler 3 and is converted into a circularly polarized wave. The circularly polarized wave passes through the square-circular transition waveguide 5 and enters the reflection waveguide 6, where it is reflected by the reflection surface. Due to the combined effect of half-wave loss and the sample under test, the circularly polarized incident wave converted by the polarization of the structure under test is converted into a circularly polarized reflected wave with the same rotation direction as the incident wave. The circularly polarized incident wave not converted by the polarization of the structure under test is converted into a circularly polarized reflected wave with the opposite rotation direction to the incident wave. The two circularly polarized reflected waves are converted into two orthogonal linearly polarized waves through the polarizer 4. They are separated by the orthogonal mode coupler 3 and received by the two coaxial waveguide converters respectively. The part not converted by the polarization of the structure under test is received by the second coaxial waveguide converter 2 and the signal S21-2 is displayed on the vector network analyzer. The part converted by the polarization of the structure under test is received by the first coaxial waveguide converter 1, i.e., the reflected signal S11.

[0032] 3) Subtract the square of the amplitude of S21-2 when the structure under test is loaded from the square of the amplitude of S21-1 obtained in step 1), and the result is the amplitude of the structure under test (at this time, it is the attached structure). Figure 2 The circular polarization conversion efficiency (S21-1) of the single metasurface unit structure shown. 2 -(S21-2) 2 It should be noted that the first coaxial waveguide converter 1 radiates H-polarized waves here for ease of explanation. In addition, V-polarized waves or other directional polarized waves can also be selected.

[0033] The results of the circular polarization conversion efficiency test are as follows: Figure 3 As shown in this embodiment, numerical simulation confirms that the polarization conversion efficiency test results (as shown by the dashed line) performed by the test device are consistent with the CST theoretical simulation results (as shown by the solid line). It is important to note that when using CST theoretical simulation to verify the performance of the test device, the parameter settings of the CST theoretical simulation must be consistent with the actual test device. For example, in this embodiment, the structure under test is connected to a motor shaft with a diameter of 3mm. A 3.1mm diameter hole is pre-drilled at the center of the reflecting surface of the reflecting waveguide 6 to facilitate the motor shaft entering the reflecting waveguide 6. The position of the motor shaft is adjusted so that the distance between the structure under test and the reflecting surface of the reflecting waveguide 6 is 7.5mm. Therefore, when performing the CST theoretical simulation, the same distance between the motor shaft and the structure under test and the reflecting surface of the reflecting waveguide 6 must be simulated to ensure the comparability of the simulation results with the test device. In the 10-11GHz range, the maximum polarization conversion rate of the selected structure under test is 97.87%, and near f = 10.588GHz, the polarization conversion rate is close to 100%.

[0034] This testing apparatus can also be used for PB phase testing to determine whether the designed metasurface unit structure has excellent geometric phase manipulation capabilities. Specific steps include:

[0035] The reflected signal S11 is measured by loading the structure under test. The structure under test is rotated at a speed of v1, and the angle of rotation is θ. Since the phase change of PB is 2π for every 180° rotation of the structure under test, a slower rotation speed can usually obtain a more accurate PB phase. However, too low a speed will affect the efficiency of data measurement. Therefore, its value can be selected by those skilled in the art based on the actual situation. The phase information of S11 corresponding to different angles θ is automatically collected. Any frequency point within the measured frequency band is selected, and a coordinate graph of θ and phase information is plotted. It should be noted that the first coaxial waveguide converter 1 radiates H-polarized waves here for ease of explanation. In addition, V-polarized waves or other directional polarized waves can also be selected.

[0036] The test setup is used to test the PB phase results as follows: Figure 4 As shown, the phase change relationship of S11 corresponding to different angles θ at frequency f = 10.588 GHz is extracted. The PB phase measured by this waveguide device is consistent with the theory, that is, this test device has excellent PB phase test accuracy.

[0037] In summary, this invention proposes a cross-polarization testing device and method for polarization conversion metasurface unit structures. This testing method can obtain the polarization conversion performance and PB phase of the tested structure relatively quickly and accurately.

[0038] Therefore, the embodiments of the present invention have been described above with reference to the accompanying drawings. However, the present invention is not limited to the specific embodiments described above; the embodiments described above are merely illustrative and not restrictive. Those skilled in the art, under the guidance of the present invention, can make many modifications without departing from the spirit and scope of the claims, and all such modifications are within the protection scope of the present invention. The parts of the present invention not described in detail are well-known to those skilled in the art.

Claims

1. A metasurface testing apparatus, the testing apparatus comprising: The system comprises a first coaxial waveguide converter (1), a second coaxial waveguide converter (2), an orthogonal mode coupler (3), a polarizer (4), a reflecting waveguide (6), and a vector network analyzer, characterized in that: The coaxial ends of the first and second coaxial waveguide converters are connected to the vector network analyzer, and the waveguide ends are connected to the orthogonal mode coupler (3); the orthogonal mode coupler (3), the polarizer (4), and the reflection waveguide (6) are connected in sequence; the reflection waveguide (6) has a reflecting surface for reflecting incident circularly polarized waves; When the metasurface testing device is loaded with the structure under test, the reflected signal S11 is measured: the first coaxial waveguide converter (1) radiates a linearly polarized wave with the same polarization direction as the first coaxial waveguide converter radiated when the metasurface unit structure is not loaded. The wave passes through the orthogonal mode coupler (3), the polarizer (4), and the reflection waveguide (6) in sequence. After being reflected by the reflection surface of the reflection waveguide (6) and the structure under test, the wave passes through the polarizer (4) and the orthogonal mode coupler (3) again. The reflected wave polarized by the structure under test is received by the first coaxial waveguide converter (1), and the corresponding reflected signal S11 is displayed on the vector network analyzer.

2. The metasurface testing device according to claim 1, characterized in that: The testing device also includes a motor that can drive the structure under test to rotate.

3. The metasurface testing device according to claim 2, characterized in that: The structure under test is mechanically connected to the motor shaft of the motor.

4. The metasurface testing device according to claim 1, characterized in that: The polarizer (4) is a circular polarizer and the reflecting waveguide (6) is a reflecting square waveguide. A square-to-circular transition waveguide (5) is used to connect the two.

5. The metasurface testing device according to claim 1, characterized in that: The first coaxial waveguide converter (1), the second coaxial waveguide converter (2), the orthogonal mode coupler (3), the polarizer (4), and the reflecting waveguide (6) are fixedly or detachably connected.

6. The metasurface testing device according to claim 1, characterized in that: The structure under test is a single metasurface unit structure or an array of N×M metasurface unit structures, where N and M are positive integers.

7. A PB phase testing method based on the metasurface testing apparatus according to any one of claims 1-6, characterized in that, The PB phase testing method includes: 1) The reflected signal S11 was measured, specifically including: When the structure under test is loaded, the first coaxial waveguide converter (1) radiates a linearly polarized wave. The linearly polarized wave enters the polarizer (4) through the orthogonal mode coupler (3) and is converted into a circularly polarized wave. The circularly polarized wave enters the reflecting waveguide (6) and is reflected by the reflecting surface and the structure under test. The reflected circularly polarized wave is converted into two orthogonal linearly polarized waves through the polarizer (4). The two orthogonal linearly polarized waves are separated by the orthogonal mode coupler (3) and the reflected waves are received by the first and second coaxial waveguide converters respectively. The reflected wave polarized by the structure under test is received by the first coaxial waveguide converter (1), that is, the corresponding reflected signal S11 is obtained. 2) Rotate the structure being measured by an angle of _____. Automatically collect data from different angles. The phase information of the corresponding reflected signal S11; 3) Select any frequency point within the measured frequency band range and plot the results. Phase information coordinate diagram.

8. The test method according to claim 7, characterized in that: The linearly polarized wave radiated by the first coaxial waveguide converter (1) is a linearly polarized wave in H-polarization, V-polarization or other polarization directions.

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