CN114371348A - Super-surface testing device, testing method and PB phase testing method - Google Patents

Abstract

The invention provides a metasurface testing device, a testing method and a PB phase testing method. The testing device comprises: a first coaxial waveguide converter, a second coaxial waveguide converter, an orthogonal mode coupler, and a polarizer , reflection waveguide, vector network analyzer (VNA), the coaxial ends of the two coaxial waveguide converters are connected to the vector network analyzer, and the waveguide ends are connected to the orthogonal mode coupler; the orthogonal mode coupler, polarizer, The reflective waveguides are connected in sequence; the reflective waveguide has a reflective surface for reflecting incident circularly polarized waves. The present invention can collect the amplitude and phase of the polarization conversion reflected beam by using the test device, so as to realize the circular polarization conversion efficiency and PB (Pancharatnam-Berry) phase test. Compared with the currently commonly used free space test method, the proposed waveguide test system can effectively save the sample processing cost and improve the test work efficiency.

Description

A kind of metasurface testing device, testing method and PB phase testing method

technical field

The invention provides a metasurface test device, a test method and a PB phase test method, which relate to the field of metasurface unit structure performance test, in particular to a metasurface unit structure polarization conversion efficiency, PB phase test device and method.

Background technique

Metasurfaces can confine and control electromagnetic waves at the subwavelength scale through specific unit structures and novel physical properties. At the same time, relying on its own advantages such as low loss, low profile, easy design and fabrication, etc., it has received extensive attention from the scientific and industrial circles. With the continuous development of metasurfaces, the design of unit structures has changed from simple to complex, and the functions that can be presented have changed from single to diverse, which determines the diversity and complexity of the performance index requirements and evaluation criteria of these metasurfaces. Making accurate measurements of the properties of these metasurfaces is an important task.

At present, the analysis of metasurface performance mainly focuses on the entire metasurface, that is, the full mold test. This test method can accurately and completely obtain all the properties of the metasurface, but the processing cost of the full mold sample is high and the time is long. Polarization is an important property of electromagnetic waves, and the polarization regulation of electromagnetic waves is widely used in communication, detection and other fields. By consulting the published literature, it is found that the test of the polarization conversion characteristics of the metasurface is carried out by the far-field transmission and reception method, which requires high test system and high test cost. Therefore, performance testing of full-scale metasurfaces is not an ideal choice, and more often, a testing solution with low processing and testing costs, simple system and high efficiency is required.

SUMMARY OF THE INVENTION

In order to solve the above problems, the present invention provides a metasurface test device, a test method and a PB phase test method, which can obtain the polarization conversion performance of the metasurface unit structure relatively quickly and accurately. At the same time, the PB phase can be obtained by measuring the metasurface unit structure with different rotation angles, so as to obtain the geometric phase control ability of the unit structure. The PB (Pancharatnam-Berry) phase is a geometric phase related to the polarization or polarization of the electromagnetic wave, that is, the PB phase based on the subwavelength unit structure can tune the electromagnetic wave more flexibly.

The technical scheme adopted by the present invention to solve its technical problems is:

A metasurface testing device, the testing device includes: a first coaxial waveguide converter, a second coaxial waveguide converter, an orthogonal mode coupler, a polarizer, a reflective waveguide, and a vector network analyzer (VNA): two The coaxial end of the coaxial waveguide converter is connected with the vector network analyzer, and the waveguide end is connected with the orthogonal mode coupler; the orthogonal mode coupler, the polarizer and the reflection waveguide are connected in sequence; reflective surface of the chemical wave.

Further, the testing device includes a motor that can drive the structure to be tested to rotate.

Further, the polarizer is a circular polarizer, the reflective waveguide is a reflective square waveguide, and a square-circle transition waveguide is used for the connection between the two.

Further, the first coaxial waveguide converter, the second coaxial waveguide converter, the orthogonal mode coupler, the polarizer, and the reflective waveguides are fixedly or detachably connected.

Further, the measured structure can be a single metasurface unit structure or an array composed of N×M metasurface unit structures, where N and M are positive integers.

The present invention also proposes the following technical solutions:

A test method based on the above-mentioned metasurface test device, comprising the following steps:

1) When the measured structure is not loaded, the normalized reference reflection signal S21-1 is measured: the first coaxial waveguide converter (1) radiates the linearly polarized wave, which enters through the common port of the orthogonal mode coupler (3). The polarizer (4) is converted into a circularly polarized wave, the circularly polarized wave enters the reflective waveguide (6), is reflected by the reflective surface of the reflective waveguide (6), and is polarized and converted into an orthogonal circularly polarized reflected wave, The orthogonal circularly polarized reflected wave is converted into an orthogonal linearly polarized wave through the polarizer (4), and then separated by the orthogonal mode coupler (3), and finally transmitted by the second coaxial waveguide converter (2). ) to receive the reflected wave, at this time, the acquired reflected wave signal, that is, the normalized reference reflected signal S21-1, is displayed on the vector network analyzer, and the amplitude value of the signal S21-1 is directly calibrated. The amplitude value is approximately 1;

2) Load the measured structure, and measure the reflected signal S21-2: the first coaxial waveguide converter 1 radiates a linearly polarized wave in the same polarization direction as the aforementioned, and enters the polarizer ( 4) Converted into circularly polarized waves, the circularly polarized waves enter the reflective waveguide (6) and are reflected by the reflective surface and the structure, and the partially circularly polarized incident waves converted by the structural polarization are converted into circular polarized waves with the same rotation as the incident waves. Part of the circularly polarized incident wave that is not converted by the structural polarization is converted into a circularly polarized reflected wave whose handedness is opposite to that of the incident wave; the two circularly polarized reflected waves are converted into positive polarized waves through the polarizer (4). The linearly polarized waves in the two directions are separated by the orthogonal mode coupler (3) and respectively receive the reflected waves through two coaxial waveguide converters. The two coaxial waveguide converters (2) receive and display the corresponding reflected signal S21-2 on the vector network analyzer; the reflected wave polarized by the structure is received by the first coaxial waveguide converter (1), that is, reflected signal S11;

3) Subtract the obtained amplitude square of S21-1 from the amplitude square of S21-2 when the tested structure is loaded, and obtain the circular polarization conversion efficiency of the tested structure as (S21-1) ² -(S21-2) ² .

Further, the linearly polarized waves radiated by the first coaxial waveguide converter may be H-polarized, V-polarized or linearly polarized waves in other polarization directions.

The present invention also proposes another technical solution:

A PB phase testing method based on the above-mentioned metasurface testing device, comprising:

1) Measure the reflected signal S11, which specifically includes:

Loading the structure under test, the first coaxial waveguide converter radiates a linearly polarized wave in the same polarization direction as the aforementioned, enters the polarizer through the orthogonal mode coupler and is converted into a circularly polarized wave, and the circularly polarized wave enters the reflection waveguide Reflected by the reflective surface and the structure, the partially circularly polarized incident wave converted by the structural polarization is converted into a circularly polarized reflected wave with the same handedness as the incident wave, and the partially circularly polarized incident wave that is not converted by the structural polarization is converted into a circularly polarized incident wave. The circularly polarized reflected wave is opposite to the incident wave; the two circularly polarized reflected waves are converted into two orthogonal linearly polarized waves by the polarizer, which are separated by the orthogonal mode coupler and pass through two The coaxial waveguide converter receives the reflected wave, and the partially reflected wave converted by the structural polarization is received by the first coaxial waveguide converter, that is, the reflected signal S11;

2) Rotate the measured structure, the rotation angle is θ; automatically collect the phase information of S11 corresponding to different angles θ;

3) Select any frequency point in the measured frequency range, and draw a coordinate diagram of θ and phase information.

Among them, the testing device of the present invention can customize the size of the waveguide structure according to the size of the tested structure and the operating frequency range.

Compared with the prior art, the present invention has the following beneficial effects: using the testing device to test the metasurface unit structure does not require far-field testing equipment, has a compact structure, and can effectively reduce the processing required for the full-scale metasurface polarization characteristic testing process. and test cost, improve test work efficiency.

Description of drawings

Fig. 1 is the structural representation of the present invention;

Fig. 2 is the tested structure used in the example of the present invention;

Fig. 3 is the polarization conversion test and theoretical comparison diagram of the structure under test in the example of the present invention;

FIG. 4 is a comparison diagram of the PB phase test and theoretical comparison of the structure under test in the example of the present invention.

Reference number:

1-First coaxial waveguide converter, 2-Second coaxial waveguide converter, 3-Orthogonal mode coupler, 4-Polarizer, 5-Square transition waveguide, 6-Reflection waveguide, 7-Measured structure .

Detailed ways

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

As shown in Figure 1, 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 reflection waveguide 6, a vector Network analyzer (VNA); two coaxial waveguide converters 1 and 2 are used to transmit and receive orthogonal linearly polarized waves, and the coaxial ends of the two coaxial waveguide converters are connected to the vector network analyzer for transmitting and receiving orthogonal linearly polarized waves. The vector network analyzer transmits signals, and the waveguide end is connected to the orthogonal mode coupler 3; the orthogonal mode coupler 3 can separate or synthesize orthogonal linearly polarized waves; the orthogonal mode coupler 3, the polarizer 4, the reflective square waveguide 6 are connected in turn. The first coaxial waveguide converter 1, the second coaxial waveguide converter 2, the orthogonal mode coupler 3, the polarizer 4, and the reflective waveguide 6 can be fixedly connected or detachably connected, and the connection method does not affect the To realize the function, in this embodiment, the screws are connected to each other in sequence. The polarizer 4 can realize the conversion of incident linear polarization into circularly polarized waves, and can also convert the reflected circularly polarized waves into linearly polarized waves. The reflection waveguide 6 has a reflection surface for reflecting the incident circularly polarized wave. In this embodiment, for the convenience of description, the system is arranged in a horizontal direction. In actual application, the placement position of the system may be set to be vertical or in other directions. Those skilled in the art can customize the size of the waveguide structure according to the size of the structure under test and the operating frequency range.

In this embodiment, the selected model of the first coaxial waveguide converter 1 and the second coaxial waveguide converter 2 is HD-100WCAS, the selected model of the orthogonal mode coupler 3 is HD-100CWOMT23.825T3, and the polarizer 4 The selected model is HD-23.825CWPST1, and the selected model of reflective waveguide 6 is HD-20X20WSST1. In addition, since the selected polarizer 4 has a circular cross-section and the reflective waveguide 6 has a square cross-section, in order to connect the above two devices, The square-circle transition waveguide 5 with model HD-20X20RCA23.825T1 is selected here. The circular waveguide port of the square-circle transition waveguide 5 is connected to the circular polarizer 4, and the square waveguide port is connected to the reflection square waveguide 6. If the above two devices have the same cross-sectional shape , it can be directly connected without selecting other devices; in addition, only the model selected in this embodiment is illustrated here, and those skilled in the art can perform coaxial waveguide converters, orthogonal mode couplers, circular polarization according to actual conditions. The selection of the device, the square-circle transition waveguide, and the reflective square waveguide. During testing, the tested structure can be a single metasurface unit structure, as shown in Figure 2; it can also be an array composed of multiple metasurface unit structures, such as N×N or N×M as shown in Figure 2 An array of metasurface unit structures, where N and M are positive integers. During testing, the metasurface unit structure shown in FIG. 2 can be assembled to the position of 7 in FIG. 1 . The measured structure is a rectangular patch with a length of l and a width of w. In this embodiment, the values are l=18mm, w=5mm, the material is stainless steel, and the thickness of the patch is 1mm. The distance between the patch and the reflective surface is 7.5mm. The material of the metasurface unit structure can also be a medium. The measurement principle of this measuring device has nothing to do with the material of the metasurface unit structure, and can be used to test the circular polarization conversion efficiency of the metasurface unit structure 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, and the motor can change the rotation angle θ of the measured structure. In actual use, the measurement of the PB phase can be achieved as long as the structure under test or the aforementioned test device can rotate relative to each other, and the specific structure that generates the relative rotation is not limited here.

The method of using the polarization conversion efficiency test of the test device is as follows: it includes the following steps:

1) Obtain a reference signal: the metasurface unit structure is not loaded, and the normalized reflection signal S21 is measured. Here S21 represents the signal sent by the first coaxial waveguide converter 1 and received by the second coaxial waveguide converter 2. Similarly, S11 represents the signal sent by the first coaxial waveguide converter 1 , and the signal received by the first coaxial waveguide converter 1 . For ease of identification, S21 in this step is identified as S21-1 here. In the frequency band of the electromagnetic wave output by the first coaxial waveguide converter 1, the amplitude value of the reflected signal S21 is calibrated through the straight-through to represent the difference between the input linearly polarized wave energy and the output linearly polarized wave energy of the first coaxial waveguide converter 1 Compare. The electromagnetic wave transmitting and receiving process is as follows: the first coaxial waveguide converter 1 radiates the H-polarized wave, enters the polarizer 4 through the common port of the orthogonal mode coupler 3 and is converted into a circularly polarized wave, and the circularly polarized wave passes through the square circle. The transition waveguide 5 enters the reflective waveguide 6. At this time, the circularly polarized wave entering the reflective waveguide 6 is reflected by the reflective surface, and at the same time, due to the half-wave loss, the incident wave is polarized and converted into the orthogonal circularly polarized reflected wave by the reflective waveguide 6 , the orthogonal circularly polarized reflected wave is converted into V polarization by polarizer 4, and then separated by orthogonal mode coupler 3, received by the second coaxial waveguide converter 2, and displayed on the vector network analyzer Signal S21-1, and then perform a straight-through calibration on the amplitude value of S21-1 by operating a vector network analyzer, and the value is approximately 1 after calibration.

2) Load the structure under test, before the structure under test is loaded on the reflective surface, the reflected signal S21-2 is measured. The electromagnetic wave transmitting and receiving process is as follows: the first coaxial waveguide converter 1 radiates the same polarized wave as step 1), which is H-polarized wave in this embodiment, and enters the polarizer through the orthogonal mode coupler 3 and is converted into Circularly polarized wave, the circularly polarized wave passes through the square-circle transition waveguide 5, enters the reflective waveguide 6 and is reflected by the reflective surface. Due to the joint action of the half-wave loss and the measured junction sample, the circularly polarized incident wave converted by the polarization conversion of the measured structure is converted It is a circularly polarized reflected wave with the same handedness as the incident wave. The circularly polarized incident wave that is not polarized by the measured structure is converted into a circularly polarized reflected wave with the opposite handedness to the incident wave; the two circularly polarized reflected waves pass through The polarizer 4 is converted into two orthogonal linearly polarized waves, which are separated by the orthogonal mode coupler 3 and received through two coaxial waveguide converters respectively. The second coaxial waveguide converter (2) receives and displays the signal S21-2 on the vector network analyzer, and the polarization-converted part of the structure under test is received by the first coaxial waveguide converter (1), that is, the reflected signal S11 ;

3) The square of the amplitude of S21-1 obtained in step 1) minus the square of the amplitude of S21-2 when the tested structure is loaded, which is the circle of the tested structure (in this case, the single metasurface unit structure shown in Figure 2). Polarization conversion efficiency (S21-1) ² -(S21-2) ² . It should be noted that the first coaxial waveguide converter 1 here radiates H-polarized waves for the convenience of description, and in addition, V-polarized waves or polarized waves in other directions can also be selected.

The test results of the circular polarization conversion efficiency are shown in Figure 3. In this embodiment, it is confirmed by numerical simulation that the test results of the polarization conversion efficiency (shown by the dotted line) and the CST theoretical simulation results (shown by the solid line) performed by the test device ) are consistent. It should be noted that when using CST theoretical simulation to verify the performance of the test device, the parameter settings of the CST theoretical simulation need to be consistent with the actual test device. A small hole with a diameter of 3.1mm is reserved in the center of the reflective surface of 6, so that the motor shaft can enter the reflective waveguide 6. Adjust the position of the motor shaft so that the measured structure is 7.5mm away from the reflective surface of the reflective waveguide 6. Then, when doing CST theoretical simulation, it is also necessary to Only by simulating the same motor shaft and the distance between the measured structure and the reflective surface of the reflective waveguide 6 can the comparability of the simulation results and the test device be ensured. In the range of 10-11 GHz, the maximum polarization conversion rate of the selected tested structure is 97.87%, and in the vicinity of f=10.588 GHz, the polarization conversion rate is close to 100%.

The test device can also be used for PB phase test to determine whether the designed metasurface unit structure has excellent geometric phase control capability. The specific steps include:

The reflected signal S11 is measured by loading the structure under test, and the structure under test is rotated, the rotational speed is v ₁ , and the rotated angle is θ. Because the measured structure rotates 180°, its PB phase changes by 2π. Usually, a slower rotation speed can obtain a more accurate PB phase. However, if the speed is too low, the efficiency of data measurement will be affected, so its value can be determined by those skilled in the art. The specific selection is made according to the actual situation; the phase information of S11 corresponding to different angles θ is automatically collected; any frequency point in the measured frequency range is selected, and a coordinate diagram of θ and phase information is drawn. It should be noted that the first coaxial waveguide converter 1 here radiates H-polarized waves for the convenience of description, and in addition, V-polarized waves or polarized waves in other directions can also be selected.

The results of the test device used to test the PB phase are shown in Figure 4. The phase change relationship of S11 corresponding to different angles θ at the frequency f=10.588GHz is extracted. The PB phase tested by the waveguide device is consistent with the theory, that is, The test device has excellent PB phase test accuracy.

To sum up, the present invention proposes a cross-polarization test device and a test method for a polarization conversion metasurface unit structure, and the test method can obtain the polarization conversion performance and PB of the tested structure relatively quickly and accurately. phase.

Therefore, the embodiments of the present invention are described above with reference to the accompanying drawings, but the present invention is not limited to the above-mentioned specific implementation manners, which are merely illustrative rather than restrictive. Under the inspiration of the present invention, those of ordinary skill in the art can also make many forms without departing from the spirit of the present invention and the scope protected by the claims, which all belong to the protection of the present invention. Parts not described in detail in the present invention belong to the well-known technologies of those skilled in the art.

Claims (9)

1. A metasurface testing device comprising: a first coaxial waveguide converter (1), a second coaxial waveguide converter (2), an orthogonal mode coupler (3), a polarizer ( 4), reflection waveguide (6), vector network analyzer, it is 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 reflection surface for reflecting the incident circularly polarized wave. 2. a kind of metasurface testing device according to claim 1, is characterized in that: The testing device also includes a motor that can drive the structure to be tested to rotate. 3. a kind of metasurface testing device according to claim 2, is characterized in that: The structure under test is connected with the motor shaft of the motor in a mechanical connection manner. 4. a kind of metasurface testing device according to claim 1, is characterized in that: The polarizer (4) is a circular polarizer, and the reflective waveguide (6) is a reflective square waveguide, wherein a square-circular transition waveguide (5) is used for the connection between the two. 5. a kind of metasurface testing device according to claim 1, is 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 reflective waveguide (6) are fixedly connected or can be connected. Remove the connection. 6. a kind of metasurface testing device according to claim 1, is characterized in that: The measured structure can be a single metasurface unit structure or an array composed of N×M metasurface unit structures, where N and M are positive integers. 7. A test method based on the metasurface testing device described in any one of claims 1-6, wherein the test method comprises the following steps: Step 1): when the structure to be tested is not loaded, the normalized reference reflection signal S21-1 is measured, which specifically includes: The first coaxial waveguide converter (1) radiates linearly polarized waves, and the linearly polarized waves enter the polarizer (4) through the common port of the orthogonal mode coupler (3) and are converted into circularly polarized waves, which are circularly polarized The wave enters the reflective waveguide (6), is reflected by the reflective surface of the reflective waveguide (6), and is polarized and converted into an orthogonal circularly polarized reflected wave, and the orthogonal circularly polarized reflected wave is passed through the polarizer (4). It is converted into an orthogonal linearly polarized wave, the orthogonal linearly polarized wave is separated by the orthogonal mode coupler (3), and finally the reflected wave is received by the second coaxial waveguide converter (2). The acquired reflected wave signal, that is, the normalized reference reflected signal S21-1, is displayed on the vector network analyzer, and the amplitude value of the signal S21-1 is directly calibrated; Step 2): load the structure to be tested, and measure the reflected signal S21-2, which specifically includes: The first coaxial waveguide converter (1) radiates a linearly polarized wave in the same polarization direction as the aforementioned linearly polarized wave, and the linearly polarized wave enters the polarizer (4) through the orthogonal mode coupler (3) and is converted It is a circularly polarized wave. The circularly polarized wave enters the reflective waveguide (6) and is reflected by the reflective surface and the measured structure. The reflected circularly polarized wave is converted into two orthogonal linear poles through the polarizer (4). The linearly polarized waves in the orthogonal two directions are separated by the orthogonal mode coupler (3) and respectively receive the reflected waves through the first and second coaxial waveguide converters, which are not affected by the measured structure. The converted partial reflected wave is received by the second coaxial waveguide converter (2), and the corresponding reflected signal S21-2 is displayed on the vector network analyzer; Step 3): subtract the amplitude square of the signal S21-2 obtained when the structure under test is loaded from the square of the amplitude of the obtained signal S21-1 to obtain the circular polarization conversion efficiency of the structure under test. 8. testing method according to claim 7, is characterized in that: The linearly polarized waves radiated by the first coaxial waveguide converter (1) may be H-polarized, V-polarized or linearly polarized waves in other polarization directions. 9. a PB phase testing method based on the metasurface testing device described in any one of claims 1-6, is characterized in that, this PB phase testing method comprises: 1) Measure the reflected signal S11, which specifically includes: Loading the structure under test, the first coaxial waveguide converter (1) radiates a linearly polarized wave, and 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 reflective waveguide (6) and is reflected by the reflective surface and the measured structure, and the reflected circularly polarized wave is converted into two orthogonal linearly polarized waves through the polarizer (4). The linearly polarized waves in the two directions are separated by the orthogonal mode coupler (3) and the reflected waves are respectively received by the first and second coaxial waveguide converters. The shaft waveguide converter (1) receives, that is, the corresponding reflected signal S11 is obtained; 2) Rotate the measured structure, the rotation angle is θ; automatically collect the phase information of the reflected signal S11 corresponding to different angles θ; 3) Select any frequency point in the measured frequency range, and draw a coordinate diagram of θ and phase information.

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