A Portable Measuring Device and Method for Measuring the Reflectivity of Absorbing Materials

Abstract

The present invention provides a portable reflectivity measuring device for absorbing materials, which includes a vector network analyzer, a broadband antenna, an adjustable antenna support, a connecting device and an absorbing window. The vector network analyzer includes a liquid crystal display screen, mechanical keys or touch screen keys, an interface for an external USB storage device and a battery; the broadband antenna is a double-ridge waveguide probe; the adjustable antenna support includes a fixing mechanism, a tripod and a locking screw; the fixing mechanism surrounds the outer contour of the antenna and is fastened by the locking screw; the tripod consists of two П-shaped brackets and is locked by the locking screw; the broadband absorbing window has a rectangular window cut out at its center, which is consistent with the radiation aperture surface of the antenna; the vector network analyzer is connected and fixed to the broadband antenna through the connecting device, and a signal separator and a radio frequency cable are arranged inside the connecting device. The present invention also provides a portable method for measuring the reflectivity of absorbing materials, and the present invention is applicable to operation sites such as construction sites of absorbing materials, repair sites of stealth equipment and storage warehouses, etc.

Description

Technical Field

[0001] The present invention belongs to the field of measuring the reflectivity of microwave absorbing materials, and particularly relates to a portable device and method for measuring the reflectivity of microwave absorbing materials. Background Art

[0002] The performance detection of microwave absorbing materials is generally carried out under ideal conditions such as in anechoic chambers. The stealth effect of equipment after applying microwave absorbing materials is generally verified by indoor compact range or outdoor range RCS tests. However, there is a lack of effective detection methods for the stealth effect of microwave absorbing materials during the equipment development stage, delivery and acceptance stage, especially during the use and maintenance stage. During the use and maintenance stage after the equipment is delivered, due to various reasons, the radar absorbing materials on the equipment surface are locally damaged, which may seriously affect the overall stealth effect of the equipment. After local repair of the damaged part, at present, it is still necessary to rely on the full-scale target stealth performance test to complete the stealth performance integrity evaluation, which has problems such as high test cost and long test cycle. Therefore, a fast, convenient and low-cost detection means for the stealth effect of microwave absorbing materials is needed to complete engineering problems such as weapon equipment stealth defect detection and positioning, local stealth performance data acquisition, and local stealth performance integrity evaluation after the use and maintenance of weapon equipment at the construction site, repair site, warehouse and other operation sites.

[0003] In view of the above requirements, a device disclosed in Chinese Patent No. CN202256192U uses instruments such as a vector network analyzer or a voltage reflectometer as the core, and a radio frequency cable connects it to a microwave probe or an antenna. During measurement, the microwave probe is attached to the surface of the sample to be measured, and after measuring its S11 parameter, its reflectivity is obtained through calibration. In practical applications, the disadvantages of this solution are as follows: (1) The working frequency band range of the probe is divided according to the standard wave band (taking 2.6 GHz to 18 GHz as an example, which is divided into 5 segments in total). When measuring different frequency bands, the feed source needs to be frequently disassembled and replaced; at the same time, it is easy to cause the performance of the radio frequency cable to decline due to frequent wear; (2) When measuring, it is inevitable to move the measurement system over a large range, and bending, stretching, twisting, etc. of the radio frequency cable will have a great impact on its transmission performance, resulting in poor measurement stability of the system. A handheld radar system material reflectivity on-site measuring instrument disclosed in Chinese Patent No. CN205982130U has the characteristics of high integration and miniaturization, has the shape of an electric drill, and the waveguide probe used is applicable to wave bands such as 2 GHz to 4 GHz, 4 GHz to 8.2 GHz, 8.2 GHz to 12 GHz, 12 GHz to 18 GHz, 18 GHz to 26.5 GHz, etc. In practical applications, the disadvantages of this measuring instrument solution are as follows: (1) Limited by the limitation of the waveguide on the working frequency, a complete set of independent test systems needs to be configured for each working wave band. Taking 2 GHz to 18 GHz as an example, 4 measuring instruments need to be configured; (2) The waveguide probe and the surface of the sample to be measured adopt a contact measurement method, which does not meet the far-field conditions and is not suitable for curved surface measurement. A handheld absorbing material reflectivity measuring device disclosed in Chinese Patent No. CN105352978A uses a pair of miniaturized near-field focusing antennas to replace the traditional horn antenna, reduces the requirements of the test system for the test space, and realizes a miniaturized test system. The disadvantages of this invention are as follows: (1) The measurement distance is small, and the transmitting and receiving antennas are separated, resulting in a bistatic angle in the measurement; (2) It is not suitable for curved surface measurement. Summary of the Invention

[0004] The present invention provides a portable absorbing material reflectivity measuring device and a measuring method, which can be conveniently used for measuring the reflectivity of absorbing materials on flat and curved surfaces.

[0005] A portable absorbing material reflectivity measuring device includes a vector network analyzer, a broadband antenna, an adjustable antenna bracket, a connecting device, and an absorbing window;

[0006] The vector network analyzer is a single-source dual-port instrument, which is used to generate and measure microwave signals within the working frequency range, has amplitude and phase measurement functions, and its components include a liquid crystal display screen, mechanical buttons or touch screen buttons, an interface for an external USB storage device, and a battery;

[0007] The broadband antenna is a double-ridge waveguide probe;

[0008] The adjustable antenna support includes a fixing mechanism, a tripod and a locking screw; the fixing mechanism surrounds the outer contour of the antenna and is fastened by the locking screw; the tripod consists of two П-shaped brackets and is locked by the locking screw;

[0009] For the broadband absorber window, a rectangular window consistent with the antenna radiation aperture is cut out at its center; during the test, the legs of the adjustable antenna support pass through the absorber window, and the end of the support away from the antenna is attached to the surface of the area to be measured;

[0010] The vector network analyzer is connected and fixed to the broadband antenna through a connecting device, making the instrument and the antenna form an integral whole. A signal separator and a radio frequency cable are arranged inside the connecting device for separating the transmitted and received signals.

[0011] Furthermore, when the broadband antenna is used in conjunction with the adjustable antenna support, the measurement distance between the antenna and the surface of the area to be measured can be adjusted to meet the far-field condition:

[0012]

[0013] In the formula, R is the measurement distance, λ is the operating wavelength, and D is the maximum characteristic dimension of the antenna aperture; according to the test frequency, the minimum distance that meets the above conditions is selected.

[0014] Furthermore, four equidistant support points are formed at the end of the adjustable antenna support away from the antenna for measuring the perpendicular reflectivity of a plane, a single-curved / double-curved surface; by adjusting the extended lengths of the two П-shaped brackets, an oblique incidence test condition is formed, which is applicable to measuring the oblique reflectivity of a plane, a single-curved / double-curved surface.

[0015] Furthermore, the material of the fixing mechanism of the adjustable antenna support is engineering plastic, alloy or other hard materials; the material of the legs is selected from hard materials such as ASA plastic, fiberglass, and PMI foam with good wave transmission performance.

[0016] A method for measuring the reflectivity of portable absorbing materials includes the following steps:

[0017] First step, align the portable absorbing material reflectivity measuring device with the area to be measured, make the 4 support points of the antenna support contact the surface of the area to be measured, measure and store the S21 parameter of the absorbing material on the surface of the equipment to be measured, denoted as S RAM ;

[0018] Second step, paste a thin patch made of aluminum foil or other good conductor material on the surface of the absorbing material in the area measured in the first step, keep the test position, measurement attitude and test parameters of the portable absorbing material reflectivity measuring device unchanged, measure and store the S21 parameter of the good conductor thin patch, denoted as S Metal ;

[0019] In the third step, with the parameters of the portable radar-absorbing material reflectivity measurement device remaining unchanged, point the measurement antenna towards the open space, measure the S21 parameter of the open space and store it, denoted as S 背景 ;

[0020] In the fourth step, obtain the echo signals of the radar-absorbing material on the equipment surface and the metal surface through background cancellation processing. The background cancellation process is as follows:

[0021] S' RAM = S RAM - S 背景 (2)

[0022] S' Metal = S Metal - S 背景 (3)

[0023] In the fifth step, for the echo signals of the radar-absorbing material and the metal surface after background cancellation processing, use the software time domain gate to perform clutter suppression processing on them respectively. The processed echo signals are denoted as and

[0024]

[0025] In the sixth step, calculate the reflectivity of the radar-absorbing material. The calculation formula is as follows

[0026]

[0027] Furthermore, when conducting oblique incidence reflectivity measurement, the data acquisition steps are as follows:

[0028] (1) Replace the fastening screw in contact with the fixed tripod with an adjustment screw for adjusting the telescoping of the tripod;

[0029] (2) According to the test angle of the single-station oblique incidence reflectivity to be tested, calculate the length difference between the two tripods and adjust the lengths of the corresponding tripods to the required positions.

[0030] Advantages of the present invention:

[0031] (1) The portable radar-absorbing material reflectivity measurement device proposed by the present invention has the characteristics of miniaturization and light weight, and can be used for measuring the reflectivity of radar-absorbing materials on flat and curved surfaces. It is very suitable for use in operation sites such as the construction site of radar-absorbing materials, the repair site of stealth equipment, and the storage warehouse.

[0032] (2) The measurement device proposed by the present invention adopts an integrated integration scheme. The miniaturized vector network analyzer, broadband antenna, and RF cable are solidified into one body through a connecting device, avoiding problems such as unstable testing caused by the jitter of the RF cable and inaccurate antenna pointing during use, and having good consistency in measurement results;

[0033] (3) In the test scheme proposed by the present invention, there is a certain distance between the antenna and the surface to be measured, making the measurement approximately meet the far-field condition, closer to the ideal measurement condition, and with higher measurement accuracy.

[0034] (4) The measuring device proposed by the present invention can change the antenna pointing by adjusting the antenna support, making it applicable to the measurement of the oblique incidence reflectivity. Description of the Drawings

[0035] Figure 1 It is a schematic diagram of a portable reflectivity measuring device for absorbing materials.

[0036] Figure 2 It is a schematic diagram of the adjustable antenna support structure.

[0037] Figure 3 It is a schematic diagram of the connecting device.

[0038] Figure 4 It is the work flow of the on-site reflectivity test method. Detailed Embodiment

[0039] The present invention will be further described in detail below with reference to the drawings.

[0040] The portable reflectivity measuring device for absorbing materials includes a miniaturized vector network analyzer, a broadband antenna, an adjustable antenna support, a connecting device, and an absorbing window, as shown in Figure 1 .

[0041] The miniaturized vector network analyzer is a single-source and dual-port instrument, used to generate and measure microwave signals within the working frequency range, and has the functions of amplitude and phase measurement. It includes components such as a liquid crystal display screen, mechanical buttons or touch screen buttons, an interface for an external USB storage device, and a battery.

[0042] The broadband antenna is a double-ridge waveguide probe, with a working frequency band of 6 GHz to 18 GHz, and the characteristic size of the radiation aperture is 32 mm × 21 mm.

[0043] As Figure 2 shown, the adjustable antenna support includes three parts: a fixing mechanism, a tripod, and a locking screw. The fixing mechanism surrounds the outer contour of the antenna and can be fastened by the locking screw. Its material can be engineering plastic, alloy, or other hard materials. The tripod consists of two П-shaped brackets, which can be adjusted to an appropriate position according to needs and then locked by the locking screw to form a stable antenna support structure. Four equally spaced support points are formed at the end of the bracket away from the antenna, and its material is a hard material with good wave transmission performance such as ASA plastic, fiberglass, or PMI foam.

[0044] When the broadband antenna is used in cooperation with the adjustable antenna support, the measurement distance between the antenna and the surface of the area to be measured can be adjusted. The selection of the distance needs to meet the far-field condition:

[0045]

[0046] In the formula, R is the measurement distance, λ is the working wavelength, and D is the maximum characteristic dimension of the antenna aperture. According to the test frequency, the minimum distance that satisfies the above conditions is usually selected to reduce the energy loss of electromagnetic waves during spatial transmission.

[0047] Taking the ultra-wideband measurement from 6 GHz to 18 GHz as an example, for an antenna radiation aperture with characteristic dimensions of 32 mm × 21 mm, if the far-field condition is to be satisfied in the entire frequency band, the measurement distance is required to be not less than 61.4 mm. To reduce the energy loss of electromagnetic waves during spatial transmission, the measurement distance is selected as 62 mm.

[0048] Furthermore, a broadband absorbing window is fabricated. The selected material is a polyurethane absorbing flat / plate-cone material, and the material thickness should not exceed the distance from the antenna to the surface to be measured. A rectangular window consistent with the antenna radiation aperture is cut out at its center. During testing, the adjustable antenna support tripod passes through the absorbing window, and the end of the support away from the antenna is attached to the surface of the area to be measured. The absorbing window can absorb and consume most of the electromagnetic wave energy transmitted deviating from the direction of the antenna main beam.

[0049] The miniaturized vector network analyzer is connected and fixed to the broadband antenna through a connecting device, so that the instrument and the antenna form an integral body. A signal separator and a radio frequency cable are arranged inside the connecting device for separating the transmitted and received signals, as shown in Figure 3 .

[0050] As Figure 3 shown, the in-situ reflectivity measurement method based on the portable absorbing material reflectivity measurement device mainly includes the following steps:

[0051] First step, align the portable absorbing material reflectivity measurement device with the area to be measured, make the 4 support points of the antenna support contact the surface of the area to be measured, measure and store the S21 parameter of the absorbing material on the surface of the equipment to be measured, denoted as S RAM ;

[0052] Second step, paste a thin patch made of aluminum foil or other good conductor materials on the surface of the absorbing material in the area measured in the first step. Keep the test position, measurement attitude and test parameters of the portable absorbing material reflectivity measurement device unchanged, measure and store the S21 parameter of the good conductor thin patch, denoted as S Metal ;

[0053] Third step, keep the parameters of the portable absorbing material reflectivity measurement device unchanged, point the measurement antenna to the open space, measure and store the S21 parameter of the open space, denoted as S 背景 ;

[0054] Step 4: Obtain the echo signals of the absorbing material on the equipment surface and the metal surface through background cancellation processing. The background cancellation processing procedure is as follows:

[0055] S' RAM = S RAM - S 背景 (2)

[0056] S' Metal = S Metal - S 背景 (3)

[0057] Step 5: Apply the software time domain gate to the echo signals of the absorbing material and the metal surface after background cancellation processing to perform clutter suppression processing on them respectively. The processed echo signals are respectively denoted as and

[0058]

[0059] Step 6: Calculate the reflectivity of the absorbing material. The calculation formula is as follows

[0060]

[0061] When conducting the measurement of the oblique incidence reflectivity, the data acquisition steps are as follows:

[0062] (1) Replace the fastening screw in contact with the fixed tripod with an adjustment screw for adjusting the telescoping of the tripod;

[0063] (2) Calculate the length difference between the two tripods according to the test angle of the single - station oblique incidence reflectivity to be tested, and adjust the lengths of the corresponding tripods to the required positions.

[0064] The above specific implementation manners are only limited to explaining and illustrating the technical solution of the present invention, but do not constitute a limitation on the protection scope of the claims. Those skilled in the art should clearly understand that any new technical solution obtained by making any simple deformation or substitution on the basis of the technical solution of the present invention falls within the protection scope of the present invention.

Claims

1. A portable reflectivity measuring device for microwave absorbing materials, characterized in that, It includes a vector network analyzer, a broadband antenna, an adjustable antenna support, a connecting device, and an absorbing window; The vector network analyzer is a single-source dual-port instrument used to generate and measure microwave signals within the operating frequency range, with amplitude and phase measurement functions. Its components include a liquid crystal display screen, mechanical buttons or touch screen buttons, an interface for an external USB storage device, and a battery; The broadband antenna is a double-ridge waveguide probe; The adjustable antenna support includes a fixing mechanism, tripod legs, and locking screws; the fixing mechanism surrounds the outer contour of the antenna and is fastened by the locking screws; the tripod legs are two П-shaped brackets and are locked by the locking screws; The broadband absorbing window has a rectangular window cut out at its center that is the same as the antenna radiation aperture surface; during testing, the tripod legs of the adjustable antenna support pass through the absorbing window, and the end of the support away from the antenna is attached to the surface of the area to be measured; The vector network analyzer is connected and fixed to the broadband antenna through the connecting device, making the instrument and the antenna form an integral whole. The connecting device internally arranges a signal separator and a radio frequency cable for separating the transmitted and received signals; The broadband antenna is used in conjunction with the adjustable antenna support, which can achieve an adjustable measurement distance between the antenna and the surface of the area to be measured, so that the measurement distance meets the far-field condition: In the formula, R is the measurement distance, λ is the operating wavelength, and D is the maximum characteristic dimension of the antenna aperture; According to the test frequency, select the minimum distance that meets the above conditions; Four equally spaced support points are formed at the end of the adjustable antenna support away from the antenna. The four support points are in contact with the surface of the area to be measured and are used for measuring the perpendicular reflectivity of a plane, a single-curved / double-curved surface; by adjusting the extended lengths of the two П-shaped brackets, an oblique incidence test condition is formed, which is applicable to measuring the oblique reflectivity of a plane, a single-curved / double-curved surface.

2. The portable reflectivity measuring device for microwave absorbing materials according to claim 1, characterized in that, The material of the fixing mechanism of the adjustable antenna support is engineering plastic, alloy, or other hard materials; the material of the tripod legs is selected from hard materials such as ASA plastic, fiberglass, and PMI foam with good wave transmission performance.

3. A portable reflectivity measuring method for microwave absorbing materials using the portable reflectivity measuring device according to claim 1 or 2, characterized in that, It includes the following steps: First step, align the portable radar-absorbing material reflectivity measurement device with the area to be measured, make the 4 support points of the antenna bracket contact the surface of the area to be measured, measure and store the S21 parameter of the radar-absorbing material on the surface of the equipment to be measured, denoted as S RAM ; Step 2: Paste a thin patch made of aluminum foil or other good conductor materials on the surface of the absorbing material in the area measured in Step 1. Keep the test position, measurement attitude, and test parameters of the portable absorbing material reflectivity measurement device unchanged, measure the S21 parameter of the good conductor thin patch and store it, denoted as S Metal ; In the third step, with the parameters of the portable microwave absorber reflectivity measurement device remaining unchanged, point the measurement antenna towards open space, measure the S21 parameter of the open space and store it, denoted as S 背景 ; The fourth step is to obtain the echo signals of the absorbing material on the equipment surface and the metal surface through background cancellation processing. The background cancellation processing process is as follows: S' RAM = S RAM - S 背景 (2) S' Metal = S Metal - S 背景 (3) Step 5: For the echo signals of the wave-absorbing material and the metal surface after background cancellation processing, use the software time domain gate to perform clutter suppression processing on them respectively. The processed echo signals are respectively denoted as and The sixth step is to calculate the reflectivity of the absorbing material. The calculation formula is as follows 4. The portable reflectivity measuring method for microwave absorbing materials according to claim 3, characterized in that, When conducting oblique incidence reflectivity measurement, the data acquisition steps are as follows: (1) Replace the fastening screw in contact with the fixed tripod leg with an adjustment screw that can adjust the telescoping of the tripod leg; (2) According to the test angle of the single-station oblique incidence reflectivity to be tested, calculate the length difference between the two tripod legs and adjust the lengths of the corresponding tripod legs to the required positions.

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