CN106654598A - Non-equidistant arrangement-based polarization wire grating apparatus - Google Patents

Abstract

The invention discloses a non-equidistantly arranged polarized wire grid device, which comprises: several non-equidistantly arranged metal wires and a frame; several metal wires are embedded in the frame in a vertical arrangement; non-equidistantly arranged The equidistant arrangement of wires means that the distances between the wires are different, and there are two types of distances: wide spacing and narrow spacing, by setting the value of wide spacing and narrow spacing, the number of narrow spacing and wide spacing, and the diameter of the wire To adjust and optimize the core parameters of the fill factor, insertion loss and extinction ratio of the polarized wire grid. The device of the invention has the characteristics of low actual filling factor, high equivalent filling factor, low insertion loss, high extinction ratio, and low requirement for processing technology.

Description

A non-equidistantly arranged polarized wire grid device

technical field

The invention relates to the application field of microwave (millimeter wave, terahertz) remote sensing, in particular to a non-equidistantly arranged polarized wire grid device.

Background technique

Microwave (including millimeter wave and terahertz) remote sensing can provide space weather data such as global atmospheric temperature and humidity, water vapor content, and rainfall all day and all weather, as well as ocean surface temperature, ocean wind field, and soil moisture. It plays an important role in detection and ocean and land observation. In practical remote sensing applications, it is necessary to use a polarization separator to separate microwave (millimeter wave, terahertz) radiation into two mutually perpendicular polarization directions, so as to obtain more remote sensing information. Polarized wire grids are widely used as a quasi-optical polarization separator; in my country's "Gaofen-1" satellite, Fengyun-3 "microwave hygrometer" and the "fully polarized microwave" developed by the Microwave Remote Sensing Department of the National Space Center Radiometer calibration source" and other aspects have important applications.

Polarized wire grid is a quasi-optical device that can convert non-polarized electromagnetic waves into two linearly polarized components perpendicular to each other. As shown in Figure 1, common polarized wire grids are arranged equidistantly.

Polarized wire grid has two core parameters: insertion loss and extinction ratio. The extinction ratio indicates the proportion of the vertical polarization component, and the higher the extinction ratio, the stronger the polarization separation ability of the polarized wire grid. The metal filling factor of the polarized wire grid represents the density of the polarized wire grid. When the fill factor is 1, the polarized wire grid is a complete metal plate, and when the fill factor is 0, the polarized wire grid is an air wall. The filling factor generally takes a value between 0 and 1, so that the polarized wire grid is distributed between metal and air.

The insertion loss of a polarized wire grid is frequency and fill factor dependent. The fill factor of the polarized wire grid affects the transmission characteristics of electromagnetic waves of different frequencies and polarization modes. The transmission loss of electromagnetic waves whose polarization direction is perpendicular to the wire grid metal arrangement direction is basically flat when the fill factor is less than 98%, but increases sharply after 98%. In contrast, the transmission loss of electromagnetic waves whose polarization direction is parallel to the wire grid arrangement increases steadily with the increase of fill factor. The extinction ratio refers to the ratio between the transmission loss of the electromagnetic wave whose polarization direction is perpendicular to the wire grid arrangement direction and the electromagnetic wave transmission loss whose polarization direction is parallel to the wire grid arrangement direction. The extinction ratio will increase with the increase of the fill factor of the polarized wire grid. When the fill factor is between 90% and 100%, it can reach a maximum value of about 60dB. After the highest point, the polarization direction is perpendicular to the line The transmission loss and extinction ratio of the electromagnetic wave in the direction of the grid arrangement are sharply reduced at the same time.

Therefore, the fill factor has a very important influence on the two core parameters of the polarized wire grid. As the frequency increases, to achieve a high fill factor, it is necessary to reduce the spacing between adjacent metal wires (bars) in the wire grid. When the frequency is high (submillimeter wave/terahertz frequency band), the polarization The processing accuracy and processing technology of the wire grid put forward very high requirements.

When the equidistant arrangement of the traditional polarized wire grid obtains a higher filling factor, the proportion of the metal part is larger, and the penetration rate of the electromagnetic wave whose polarization direction is perpendicular to the direction of the wire grid arrangement is low; The interval is very narrow, increasing the difficulty of processing.

Contents of the invention

The purpose of the present invention is to overcome the above-mentioned defects in the equidistant arrangement of traditional polarized wire grids, and provide a new polarized wire grid for quasi-optical polarization separators through the non-equidistantly arranged design of metal wires. The polarization wire grid is divided into narrow-pitch clusters by rational arrangement of metal wires, and the narrow-pitch clusters are separated by wide intervals; the combination of narrow and wide intervals changes the equal spacing of traditional polarization wire grids. Compared with the traditional polarized wire grid arranged at equal intervals, the arrangement method has a higher extinction ratio under the same insertion loss. In the case of the same extinction ratio, it has lower insertion loss. At the same time, when the actual filling factor is only about 48%, an equivalent filling factor of more than 80% can be obtained, and the processing difficulty can be appropriately reduced in the high-frequency region.

In order to achieve the above object, the present invention provides a non-equidistantly arranged polarization wire grid device, which includes: several non-equidistantly arranged metal wires and a frame; several metal wires are inlaid in a vertical arrangement In the frame; non-equidistantly arranged metal wires mean that the distances between the metal wires are different, and there are two distances: wide spacing and narrow spacing, by setting the value of wide spacing and narrow spacing, the number of narrow spacing and wide spacing And the diameter of the metal wire to adjust and optimize the core parameters of the fill factor, insertion loss and extinction ratio of the polarized wire grid.

In the above technical solution, the core parameters such as the fill factor of the optimized polarized wire grid, insertion loss and extinction ratio are adjusted by setting the value of the wide pitch and the narrow pitch, the number of the narrow pitch and the wide pitch, and the diameter of the metal wire. The specific process is as follows: first, set the ratio of the number of narrow pitches to the number of wide pitches according to the fill factor of the polarized wire grid; then set the value ranges of wide pitches, narrow pitches, and wire diameters; pitch, narrow pitch, and wire diameter, according to the fill factor, insertion loss, and extinction ratio of the polarized wire grid, the optimal values of wide pitch, narrow pitch, and wire diameter are determined.

In the above technical solution, if printed board printing technology is adopted, the device further includes: a printed board substrate.

The advantages of the present invention are:

1. The non-equidistantly arranged polarized wire grid device of the present invention is composed of non-equidistantly arranged metal wires and a frame. By adjusting the thickness of the metal wires, setting the size of the wide pitch and the narrow pitch and the distribution characteristics of the wide and narrow pitches When the actual fill factor is low, a higher equivalent fill factor is obtained, so as to achieve a higher extinction ratio while meeting the requirements of insertion loss, and provide the polarization separation capability of the polarized wire grid; at the same time, at the same extinction ratio Under normal circumstances, the insertion loss of non-equidistantly arranged polarized wire grids is much lower than that of traditional equidistantly arranged polarized wire grids, especially at higher frequencies;

2. The device of the present invention has the characteristics of low actual filling factor, high equivalent filling factor, low insertion loss, high extinction ratio, and low requirements for processing technology;

3. The polarized wire grid device of the present invention can be applied in space-borne and ground-based radiometer systems. It can also be used in various radiometer variable temperature source devices, including fully polarized radiometer calibration sources;

4. The polarized wire grid device of the present invention can be used in outdoor and laboratory environments, thermal vacuum environments and satellite platforms.

Description of drawings

FIG. 1 is a schematic diagram of an existing equidistant arrangement of polarized wire grids;

Fig. 2 is a schematic diagram of a non-equidistantly arranged polarized wire grid of the present invention.

detailed description

The invention proposes a method of improving the equivalent filling factor of the polarized wire grid by changing the arrangement and distribution mode of the polarized wire grid. The equidistant arrangement of the traditional polarized wire grid is changed to the non-equidistant arrangement, and the non-equidistant arrangement of the actual low fill factor is used to achieve the same technical parameters as the equidistant arrangement of the high fill factor polarized wire grid. Thereby greatly reducing the requirements of the high-frequency polarization wire grid on the process, and better designing and processing the polarization wire grid that meets the submillimeter wave/terahertz frequency band.

The non-equidistantly arranged polarization wire grid of the present invention will be described in detail below with reference to the accompanying drawings.

As shown in Figure 2, a non-equidistantly arranged polarized wire grid device, the device includes: several non-equidistantly arranged metal wires and a frame; the frame is circular, and several metal wires pass through the vertical The arrangement is inlaid in the frame; the non-equidistant arrangement of metal wires means that the distance between the metal wires is different. There are two kinds of distances: wide spacing and narrow spacing. By setting the value of wide spacing and narrow spacing, setting narrow spacing The number of spacing and wide spacing, as well as the diameter of the wire to adjust and optimize the core parameters of the polarized wire grid fill factor, insertion loss and extinction ratio; the specific process is: first set the narrow according to the fill factor of the polarized wire grid The ratio of the number of spacing to the number of wide spacing; then set the value range of wide spacing, narrow spacing and wire diameter; within the value range, traverse the wide spacing, narrow spacing and the diameter of the wire, according to the obtained polarization line The fill factor, insertion loss and extinction ratio of the grid are used to determine the optimal value of wide pitch, narrow pitch, and wire diameter, thereby fabricating a non-equidistantly arranged polarized wire grid device.

If printed board printing technology is used, the device further includes: a printed board substrate.

The self-resonant frequency f ₀ of the polarized wire grid can be described by a lumped parameter:

Among them, L _s is the chip inductor, and C _g is the gap capacitance.

The relationship between the chip inductor and the fill factor of the polarized wire grid is as follows:

ff is the fill factor, l is the period of the polarized wire grid, μ ₀ is the permittivity of free space, σ is the metal conductivity, f is the frequency; the unit of L _s is H/m ₂ . It can be seen from the above formula that the chip inductance is directly proportional to the fill factor. This is also physically plausible, since increasing the fill factor means increasing the proportion of the metal portion, thus increasing the inductance.

The gap capacitance of the polarized wire grid is as follows: (unit F/m ² )

Among them, ε _e is the effective dielectric constant, Z ₀ is the characteristic impedance of the metal wire, c is the speed of light in vacuum, and l is the period of the wire grid. In order to determine the effective dielectric constant ε _e in the above formula, the metal wire in the polarized wire grid can be regarded as a microstrip transmission line. Based on the microstrip line theory, the effective dielectric constant can be regarded as a homogeneous medium that equivalently replaces the air and substrate around the microstrip line. The effective dielectric constant is frequency-dependent, and the gap capacitance increases monotonically with the fill factor and frequency. It is also physically plausible because increasing the fill factor reduces the spacing between the wires and thus increases the gap capacitance (similar to parallel plate capacitance).

The self-resonant frequency of the polarized wire grid can be obtained by combining the calculation of the chip inductance and the gap capacitance and using formula (1). The self-resonant frequency decreases monotonically with the fill factor, which also has physical meaning. Because as the fill factor increases, the chip inductance and gap capacitance increase at the same time. The self-resonant frequency is very high when the fill factor is low, and can reach more than 2000 GHz when ff=2.5%. Initially, the self-resonant frequency drops rapidly when the fill factor is low and increases. When the fill factor becomes larger, the self-resonant frequency changes slowly with the fill factor, and tends to remain unchanged at about 125 GHz when the fill factor is high.

The present invention adopts the polarized wire grid with actually low fill factor to achieve higher equivalent fill factor, and can make the polarized wire grid with actual 48% metal fill factor reach an equivalent fill factor of 80%; the actual 30% metal fill factor The polarized wire grid achieves an equivalent fill factor of 50%. When the actual metal filling factor is only 48% (30%), its extinction ratio can reach the level equivalent to the 80% (50%) filling factor of the uniform arrangement, especially when the frequency is high.

The non-equidistantly arranged polarized wire grid provided by the present invention can realize the design of high equivalent fill factor; compared with the traditional uniformly arranged polarized wire grid, it contains less metal parts, but for the polarization direction perpendicular to the wire grid arrangement Electromagnetic waves in the opposite direction have better penetration characteristics, especially at high frequencies. At the same time, although the transmission suppression characteristics of the polarization direction parallel to the wire grid arrangement direction are slightly lower than the real high fill factor, it is also better than the uniformly arranged polarized wire grid with the actual low fill factor. However, designs that achieve high equivalent fill factors through non-equidistant arrangements still achieve high extinction ratios, comparable to the case of uniform arrangements with high fill factors. Therefore, the design of obtaining high equivalent fill factor by adopting non-equidistant arrangement can meet the application scenario of achieving high extinction ratio under the requirement of high transmittance.

Claims (3)

1. A non-equidistantly arranged polarized wire grid device, said device comprising: several non-equidistantly arranged metal wires and a frame; it is characterized in that several metal wires are embedded in the frame in a vertical arrangement ;Non-equidistant arrangement of metal wires means that the distances between the metal wires are different. There are two types of distances: wide spacing and narrow spacing, by setting the value of wide spacing and narrow spacing, the number of narrow spacing and wide spacing and the wire The core parameters such as fill factor, insertion loss and extinction ratio of the polarized wire grid are adjusted and optimized by adjusting the diameter of the polarized wire grid. 2. The non-equidistantly arranged polarized wire grid device according to claim 1, characterized in that, said setting the value of the wide pitch and the narrow pitch, the quantity of the narrow pitch and the wide pitch, and the diameter of the metal wire The specific process of adjusting and optimizing the core parameters of the polarized wire grid’s fill factor, insertion loss, and extinction ratio is as follows: first, set the ratio of the number of narrow pitches and wide pitches according to the fill factor of the polarized wire grid; then set the wide pitch, narrow pitch, and The value range of spacing and wire diameter; within the value range of , traverse the wide spacing, narrow spacing and the diameter of the metal wire, and determine the wide spacing according to the fill factor, insertion loss and extinction ratio of the obtained polarized wire grid , narrow pitch and optimal value of wire diameter. 3. The non-equidistantly arranged polarized wire grid device according to claim 1 or 2, wherein if printed board printing technology is used, the device further comprises: a printed board substrate.