CN107732460A - Ka-band fully polarized ultra-thin frequency selective surface and radome - Google Patents

Abstract

The invention provides a Ka-band fully-polarized ultrathin frequency selective surface, which comprises a dielectric substrate and metal foil layers attached to the upper surface and the lower surface of the substrate; the metal foil layer of the upper/lower surface comprises an upper/lower periodic microcell structure which is periodically arranged; the unit structure is square and comprises three circular gaps, four metal short circuit gaps are loaded on the circular gaps at the outer side, and the metal short circuit gaps are uniformly distributed on the circular rings; the lower periodic microcell structure corresponds to the upper periodic microcell structure. Wherein. The invention also provides an antenna housing manufactured by adopting the surface, which can be covered in the radiation direction of an antenna system. The all-polarization ultrathin frequency selective surface radome can ensure that the antenna keeps good radiation characteristic in a frequency band of a Ka wave band from 33GHz to 37.5GHz, and can freely receive and transmit communication; meanwhile, the antenna has good out-of-band rejection performance outside the passband, so that the RCS of the antenna is reduced, and the stealth purpose of the antenna is realized.

Description

Ka-band fully polarized ultra-thin frequency selective surface and radome

technical field

The invention belongs to the technical field of materials and radome, and in particular relates to a Ka-band fully polarized ultra-thin frequency selective surface and a radome.

Background technique

A frequency selective surface is an artificial periodic material. The electromagnetic properties of the original dielectric substrate are changed by designing the geometric shape of the metal foil coated on the surface of the dielectric substrate. By design, a frequency selective surface can transmit waves in certain frequency bands and reflect incoming waves in other frequency bands. Combining these frequency selective surfaces with the antenna can physically protect the antenna, act as a radome, improve the radiation performance of the antenna and reduce the radar cross section of the antenna to achieve stealth, etc.; it can also be made in the feed source The reflective surface that reflects electromagnetic waves in the working frequency band of the antenna, and the feed antenna form a reflective surface antenna. The frequency selective surface working in the Ka-band has certain challenges to the design due to the existence of problems such as small structure size, difficult processing and difficult testing.

At present, some research results of new Ka-band frequency selective surfaces have been published. When it is used as a radome, within the working frequency band of the antenna, the frequency selective surface is transparent to the antenna, and does not affect the radiation performance of the antenna or has little influence on the radiation performance of the antenna; but outside the working frequency band, the frequency selection The surface radome reflects the incident electromagnetic wave back along the incoming wave direction, preventing the electromagnetic wave from passing through. When used as part of a reflector antenna, the reflective properties of the frequency selective surface are fully exploited. The reflective surface reflects the electromagnetic wave emitted by the feed source, forms a plane electromagnetic wave in space and transmits the electromagnetic energy to the far area. However, these research results have some shortcomings. Some Ka-band frequency selection surfaces are multi-layer structures, thick, heavy, and not low in profile, so they are not suitable for low-profile antenna application platforms. Although some frequency selective surfaces are light and thin, they do not achieve full polarization characteristics in the Ka band. The passband characteristics of the frequency selective surface are only characterized when a polarized incident electromagnetic wave in a certain direction is irradiated on it. Therefore prior art has its limitation in application.

Contents of the invention

Aiming at the shortcomings of the existing Ka-band frequency selective surface radome that it is difficult to achieve full polarization, poor out-of-band suppression, large thickness and heavy weight, a fully polarized ultra-thin frequency selective surface radome with a thickness of only 0.5 mm is provided. In the 30GHz to 40GHz frequency band, the frequency selection surface is a high-transmittance passband from 33GHz to 37.5GHz, and the in-band transmittance is greater than 95%. When a linearly polarized electromagnetic wave of arbitrary polarization is irradiated onto the frequency selective surface, its electromagnetic properties remain substantially unchanged. Outside the passband, the measured out-of-band suppression can reach about -20dB.

The specific technical scheme is as follows: a Ka-band fully polarized ultra-thin frequency selective surface, including a dielectric substrate made of non-conductive material, and a metal foil layer attached to the upper surface and the lower surface of the dielectric substrate; The metal foil layer on the surface contains several upper periodic micro-unit structures arranged horizontally and vertically periodically, and the metal foil layer on the lower surface contains several lower periodic micro-unit structures arranged horizontally and vertically periodically; the upper / The geometrical configuration of the micro-unit structure of the next period is the same;

The number of micro-unit structures in the last cycle is greater than or equal to 20*20, and the micro-unit structure in the next cycle corresponds to the micro-unit structure in the previous cycle.

According to the above scheme, the micro-unit structure of the last period is a square, including three ring-shaped gaps corroded by the circuit board processing technology, the three rings are concentric rings, and the center of the circle is the geometric center of the micro-unit structure of the last period ;

The micro-unit structure of the lower period is square, including three ring-shaped slits, which are aligned with the corresponding slits of the micro-unit structure of the upper period.

According to the above scheme, four metal short-circuit gaps can also be loaded on the annular gap with the largest inner diameter in the upper/lower period micro-unit structure, and the four metal short-circuit gaps are evenly distributed on the ring, dividing the ring into Four paragraphs of equal length.

According to the above scheme, the symmetry centers of the four metal short-circuit gaps are arranged on the X-axis and Y-axis of the local coordinate system of the upper/lower periodic micro-unit structure, wherein the origin of the local coordinate system is the upper/lower periodic micro-unit structure. The geometric center of the unit structure, the X axis and the Y axis are respectively parallel to the two adjacent sides of the upper/lower periodic micro unit structure.

According to the above scheme, the symmetry centers of the four metal short-circuit gaps are arranged on the angle bisectors of the four quadrants of the local coordinate system, wherein the origin of the local coordinate system is the geometric center of the upper/lower periodic micro-unit structure, The X-axis and the Y-axis are respectively parallel to two adjacent sides of the upper/lower periodic micro-unit structure.

According to the above solution, the length of the metal short-circuit gap is 0.2-0.5 mm.

According to the above scheme, the inner radius of the inner annular gap in the upper/lower periodic micro-unit structure is 1 to 1.2 mm, and the difference between the inner and outer radius is 0.15 to 0.25 mm; the inner radius of the middle annular gap is 1.4 to 1.6 mm. mm, the difference between the inner and outer radii is 0.15 to 0.25 mm; the inner radius of the outer annular gap is 1.8 to 2 mm, and the difference between the inner and outer radii is 0.15 to 0.25 mm.

According to the above solution, the thickness of the dielectric substrate is 0.5 mm, and the thickness of the metal foil is 0.035 mm.

According to the above scheme, the side length of the up/down period micro-unit structure is 4-5 mm

According to the above solution, the metal foil layer can be selected from any material of gold foil, silver foil or copper foil in the metal foil.

The present invention also provides a radome, which includes the Ka-band fully polarized ultra-thin frequency selective surface, which can be used to cover the radiation direction of the antenna system.

Adopting the present invention has the following beneficial effects: the fully polarized ultra-thin frequency selective surface radome in the present invention can make the antenna maintain good radiation characteristics in the frequency band from 33GHz to 37.5GHz in the Ka band, and can freely send and receive communications; at the same time, in the communication The out-of-band has very good out-of-band suppression performance, which reduces the RCS of the antenna and realizes the stealth purpose of the antenna.

Description of drawings

In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings that need to be used in the description of the embodiments or the prior art. Obviously, the accompanying drawings in the following description are only These are some embodiments of the present invention. For those skilled in the art, other drawings can also be obtained according to these drawings without any creative effort.

Fig. 1 is the schematic plan view of Ka wave band fully polarized ultra-thin frequency selective surface of the present invention;

Fig. 2 is a three-dimensional schematic diagram of the upper/lower period micro-unit structure in the present invention;

Fig. 3 is the geometric configuration one of the upper/lower period micro-unit structure in the first embodiment;

Fig. 4 is the geometric configuration two of the upper/lower period micro-unit structure in the first embodiment;

Fig. 5 is the geometric configuration three of the upper/lower period micro-unit structure in the embodiment one;

Fig. 6 is a schematic diagram of the simulation results of the transmission coefficient of the unit structure shown in Fig. 3;

Fig. 7 is a schematic diagram of the simulation result of the transmission coefficient of the unit structure shown in Fig. 4;

Fig. 8 is a schematic diagram of the simulation result of the transmission coefficient of the unit structure shown in Fig. 5;

Fig. 9 is a schematic diagram of the simulation results of the transmission coefficient when the TE wave is incident on the unit structure shown in Fig. 5 at different angles in the first embodiment;

Fig. 10 is a schematic diagram of the simulation results of the transmission coefficient when the TM wave is incident on the unit structure shown in Fig. 5 at different angles in the first embodiment;

11 is a schematic diagram of an experimental platform for testing the frequency selective surface radome in Embodiment 2;

Figure 12 is a diagram of the measured transmission coefficient results when the incident waves are TE waves and TM waves, and the incident angle is 0 degrees;

Figure 13 is a diagram of the measured transmission coefficient results when the TE wave illuminates the radome at different angles;

Figure 14 shows the measured transmission coefficients when the distance d between the radome and the receiving antenna aperture of the standard horn is different.

detailed description

The following will clearly and completely describe the technical solutions in the embodiments of the present invention with reference to the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only some, not all, embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by persons of ordinary skill in the art without creative efforts fall within the protection scope of the present invention.

Embodiment one

As shown in Figure 1, a Ka-band fully polarized ultra-thin frequency selective surface 10x is provided in this embodiment, comprising a dielectric substrate made of a non-conductive material, and a substrate attached to the upper surface and the lower surface of the dielectric substrate. metal foil layer; the metal foil layer on the upper surface contains several upper periodic micro-unit structures 12x arranged horizontally and vertically periodically, and the metal foil layer on the lower surface contains several horizontally and vertically periodically arranged Lay out the micro-unit structure 13x of the lower period; the geometric configuration of the micro-unit structure of the upper and lower periods is the same; the micro-unit structure of the lower period corresponds to the micro-unit structure of the upper period.

As shown in Figure 2, the described upper/lower periodic micro-unit structure 12x/13x is a square, including three ring-shaped gaps corroded by the circuit board processing technology, the three rings are concentric rings, and the center of the circle is the upper / the geometric center of the micro-unit structure in the next period;

The upper/lower periodic microunit structure in FIG. 3 only includes three annular slits 14a, 15a and 16a.

In FIG. 4, the upper/lower periodic micro-unit structure includes three annular slits 14b, 15b and 16b. Metal short-circuit gaps 161b, 162b, 163b and 164b are loaded on the outer annular gap 16b with the largest inner diameter. The symmetry centers Ab, Bb, Cb and Db of the four metal short-circuit gaps are on the X-axis, Y-axis, -X-axis and -Y-axis respectively.

In Fig. 5, the upper/lower periodic micro-unit structure includes three annular slits 14c, 15c and 16c. Metal short-circuit gaps 161c, 162c, 163c and 164c are loaded on the outer annular gap 16c with the largest inner diameter. The centers Ac, Bc, Cc and Dc of the four metal short-circuit gaps are respectively arranged on the angle bisectors of the four quadrants.

The loading position of the slit is very important, which directly determines whether the periodic structure is sensitive to the polarization direction of the incident linearly polarized wave. If the symmetry center of the metal short-circuit gap is at the positions of Ab, Bb, Cb and Db, the transmission characteristics of the unit structure are polarization-sensitive functions. If the center of symmetry of the metal shorting gap is at the positions of Ac, Bc, Cc and Dc, the transmission characteristics of the cell structure are not a sensitive function of polarization.

The non-conductive material in this embodiment is RO4350 from Rogers Company, with a relative permittivity of 3.66 and a loss tangent of 0.004. Gold foil material is selected for the metal foil layer.

Figures 6 to 8 show three different transmission curves obtained by simulation when linearly polarized waves are incident on the three unit structures shown in Figures 3 to 5 respectively. As shown in FIG. 6, when incident on the first cell structure shown in FIG. 3, a wide passband is not formed in the frequency band from 30 GHz to 40 GHz. A narrower resonant frequency band is around 29GHz. Here, S _21@29GHz = -0.02dB. Another resonant frequency band is around 36.8GHz. Here, S _21@36.8GHz = -0.2dB.

As shown in FIG. 7, when incident on the second cell structure shown in FIG. 4, a single passband is formed in the frequency band from 30 GHz to 40 GHz. Its 3dB passband is from 33GHz to 37.5GHz. But around 34.8GHz, there is a deep reflection point that splits the passband in two.

As shown in FIG. 8 , when incident on the third unit structure shown in FIG. 5 , a single passband is formed in the frequency band from 30 GHz to 40 GHz. Its 3dB passband is from 33GHz to 37.5GHz. The reflection point near 34.8GHz disappears. That is, by changing the positions of the four metal short-circuit gaps 161b, 162b, 163b and 164b to the positions of 161c, 162c, 163c and 164c, the reflection point problem is improved.

7 to 8 show that the loading position of the short-circuit gap is very important, which directly determines whether the frequency selective surface is sensitive to the polarization direction of the incident linearly polarized wave.

As shown in FIG. 9 , it is the transmission coefficient of the third unit structure shown in FIG. 5 when horizontally polarized waves (ie, TE waves) are incident at different angles. When the incident angle is less than 30°, the transmission coefficient is greater than -0.5dB in the frequency band from 33GHz to 37.5GHz.

As shown in FIG. 10 , it is the transmission coefficient when vertically polarized waves (ie, TM waves) are incident at different angles to the third unit structure shown in FIG. 5 . When the incident angle is less than 45°, the transmission coefficient is greater than -0.5dB in the frequency band from 33GHz to 37.5GHz. When the incident angle is equal to 60°, a deep reflection point appears near 35.4GHz, which divides the passband into two parts.

Embodiment two

This embodiment provides a radome made by using the Ka-band fully polarized ultra-thin frequency selective surface. The frequency selective surface adopts the third unit structure as shown in FIG. 5 . The side length of the cell structure is 4mm. The radome includes 625 square unit structures, and its size is 100mm×100mm×0.5mm. The dielectric substrate of the radome adopts the sheet material of Rogers Company, the dielectric constant is 3.66, the loss tangent is 0.004, and the thickness is 0.5 mm.

Figure 11 shows a test platform for testing the frequency selective surface radome. The test platform includes a flat radome 2, two Ka-band standard horn antennas 31, 32, and a vector network analyzer 4 connected to the antennas. The working frequency bands of the two Ka-band standard horn antennas 31 and 32 are from 26.5 GHz to 40 GHz. Wherein 31 is a transmitting antenna, 32 is a receiving antenna, 31 and 32 are respectively connected with two ports of the vector network analyzer 4 . Both antennas point the direction of maximum radiation towards each other. Assuming that the radome can rotate around its own vertical center line of symmetry, an angle θ is defined to mark the rotation angle of the radome. When θ=0°, it means that the plane of the radome is parallel to the aperture plane of the receiving antenna 32 . When the planar radome 2 rotates around the center line of symmetry, the angle θ changes. In addition, the distance between the radome and the aperture plane of the receiving antenna 32 is defined as d, and the value of d indicates the distance between the two planes when the plane of the radome is parallel to the aperture plane of the receiving antenna 32 .

Figure 12 shows the transmission coefficient obtained by irradiating the frequency selective surface radome when the polarizations of the two horn antennas are set as horizontally polarized waves (TE waves) or vertically polarized waves (TM waves) at the same time. Both polarized waves are incident vertically on the radome plate, that is, the incident angle θ=0°. At this time, the measured 3dB passband is from 33GHz to 37.5GHz.

Figure 13 shows the measured transmission coefficients when the two horn antennas are set as horizontally polarized waves (TE waves) and the incident angle θ of the incident waves is changed. The incident angles θ are 0°, 15°, 30°, 45°, 60°, respectively. It can be seen from the figure that when the incident angle θ≤30°, the transmission coefficients are all greater than -3dB. When the incident angle θ≥45°, the transmission coefficient in the passband becomes worse. The difference between the simulation results in Fig. 8 and the test results in Fig. 12 is mainly caused by the different boundary conditions. When using high-frequency simulation software to simulate the unit structure, its boundary conditions are master/slave boundary conditions. In the actual measurement, the boundary condition of the radome enclosing the entire frequency selective surface is an open free space.

Figure 14 shows the measured transmission coefficients when the horizontally polarized wave (TE wave) is vertically incident (θ=0°), and the distance between the radome plane and the aperture plane of the receiving horn antenna is different. The plane of the radome is parallel to the aperture plane of the receiving horn antenna. Wherein, d=0mm means that the plane of the radome is directly attached to the aperture surface of the receiving horn antenna. From Figure 14, it can be seen that the transmission coefficient does not change much when the spacing is changed, so the transmission coefficient is not a sensitive function of the spacing. In order to reduce the size of the radome-antenna integrated structure and form a low-profile integrated structure, the radome can be directly attached to the aperture surface of the horn antenna.

Claims (9)

1. A fully polarized ultra-thin frequency selective surface in Ka wave band, comprising a dielectric substrate made of non-conductive material, and a metal foil layer attached to the upper surface and the lower surface of the dielectric substrate; the metal on the upper surface The foil layer contains several upper-period micro-unit structures that are periodically arranged horizontally and vertically, and the metal foil layer on the lower surface contains several lower-period micro-unit structures that are periodically arranged horizontally and vertically; the upper/lower period The geometric configuration of the micro-unit structure is the same; The number of micro-unit structures in the previous period is greater than or equal to 20*20, and the micro-unit structure in the next period corresponds to the micro-unit structure in the previous period; The micro-unit structure of the last period is a square, including three ring-shaped slits, the three rings are concentric rings, and the center of the circle is the geometric center of the micro-unit structure of the last period; The micro-unit structure of the lower period is a square, including three annular slits, which are aligned with the corresponding slits of the micro-unit structure of the upper period; Four metal short-circuit gaps can also be loaded on the annular gap with the largest inner diameter in the upper/lower period micro-unit structure, and the four metal short-circuit gaps are evenly distributed on the ring, and the ring is divided into four equal lengths. part. 2. The surface according to claim 1, wherein the centers of symmetry of the four metal short-circuit gaps are arranged on the X-axis and the Y-axis of the local coordinate system, wherein the origin of the local coordinate system is the upper/ The geometric center of the lower periodic micro-unit structure, the X-axis and the Y-axis are respectively parallel to the two adjacent sides of the upper/lower periodic micro-unit structure. 3. The surface as claimed in claim 1, wherein the centers of symmetry of the four metal short-circuit gaps are arranged on the angle bisectors of the four quadrants of the local coordinate system, wherein the origin of the local coordinate system is the The geometric center of the up/down period micro-unit structure, the X-axis and the Y-axis are respectively parallel to the two adjacent sides of the up/down period micro-unit structure. 4. The surface according to claim 1, wherein the metal short-circuit gap has a length of 0.2-0.5 mm. 5. The surface according to claim 1, characterized in that, the inner radius of the inner annular gap in the upper/lower periodic micro-unit structure is 1-1.2 mm, and the difference between the inner and outer radii is 0.15-0.25 mm; The inner radius of the ring-shaped gap is 1.4-1.6 mm, and the difference between the inner and outer radii is 0.15-0.25 mm; the inner radius of the outer ring-shaped gap is 1.8-2 mm, and the difference between the inner and outer radii is 0.15-0.25 mm. 6. The surface of claim 1, wherein the dielectric substrate has a thickness of 0.5 mm, and the metal foil has a thickness of 0.035 mm. 7. The surface according to claim 1, characterized in that, the side length of the up/down periodic micro-unit structure is 4-5 mm. 8. The surface according to claim 1, wherein the metal foil layer can be selected from gold foil, silver foil, or copper foil. 9. A radome, comprising the Ka-band fully polarized ultra-thin frequency selective surface according to claims 1-8, the radome cover is arranged in the radiation direction of the antenna system.