Frequency selective unit, frequency selective surface, and base station antenna

Abstract

Provided in the present application is a frequency selective unit. The frequency selective unit comprises a dielectric layer, a first metal layer, and a second metal layer, wherein the first metal layer covers one side of the dielectric layer, and the second metal layer covers the other side of the dielectric layer; and the first metal layer has a cut-off portion in the middle, the projection area of the cut-off portion on the second metal layer comprises a first region, and the first region comprises a metal pattern. Further provided in the present application are a frequency selective surface and a base station antenna.

Description

Frequency selective unit, frequency selective surface and base station antenna

[0001] Cross-references

[0002] This application claims priority to the Chinese patent application filed with the China Patent Office on March 27, 2024, with application number 202410359046.6 and invention name “Frequency Selection Unit, Frequency Selection Surface and Base Station Antenna”. The entire contents of the application are incorporated by reference into this application. Technical Field

[0003] The present application relates to the field of communication technology, and in particular to a frequency selection unit, a frequency selection surface and a base station antenna. Background Art

[0004] In current communications technology, to meet users' multi-standard needs, base station antennas can use multi-frequency antennas. Furthermore, to reduce inter-frequency interference between different antennas, frequency selective surfaces (FSS) can be used within the base station antennas. For example, in some typical application scenarios, the base station antenna includes a high-frequency antenna and a low-frequency antenna. The radiating surface of the high-frequency antenna overlaps with the radiating surface of the low-frequency antenna in the vertical direction. To reduce inter-frequency interference between the high-frequency and low-frequency antennas, a frequency selective surface can be introduced vertically between the high-frequency and low-frequency antennas. The frequency selective surface has low resistance and high pass properties, and can serve as both a reflective surface for the low-frequency antenna and a radome for the high-frequency antenna, effectively alleviating the problem of inter-frequency interference.

[0005] In related art, frequency selective surfaces (FSSs) typically employ multilayer structures to achieve low-impedance, high-pass characteristics across a wide frequency band or to achieve pass-stop / block transitions within a narrow frequency interval. However, these multilayer FSSs are not only thick but also difficult to manufacture, and their performance at high oblique incidence angles often fails to meet practical requirements. Summary of the Invention

[0006] The present application provides a frequency selection unit, a frequency selection surface and a base station antenna.

[0007] In a first aspect, a frequency selection unit is provided, comprising a dielectric layer, a first metal layer, and a second metal layer, wherein: the first metal layer is covered on one side of the dielectric layer, the second metal layer is covered on the other side of the dielectric layer, the first metal layer is cut off in the middle, and the projection area of ​​the cut-off part on the second metal layer includes a first area, and the first area includes a metal pattern.

[0008] In a second aspect, a frequency selective surface is provided, comprising the frequency selective unit as described in the first aspect.

[0009] In a third aspect, a base station antenna is provided, comprising a high-frequency antenna, a low-frequency antenna, and a frequency selective surface as described in the second aspect above, wherein: the frequency selective surface is located above the high-frequency antenna, and the low-frequency antenna is located above the frequency selective surface; the frequency selective surface is used to reflect the electromagnetic waves of the low-frequency antenna and to transmit the electromagnetic waves of the high-frequency antenna. BRIEF DESCRIPTION OF THE DRAWINGS

[0010] In order to more clearly illustrate the technical solutions in this application or the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are only some embodiments recorded in this application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative labor.

[0011] FIG1 is a schematic structural diagram of a frequency selection unit according to an embodiment of the present application;

[0012] FIG2 is a schematic structural diagram of a frequency selection unit according to an embodiment of the present application;

[0013] FIG3 is a schematic diagram of an equivalent circuit of a frequency selection unit according to an embodiment of the present application;

[0014] FIG4 is a schematic diagram of the transmission characteristics of a frequency selection unit according to an embodiment of the present application;

[0015] FIG5 is a schematic structural diagram of an inductor in a frequency selection unit according to an embodiment of the present application;

[0016] FIG6 is a schematic diagram of the structure of a capacitor in a frequency selection unit according to an embodiment of the present application;

[0017] FIG7 is a schematic diagram of a periodic structure of a frequency selective surface formed by combining frequency selective units according to an embodiment of the present application;

[0018] FIG8 is a schematic diagram of a periodic structure of a frequency selective surface formed by combining frequency selective units according to an embodiment of the present application;

[0019] FIG9 is a schematic diagram of a periodic structure of a frequency selective surface formed by combining frequency selective units according to an embodiment of the present application;

[0020] FIG10 is a schematic diagram comparing the scattered fields of a frequency selective surface in an embodiment of the present application and a conventional frequency selective surface in a transmission frequency band;

[0021] FIG11 is a schematic structural diagram of a base station antenna according to an embodiment of the present application;

[0022] FIG12 is a schematic structural diagram of a frequency selection unit according to an embodiment of the present application;

[0023] FIG13 is a schematic structural diagram of a frequency selective surface according to an embodiment of the present application;

[0024] FIG14 is a schematic diagram of an equivalent circuit of a frequency selection unit according to an embodiment of the present application;

[0025] FIG15 is a schematic structural diagram of a frequency selection unit according to an embodiment of the present application;

[0026] FIG16 is a schematic structural diagram of a frequency selection unit according to an embodiment of the present application;

[0027] FIG17 is a schematic diagram of an equivalent circuit of a frequency selection unit according to an embodiment of the present application;

[0028] FIG18 is a schematic structural diagram of a frequency selection unit according to an embodiment of the present application;

[0029] FIG19 is a schematic diagram of an equivalent circuit of a frequency selection unit according to an embodiment of the present application. DETAILED DESCRIPTION

[0030] With the continuous development of communication technology, different mobile communication technologies are assigned different frequency bands. In order to meet the multi-standard needs of different users at the same time, base station antennas are developing in the direction of multi-frequency. One type is the multi-frequency antenna co-aperture system (that is, antenna units in different frequency bands share the same radiation aperture). In the multi-frequency antenna co-aperture system, due to the overlap of radiation apertures, the overall structure of the multi-frequency antenna co-aperture system is compact, but it also faces the problem of inter-frequency interference between antennas. In related technologies, the impact of inter-frequency interference can be reduced by designing feed, high and low frequency antenna decoupling and co-design, etc., but the design complexity of this method is very high. A more effective method is to use frequency selective surfaces to reduce the mutual interference problem, so that antennas in different frequency bands can work normally in their respective frequency bands.

[0031] Currently, most base station antennas use dual-polarization antennas to combat multipath fading effects through polarization diversity. In a multi-frequency common-aperture antenna array, the radiating surface size of the low-frequency antenna is larger than that of the high-frequency antenna. To make the overall array structure compact by sharing the radiation aperture, the radiating surfaces of the high- and low-frequency antennas need to overlap in the vertical direction.

[0032] Take the example of a low-frequency antenna with a higher radiation surface than a high-frequency antenna. The low-frequency antenna and the high-frequency antenna share a common aperture. When they are working independently, cross-frequency coupling occurs between the antennas, seriously affecting the radiation performance and causing problems such as pattern distortion and reduced radiation efficiency. By introducing a high-pass and low-resistance frequency selective surface (FSS) between the high-frequency antenna and the low-frequency antenna in the vertical direction (blocking low-frequency electromagnetic waves and equivalently transparent to high-frequency electromagnetic waves), the cross-frequency coupling problem can be effectively improved. The frequency selective surface can simultaneously act as a reflective surface for the low-frequency antenna and an antenna cover for the high-frequency antenna. Low-frequency electromagnetic waves cannot pass through the frequency selective surface, achieving decoupling between the high-frequency and low-frequency antennas and suppressing the common-mode resonance that may be generated by the high-frequency antenna. As for the high-frequency antenna, the frequency selective surface covering it will not affect the radiation performance of the high-frequency antenna due to its high-pass characteristics.

[0033] When frequency selective surfaces are actually used to reduce heterodyne coupling, considering that a single-layer frequency selective surface is usually only selective within one and limited frequency band, in order to maintain selectivity within a wider frequency band or achieve a smaller interval between pass-band and stop-band, the frequency selective surface usually adopts a multi-layer structure. However, the thickness of the frequency selective surface with a multi-layer structure is relatively large, which will lead to increased losses and costs. In addition, in order to reduce the gain impact on the antenna's large-angle service beam, the frequency selective surface is usually required to have a large-angle (such as plus or minus 60 degrees) oblique incidence performance, but the current frequency selective surface cannot meet the requirements of large-angle oblique incidence performance. In order to make the frequency selective surface have large-angle oblique incidence performance, the frequency selective surface usually requires 2.5D and 3D patterns, which are more difficult to process.

[0034] The embodiment of the present application provides a frequency selection unit and a frequency selection surface, the frequency selection surface includes a plurality of frequency selection units, each frequency selection unit includes a dielectric layer, a first metal layer and a second metal layer, the first metal layer is covered on one side of the dielectric layer, the second metal layer is covered on the other side of the dielectric layer, the first metal layer is truncated in the middle, and the projection area of ​​the truncated part on the second metal layer includes a first area, and the first area includes a metal pattern. Based on the structure of the frequency selection unit provided in the embodiment of the present application, the frequency selection surface can realize the conversion of the passband in a smaller frequency interval. Compared with the multi-layer frequency selection surface in the related art, the thickness of the frequency selection surface in the embodiment of the present application is smaller, which can effectively reduce the loss and cost. In addition, since the frequency selection surface can be realized by combining a thinner dielectric and metal (i.e., a dielectric layer, a first metal layer and a second metal layer), the large-angle oblique incidence performance is good, which can meet the requirements of large-angle oblique incidence performance.

[0035] The present invention also provides a base station antenna comprising a high-frequency antenna, a low-frequency antenna, and a frequency selective surface provided by the present invention. The frequency selective surface is located above the high-frequency antenna, and the low-frequency antenna is located above the frequency selective surface. The frequency selective surface is configured to reflect electromagnetic waves from the low-frequency antenna and transmit electromagnetic waves from the high-frequency antenna. This effectively reduces the problem of inter-frequency coupling between the high-frequency and low-frequency antennas.

[0036] In order to help those skilled in the art better understand the technical solutions of this application, the following will clearly and completely describe the technical solutions of this application in conjunction with the drawings of one or more embodiments of this application. Obviously, the described embodiments are only part of the embodiments of this application, not all of the embodiments. Based on the embodiments of this application, all other embodiments obtained by ordinary technicians in this field without making creative efforts should fall within the scope of protection of this application.

[0037] The terms "first," "second," and the like in this application and the claims are used to distinguish similar objects and are not used to describe a particular order or precedence. It should be understood that such terms are interchangeable where appropriate so that this application can be implemented in sequences other than those illustrated or described herein. In addition, the term "and / or" in this application and the claims refers to at least one of the connected objects, and the character " / " generally indicates that the connected objects are in an "or" relationship.

[0038] The following describes in detail the technical solutions provided by various embodiments of the present application in conjunction with the accompanying drawings.

[0039] FIG1 is a schematic structural diagram of a frequency selection unit according to an embodiment of the present application.

[0040] The frequency selective unit shown in FIG1 includes a dielectric layer 11, a first metal layer 12, and a second metal layer 13. The first metal layer 12 covers one side of the dielectric layer 11, and the second metal layer 13 covers the other side of the dielectric layer 11 ( FIG1 illustrates an example in which the first metal layer 12 covers the upper side of the dielectric layer 11 and the second metal layer 13 covers the lower side of the dielectric layer 11). The first metal layer 12 is cut in the middle, and the projection of the cut portion on the second metal layer 13 includes a first region 131. The first region 131 includes a metal pattern (not shown in FIG1 ).

[0041] The dielectric layer 11 can be any non-metallic dielectric material and is not specifically limited herein. In one embodiment, the dielectric constant of the dielectric layer 11 can be 3 and the thickness can be 0.762 mm.

[0042] The first metal layer 12 and the second metal layer 13 can be made of any metal material, and are not specifically limited here. In one embodiment, in actual applications, to reduce costs while ensuring performance, the thickness of the first metal layer 12 and the second metal layer 13 can be designed to be thinner, for example, 0.035 mm, and are not specifically limited here.

[0043] Based on the structure of the frequency selective unit provided in the embodiments of the present application, the frequency selective surface can achieve passband and stopband conversion within a relatively small frequency interval. Compared to multi-layer frequency selective surfaces in related technologies, the frequency selective surface in the embodiments of the present application is relatively thin, which can effectively reduce losses and costs. In addition, because the frequency selective surface can be implemented by combining relatively thin dielectric and metal layers (i.e., dielectric layer, first metal layer, and second metal layer), it has excellent oblique incidence performance and can meet the requirements of high-angle oblique incidence performance.

[0044] In an embodiment of the present application, incident waves of different frequencies may be incident on the frequency selection unit. At different frequencies of the incident waves, the metal patterns in the second metal layer of the frequency selection unit may be equivalent to different metal layers. When the metal patterns are equivalent to different metal layers, the frequency selection unit may have different characteristics (i.e., different metal layers may correspond to different characteristics of the frequency selection unit), including reflection characteristics or transmission characteristics. Thus, since the metal pattern can be equivalent to different metal layers at different frequencies of the incident wave, the frequency selection unit may have reflection or transmission characteristics, thereby achieving a frequency selection function.

[0045] In some embodiments, the different metal layers may include complete metal layers and truncated metal layers. Depending on the frequency of the incident wave, the metal pattern in the second metal layer may be equivalent to a complete metal layer or a truncated metal layer. For example, when the frequency of the incident wave is within a first frequency band, the metal pattern in the second metal layer may be equivalent to a complete metal layer. In this case, the frequency selective unit has a reflective characteristic. The first frequency band is a low-frequency band, such as 690-960 MHz. When the frequency of the incident wave is relatively low, the frequency selective unit has a reflective characteristic, meaning that the frequency selective unit is capable of reflecting low-frequency incident waves and exhibits a low-impedance characteristic. For another example, when the frequency of the incident wave is within a second frequency band, the metal pattern in the second metal layer may be equivalent to a truncated metal layer. In this case, the frequency selective unit has a transmissive characteristic. The second frequency band is greater than the first frequency band and is a high-frequency band, such as 1710-2170 MHz. When the frequency of the incident wave is relatively high, the frequency selective unit has a transmissive characteristic, meaning that the frequency selective unit is capable of transmitting high-frequency incident waves and exhibits a high-pass characteristic.

[0046] In some embodiments, the non-metallic patterned portions of the first metal layer and the second metal layer can be equivalent to an LC series resonant structure. When the frequency of the incident wave is within the first frequency band, the LC series resonant structure has a transmission zero. In other words, the inclusion of the LC series resonant structure in the equivalent circuit of the frequency selective unit enables the frequency selective unit to have a transmission zero for incident waves in the low frequency band, thereby reflecting incident waves in the low frequency band and achieving low impedance characteristics.

[0047] In other embodiments, the metal pattern of the second metal layer includes a first pattern and a second pattern, the first pattern being equivalent to an inductor and the second pattern being equivalent to a capacitor, the inductor and capacitor forming an LC parallel resonant structure, and when the frequency of the incident wave is within the second frequency band, the LC parallel resonant structure has a transmission pole. In other words, the equivalent circuit of the frequency selective unit includes the LC parallel resonant structure, so that the frequency selective unit has a transmission pole for incident waves in the high frequency band, i.e., it can transmit incident waves in the high frequency band, thereby achieving a high-pass characteristic.

[0048] The first frequency band can be represented as a stop band of the frequency selection unit, which corresponds to the LC series resonant structure. In some embodiments, the stop band can be adjusted by adjusting the LC series resonant structure. Specifically, since the non-metallic pattern portion of the first metal layer and the second metal layer can be equivalent to the LC series resonant structure, the size of L and C in the LC series resonant structure can be adjusted by adjusting the shape or size of the non-metallic pattern portion of the first metal layer and the second metal layer, thereby adjusting the stop band of the frequency selection unit, that is, the first frequency band. In other words, the first frequency band is related to the shape and size of the first metal layer and the shape and size of the non-metallic pattern portion of the second metal layer. Different shapes or sizes of the first metal layer can correspond to different first frequency bands, and different shapes or sizes of the non-metallic pattern portion of the second metal layer can correspond to different first frequency bands.

[0049] The second frequency band can be expressed as a passband of the frequency selection unit, which corresponds to the LC parallel resonant structure. In some embodiments, the passband can be adjusted by adjusting the LC parallel resonant structure. Specifically, since the first pattern and the second pattern in the metal pattern portion of the second metal layer can be equivalent to an LC parallel resonant structure, the size of L and C in the LC parallel resonant structure can be adjusted by adjusting the shape or size of the first pattern and the second pattern, thereby adjusting the passband of the frequency selection unit, that is, the second frequency band. In other words, the second frequency band is related to the shape and size of the first pattern and the shape and size of the second pattern. Different shapes or sizes of the first pattern can correspond to different second frequency bands, and different shapes or sizes of the second pattern can correspond to different second frequency bands.

[0050] Since the passband and stopband of the frequency selective surface can be changed by changing the shape or size of the first metal layer and the second metal layer, the frequency selective unit can achieve passband and stopband conversion within a smaller frequency interval, thereby improving frequency selectivity. In addition, since the passband and stopband of the frequency selective unit can be changed, the application environment of the frequency selective unit is wider. It is not only suitable for 4G and 5G multi-band communication base station antennas, but also for application environments that require low-impedance and high-pass within the tunable range of the resonant frequency. The frequency selective unit provided by the embodiment of the present application can also be used.

[0051] In some embodiments, the first pattern in the second metal layer may include a meandering structure that forms an inductor in the LC parallel resonant structure. The meandering structure may include at least one of the following: a rectangular meandering line structure; a trapezoidal meandering line structure; a wavy line structure; or a meandering line structure.

[0052] It should be noted that the above four bending structures are only preferred solutions in the embodiments of the present application. In other possible implementations, other bending structures can also be used as long as they can form an inductor. Other possible bending structures will not be given examples one by one here.

[0053] In some embodiments, the second pattern in the second metal layer may include a first concave-convex structure and a second concave-convex structure, wherein the concave-convex portions of the first concave-convex structure and the concave-convex portions of the second concave-convex structure intersect to form a capacitor in the LC parallel resonant structure. The concave-convex portions of the first concave-convex structure and the concave-convex portions of the second concave-convex structure may include at least one of the following: an arc-shaped structure; or a tooth-shaped structure.

[0054] It should be noted that the above two concave-convex structures are only preferred schemes in the embodiments of the present application. In other possible implementation methods, other concave-convex structures can also be used, as long as they can be interlaced with each other to form a capacitor. Other possible concave-convex structures will not be given examples one by one here.

[0055] In order to facilitate understanding of the structure of the frequency selection unit provided in the embodiment of the present application, a more specific implementation method shown in FIG2 will be used as an example for explanation below.

[0056] Figure 2 is a schematic diagram of the structure of a frequency selective unit according to an embodiment of the present application. In Figure 2, the upper structure shown in (a) is the first metal layer of the frequency selective unit, the lower structure shown in (b) is the second metal layer of the frequency selective unit (of course, the upper structure in Figure 2 can also be the lower structure, and correspondingly, the lower structure can also be the upper structure). (c) shows the three-dimensional structure of the frequency selective unit composed of (a), (b), and the dielectric layer between (a) and (b).

[0057] The superstructure shown in Figure 2 is a truncated metal strip, which can be thought of as a rectangular metal strip with a section cut off in the middle. The chamfered ends of the superstructure indicate that the frequency selective elements can be combined in various ways to form a frequency selective surface. The specific angles of the angles can be determined based on actual conditions and are not specifically limited here.

[0058] The lower structure shown in Figure 2 is a metal strip, which can be regarded as a rectangular long metal strip with a metal pattern etched in the middle (the projection area of ​​the truncated part of the upper structure on the lower structure). The metal pattern is equivalent to an LC parallel resonant structure. The lower half of the metal pattern is a first pattern, which includes a bending structure. The bending structure is specifically a rectangular meandering line structure, which can constitute an inductor in the LC parallel resonant structure (which can be expressed as a meandering line inductor L2). The upper half of the metal pattern is a second pattern, which includes two concave and convex structures. The concave and convex parts are tooth-shaped structures. The two concave and convex structures are interlaced with each other to form a capacitor in the LC parallel resonant structure (which can be expressed as a tooth-shaped interdigitated capacitor C2). The tooth-shaped interdigitated capacitor C2 and the meandering line inductor L2 are arranged in parallel to form an LC parallel resonant structure.

[0059] The size and shape of the toothed interdigital capacitor C2 and the size and shape of the meandering line inductor L2 can be the same as or different from those shown in FIG2 . In practical applications, the size of the LC parallel resonant structure (i.e., the size of L2 and C2) can be adjusted according to the desired passband range, thereby adjusting the passband frequency. For example, the capacitance of the toothed interdigital capacitor C2 can be increased by increasing the number of teeth or the total length of the toothed capacitor (i.e., l9), or by reducing the spacing between the two concave and convex structures of the toothed interdigital capacitor (e.g., increasing w8 and decreasing l10). The inductance of the meandering line inductor L2 can be increased by increasing the number of turns of the meandering line inductor, increasing the length of the meandering line inductor (e.g., reducing l6, l7, l8, or increasing w3), or reducing the width (w) of the meandering line inductor.

[0060] The extended metal portions (i.e., non-metallic pattern portions) at both ends of the lower structure can be equivalent to an LC series resonant structure with the upper structure, wherein the two portions obtained after the upper structure is cut off constitute the inductor L1, and the portion where the upper and lower structures overlap in the projection direction constitutes the capacitor C1. The shapes and sizes of the capacitor C1 and the inductor L1 can be the same as or different from those shown in FIG2. In practical applications, the size of the LC series resonant structure can also be adjusted according to the desired stopband range (i.e., the size of L1 and C1 can be adjusted), thereby adjusting the frequency point position of the stopband. For example, the capacitance value of the capacitor C1 can be increased by increasing the width (w1) of the upper structure or the length (l3) of the lower structure, or by increasing the overlapping area of ​​the upper and lower structures, and the inductance value of the inductor L1 can be increased by increasing the length (l1) of the upper structure.

[0061] Figure 3 is a simplified equivalent circuit of the frequency selective unit shown in Figure 2. As can be seen from Figure 3, the frequency selective surface shown in Figure 2 can be equivalent to an LC series resonant structure (composed of L1 and C1 shown in Figure 3) and an LC parallel resonant structure (composed of L2 and C2 shown in Figure 3), wherein the LC series resonant structure and the LC parallel resonant structure are in a series relationship.

[0062] Figure 4 shows the transmission characteristic curve of the frequency selective element shown in Figure 2. In Figure 4, S11 is the reflection parameter, which reaches its maximum value at frequency f1 and its minimum value at frequency f2. S21 is the transmission parameter, which reaches its minimum value at frequency f1 and its maximum value at frequency f2. As can be seen from Figure 4, the frequency selective surface has a transmission zero in the low-frequency band and a transmission pole in the high-frequency band, achieving low-impedance, high-pass characteristics.

[0063] In some embodiments, the inductors L1 and L2 shown in FIG2 may also be any of the four structures shown in FIG5 , and the capacitors C1 and C2 shown in FIG2 may be any of the four structures shown in FIG6 , which may also achieve low-resistance and high-pass characteristics.

[0064] The present application also provides a frequency selective surface, comprising the frequency selective units provided in the present application. The frequency selective surface may include multiple frequency selective units, the specific number of which can be determined based on actual needs and is not specifically limited herein. In one embodiment, the frequency selective surface may include at least 3*3 frequency selective units.

[0065] In some embodiments, when the frequency selective surface includes a plurality of frequency selective units, the plurality of frequency selective units may be arranged periodically, as shown in FIG7 , FIG8 , and FIG9 .

[0066] Figure 7 shows a frequency selective surface periodic structure formed by combining frequency selective units according to an embodiment of the present application. In Figure 7, after combining the frequency selective units at 90 degrees, multiple square periodic units can be obtained (the dotted box in Figure 7 corresponds to a periodic unit). Then, according to the required antenna array size, multiple periodic units can be spliced ​​on a plane. When in use, the metal pattern direction can be aligned with the antenna polarization direction.

[0067] Experimental verification shows that the frequency selective surface shown in Figure 7 exhibits a transmission coefficient greater than -0.8dB (i.e., a transmittance greater than 83%) in the passband, and a reflection coefficient greater than -0.8dB (i.e., a reflectance greater than 83%) in the stopband, within the 0-60 degree incident angle range. The performance of the 6x6 scale frequency selective surface shown in Figure 5 was tested using a horn antenna. The test results show that the maximum gain of the horn antenna only decreases by 0.6dBi after loading the frequency selective surface. Due to the excellent angular stability of the frequency selective surface, the overall antenna pattern does not change significantly after loading the horn antenna.

[0068] Figure 8 shows a periodic frequency selective surface structure formed by combining frequency selective units according to an embodiment of the present application. In Figure 8, after combining the frequency selective units at 60°, a triangular periodic unit is obtained. Two of the most basic triangular units are combined to form a frequency selective surface periodic unit (the dotted box in Figure 8 corresponds to a periodic unit). This periodic unit can then be expanded to the required size of the antenna array by connecting the upper edge to the lower edge and the left to the right edge.

[0069] Figure 9 shows a periodic frequency selective surface structure formed by combining frequency selective elements in accordance with an embodiment of the present application. In Figure 9, by combining the frequency selective elements at 120° angles, a hexagonal periodic element is obtained (the dotted box in Figure 9 corresponds to a periodic element). This periodic element can then be expanded to the desired size for the antenna array by connecting the top edge to the bottom edge and the left edge to the right edge.

[0070] Figures 7 to 9 illustrate three periodic arrangements of multiple frequency selective elements. In practical applications, the frequency selective surface can also be arranged periodically in other ways, which will not be illustrated here. It should be noted that the density of the periodic elements resulting from the combination of frequency selective elements affects the stopband and passband performance of the frequency selective surface. Generally speaking, a greater density of periodic elements results in a wider stopband bandwidth and better performance, while a narrower passband bandwidth results in poorer performance. In practical applications, different combinations can be selected based on the performance requirements of the stopband and passband.

[0071] The principle of the embodiment of the present application is that a metal grid of appropriate size can be equivalent to a metal plate at low frequencies, and can reflect electromagnetic waves almost perfectly, showing low-resistance characteristics, but it partially blocks electromagnetic waves in the high-frequency band and cannot obtain high-pass characteristics. The truncated metal grid will not block high-frequency electromagnetic waves and show high-pass characteristics, but it cannot reflect low-frequency electromagnetic waves, that is, it has no low-resistance characteristics. In view of this, the embodiment of the present application uses an LC parallel resonant unit that is equivalent to low-frequency connection and high-frequency disconnection at the truncation of the metal grid to supplement it, so that it can appear as a metal grid at low frequencies and a truncated grid at high frequencies, thereby achieving low-resistance and high-pass frequency selective surface characteristics. That is, the principle of the embodiment of the present application is to achieve frequency selection based on the similar switching characteristics generated by the LC parallel resonant unit to connect or truncate the metal grid at different frequencies, which is very different in principle from other frequency selective surfaces that achieve frequency selection based on structural resonance through absorption, interlayer coupling and secondary radiation.

[0072] To facilitate understanding of the difference between the frequency selective surface provided in the embodiment of the present application and the traditional frequency selective surface, please refer to Figure 10. Figure 10 shows a comparison of the scattered field in the transmission frequency band of the technical solution of the present application and the traditional solution. When losses are ignored, the incident wave energy is equal to the outgoing wave energy plus the scattered wave energy. A symmetrical array antenna is placed under the frequency selective surface. The electromagnetic wave propagating in the +z axis direction is first incident on the lower surface of the frequency selective surface and then emitted from its upper surface. Comparing the field intensity distribution diagram of the scattered field, it can be seen that the technical solution of the present application is based on a switch metal grid. The electromagnetic waves in the target frequency band will be directly emitted. Therefore, the scattered field intensity generated is very small and mostly concentrated near the frequency selective surface. The traditional multi-layer frequency selective surface is based on the principle of secondary radiation, first absorbing and then radiating, so it will produce a strong scattered field. It can be seen that the frequency selective surface provided in the embodiment of the present application has better transmission performance for high-frequency electromagnetic waves. In addition, the structure of the frequency selective surface based on the metal grid is relatively simple. It can be implemented by combining a thin dielectric layer and a metal layer. It has good oblique incidence performance and meets the requirements of large-angle oblique incidence performance.

[0073] The present application also provides a base station antenna. The base station antenna includes a high-frequency antenna, a low-frequency antenna, and a frequency selective surface provided in the present application. The frequency selective surface is located above the high-frequency antenna, and the low-frequency antenna is located above the frequency selective surface. The frequency selective surface is configured to reflect electromagnetic waves from the low-frequency antenna and transmit electromagnetic waves from the high-frequency antenna.

[0074] For ease of understanding, please refer to Figure 11. Figure 11 is a schematic structural diagram of a base station antenna according to an embodiment of the present application. In the base station antenna shown in Figure 11, from bottom to top are a reflector, a high-frequency antenna, a frequency selective surface, and a low-frequency antenna. The frequency selective surface acts as both a reflective surface for the low-frequency antenna and an antenna cover for the high-frequency antenna. For low-frequency electromagnetic waves, the frequency selective surface can reflect them, and for high-frequency electromagnetic waves, the frequency selective surface can transmit them, achieving low-resistance and high-pass characteristics, thereby effectively improving the problem of heterogeneous frequency coupling.

[0075] In summary, the frequency selective surface (or frequency selective unit) provided in the embodiments of the present application has at least the following technical effects:

[0076] 1) The frequency selective surface has good performance in its transparent frequency band (passband) and reflection frequency band (stopband).

[0077] 2) The frequency selective surface has dual polarization characteristics, and the performance of the frequency selective surface remains consistent in the two polarization states.

[0078] 3) The frequency selective surface has good oblique incidence performance and can maintain good reflection and transmission performance in a large angle range of 0-60 degrees.

[0079] 4) The infinite periodic size performance of the frequency selective surface is well consistent with the finite size performance. When a finite array is applied to an antenna, the changes in its gain and radiation pattern are compounded by the expectations of its scattering parameters.

[0080] 5) The frequency selective surface has a small thickness, a simple structure, low processing difficulty, and good reflection, transmission and oblique incidence performance.

[0081] The frequency selective surface provided in the embodiment of the present application can be used for multi-band base station antennas of 690-960MHz and 1710-2170MHz (690-960MHz corresponds to the stop band of the frequency selective surface, and 1710-2170MHz corresponds to the pass band of the frequency selective surface). Since the stop band and pass band of the frequency selective surface can be adjusted by the shape or size of the first metal layer and / or the shape or size of the second metal layer in the frequency selective unit, the frequency selective surface can also be used for multi-band base station antennas in other frequency bands. Of course, the frequency selective surface provided in the embodiment of the present application, such as the antenna cover, can be used in applications where low-frequency stop bands and high-frequency stop bands are required.

[0082] The present application also provides a frequency selective unit comprising a dielectric layer and a metal layer overlying one side of the dielectric layer. The dielectric layer can be any non-metallic dielectric material, and the metal layer includes a metal pattern. The frequency selective unit exhibits dual-polarization, low-impedance, and high-pass characteristics for incident waves of different frequencies.

[0083] In some embodiments, the structure of the frequency selective unit can be as shown in FIG12. The frequency selective unit shown in FIG12 is composed of a dielectric layer 121 and a metal layer 122 attached to the dielectric layer 121, wherein the metal layer 122 includes a metal pattern. By expanding the frequency selective unit shown in FIG12 in the x and y directions, a frequency selective surface for practical use can be obtained, as shown in FIG13. Compared to other planar frequency selective units or three-dimensional frequency selective unit structures in which metal layers are attached to both sides of a dielectric layer, the frequency selective unit shown in FIG12 has greater flexibility in actual production.

[0084] For example, in an active / passive integrated base station antenna (such as the architecture in Figure 11), the low-frequency antenna is on top, the high-frequency antenna is on the bottom, and the FSS board (i.e., frequency selective surface) is in the middle. To ensure that the high- and low-frequency antennas can be used or maintained separately, the high- and low-frequency antennas must meet the reliability requirements for independent use. Each antenna is fully enclosed in a radome. If the low-frequency antenna's back cover can be used as the dielectric material, there is no need to introduce a new component (FSS board). Traditional frequency selective surfaces require printing metal patterns on at least two sides of the dielectric. When printed on both sides of the antenna back cover, the metal on one side is inevitably exposed to the outside air. The external environment will have an uncontrollable impact on the performance of the FSS board, causing performance degradation or failure of the communication system. Therefore, traditional co-aperture arrays based on FSS require the introduction of at least one additional layer of non-metallic plate and support structure. The frequency selective surface shown in Figure 12 can achieve the required performance by printing a metal pattern on only one side. In practical applications, the metal pattern can be directly attached to the inner side of the low-frequency antenna back cover (in this case, the frequency selective surface shown in Figure 12 is a multifunctional frequency selective unit, which can be used as a antenna cover and can also have dual-polarization high-pass and low-resistance characteristics). Therefore, there is no need to add an additional FSS board, which can reduce costs and assembly difficulty.

[0085] The equivalent circuit of the frequency selection unit shown in FIG12 can be shown in FIG14. As can be seen from FIG14, the frequency selection unit shown in FIG12 can be equivalent to a capacitor C4 and an LC parallel resonant structure (composed of L3 and C3 in parallel), and the capacitor C4 and the LC parallel resonant structure are in a series relationship. In FIG15, a high-impedance metal wire can be equivalent to a distributed inductor. After bending it, coupling between the wires is introduced, and its equivalent circuit can be regarded as a parallel connection of an inductor and a capacitor. Increasing the total length of the high-impedance wire or reducing the wire width can increase the value of L3. Increasing the number of bends, increasing the wire width, or other methods that are equivalent to reducing the width of the gap between the wires after bending can increase the value of C3. After copying it and rotating it 90 degrees to form the middle bending cross line (2), for electromagnetic waves with polarization direction along any azimuth plane, it can be equivalent to the series-parallel equivalent circuit structure shown in FIG14.

[0086] The metal strips (1) around the frequency selection unit shown in Figure 15 and the metal strips (1) of the adjacent frequency selection unit can form a coupling capacitor C4. By connecting a capacitor of appropriate capacitance in series in the parallel LC circuit, a transmission zero point can be introduced in the low frequency band. Increasing the length of the metal strip (1) or reducing the distance between the metal strips of the adjacent frequency selection unit can effectively increase the capacitance value of C4. Increasing the value of C3 or L3 can simultaneously move the position of the transmission zero point and the transmission pole to the low frequency (reducing it will move it to the high frequency). By changing the capacitance value of C4, the position of the transmission zero point can be adjusted almost independently. Therefore, a low-impedance high-pass frequency selection surface can be achieved through simple adjustment.

[0087] Experimental results show that when the electromagnetic wave is incident perpendicularly at 0 degrees on the frequency selective unit shown in Figure 12, the insertion loss in the stopband (0.69-0.96 GHz) is less than 0.47 dB, and the insertion loss in the passband (1.71-2.17 GHz) is less than 0.18 dB. When the electromagnetic wave is incident obliquely at 60 degrees on the frequency selective unit shown in Figure 12, the insertion loss in the stopband (0.69-0.96 GHz) is less than 0.52 dB, and the insertion loss in the passband (1.71-2.17 GHz) is less than 0.65 dB, demonstrating excellent performance.

[0088] In some implementations, the structure of the frequency selection unit may also be as shown in FIG. 16 or FIG. 18 .

[0089] The frequency selection unit shown in FIG16 includes a dielectric layer 161 and a metal layer 162 attached to one side of the dielectric layer 161. The metal layer 162 includes the metal pattern shown in FIG16 . The equivalent circuit of the frequency selection unit shown in FIG16 is shown in FIG17 . The transmission characteristics of the frequency selection unit shown in FIG16 are the same as those of the frequency selection unit shown in FIG12 and are not described in detail here. It should be noted that the frequency selection unit shown in FIG16 can also be used as a frequency selection surface with dual-polarization low-impedance high-pass transmission, and can also be used as a radome.

[0090] The frequency selection unit shown in FIG18 includes a dielectric layer 181 and a metal layer 182 attached to one side of the dielectric layer 181. The metal layer 182 includes the metal pattern shown in FIG18 . The equivalent circuit of the frequency selection unit shown in FIG18 is shown in FIG19 . The transmission characteristics of the frequency selection unit shown in FIG18 are the same as those of the frequency selection unit shown in FIG12 and are not described in detail here. It should be noted that the frequency selection unit shown in FIG18 can also be used as a frequency selection surface with dual-polarization low-impedance high-pass transmission, and can also be used as a radome.

[0091] For the frequency selection units shown in Figures 16 and 18, in order to provide a transmission zero point at the low-frequency end, both have a significant common feature in structure, that is, the metal parts of adjacent frequency selection units are not connected to each other. As shown in the local enlarged views of Figures 16 and 18, there is a gap between the metal part and the boundary of the frequency selection unit, which is used to provide capacitor C5.

[0092] The embodiment of the present application also provides a frequency selective surface, which includes a plurality of frequency selective units as shown in Figure 12, or includes a plurality of frequency selective units as shown in Figure 16, or includes a plurality of frequency selective units as shown in Figure 18. The plurality of frequency selective units are arranged periodically. For example, the periodic arrangement of the plurality of frequency selective units shown in Figure 12 can be as shown in Figure 13. Of course, the periodic arrangement of the plurality of Figures 16 or 18 can also be the periodic arrangement shown in Figure 13. In addition, in addition to the periodic arrangement shown in Figure 13, there can also be other periodic arrangements, which will not be illustrated one by one here.

[0093] An embodiment of the present application also provides a base station antenna. The base station antenna may include a frequency selective surface (FSS), which is composed of a plurality of frequency selective units shown in FIG12 , a plurality of frequency selective units shown in FIG16 , or a plurality of frequency selective units shown in FIG18 . The FSS can function as a dual-polarized low-impedance high-pass antenna and also serve as a radome, effectively alleviating the problem of inter-frequency coupling and eliminating the need for an additional FSS board, thereby reducing cost and assembly difficulty.

[0094] In short, the above description is only a preferred embodiment of the present application and is not intended to limit the scope of protection of the present application. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of the present application shall be included in the scope of protection of the present application.

[0095] It should also be noted that the terms "comprises," "includes," or any other variations thereof are intended to encompass non-exclusive inclusion, such that a process, method, commodity, or apparatus that includes a series of elements includes not only those elements but also other elements not explicitly listed, or includes elements inherent to such process, method, commodity, or apparatus. In the absence of further limitations, an element defined by the phrase "comprises a ..." does not exclude the presence of other identical elements in the process, method, commodity, or apparatus that includes the element.

[0096] The various embodiments in this application are described in a progressive manner. Similar parts between the various embodiments can be referred to in conjunction with each other. Each embodiment focuses on the differences between the other embodiments. In particular, the system embodiment is generally similar to the method embodiment, so the description is relatively simple. For relevant parts, refer to the partial description of the method embodiment.

Claims

1. A frequency selection unit, wherein: The invention comprises a dielectric layer, a first metal layer and a second metal layer, wherein: The first metal layer covers one side of the dielectric layer, the second metal layer covers the other side of the dielectric layer, the first metal layer is cut in the middle, the projection area of ​​the cut portion on the second metal layer includes a first area, and the first area includes a metal pattern.

2. The frequency selection unit according to claim 1, wherein: At different frequencies of the incident wave, the metal pattern is equivalent to different metal layers, and different metal layers correspond to different characteristics of the frequency selection unit, where the characteristics include reflection characteristics or transmission characteristics.

3. The frequency selection unit according to claim 2, wherein: When the frequency of the incident wave is in the first frequency band, the metal pattern is equivalent to a complete metal layer, and the frequency selection unit has a reflection characteristic. When the frequency of the incident wave is in the second frequency band, the metal pattern is equivalent to a truncated metal layer, and the frequency selection unit has a transmission characteristic. The first frequency band is smaller than the second frequency band.

4. The frequency selection unit according to claim 3, wherein: The non-metallic pattern portion of the first metal layer and the second metal layer is equivalent to an LC series resonant structure, the metal pattern includes a first pattern and a second pattern, the first pattern is equivalent to an inductor, the second pattern is equivalent to a capacitor, and the inductor and the capacitor form an LC parallel resonant structure; When the frequency of the incident wave is within the first frequency band, the LC series resonant structure has a transmission zero point; and when the frequency of the incident wave is within the second frequency band, the LC parallel resonant structure has a transmission pole.

5. The frequency selection unit according to claim 4, wherein: The first pattern includes a meandering structure, and the meandering structure constitutes the inductor. The frequency selection unit according to claim 5 , wherein: The bending structure includes at least one of the following: Rectangular meander line structure; Trapezoidal meandering line structure; Wavy line structure; Ring-shaped structure.

7. The frequency selection unit according to claim 4, wherein: The second pattern includes a first concave-convex structure and a second concave-convex structure, and the concave-convex portion of the first concave-convex structure and the concave-convex portion of the second concave-convex structure are interlaced to form the capacitor.

8. The frequency selection unit according to claim 7, wherein: The concave-convex portion of the first concave-convex structure and the concave-convex portion of the second concave-convex structure include at least one of the following: curved structure; Tooth-like structure.

9. The frequency selection unit according to claim 4, wherein: The second frequency band is related to the shapes and sizes of the first pattern and the second pattern. Different shapes or sizes of the first pattern and the second pattern correspond to different second frequency bands.

10. The frequency selection unit according to claim 4, wherein: The first frequency band is related to the shape and size of the first metal layer and the non-metal pattern portion. Different shapes or sizes of the first metal layer and the non-metal pattern portion correspond to different first frequency bands.

11. A frequency selective surface, wherein: Comprising the frequency selective surface according to any one of claims 1 to 10.

12. The frequency selective surface of claim 11, wherein There are multiple frequency selection units, and the multiple frequency selection units are arranged periodically.

13. A base station antenna, wherein: The method comprises a high frequency antenna, a low frequency antenna and a frequency selective surface as claimed in any one of claims 11 and 12, wherein: The frequency selective surface is located above the high frequency antenna, and the low frequency antenna is located above the frequency selective surface; The frequency selective surface is used to reflect the electromagnetic waves of the low-frequency antenna and transmit the electromagnetic waves of the high-frequency antenna.

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