A frequency selective surface (FSS) with miniaturized unit cells

Abstract

The present disclosure relates to a frequency selective surface, FSS, unit (200, 600) comprising a dielectric material (201, 601) having a first main side (202, 602) and a second main side (203, 603). The FSS unit (200, 600) further comprises at least a first LC circuit part (240; 640) and a second LC circuit part (241; 641) formed in at least one metallization layer (204, 214; 604) comprised in a corresponding main side (202, 203; 602), where the LC circuit parts (240, 241; 640, 641) mainly run in mutually perpendicular directions (x, y). Each LC circuit part (240, 241; 640, 641) comprises a first edge capacitor part (206, 226; 208, 228; 606, 608) connected in series with a first meandered conductor part (205a, 205c; 605a, 605c) and a second meandered conductor part (205b, 205d; 605b, 605d), which meandered conductor parts (205a, 205b; 205c, 205d; 605a, 605b; 605c, 605d) form a corresponding inductor and are connected in series with a second edge capacitor part (207, 227; 209, 229; 607, 609). Each edge capacitor part (207a, 227a; 209a, 229a; 607a, 609a) is adapted to form a corresponding combined capacitor together with a corresponding further edge capacitor part (226b, 206b; 228d, 208d; 606b, 608d).

Description

[0001] TITLE

[0002] A frequency selective surface (FSS) with miniaturized unit cells

[0003] TECHNICAL FIELD

[0004] The present disclosure relates to miniaturized frequency selective surface (FSS) designs, in particular FSS units, FSS layers and combined array antenna arrangements comprising such FSS layers.

[0005] BACKGROUND

[0006] So-called A+P system is a new emerging product solution for 5G and beyond radio systems, which is a configuration for base station antennas where advanced / active antenna systems (AASs) and a passive antenna system (PAS) are interleaved or combined to construct a single radio system, namely an A+P (active + passive) system. This solution allows customers to save space on antenna towers and reduce operational expenses, especially beneficial for city deployment with limited space for antennas.

[0007] A critical difficulty / problem that needs to be overcome for A+P applications is the mutual couplings / isolation between an AAS and a PAS. Using a frequency selective surface (FSS) as an interface between the AAS and PAS can allow the different antenna modules to work independently while avoiding / suppressing the undesired interference and cross-band PIM (passive intermodulation) signals. An FSS can for example be formed as a periodic array structure or material that exhibits a selective transmission or reflection response of spatial electromagnetic waves, which is also called spatial filter given the filtering capability in free space. It is commonly used in various fields, including electromagnetic shielding, antenna design, wireless communication, etc.

[0008] When being embedded into a limited-space A+P system, conventional FSS structures with unit cells of sizes comparable to the wavelength often encounter practical challenges that need to be addressed. Existing FSS structures have problems in handling angular stability for beam angles up to 60°, along with constraints associated with the FSS size. Other challenges are related to path loss, polarization stability, operating bandwidth, and out-of-band suppression / reflection.

[0009] To implement high-performance A+P systems using FSS technology, it is crucial to tackle and resolve all the technical problems simultaneously, for example those mentioned above. This is challenging for common FSS designs regarding high-performance requirements and practical application difficulties. The document “An FSS Structure With Geometrically Separable Meander-Line Inductors and Parallel-Plate Capacitors” by Peng-Chao Zhao, Zhi-Yuan Zong, Wen Wu, Bo Li, and Da-Gang Fang (IEEE TRANSACTIONS ON ANTENNAS AND PROPAGATION, VOL. 65, NO. 9, SEPTEMBER 2017) discloses miniaturized FSS designs with geometrically separable meanderline inductors and parallel-plate capacitors constructed on both sides of a dielectric substrate. These designs present different frequency responses, i.e., single-band bandpass / bandstop, or dualband bandpass, but have relatively poor stability regarding bandwidth.

[0010] It is desired to realize an FSS design that provides a stable bandpass at one frequency band as well as a stable bandstop performance at another frequency band at the same time, for different polarizations and incident angles.

[0011] SUMMARY

[0012] It is an object of the present disclosure to provide an FSS design that provides a stable bandpass at one frequency band as well as a stable bandstop performance at another frequency band at the same time, for different polarizations and incident angles.

[0013] This object is achieved by means of a frequency selective surface (FSS) unit comprising a dielectric material having a first main side and a second main side. The FSS unit further comprises at least a first LC circuit part and a second LC circuit part formed in at least one metallization layer comprised in a corresponding main side, where the LC circuit parts mainly run in mutually perpendicular directions. Each LC circuit part comprises a first edge capacitor part connected in series with a first meandered conductor part and a second meandered conductor part, which meandered conductor parts form a corresponding inductor and are connected in series with a second edge capacitor part. Each edge capacitor part is adapted to form a corresponding combined capacitor together with a corresponding further edge capacitor part.

[0014] This means that a versatile FSS unit is formed that easily can be combined with a plurality of similar FSS units in both an x direction and a y direction that is perpendicular to the x direction, enabling a two-dimensional FSS layer to be formed.

[0015] According to some aspects, the first main side comprises a first metallization layer and the second main side comprises a second metallization layer. For the first LC circuit part, the first meandered conductor part is formed in the first metallization layer, and the second meandered conductor part is formed in the second metallization layer. Furthermore, for the second LC circuit part, the first meandered conductor part is formed in the first metallization layer, and the second meandered conductor part is formed in the second metallization layer. The corresponding first meandered conductor part and second meandered conductor part are electrically connected by means of a common via connection that runs between the metallization layers.

[0016] This enables an FSS unit to be constructed on a low-profile dielectric substrate featuring two metallization layers.

[0017] According to some aspects, each edge capacitor part is constituted by a corresponding first patch element formed in one metallization layer and a corresponding opposing second patch element formed in the opposite metallization layer.

[0018] According to some aspects, at least two each edge capacitor parts are adapted to be electrically connected to corresponding further edge capacitor parts formed on an adjacent FSS unit such that a combined capacitor is formed by the connected patch elements.

[0019] The FSS unit comprises meandered wires, serving as lumped inductors, and edge capacitor parts, serving as lumped capacitors, which are symmetrically distributed along the x and y directions. The lumped components are connected in series to form the LC circuit parts that produce a desired stopband. In this manner, by having each FSS unit symmetrically formed, it can be used to form FSS layers of arbitrary size in two dimensions.

[0020] The distinguishing structural characteristics of the FSS unit offer improved filtering performance compared to previously known FSS designs, including wide transmission band with low loss, high stopband suppression / reflection, and high polarization and angular stability. In addition, serious fringing-field effects and near-field effects are suppressed, consequently ensuring a favorable level of filtering performance to a certain extent once an FSS layer, comprising a plurality of FSS units, is inserted into an array antenna arrangement. The FSS unit can be implemented with low fabrication cost and minimal complexity.

[0021] According to some aspects, the FSS unit further comprises a plurality of first LC circuit parts running parallel to each other, and a plurality of second LC circuit parts running parallel to each other.

[0022] Having several first LC circuit parts and several second LC circuit parts arranged in this manner enables several stopbands to be chosen, where the stopbands can be tuned separately by adjusting the corresponding parameter values to meet various application requirements.

[0023] According to some aspects, the FSS unit has a rectangular shape and each main side further comprises corner patches, formed in the corresponding metallization layer, one comer patch in each comer. The corner patches introduce an additional resonator for significantly improving the transmission band at higher frequency ranges.

[0024] According to some aspects, the first main side comprises a first metallization layer where the first LC circuit part and the second LC circuit part both are formed in the first metallization layer.

[0025] According to some aspects, the at least two edge capacitor parts are each formed by a corresponding interdigital structure, and where at least two interdigital structures are adapted to be electrically connected to a corresponding adjacent interdigital structure formed on an adjacent FSS unit such that a combined capacitor is formed.

[0026] Having a single conductive layer means that the FSS unit only requires one metallization layer and does not necessitate vias, resulting in reduced fabrication costs and good compatibility with a wide range of fabrication techniques. This technology offers cost savings, ease of fabrication by eliminating the need for aligning different layer and vias, and the potential for multi-layer designs. Additionally, it can be easily combined with antenna radomes or supporting materials such as glass, paper, or fabric.

[0027] According to some aspects, at least two edge capacitor parts are formed by a corresponding patch element that is adapted to form a combined capacitor together with an adjacent patch element formed on an adjacent FSS unit when the adjacent FSS unit is positioned interleaved with the FSS unit.

[0028] This is advantageous in case of building an FSS layer using several dielectric material sheets, such as for example PCBs, where each PCB comprises a plurality of FSS units according to the above. Due to the possible considerable size of such PCBs, it can be desirable to have several smaller PCBs that are combined to form the FSS layer.

[0029] This object is also achieved by means of FSS layers and combined array antenna arrangements which are associated with the above advantages.

[0030] BRIEF DESCRIPTION OF THE DRAWINGS

[0031] The present disclosure will now be described more in detail with reference to the appended drawings, where:

[0032] Figure 1 shows a schematic exploded perspective view of a combined array antenna arrangement; Figure 2 shows a schematic cross-section side view of the combined array antenna arrangement;

[0033] Figure 3 shows a schematic top view of an FSS unit according to a first example;

[0034] Figure 4 shows a see-through top view of the FSS unit according to the first example;

[0035] Figure 5 A shows a perspective top view of the FSS unit according to the first example;

[0036] Figure 5B shows a schematic cross-section side view of the FSS unit according to the first example;

[0037] Figure 6 shows a schematic top view of an FSS layer comprising a plurality of FSS units according to the first example;

[0038] Figure 7 shows a schematic see-through top view of an FSS layer comprising a plurality of FSS units according to the first example;

[0039] Figure 8 shows a schematic perspective top view of an FSS layer comprising a plurality of FSS units according to the first example;

[0040] Figure 9 A shows a perspective top view of an FSS unit according to a second example;

[0041] Figure 9B shows a schematic cross-section side view of the FSS unit according to the second example;

[0042] Figure 10 shows a schematic perspective top view of an FSS layer comprising a plurality of FSS units according to the second example;

[0043] Figure 11 A shows a schematic top view of an FSS unit according to a third example, indicating LC circuit parts;

[0044] Figure 1 IB shows a schematic top view of an FSS unit according to the third example, indicating components;

[0045] Figure 11C shows a schematic cross-section side view of the FSS unit according to the third example; Figure 12 shows a schematic top view of an FSS layer comprising a plurality of FSS units according to the third example;

[0046] Figure 13 shows a schematic perspective top view of an FSS layer comprising a plurality of FSS units according to the third example;

[0047] Figure 14A shows a schematic perspective top view of two FSS units according to the third example; and

[0048] Figure 14B shows a schematic cross-section side view of Figure 14A.

[0049] DETAILED DESCRIPTION

[0050] Aspects of the present disclosure will now be described more fully hereinafter with reference to the accompanying drawings. The different devices, systems, computer programs and methods disclosed herein can, however, be realized in many different forms and should not be construed as being limited to the aspects set forth herein. Like numbers in the drawings refer to like elements throughout.

[0051] The terminology used herein is for describing aspects of the disclosure only and is not intended to limit the invention. As used herein, the singular forms "a", "an" and "the" are intended to include the plural forms as well, unless the context clearly indicates otherwise.

[0052] With reference to Figure 1 and Figure 2, there is a combined array antenna arrangement 100 comprising at least one active array antenna arrangement 101, 101 A, 101B and at least one passive array antenna arrangement 102, where the array antenna arrangements 101, 102 at least partly are separated by a frequency selective surface (FSS) layer 300, 500, 700. As shown in the example in Figure 1, there are two active array antenna arrangements 101A, 101B mounted adjacent each other, and as shown in Figure 2, the FSS layer 300, 500, 700 is adapted to admit passage of signals 105 transmitted from and received by the active array antenna arrangement 101, while suppressing signals 106 transmitted from and received by the passive array antenna arrangement 102.

[0053] The FSS layer 300, 500, 700 is adapted to function as a ground plane of the passive array antenna arrangement 102 to reflect its radiated signals and meanwhile as a part of radome for the active array antenna arrangement 101 to pass its radiated signals.

[0054] In the following, examples of enhanced FSS unit and FSS layers, that for example can be used in an array antenna arrangement 100, will be described. As shown in Figure 3, Figure 4, Figure 5A and Figure 5B, there is a first example of an FSS unit 200 comprising a dielectric material 201 having a first main side 202 and a second main side 203. The FSS unit further comprises at least a first LC circuit part 240 and a second LC circuit part 241 formed in at least one metallization layer 204, 214 comprised in a corresponding main side 202, 203, where the LC circuit parts 240, 241 mainly run in mutually perpendicular directions x, y.

[0055] In this example, there is a first LC circuit part 240 and a second LC circuit part 241, where both LC circuit parts 240, 241 partly are formed in a first metallization layer 204 comprised in a first main side 202 and a second metallization layer 214 comprised in a second main side 203.

[0056] According to the present disclosure, each LC circuit part 240, 241 comprises a first edge capacitor part 206, 226; 208, 228 connected in series with a first meandered conductor part 205a, 205c and a second meandered conductor part 205b, 205d, which meandered conductor parts 205a, 205b; 205c, 205d form a corresponding inductor and are connected in series with a second edge capacitor part 207, 227; 209, 229.

[0057] Furthermore, with reference also to Figure 6-8, each edge capacitor part 207a, 227a; 209a, 229a is adapted to form a corresponding combined capacitor together with a corresponding further edge capacitor part 226b, 206b; 228d, 208d. This further edge capacitor part 226b, 206b; 228d, 208d is a part of an adjacent FSS unit 200b, 200d.

[0058] This means that a versatile FSS unit is formed that easily can be combined with a plurality of similar FSS units in both an x direction and a y direction that is perpendicular to the x direction, enabling a two-dimensional FSS layer 300 to be formed.

[0059] According to some aspects,

[0060] - for the first LC circuit part 240, the first meandered conductor part 205a is formed in the first metallization layer 204, and the second meandered conductor part 205b is formed in the second metallization layer 214, and

[0061] - for the second LC circuit part 241, the first meandered conductor part 205c is formed in the first metallization layer 204, and the second meandered conductor part 205d is formed in the second metallization layer 214.

[0062] Here, the corresponding first meandered conductor part 205a, 205c and the corresponding second meandered conductor part 205b, 205d are electrically connected by means of a common via connection 215 that runs between the metallization layers 204, 214. According to some aspects, in this example, each edge capacitor part 206, 226; 208, 228; 207, 227; 209, 229 is constituted by a corresponding first patch element 206, 208, 227, 229 formed in one metallization layer 204 and a corresponding opposing second patch element 226, 228, 207, 209 formed in the opposite metallization layer 214.

[0063] This means that each edge capacitor part 206, 226; 208, 228; 207, 227; 209, 229 is formed by two opposing patch elements, where, according to some aspects, the first patch elements 206, 207, 208, 209 are connected to a meandered conductor part 205a, 205b, 205c, 205d and where the second patch elements 226, 227, 228, 229 are not connected to any other part in the FSS unit 200. The second patch elements 226, 228, 227, 229 are, however, adapted to be electrically connected to corresponding first patch elements in adjacent FSS units.

[0064] In other words, according to some aspects, at least two each edge capacitor parts 207a, 227a; 209a, 229a are adapted to be electrically connected to corresponding further edge capacitor parts 226b, 206b; 228d, 208d formed on an adjacent FSS unit 200b, 200d such that a combined capacitor is formed by the connected patch elements 227a, 206b; 207a, 226b; 229a, 208d; 209a, 228d.

[0065] Those edge capacitor parts that are positioned along the outer edges of an FSS layer 300 will, however, in practice not be connected to any other edge capacitor part since there are no adjacent FSS units.

[0066] This enables an FSS unit to be constructed on a low-profile dielectric substrate 201 featuring two metallization layers 204, 214. The FSS unit 200 comprises meandered wires 205a, 205b, 205c, 205d, serving as lumped inductors, and edge capacitor parts 206, 226; 208, 228; 207, 227; 209, 229, serving as lumped capacitors, which are symmetrically distributed along the x and y directions. The lumped components are connected in series to form the LC circuit parts 240, 241 that produce a desired stopband.

[0067] In this manner, by having each FSS unit 200 symmetrically formed, it can be used to form FSS layers of arbitrary size in two dimensions.

[0068] The distinguishing structural characteristics of the FSS unit 200 offer improved filtering performance compared to previously known FSS designs, including wide transmission band with low loss, high stopband suppression / reflection, and high polarization and angular stability, up to 45760°. In addition, serious fringing-field effects and near-field effects are suppressed, consequently ensuring a favorable level of filtering performance to a certain extent once an FSS layer comprising a plurality of FSS units 200 is inserted into an array antenna arrangement 100. Each FSS unit 200 can be implemented with low fabrication cost and minimal complexity. By means of the present disclosure, the FSS unit 200 is miniaturized and compact, having a size that for example can be around 5% of the wavelength at the center frequency of the desired stopband. This feature allows a limited-size array antenna arrangement 100 to accommodate as many FSS units 200 as possible; as a result, these FSS units 200 can withstand the unwanted impact of some practical factors, such as fringing-field effects and near-field effects.

[0069] The FSS unit 200 is formed upon a single dielectric material 201, and there is no strict design limit to the material thickness regarding the filtering performance; in fact, the thinner material, the smaller and more compact FSS units 200. Thanks to the uncomplicated structures, FSS units 200 can be easily fabricated at a low fabrication cost and with minimal complexity.

[0070] Benefiting from the above structural characteristics, the FSS unit 200 enables a stable frequency performance, i.e., transmission and reflection performance in the operating frequency ranges, for different incident angles, up to 45760°, and polarizations.

[0071] With reference to Figure 9A, Figure 9B and Figure 10, there is a second example of an FSS unit 400 that further comprises a plurality of first LC circuit parts 440a, 440b according to the first example that run parallel to each other, and a plurality of second LC circuit parts 441a, 441b according to the first example that run parallel to each other. In this example, there are two first LC circuit parts 440a, 440b and two second LC circuit parts 441a, 441b. The meandered conductor parts of the LC circuit parts 440a, 440b, 441a, 441b are electrically connected by means of corresponding via connections 415a, 415b that run between the metallization layers 404, 414 in the same manner as for the FSS unit 200 described above for the first example with only two LC circuit parts 240, 241.

[0072] Having several first LC circuit parts 440a, 440b and several second LC circuit parts 441a, 441b arranged in this manner enables several stopbands to be chosen, where the stopbands can be tuned separately by adjusting the corresponding parameter values to meet various application requirements. The first LC circuit parts 440a, 440b and the second LC circuit parts 441a, 441b differ slightly in size to generate two stopbands. Due to the relatively complex patterns involved, the size of the FSS unit 400 is larger than the FSS unit 200. In general, the main structural characteristics and frequency performance of the presented FSS units are almost the same or at least relatively similar.

[0073] According to some aspects, for the FSS units described, the FSS unit 200, 400 has a rectangular shape and each main side 202, 203; 402, 403 further comprises corner patches 210, 211, 212, 213; 230, 231, 232, 233; 410, 411, 412, 413; 430, 431, 432, 433, formed in the corresponding metallization layer 204, 214; 404, 414, one corner patch 210, 211, 212, 213; 230, 231, 232, 233; 410, 411, 412, 413; 430, 431, 432, 433 in each comer. The corner patches 210, 211, 212, 213; 230, 231, 232, 233 introduce an additional resonator for significantly improving the transmission band at higher frequency ranges.

[0074] It should be noted that the meandered wires, end patches, and corner patches are distributed in a compact manner, but their shapes do not need to be fixed. Similarly, the FSS unit can take on various shapes, such as triangular, square, hexagonal, or other similar shapes, depending on the specific design requirements and preferences.

[0075] A third example of an FSS unit 600 will be provided in the following with reference to Figure 11 A-C and Figure 14, where the edge capacitor parts have a different structure. According to some aspects, the first main side 602 comprises a first metallization layer 604 where the first LC circuit part 640 and the second LC circuit part 641 are both formed in the first metallization layer 604.

[0076] More in detail, there is an FSS unit 600 comprising a dielectric material 601 having a first main side 602 and a second main side 603. The FSS unit further comprises at least a first LC circuit part 640 and a second LC circuit part 641 formed in a first metallization layer 604 comprised in the first main side 602, where the LC circuit parts 640, 641 mainly run in mutually perpendicular directions x, y.

[0077] According to the present disclosure, each LC circuit part 640, 641 comprises a first edge capacitor part 606, 608 connected in series with a first meandered conductor part 605a, 605c and a second meandered conductor part 605b, 605d, which meandered conductor parts 605a, 605b; 605c, 605d form a corresponding inductor and are connected in series with a second edge capacitor part 607, 609.

[0078] Furthermore, as shown in Figure 12 and Figure 13, each edge capacitor part 607a, 609a is adapted to form a corresponding combined capacitor together with a corresponding further edge capacitor part 606b, 608d. This further edge capacitor part 606b, 608d is a part of an adjacent FSS unit 600b, 600d.

[0079] According to some aspects, the at least two edge capacitor parts 607a, 609a are each formed by a corresponding interdigital structure, and at least two interdigital structures 607a, 609a are adapted to be electrically connected to a corresponding adjacent interdigital structure 606b, 608d formed on an adjacent FSS unit 600b, 600d such that a combined capacitor is formed. Having a single conductive layer, the first metallization layer 604, means that the FSS unit 600 according to the third example only requires one metallization layer and does not necessitate vias, resulting in reduced fabrication costs and good compatibility with a wide range of fabrication techniques. This technology offers cost savings, ease of fabrication by eliminating the need for aligning different layer and vias, and the potential for multi-layer designs. Additionally, it can be easily combined with antenna radomes or supporting materials such as glass, paper, or fabric.

[0080] This enables an FSS unit to be constructed on a low-profile dielectric substrate 601 featuring one metallization layer 604. The FSS unit 600 comprises meandered wires 605a, 605b, 605c, 605d, serving as lumped inductors, and edge capacitor parts 606, 607, 608, 609, serving as lumped capacitors, which are symmetrically distributed along the x and y directions. The lumped components are connected in series to form the LC circuit parts 640, 641 that produce a desired stopband.

[0081] In this manner, by having each FSS unit 600 symmetrically formed, it can be used to form FSS layers 700 of arbitrary size in two dimensions. Those edge capacitor parts that are positioned along the outer edges of an FSS layer 700 will, however, in practice not be connected to any other edge capacitor part since there are no adjacent FSS units.

[0082] According to some aspects, the FSS unit 600 has a rectangular shape and the first main side 602 further comprises corner patches 610, 611, 612, 613, formed in the first metallization layer 604, one corner patch 610, 611, 612, 613 in each corner. The comer patches 610, 611, 612, 613 introduce an additional resonator for significantly improving the transmission band at higher frequency ranges.

[0083] Furthermore, the FSS unit 600 is of course associated with the advantages and alternatives described for the FSS unit 200, 400 described above which is realized in two metallization layers.

[0084] According to some aspects, as shown in Figure 14A and Figure 14B, at least two edge capacitor parts are formed by a corresponding patch element 680, 681 that is adapted to form a combined capacitor together with an adjacent patch element 680, 681 formed on an adjacent FSS unit 600a’, 600b’ when the adjacent FSS unit 600a’, 600b’ is positioned interleaved with the FSS unit 600a’, 600b’.

[0085] This is advantageous in case of building an FSS layer using several dielectric material sheets, such as for example PCBs, where each PCB comprises a plurality of FSS units 600. Due to the possible considerable size of such PCBs which can reach lengths of up to 1.2 meters, it can be desirable to have several smaller PCBs that are combined to form the FSS layer. Here, two edge capacitor parts are formed by corresponding patch elements 680, 681 positioned exclusively at the periphery of the PCB 601’, 601”. This arrangement ensures that the FSS units 600a’ of each PCB 601’ is enabled to effectively interact with their counterparts 600b’ on adjacent PCBs 601”.

[0086] By utilizing only straight cuts on edges of the PCB and avoiding non-straight cuts, especially in meandered lines with 0.3mm thick PCB prongs containing interdigital conductor traces, the manufacturing process becomes more cost-effective. This streamlined approach reduces production complexities and associated expenses.

[0087] The exclusion of non-straight cuts and complex edges makes the PCB more feasible to produce. It simplifies the manufacturing process, leading to higher efficiency and reduced risk of errors during production.

[0088] The thickness of the dielectric material of one PCB, particularly the top PCB 601’, serves as a natural spacer for the capacitor plates 680, 681. This simplifies the assembly process, eliminating the need for additional spacers or components and making the overall assembly more straightforward and efficient.

[0089] With reference to Figure 6, Figure 7, Figure 8, Figure 10, Figure 12 and Figure 13, the present disclosure also relates to an FSS layer 300, 500, 700 comprising a plurality of FSS units 200, 400, 600 as described herein, where the FSS units 200, 400, 600 are positioned adjacent to each other. In this manner, the FSS units 200, 400, 600 as described herein can be combined to form an array of FSS units 200a-i, 400a-i, 600a-i such that an FSS layer 300, 500, 700 is formed, being associated with the advantages discussed above.

[0090] This means that the edge capacitor parts 207a, 227a; 209a, 229a; 607a, 609a form a corresponding combined capacitor together with a corresponding further edge capacitor part 226b, 206b; 228d, 208d; 606b, 608d where there are adjacent FSS units 200a-i, 400a-i, 600a-i. This also means that some edge capacitor parts remain unconnected along the edges of the FSS layer 300, 500, 700.

[0091] The sizes and numbers of FSS units 200a-i, 400a-i, 600a-i along the x and y directions in an FSS layer 300, 500, 700 do not need to be the same and may be adapted to the available internal space where the FSS layer 300, 500, 700 is intended to be positioned.

[0092] According to some aspects, at least a sub-plurality of FSS units 200a-i, 400a-i, 600a-i are formed on one and the same dielectric material 201, 401, 601, such as for example a common PCB. In case an FSS layer is formed by several dielectric material sheets, such as for example PCBs, where each dielectric material sheet comprises a plurality FSS units, these dielectric material sheets are combined in any suitable manner, for example as described above with reference to Figure 14A and Figure 14B.

[0093] With reference to Figure 1 and Figure 2, the present disclosure also relates to a combined array antenna arrangement 100 comprising at least one active array antenna arrangement 101, 101A, 10 IB and at least one passive array antenna arrangement 102, where the array antenna arrangements 101, 102 at least partly are separated by an FSS layer 300, 500, 700 as described herein. An example of such an array antenna arrangement 100 is described initially.

[0094] By means of the present disclosure, the FSS unit 200, 400, 600 is miniaturized and compact, having a size that for example can be around 5% or 10% of the wavelength at the center frequency of the desired stopband. This feature allows a limited-size array antenna arrangement 100 to accommodate as many FSS units 200 as possible; as a result, these FSS units 200 can withstand the unwanted impact of some practical factors, such as fringing-field effects and near-field effects.

[0095] The present disclosure is not limited to the examples described above, but may vary freely within the scope of the appended claims. For all examples where corner patches are present, the corner patches of neighboring FSS units may, or may not, be electrically connected to each other.

Claims

CLAIMS1. A frequency selective surface, FSS, unit (200, 600) comprising a dielectric material (201, 601) having a first main side (202, 602) and a second main side (203, 603), further comprising at least a first LC circuit part (240; 640) and a second LC circuit part (241; 641) formed in at least one metallization layer (204, 214; 604) comprised in a corresponding main side (202, 203; 602), where the LC circuit parts (240, 241; 640, 641) mainly run in mutually perpendicular directions (x, y), wherein each LC circuit part (240, 241; 640, 641) comprises a first edge capacitor part (206, 226; 208, 228; 606, 608) connected in series with a first meandered conductor part (205a, 205c; 605a, 605c) and a second meandered conductor part (205b, 205d; 605b, 605d), which meandered conductor parts (205a, 205b; 205c, 205d; 605a, 605b; 605c, 605d) form a corresponding inductor and are connected in series with a second edge capacitor part (207, 227; 209, 229; 607, 609), where each edge capacitor part (207a, 227a; 209a, 229a; 607a, 609a) is adapted to form a corresponding combined capacitor together with a corresponding further edge capacitor part (226b, 206b; 228d, 208d; 606b, 608d).

2. The FSS unit (200) according to claim 1, wherein the first main side (202) comprises a first metallization layer (204) and where the second main side (203) comprises a second metallization layer (214), where,- for the first LC circuit part (240), the first meandered conductor part (205a) is formed in the first metallization layer (204), and the second meandered conductor part (205b) is formed in the second metallization layer (214), and where- for the second LC circuit part (241), the first meandered conductor part (205c) is formed in the first metallization layer (204), and the second meandered conductor part (205d) is formed in the second metallization layer (214), where the corresponding first meandered conductor part (205a; 205c) and second meandered conductor part (205b, 205d) are electrically connected by means of a common via connection (215) that runs between the metallization layers (204, 214).

3. The FSS unit 200 according to claim 2, wherein each edge capacitor part (206, 226; 208, 228; 207, 227; 209, 229) is constituted by a corresponding first patch element (206, 208, 227, 229) formed in one metallization layer (204) and a corresponding opposing second patch element (226, 228, 207, 209) formed in the opposite metallization layer (214).

4. The FSS unit (200a) according to claim 3, wherein at least two each edge capacitor parts (207a, 227a; 209a, 229a) are adapted to be electrically connected to corresponding further edge capacitor parts (226b, 206b; 228d, 208d) formed on an adjacent FSS unit (200b, 200d) suchthat a combined capacitor is formed by the connected patch elements (227a, 206b; 207a, 226b; 229a, 208d; 209a, 228d).

5. The FSS unit (400) according to any one of the claims 2-4, further comprising a plurality of first LC circuit parts (440a, 440b) running parallel to each other, and a plurality of second LC circuit parts (441a, 441b) running parallel to each other.

6. The FSS unit (200, 400) according to any one of the claims 2-5, wherein the FSS unit (200, 400) has a rectangular shape and where each main side (202, 203; 402, 403) further comprises corner patches (210, 211, 212, 213; 230, 231, 232, 233; 410, 411, 412, 413; 430, 431, 432, 433), formed in the corresponding metallization layer (204, 214; 404, 414), one corner patch (210, 211, 212, 213; 230, 231, 232, 233; 410, 411, 412, 413; 430, 431, 432, 433) in each corner.

7. The FSS unit (600) according to claim 1, wherein the first main side (602) comprises a first metallization layer (604) where the first LC circuit part (640) and the second LC circuit part (641) both are formed in the first metallization layer (604).

8. The FSS unit (600a) according to claim 7, wherein the at least two edge capacitor parts (607a, 609a) are each formed by a corresponding interdigital structure, and where at least two interdigital structures (607a, 609a) are adapted to be electrically connected to a corresponding adjacent interdigital structure (606b, 608d) formed on an adjacent FSS unit (600b, 600d) such that a combined capacitor is formed.

9. The FSS unit (600a’, 600b’) according to claim 8, wherein at least two edge capacitor parts are formed by a corresponding patch element (680, 681) that is adapted to form a combined capacitor together with an adjacent patch element (680, 681) formed on an adjacent FSS unit (600a’, 600b’) when the adjacent FSS unit (600a’, 600b’) is positioned interleaved with the FSS unit (600a’, 600b’).

10. The FSS unit (600; 600a’, 600b’) according any one of the claims 8 or 9, wherein the FSS unit (600) has a rectangular shape and where the first main side (602) further comprises comer patches (610, 611, 612, 613), formed in the first metallization layer (604), one comer patch (610, 611, 612, 613) in each comer.

11. An FSS layer (300, 500, 700) comprising a plurality of FSS units (200, 400, 600) according to any one of the previous claims, where the FSS units (200, 400, 600) are positioned adjacent to each other.

12. The FSS layer (300, 500, 700) according to claim 11, wherein at least a sub-plurality of FSS units (200a-i, 400a-i, 600a-i) are formed on one and the same dielectric material (201, 401, 601).

13. A combined array antenna arrangement (100) comprising at least one active array antenna arrangement (101, 101 A, 101B) and at least one passive array antenna arrangement (102), where the array antenna arrangements (101, 102) at least partly are separated by an FSS layer (300, 500, 700) according to any one of the claims 11 or 12.

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