Abstract
The invention relates to an improved electromagnetic band gap (EBG) structure. The invention also relates to an electromagnetic band gap (EBG) component for use in an EBG structure according to the invention. The invention further relates to an antenna device comprising at least one EBG structure according to the invention.
Claims
1. An Electromagnetic Band Gap (EBG) structure comprising: a conductive ground plane; at least one dielectric layer disposed on said ground plane; and a plurality of conductive tiles disposed on the at least one dielectric layer and electrically connected to the conductive ground plane, wherein at least a number of the conductive tiles have a base profile defined by the polar function: wherein: ρ.sub.d(φ) is a curve located in the XY-plane, and φ∈[0, 2π) is the angular coordinate, and wherein the conductive ground plane and/or the at least one dielectric layer has a base profile also defined by ρ.sub.d(φ).
2. The EBG structure according to claim 1, wherein all tiles have a base profile defined by the polar function: wherein: ρ.sub.d (φ) is a curve located in the XY-plane; and φ∈[0, 2π) is the angular coordinate.
3. The EBG structure according to claim 1, wherein the EBG structure comprises a plurality of differently shaped conductive tiles disposed on each dielectric layer and electrically connected to the ground plane, wherein preferably all tiles have a base profile defined by the polar function: wherein: ρ.sub.d (φ) is a curve located in the XY-plane; and φ−[0, 2π) is the angular coordinate.
4. The EBG structure according to claim 3, wherein the base profiles of at least two differently shaped tiles have an at least partially complementary shape.
5. The EBG structure according to claim 1, wherein the conductive tiles disposed on each said dielectric layer are arranged in a pattern.
6. The EBG structure according to claim 1, wherein the tiles disposed on each dielectric layer are arranged at a distance from each other.
7. The EBG structure according to claim 1, wherein at least a number of tiles have a substantially flat (2D) geometry.
8. The EBG structure according to claim 1, wherein each tile is physically connected to the ground plane by a conductive via enclosed by a through-hole made in at least one dielectric layer.
9. The EBG structure according to claim 1, wherein the EBG structure comprises a plurality of dielectric layers stacked or disposed on top of each other, wherein a plurality of conductive tiles is disposed on each dielectric layer.
10. The EBG structure according to claim 1, wherein a plurality of tiles disposed on different dielectric layers are physically connected to the ground plane by the same via enclosed by a through-hole made in each dielectric layer.
11. The EBG structure according to claim 1, wherein a≠b.
12. The EBG structure according to claim 1, wherein at least one value of n.sub.1, n.sub.2, and n.sub.3 deviates from 2.
13. The EBG structure according claim 1, wherein the parametric representation of the three-dimensional shape of at least a number of tiles, in particular tiles disposed on an upper dielectric layer, is based on two perpendicular cross sections ρ.sub.1(ε) and ρ.sub.2(φ): wherein: ρ is defined by the function according to claim 1, 0≤ε≤2π, and −½π≤φ≤½π.
14. The EBG structure according to claim 1, wherein the ground plane is larger than the at least one dielectric layer.
15. The EBG structure according to claim 1, wherein the EBG structure comprises: a shared ground plane, and a plurality of distant EBG components disposed on said shared ground plane, wherein each EBG component comprises: at least one dielectric layer, and a plurality of conductive tiles disposed on each dielectric layer and electromagnetically coupled to the shared ground plane, wherein at least a number of tiles has a base profile defined by the polar function: wherein: ρ.sub.d(φ) is a curve located in the XY-plane; and φ∈[0, 2π) is the angular coordinate.
16. The EBG structure according to claim 5, wherein the conductive tiles disposed on each of the dielectric layers are arranged in a periodic pattern.
17. An EBG component for use in a EBG structure according to claim 1, said component comprising at least one dielectric layer configured to be disposed on the conductive ground plane of the EBG structure; and a plurality of conductive patches disposed on each dielectric layer and configured to be electromagnetically coupled to the ground plane, wherein at least a number of patches has a base profile defined by the polar function: wherein: ρ.sub.d(φ) is a curve located in the XY-plane; and φ∈[0, 2π) is the angular coordinate.
18. An antenna device comprising: at least one EBG structure according to claim 1; at least one EBG component disposed on said conductive ground plane of the at least one EBG structure, wherein each EBG component comprises: at least one dielectric layer, and a plurality of conductive tiles disposed on each dielectric layer and electrically connected to the shared ground plane, wherein at least a number of tiles has a base profile defined by the polar function: wherein: ρ.sub.d(φ) is a curve located in the XY-plane; and φ∈[0, 2π) is the angular coordinate; and a plurality of antenna units, wherein the conductive ground plane of the EBG structure serves as a ground plane for said plurality of antenna units, and wherein the at least one EBG component is positioned in between two antenna units.
19. The antenna device according to claim 18, wherein the EBG structure comprises a plurality of EBG components sharing the same ground plane, wherein the shared ground plane of the EBG components serves a ground plane for said plurality of antenna units.
Description
(1) The invention will be elucidated on the basis of non-limitative exemplary embodiments shown in the enclosed figures. Herein:
(2) FIG. 1a shows a schematic representation of an antenna device according to the invention;
(3) FIG. 1b shows a graph of the isolation enhancement which can be achieved by the antenna device of FIG. 1a;
(4) FIGS. 2a-c show schematic representations of an EBG structure according to the invention;
(5) FIGS. 3a and 3b show schematic representations of further embodiment of an antenna device according to the invention;
(6) FIG. 4 shows a schematic representation of a possible single supershape structure of an EBG component according to the invention;
(7) FIG. 5 shows a schematic representation of a possible dual supershape structure of an EBG component according to the invention;
(8) FIG. 6 shows a schematic representation of a single supershape structure of an EBG component according to the invention;
(9) FIGS. 7a-h show a plurality of examples of possible shapes of base profiles of conductive patches of EBG components according to the invention;
(10) FIG. 8 shows a schematic representation of a supershaped EBG component;
(11) FIGS. 9a-h show a plurality of examples of possible supershapes of EBG components according to the invention;
(12) FIG. 10 shows a schematic representation of a supershaped EBG component comprising two independent supershaped structures according to the invention;
(13) FIG. 11 shows a perspective view of a supershaped structure as shown in FIG. 10;
(14) FIGS. 12a-c show the measurement set-up of three different antenna devices, wherein FIG. 12c shows an antenna device according to the invention;
(15) FIG. 12d shows a graph of the isolation enhancement between the antenna devices as shown in FIGS. 12a-c;
(16) FIGS. 13a and 13b show an antenna unit according to the invention, in particular a single-band antenna unit as shown in FIGS. 12a-c; and
(17) FIG. 14 shows in more detail the ground plane and the slot antenna of the antenna unit shown in FIG. 13.
(18) FIG. 1a shows a schematic representation of an antenna device (1) according to the invention. The antenna device (1) comprises a conductive metal plate (3), also referred to as ground plane (3), and an electromagnetic band gap (EBG) component (4) disposed on said ground plane (3). The assembly of the EBG component (4) and the ground plane (3) is referred to as an EBG structure according to the invention. The EBG component (4) comprises a plurality of conductive tiles (6), arranged according to a periodic pattern and separated by small gaps. Tiles (6) positioned on top of each other are mutually connected by means of vias (not shown), by means of which the tiles (6) are connected to the ground plane (3). The EGB component (4) comprises at least one dielectric layer (5) disposed on said ground plane (3) and a plurality of conductive tiles (6) disposed on the dielectric layer (5) and electrically connected to the shared ground plane (3). The conductive tiles (6) have a base profile defined by the polar function of the Gielis' Formula. More detailed sketches of the EBG structure (4) are shown in FIGS. 2a-c. The antenna device (1) furthermore comprises a plurality of antenna units (7, 8). In the shown embodiment, the antenna device (1) comprises a first antenna unit (7) and a second antenna unit (8). The metal plate (3) of the antenna device (1) serves as a ground plane (3) for said plurality of antenna units (7,8). In the shown configuration, the EBG component (4) is positioned in between two antenna units (7, 8). The EBG component (4) functions as an additional coupling path between the two antennas (7, 8). The presence of the EBG component (4) increases the isolation between the first antenna unit (7) and the second antenna unit (8) without compromising efficiency, gain and radiation pattern characteristics of the antennas (7, 8).
(19) FIG. 1b shows a graph of the isolation enhancement between an antenna device (1) which makes use of an EBG component (4), as shown in FIG. 1b, and an antenna device without an EBG component. The x-axis shows the frequency (in GHz) and the y-axis shows the isolation value (in dB). FIG. 1b shows that the EBG component according to the invention can improve isolation by 10 to 20 dB as compared to systems without an EBG component. This is achieved by tiling a laminate using supershaped conductive tiles based on the Gielis Formula, which laminate is shown in more details in FIGS. 2a-2c.
(20) FIGS. 2a-c show schematic representations of the EBG component (4) as shown in FIG. 1a. Corresponding reference signs therefore correspond to similar units. The EGB component (4) comprises a first dielectric layer (5A) and a second dielectric layer (5B). The first dielectric layer (5A) and the second dielectric layer (5B) are disposed on top of each other, and form a laminate together. Both dielectric layers (5A, 5B) comprise a plurality of conductive tiles (6A, 6B). The tiles (6A, 6B) of each dielectric layer (5A, 5B) have a base profile defined by the Gielis' formula, resulting in a supershaped profile. In the shown embodiment, the tiles (6A) of the first dielectric layer (5A) are arranged in a periodic pattern. The tiles (6B) of the second dielectric layer (5B) are arranged according to substantially the same pattern as the periodic pattern of the first dielectric layer (5A). The conductive tiles (6A, 6B) on both dielectric layers (5A, 5B) can both be physically connected to the ground plane (not shown) by the same via conductor (9). The EBG component (4) comprises a plurality of via conductors (9), wherein each via conductor (9) is enclosed by a through-hole (10) made in each dielectric layer (5A, 5B). Reference number 5″ of FIG. 2c indicates the stacked dielectric layers (5A, 5B).
(21) FIGS. 3a and 3b show a schematic representation of another possible embodiment of an antenna device (11) according to the invention. FIG. 3a shows a perspective view, whereas FIG. 3b shows a top view. The antenna device (11) comprises a (shared) ground plane (13) and a plurality of EBG components (14A, 14B) disposed on the ground plane (13). The EBG components (14A, 14B) each comprises a plurality of dielectric layers, and a plurality of conductive tiles disposed on each dielectric layer and electromagnetically coupled to the shared ground plane (13). Stacked tiles are connected by means of vias, wherein each via is also connected to the ground plane (13). The antenna device (11) comprises a first EBG structure (14A) and a second EBG structure (14B). Both the first and the second EBG structures (14A, 14B) are substantially similar to the EBG structure shown in FIGS. 2a-c. The antenna device (11) furthermore comprises a plurality of dual-band antenna units (17A, 17B, 17C, 18A, 18B, 18C). Each dual-band antenna unit (17A, 17B, 17C, 18A, 8B, 8C) is configured to operate in various regions of the electromagnetic spectrum, such as for example the Wi-Fi bands (2.4 GHz/5 GHz). The antenna device (11) also comprises a plurality of single-band antenna units (19A, 19B, 19C, 19D). Each single-band antenna unit (19A, 19B, 19C, 19D) is configured to operate for example at 5 GHz. The arrangement of the single-band antenna units (19A, 19B, 19C, 19D) is a non-limitative example of a possible arrangement of the antenna units. A more detailed description of this dual-band antenna unit (19A, 19B, 19C, 19D) is provided in the non-prepublished Dutch patent applications NL2019365 and NL2019798, the subject-matter of which patent applications is hereby incorporated by reference.
(22) FIG. 4 shows a schematic representation of a possible single supershaped structure of an EBG component (24) according to the invention. The EGB component (24) comprises a first dielectric layer (25A), a second dielectric layer (25B) and a third dielectric layer (25C). The dielectric layers (25A, 25B, 25C) are disposed on top of each other, and form a laminate together. Each dielectric layer (25A, 25B, 25C) comprises a plurality of conductive tiles (26A, 26B, 26C). The tiles (26A, 26B, 26C) of each dielectric layer (25A, 25B, 25C) have a base profile defined by the Gielis' formula. The tiles (26A, 26B, 260) featuring supershaped geometry are also shown isolated from the dielectric layer in this figure. The conductive tiles (26A, 26B, 26C) are physically connected to each other and to the ground plane (23) by a via (29).
(23) FIG. 5 shows a schematic representation of a possible dual complementarily supershaped unit cell of an EBG component (34) according to the invention, and of an EBG structure according to the invention. The figure shows a first supershaped structure (S1) and a second supershaped structure (S2). The EBG component (34) consists of a three layer (35A, 35B, 35C) dielectric laminate structure. The supershapes (S1, S2) are separated from each other by small gaps (30).
(24) FIG. 6 shows a schematic representation of a single supershaped structure of an EBG component (44). The EBG component (44) is a single layer (45) component. The shape of the conductive tiles (46) is defined by the polar function of the Gielis Formula.
(25) FIGS. 7a-h show a plurality of examples of possible shapes of base profiles (20a-h) of conductive tiles of EBG components according to the invention. Each base profile (20a-h) has a different supershape based on the Gielis' formula:
(26)
wherein: ρ.sub.d(φ) is a curve located in the XY-plane; and φ∈[0, 2π) is the angular coordinate.
(27) Each figure reports the parameter values used in the Gielis' formula to create the shown supershape. The parameter m determines the number of pseudo-vertices of the supershaped base profile (20a-h). The parameters n1, n2 and n3 determine the convexity/concavity characteristics of the supershaped curve. The parameters a and b are fixed in the shown examples and determine the area of the curve.
(28) FIG. 8 shows a schematic representation of a supershaped EBG component. The figure shows a unit cell (80). The unit cell (80) is a supershaped structure that repeats itself infinitely with a repetition factor dx and dy. A perspective view of one isolated unit cell (80) is shown. The unit cell (80) comprises at least one conductive tile (86). The figures show that the conductive layer (86) can comprise a first supershaped tile (S1) or a second supershaped tile (S2). The second supershaped structure (S2) is complementary to the first supershaped structure (S1). This results in that the unit structure comprises two dependent supershapes. The dielectric substrate layer (85) is only shown in the first perspective view and is made invisible in the second perspective view. The supershapes (S1, S2) are separated by a gap (G). Each conductive tile (86) is physically connected to the ground plane (83) by an individual via (89). The thickness of the substrate (85) is for example 3 mm, the material can be FR4 (relative permittivity=4.3, tan delta 0.025), the diameter of the via (89) is for example 0.9 mm, and the gap is for example 0.26 mm. The supershape of the tiles in FIG. 8 are based on the Gielis' formula, using the following parameters: a=b=2.44 mm, m=8, n1=n2=n3=5.
(29) FIGS. 9a-h show a plurality of examples of possible complementary supershapes of EBG components according to the invention. The supershapes are created by changing only a single parameter (m) in contrast to the supershapes shown in FIG. 8. All FIGS. 9a-h show a structure which comprises two dependent complementary supershapes (S1, S2).
(30) FIG. 10 shows a schematic representation of a supershaped EBG structure comprising two independent supershaped tiles (S1 and S2). The independent supershapes (S1, S2) are separated by each other via a gap (G).
(31) The Gielis equation parameters for obtaining the first tile (S1) as shown in this figure are: a=b=1, m=4, n1=2.1 and n2=n3=9.
(32) The Gielis equation parameters for obtaining the second tile (S2) as shown in this figure are: a=b=2.26, m=4, n1=10 and n2=n3=11. The dimension of a and b is typically related to the ratio of n1 to n2=n3.
(33) FIG. 11 shows a perspective view of a supershaped structure as shown in FIG. 10, comprising two independent supershapes (S1, S2). Each supershaped tile is electrically connected to a ground plate by means of a via (119).
(34) FIGS. 12a-c show the measurement set-up of three different antenna devices. The first antenna device (101) (FIG. 12a) shows an antenna device without an EBG component. The second antenna device (201) (FIG. 12b) shows an antenna device with two square-shaped EBG components (204). These are conventional EBG components, which do not comprise a supershape. The third antenna device (301) (FIG. 12c) shows an antenna device (301) with two EBG components (304) comprising a supershaped structure. Each antenna device (101, 201, 301) comprises a plurality of dual-band antenna units (107A, 107B, 108A, 108B, 108C, 207A, 207B, 208A, 208B, 208C, 307A, 307B, 308A, 308B, 308C). Each dual-band antenna unit (107A, 107B, 108A, 108B, 108C, 207A, 207B, 208A, 208B, 208C, 307A, 307B, 308A, 308B, 308C) is configured to operate in various regions of the electromagnetic spectrum, such as for example Wi-Fi bands (2.4 GHz/5 GHz). Each antenna device (101, 201, 301) also comprises a plurality of single-band antenna units (109A, 109B, 109C, 109D, 209A, 209B, 209C, 209D, 309A, 309B, 309C, 309D). Each single-band antenna units (109A, 109B, 109C, 1090, 209A, 209B, 209C, 209D, 309A, 309B, 309C, 309D) is configured to operate for example at 5 GHz. Each antenna device (101, 201, 301) comprises a conductive, metal ground plane (103, 203, 303). The EGB components (204, 304) are optimized to cover the 5.15 GHz-5.875 GHz frequency range. The EBG components of the second antenna device (201) and the third antenna device (301) are realized on the same substrate material. The dimensions of the EBG components (204, 304) are equal.
(35) FIG. 12d shows a graph of the isolation enhancement when comparing the first antenna device (101), to the second antenna device (201), to the third antenna device (301), as shown in FIGS. 12a-c. The x-axis of the graph shows the frequency (in GHz) and the y-axis shows the isolation value (in dB). FIG. 12d shows that using a conventional EBG component (204) already can improve isolation by about 5 dB as compared to the antenna system without an EBG component. The graph further shows that by using a supershaped EBG component (304) the isolation can be further improved by additional 5-10 dB, at least.
(36) FIGS. 13a and 13b show an antenna unit (109) according to the invention, in particular a single-band antenna unit as shown in FIGS. 12a-c. This is referred to 109A, 109B, 109C, 109D, 209A, 209B, 209C, 209D, 309A, 309B, 309C and 309D.
(37) FIGS. 13a and 13b show a different perspective view of the antenna unit (109). The antenna unit (109) is a dual-port antenna, comprising a slot antenna (130) and a dipole antenna (131). The single-band antenna (109) is configured to operate for example at 5 GHz. In the shown embodiment, both the slot antenna (130) and the dipole antenna (131) are configured to operate in the Wi-Fi band at 5 GHz. The slot antenna (130) is mounted on a conductive ground plane (132). The ground plane (132) is shown in more detail in FIG. 14. The dipole antenna (131) comprises a PCB and is placed at a predefined distance (d1) from the ground plane (132). This distance is preferably relatively small, for example between 5 and 10 mm. Between the ground plane (132) and the dipole antenna (131) a distance holder (134) is present. In the shown embodiment, the distance holder (134) comprises a reinforcement rib (135). The distance holder (134) and/or reinforcement rib (135) can for example be made out of plastic. The dipole antenna (131) comprises two flares (133A, 133B). The shape of the conductive flares (133A, 133B) is defined by the polar function of the Gielis' formula:
(38)
(39) Where the x-dimension of the flare is scaled by a factor K.sub.1 according to:
X.sub.d(φ)=K.sub.1ρ.sub.d(φ)cos(θ)
and the y-dimension of the flare is scaled by a factor K.sub.2 according to:
Y.sub.d(φ)=K.sub.2ρ.sub.d(φ)sin(θ)
(40) The optimized parameters for the dipole flares as shown in the figure are K.sub.1=5.3 mm, K.sub.2=4.2 mm, a=b=1, m=1, n1=18 and n2=n3=2.2. Possibly the parameters for the dipole flares can be chosen within the following ranges: K.sub.1=5.3-5.4, K.sub.2=4.2-5.2, a=b=1, m=1.2, n1=15-50, n2=n3=2.2-5.
(41) The flares (133A, 133B) are not in contact with each other. The distance between the flares (133A, 133B) is preferably about 0.3 mm. The slot antenna (130) is mounted perpendicular to the dipole antenna (131). Each flare (133A, 133B) is positioned at a different side of the slot antenna (130) (as seen from a top view). The slot antenna (130) is shown in more detail in FIG. 14. The antenna unit (109) according to the invention features good isolation characteristics. Furthermore, the antenna unit (109) according to the invention features well behaved radiation patterns. Another benefit is that the antenna unit according to the invention is relatively easy to manufacture. Experiments show that the isolation between two ports, where the first port is connected to the dipole antenna (131) and the second port is connected to the slot antenna (130), is about 28 dB in the 5.15-5.875 GHz frequency range. This results in a total measured antenna efficiency for the first port between 75 and 80% and a total measured antenna efficiency for the second port between 64 and 75%. The measured efficiency accounts for the losses of a 15 cm long 1.32 mm thick coaxial cable. The peak realized gain for the first port is between 5.4 dBi and 5.8 dBi. The peak realized gain for the second port is between 4.4 dBi and 5.5 dBi.
(42) FIG. 14 shows the antenna unit (109) of FIG. 13, and in more detail the ground plane (132) and the slot antenna (130). The ground plane (132) is a conductive metal plate (132). The ground plane (132) is for example manufactured from metal or stainless steel. The ground plane (132) comprises holes (137A) for positioning the antenna unit (109) on an antenna device according to the invention, in particular to the ground plane of such antenna device, via mechanical securing. The ground plane (132) furthermore comprises holes (137B) for enabling mounting the distance holder. The slot antenna (130) comprises a PCB which comprises a radiating slot (138). The radiating slot (138) is shown in the front side of the slot antenna (130). The radiating slot (138) has a Roman I-shaped configuration. Obviously, other slot configurations are also possible. For example, an H-shaped radiating slot. The back side of the slot antenna (130) comprises a feeding pin (139). A RF feeding cable can be connected to the feeding pin (139).
(43) In a possible embodiment, the antenna unit can be modified such that it is configured to operate at both 5 GHz and 2.4 GHz. The dipole antenna (131) can for example operate at 2.4 GHz and the slot antenna (130) can operate at 5 GHz, or vice versa.
(44) It will be apparent that the invention is not limited to the working examples shown and described herein, but that numerous variants are possible within the scope of the attached claims that will be obvious to a person skilled in the art.
(45) The above-described inventive concepts are illustrated by several illustrative embodiments. It is conceivable that individual inventive concepts may be applied without, in so doing, also applying other details of the described example. It is not necessary to elaborate on examples of all conceivable combinations of the above-described inventive concepts, as a person skilled in the art will understand numerous inventive concepts can be (re)combined in order to arrive at a specific application.
(46) The verb “comprise” and conjugations thereof used in this patent publication are understood to mean not only “comprise”, but are also understood to mean the phrases “contain”, “substantially consist of”, “formed by” and conjugations thereof.
