Metamaterial antenna array with isolated antennas

Abstract

An antenna array utilizing a ground protection ring and a metamaterial structure is disclosed. In certain embodiments, the antenna array includes a plurality of antenna elements, where each antenna element is identical. The antenna element includes an upper surface that includes a patch antenna and a ground protection ring. A reactive impedance surface (RIS) layer is disposed below the upper surface and includes a metamaterial structure. The metamaterial structure is configured to provide inductance to the patch antenna, thereby allowing the patch antenna to be smaller than otherwise possible. In some embodiments, the metamaterial structure includes a hollow square frame. An antenna array constructed using such antenna elements has less coupling than a conventional antenna array, thereby resulting in better performance. Furthermore, such a new antenna array also requires less space than a conventional antenna array.

Description

TECHNICAL FIELD

[0001] The present disclosure describes an antenna array, and more specifically, an antenna array utilizing a reactive impedance surface and a ground shield. BACKGROUND

[0002] The proliferation of network-connected devices has led to an increase in the use of certain wireless protocols. For example, simple wireless network devices are implemented as temperature sensors, humidity sensors, pressure sensors, motion sensors, cameras, light sensors, dimmers, light sources, and other functions. Moreover, these wireless network devices have become increasingly smaller.

[0003] These wireless network devices are typically equipped with embedded antennas. In certain embodiments, an antenna array can be required. For example, for angle of arrival and angle of departure calculations, an antenna array is necessary. In certain embodiments, the array can be a two-dimensional array, such as an N x M array, where both N and M are greater than 1. In other embodiments, the array can be a one-dimensional array, such as N x 1 or 1 x M, where N and M are greater than 1.

[0004] There are many design considerations that must be taken into account when designing an antenna array. For example, for accurate direction angle estimation in AoX solutions, well-isolated radiator elements are required in the antenna array to reduce cross-talk between them.

[0005] In certain embodiments, a ground shield ring can not be used. In this configuration, the coupling between the antenna elements causes the impedance, radiation pattern, and radiation efficiency to spread, depending on the location within the array. This complicates the array design and makes EM simulation and tuning time-consuming.

[0006] To address this issue, a large number of ground rings can be placed around each antenna element. However, a considerable gap is required between the antenna and the ground shield ring to avoid return loss (S11) and radiation pattern detuning, as well as a drop in radiation gain and efficiency. These gaps, together with the large number of ground shield rings, increase the size of the entire array.

[0007] In some wireless devices, the amount of space that can be allocated for an antenna array is limited. Therefore, it can be difficult to provide the space necessary to incorporate a ground shield ring.

[0008] Therefore, it would be advantageous if there were an antenna array with a small form factor, but also with very limited coupling between the antennas. SUMMARY

[0009] An antenna array utilizing a ground protection ring and a metamaterial structure is disclosed. In certain embodiments, the antenna array includes a plurality of antenna elements, where each antenna element is identical. The antenna element includes an upper surface that includes a patch antenna and a ground protection ring. A reactive impedance surface (RIS) layer is disposed below the upper surface and includes a metamaterial structure. The metamaterial structure is configured to provide inductance to the patch antenna, thereby allowing the patch antenna to be smaller than otherwise possible. In some embodiments, the metamaterial structure includes a hollow square frame. An antenna array constructed using such antenna elements has less coupling than a conventional antenna array, thereby resulting in better performance. Moreover, such a new antenna array also requires less space than a conventional antenna array.

[0010] According to one embodiment, an antenna element is disclosed. The antenna element includes: an upper surface that includes a patch antenna and a ground protection ring surrounding the patch antenna; a reactive impedance surface (RIS) layer disposed below the upper surface, where the RIS layer includes a metamaterial structure; and a ground layer disposed below the RIS layer, where a via electrically connects the ground protection ring to the ground layer. In certain embodiments, the RIS layer is immediately adjacent to the top layer. In some embodiments, the ground layer is immediately adjacent to the RIS layer. In certain embodiments, the metamaterial structure includes a hollow square frame. In some embodiments, an integer number of metamaterial structures are disposed on the RIS layer in an area defined by the ground protection ring. In certain embodiments, the integer number is N 2 where N is an integer. In some embodiments, the antenna element further includes a RIS ground protection ring disposed on the RIS layer, vertically aligned with the ground protection ring, and electrically connected to the via and the ground layer.

[0011] According to another embodiment, an antenna array including a plurality of the above-described antenna elements is disclosed. The antenna array can include N x M antenna elements, where at least one of N and M is greater than 1.

[0012] According to another embodiment, an antenna element is disclosed. The antenna element includes: an upper surface that includes a patch antenna and a ground protection ring surrounding the patch antenna; a reactive impedance surface (RIS) layer disposed below the upper surface, where the RIS layer includes a metamaterial structure; a ground layer disposed below the RIS layer, where a via electrically connects the ground protection ring to the ground layer; and one or more unused metal layers disposed between the upper surface and the RIS layer and / or between the RIS layer and the ground layer. In certain embodiments, the antenna element includes a RIS ground protection ring disposed on the RIS layer, vertically aligned with the ground protection ring, and electrically connected to the via and the ground layer. In some embodiments, the metamaterial structure includes a hollow square frame. In some embodiments, an integer number of metamaterial structures are disposed on the RIS layer in an area defined by the ground protection ring. In certain embodiments, the integer number is N2 where N is an integer. In some embodiments, one or more unused metal layers are disposed between the upper surface and the RIS layer and between the ground layer and the RIS layer. In certain embodiments, the antenna unit further comprises an auxiliary ground guard ring disposed on at least one of the one or more unused metal layers, vertically aligned with the ground guard ring, and electrically connected to the via and the ground layer.

[0013] According to another embodiment, an antenna array comprising a plurality of the above-described antenna units is disclosed. The antenna array can comprise N x M antenna units, where at least one of N and M is greater than 1. BRIEF DESCRIPTION OF DRAWINGS

[0014] For a better understanding of the present disclosure, reference will be made to the accompanying drawings, in which the same elements will be referred to with the same reference numerals, and in which:

[0015] Figure 1 An exploded view of the structure of one antenna unit in an antenna array is shown;

[0016] Figure 2 A top view of an antenna array is shown;

[0017] Figure 3 A top view of a patch antenna and a ground guard ring is shown;

[0018] Figure 4 A top view of a RIS layer and a metamaterial structure is shown;

[0019] Figure 5A An exploded view of the structure of one antenna unit according to another embodiment is shown;

[0020] Figure 5B An exploded view of the structure of one antenna unit according to a third embodiment is shown;

[0021] Figure 6 A top view of a RIS layer and a metamaterial structure for the antenna unit shown in Figure 5A

[0022] Figure 7 is a plot showing return loss for each antenna in a 4 x 4 antenna array;

[0023] Figure 8 is a plot showing phase for each antenna in a 4 x 4 antenna array applying separate vertical and horizontal polarized signals; and

[0024] Figure 9 is a comparison of various parameters for the present antenna array and a conventional antenna array. DETAILED DESCRIPTION

[0025] ​Figure 1 An exploded view of one antenna element 10, which can be part of an antenna array, is shown. Figure 2 A top view of an antenna array utilizing multiple antenna elements 10 is shown.

[0026] As Figure 1 shown, the structure of the antenna element 10 uses three layers of a conventional printed circuit board. Other layers of the printed circuit board can be used to provide power plane, additional ground layers, and signal layers. Figure 3 is a top view of the top surface of the printed circuit board. Figure 4 is a top view of the RIS layer 60.

[0027] The top surface of the printed circuit board is used for the patch antenna 20, while the lower layer is used for the ground layer 80. The reactive impedance surface (RIS) layer 60 is disposed below the top surface and above the ground layer 80. In certain embodiments, the RIS layer 60 is the layer immediately adjacent to the top surface. In some embodiments, the ground layer 80 is the layer immediately below the RIS layer 60, such that the top layer, RIS layer 60, and ground layer 80 are adjacent.

[0028] In other embodiments, if a thicker dielectric is needed between the RIS layer 60 and the ground layer 80, there can be one or more intermediate layers between the RIS layer 60 and the ground layer 80. In certain embodiments, no metal is disposed on these intermediate layers, except for another instance of the top protective ring.

[0029] As mentioned above, in certain embodiments, the patch antenna 20 is disposed on the top layer of the printed circuit board. The patch antenna 20 can be square shaped, such that the patch antenna 20 can be used to receive and transmit horizontally and vertically polarized signals. The size of the patch antenna 20 is generally defined by the desired resonant frequency, the thickness of the printed circuit board, and the dielectric constant of the printed circuit board. In the RIS antenna group structure, additional tuning knobs can include the dielectric thickness between the patch antenna 20 and the RIS layer 60, and the dielectric thickness between the RIS layer 60 and the ground layer 80. In addition, additional tuning knobs are the metamaterial structure frame size and width on the RIS layer.

[0030] The patch antenna 20 can be made of copper or other conductive material. The process of creating a plated area on the surface of a printed circuit board is well known.

[0031] As Figure 3As best shown, in certain embodiments, the patch antenna 20 includes two signal vias 40 for electrically connecting the patch antenna 20 to a signal layer or multiple signal layers. All signal layers are located below the ground plane 80. In certain embodiments, the signal vias 40 pass through the ground plane 80 to a signal layer disposed below the ground plane 80. In certain embodiments, each signal via 40 can be disposed at or near the midpoint of the patch antenna 20 in a direction near the edge of the patch antenna 20. In this way, the patch antenna 20 can be used to transmit and receive horizontally and vertically polarized signals. In embodiments where only one polarization is needed, only one signal via 40 can be used. In other embodiments, one signal via 40 can be located at the diagonal of the patch to generate circularly polarized signals.

[0032] A ground guard ring 30 is disposed around the outer edge of the patch antenna 20. In certain embodiments, the ground guard ring 30 can be a hollow square frame with a thickness of at least half the total thickness between the top layer and the ground plane 80. The inner dimensions of the ground guard ring are larger than the outer dimensions of the patch antenna 20 so that there can be a gap 25 separating the patch antenna 20 from the ground guard ring 30 on all sides. In certain embodiments, the gap 25 can be about three times or more the total thickness between the top layer and the ground plane 80.

[0033] As Figure 1 can be seen, the ground guard ring 30 is electrically connected to the ground plane 80 using a plurality of conductive vias 50. These vias 50 extend from the upper surface to the ground plane 80. In certain embodiments, the distance between adjacent vias 50 can be less than λ / 8, where λ is the wavelength of interest.

[0034] Below the upper surface is the RIS layer 60, which is also shown in Figure 4 . The RIS layer 60 includes a plurality of periodic metamaterial structures 70 shaped to achieve a reactance impedance to incident electromagnetic waves. Metamaterial refers to the term for any material engineered (typically by changing its shape) to provide electromagnetic properties not found in the base material. These metamaterial structures 70 can be many different shapes, including Hilbert fractals containing second, third, or fourth order, rectangular spiral resonators, square spiral resonators, rectangular loop resonators, or split ring resonators.

[0035] In one particular embodiment, the metamaterial structure 70 may be a hollow rectangular frame having external and internal dimensions defining a hollow internal portion 75. The width of the frame, defined as half the difference between the external and internal dimensions, can be adjusted to tune the resonant frequency of the metamaterial structure 70. Again, the dimensions of the metamaterial structure 70 may depend on the resonant frequency, the dielectric constant of the printed circuit board, the thickness of the dielectric between the RIS layer 60 and the ground layer 80, the thickness of the applied metal, the spacing between consecutive metamaterial structures, and the width of the frame of the metamaterial structure 70.

[0036] In some embodiments, the metamaterial structure 70 is fabricated to a certain size such that an integer number of these structures can be arranged within the area defined by the grounding guard ring 30 on the upper surface of the printed circuit board. In some embodiments, this integer can be N. 2 , where N is an integer. In other embodiments, this integer can be N×M, where both N and M are integers. Figure 1 As can be seen, four metamaterial structures 70 are disposed in the region defined by the grounding protection ring 30 on the upper surface. However, this disclosure is not limited to this embodiment. Furthermore, as Figure 4 As shown, through-holes 50 connecting the grounding protection ring 30 to the grounding layer 80 can be seen around the outer edge of the metamaterial structure. Additionally, signal vias 40 are also shown. Note that if N is an even number, the signal via 40 can pass between two adjacent metamaterial structures 70.

[0037] Figure 2 The figure shows a top view of the antenna array. In this figure, there are 16 antenna elements 10 arranged in a 4×4 array. Note that a grounding guard ring 30 surrounds each patch antenna 20. Furthermore, note that the RIS layer 60 is aligned with the upper surface such that the configuration of the RIS layer 60 in each antenna element 10 is identical. Of course, the antenna array can have any number of antenna elements and is not limited to this embodiment. For example, the antenna array may include N×M antenna elements 10, where at least one of N and M is greater than 1.

[0038] Figure 5A It shows Figure 1 A variation of the antenna element 11 is shown. In this variation, a RIS grounding protection ring 65 surrounds the metamaterial structure 70 on the RIS layer 60 to further improve isolation. This RIS grounding protection ring 65 can have the same dimensions as the grounding protection ring 30 on the upper surface and can be vertically aligned with that ring. This also... Figure 6As shown in the diagram. Note that in this embodiment, the via 50 connects the ground protection ring 30 to the RIS ground protection ring 65 and the ground layer 80. The remainder of the antenna element 11 is as described above. In this embodiment, the gap between the metamaterial structure 70 and the RIS ground protection ring 65 should be at least the dielectric thickness between the RIS layer 60 and the ground layer 80 to avoid any impact on the RIS resonant frequency. If the gap is too small, the RIS resonant frequency will shift downward, but the radiation efficiency will also be degraded.

[0039] Figure 5B It shows Figure 1 Another variation of the antenna element 11 shown is used. In this variation, a 6-layer PCB is used to allow for greater flexibility in the design, and some metal layers are left unused below the antenna for better radiation. Of course, more layers can be used. Thus, in effect, some dielectric layers are unified in this way to form a thicker dielectric layer. Optionally, auxiliary grounding protection rings 66 can also be applied to these unused metal layers. This is advantageous for two reasons. First, these auxiliary grounding protection rings 66 further improve the isolation between the antenna elements 11. Second, these additional auxiliary grounding protection rings 66 make PCB manufacturing more balanced from the perspective of PCB tension: because leaving completely unused metal layers can lead to metal imbalance, resulting in undesirable mechanical tension in the PCB. Figure 5B In this configuration, unused metal layers are disposed on the opposite side of RIS layer 60. However, unused layers can be disposed in other locations. For example, unused metal layers can be disposed only between the top surface and RIS layer 60, or only between RIS layer 60 and ground layer 80.

[0040] Therefore, this disclosure describes an antenna unit utilizing a three-layer printed circuit board. The top layer includes a patch antenna 20 and a ground guard ring 30 surrounding the patch antenna 20. Below the top layer is a RIS layer 60, which includes an integer number of metamaterial structures 70 mounted within the area defined by the ground guard ring 30 on the top layer. In some embodiments, the RIS layer 60 further includes a RIS ground guard ring 65. Below the RIS layer 60 is a ground layer.

[0041] Therefore, in one embodiment, this disclosure describes an antenna array utilizing multiple antennas, wherein each antenna includes a metamaterial structure disposed on a RIS layer and a grounding protection ring.

[0042] Furthermore, in another embodiment, the present disclosure describes an antenna unit that is modular in design. In other words, an antenna array can be constructed simply by arranging the required number of antenna units 10 adjacent to each other in one or two perpendicular directions. The dimensions of the metamaterial structure 70 are determined such that an integer number of structures are contained in the area defined by the ground protection ring 30. In this way, the antenna unit for each antenna in the antenna array is identical.

[0043] Importantly, the RIS layer 60 has the effect of presenting a larger inductance. Thus, a smaller patch antenna with a lower capacitance can achieve the same resonant frequency as a larger patch antenna without the RIS layer 60.

[0044] In one particular embodiment, the antenna array can be designed to transmit and receive radio frequency signals having a nominal frequency of approximately 2.45 GHz. This is the frequency used by many wireless protocols, including Bluetooth, WiFi, Zigbee, Thread, and other 802.15.4 protocols.

[0045] In these embodiments, the patch antenna 20 can be square in shape with dimensions of 22 x 22 mm. Furthermore, in these embodiments, the inner dimensions of the metamaterial structure 70 can be 4 x 4 mm, while the outer dimensions can be 16 x 16 mm. In certain embodiments, the dimensions of each metamaterial structure 70 can be determined such that one side of the square structure is approximately λ / 4. This dimension can vary based on the distance between adjacent metamaterial structures and the cumulative dielectric thickness between the RIS layer 60 and the ground layer 80.

[0046] In some embodiments, the antenna array can be used in conjunction with an angle of arrival or departure (combined, AoX) algorithm to determine the location of another wireless device. There are various algorithms to determine the AoX of another device. For example, depending on the configuration of the antenna array, the MUSIC algorithm creates a one- or two-dimensional plot, where each peak on the plot represents the direction of arrival of an input signal. This one- or two-dimensional plot can be referred to as a pseudo-spectrum. The MUSIC algorithm computes a value for each point on the plot.

[0047] In addition to the MUSIC algorithm, other algorithms can also be used. For example, a minimum variance distortion response (MVDR) beamformer algorithm (also known as a Capon beamformer), a Bartlett beamformer algorithm, and variations of the MUSIC algorithm can also be used. In each of these algorithms, the algorithm uses a different mathematical formula to compute the angle of arrival.

[0048] The system and method have a number of advantages.

[0049] The use of the RIS layer 60 in conjunction with the ground protection ring results in a smaller antenna array with improved performance.

[0050] First, regarding size, a conventional antenna array optimized for operation at 2.45 GHz can use patch antennas, each 27.50 square millimeters wide and spaced 12.5 millimeters apart. Therefore, a conventional 4×4 antenna array might occupy an area of ​​approximately 170mm × 170mm. In contrast, each element in this antenna array operating at the same frequency has an area of ​​37.5mm × 37.5mm. Therefore, the 4×4 antenna array occupies only approximately 150mm × 150mm. Thus, the new antenna array occupies less than 80% of the area of ​​a conventional antenna array.

[0051] Second, regarding performance, such as Figure 7 As shown, in an embodiment using a 4×4 antenna array configured to operate at 2.45 GHz, all antennas in the array exhibit return losses of less than -10 dB in the frequency range of 2.4 GHz to 2.49 GHz. Therefore, the bandwidth of the antenna array is 30%-50% wider than that of conventional antenna arrays. Furthermore, as... Figure 8 As shown, due to reduced coupling, the reflection phase difference between different antennas is approximately 10° at 2.45 GHz. Furthermore, in another test, it was found that the total radiation efficiency of the various antennas in the array differed from each other by less than 1 dB. This is about 1 dB better than what can be achieved using conventional antenna arrays. In this disclosure, total radiation efficiency (Ei) is defined as... T ) is defined as radiation efficiency (E R Multiply by impedance mismatch loss (M) L Furthermore, radiation efficiency is defined as radiant power (P). RAD Divide by input power (P) INPUT );in other words:

[0052] E R =P RAD / P INPUT .

[0053] Third, as mentioned above, in some embodiments, the antenna array is used in conjunction with the AoX algorithm. In each of these algorithms, the algorithm utilizes phase information from each of the multiple antennas in the antenna array. Because the grounding guard loop reduces the phase error of each antenna, the results of the AoX calculation are significantly improved.

[0054] Figure 9 All the aforementioned benefits are illustrated. It can be seen that the return loss of this antenna at both band edges is approximately -10 dB, while the return loss of a conventional array at higher frequencies is less than -6 dB. Furthermore, due to improved isolation between antennas and less spread, the use of this antenna significantly reduces variations in overall radiation efficiency. Finally, due to better antenna element isolation and reduced errors, this antenna greatly improves AoX estimation.

[0055] Furthermore, the improved isolation between adjacent antenna elements simplifies the design and simulation of the antenna array. Using this well-isolated element building block concept, return loss, bandwidth, radiation pattern, and gain and efficiency extension are minimized. Furthermore, these RF characteristics are stable everywhere within the antenna array. Therefore, it is sufficient to tune and design the element building block only, not the entire array. This saves simulation processing time and makes the array design much simpler.

[0056] The scope of the disclosure is not intended to be limited to the particular embodiments described herein. Indeed, various embodiments of the present disclosure and modifications thereof, in addition to those described herein, will be apparent to those of ordinary skill in the art from the foregoing description and drawings. Accordingly, such other embodiments and modifications are intended to fall within the scope of the present disclosure. Further, although the present disclosure has been described herein in the context of particular embodiments for purposes of clarity and exemplification, it will be apparent to those of ordinary skill in the art that the present disclosure is not limited to the embodiments described and can be beneficially implemented in any number of environments for any number of purposes. Accordingly, the claims set forth below are not intended to be limited by the disclosure as set forth herein.

Claims

1. An antenna array comprising multiple antenna elements, wherein, Each of the plurality of antenna elements includes: The upper surface includes a patch antenna and a grounding protection ring surrounding the patch antenna, wherein the patch antenna is square. A reactive impedance surface (RIS) layer, the RIS layer being disposed below the upper surface, wherein the RIS layer comprises a metamaterial structure; A grounding layer, wherein the grounding layer is disposed below the RIS layer, wherein vias electrically connect the grounding protection ring to the grounding layer, and the metamaterial structure is electrically isolated from the grounding layer; and A RIS grounding protection ring is disposed on the RIS layer, vertically aligned with the grounding protection ring, and electrically connected to the via and the grounding layer.

2. The antenna array according to claim 1, wherein, The RIS layer is located immediately adjacent to the top layer.

3. The antenna array according to claim 2, wherein, The grounding layer is adjacent to the RIS layer.

4. The antenna array according to claim 1, wherein, The metamaterial structure includes a hollow square frame.

5. The antenna array according to claim 1, wherein, An integer number of metamaterial structures are disposed on the RIS layer in the region defined by the grounding protection ring.

6. The antenna array according to claim 5, wherein, The integer is N 2 , where N is an integer.

7. The antenna array according to claim 1, comprising N×M antenna elements, wherein at least one of N and M is greater than 1.

8. An antenna array comprising multiple antenna elements, wherein, Each of the plurality of antenna elements includes: The upper surface includes a patch antenna and a grounding protection ring surrounding the patch antenna, wherein the patch antenna is square. A reactive impedance surface (RIS) layer, the RIS layer being disposed below the upper surface, wherein the RIS layer comprises a metamaterial structure; A grounding layer is disposed below the RIS layer, wherein a via electrically connects the grounding protection ring to the grounding layer, and the metamaterial structure is electrically isolated from the grounding layer; One or more unused metal layers, wherein the one or more unused metal layers are disposed between the upper surface and the RIS layer and / or between the RIS layer and the ground layer; and A RIS grounding protection ring is disposed on the RIS layer, vertically aligned with the grounding protection ring, and electrically connected to the via and the grounding layer.

9. The antenna array according to claim 8, wherein, The metamaterial structure includes a hollow square frame.

10. The antenna array according to claim 8, wherein, An integer number of metamaterial structures are disposed on the RIS layer in the region defined by the grounding protection ring.

11. The antenna array according to claim 10, wherein, The integer is N 2 , where N is an integer.

12. The antenna array according to claim 8, wherein, One or more unused metal layers are disposed between the upper surface and the RIS layer, and between the ground layer and the RIS layer.

13. The antenna array of claim 8 further includes an auxiliary grounding protection ring disposed on at least one of the one or more unused metal layers, perpendicularly aligned with the grounding protection ring and electrically connected to the via and the grounding layer.

14. The antenna array according to claim 8, comprising N×M antenna elements, wherein at least one of N and M is greater than 1.

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