Broadband wide-beam artificial magnetic conductor monopole antenna

Abstract

The invention relates to the technical field of antenna technology and wireless communication, and discloses a broadband wide-beam artificial magnetic conductor monopole antenna, which comprises a dielectric substrate comprising a first welding film layer, a first prepreg layer, a core layer, a second prepreg layer and a second welding film layer which are sequentially stacked from top to bottom, a second metal layer and a third metal layer are respectively arranged on the upper and lower surfaces of the core layer; a first metal layer is arranged on the upper surface of the first prepreg layer; the radiation unit is arranged on the first metal layer; the AMC structure comprises an AMC area and a plurality of AMC vertical through holes, the AMC area is arranged at the position, opposite to the radiation unit, of the second metal layer, and the AMC area comprises a plurality of AMC metal units arranged in a periodic array; and two ends of each AMC vertical through hole are respectively connected with one AMC metal unit and the third metal layer. Through the design that the radiation unit is back to the AMC structure, part of electromagnetic waves are reflected by the AMC structure to form coherent enhancement, and it is ensured that S11 is lower than-10 dB in the 2GHz frequency band.

Description

Technical Field

[0001] The embodiments of the present invention relate to the fields of antenna technology and wireless communication technology, specifically to a wide-bandwidth beam artificial magnetic conductor monopole antenna. Background Technology

[0002] With the development of vehicle connectivity and intelligence, ultra-wideband (UWB) vehicle surveillance systems have become a key solution for vehicle security. This system utilizes the wide bandwidth and fine time resolution of UWB signals to achieve accurate detection and location of people and objects around parked vehicles. Compared to traditional passive infrared or microwave sensors, it has stronger resistance to environmental noise, higher spatial resolution, and a lower false alarm rate, making it suitable for scenarios such as intrusion detection and surrounding environment perception.

[0003] The core requirement for UWB antennas in the above application scenarios is an extremely wide beam coverage range to ensure that there are no blind spots in the monitoring around the vehicle. The beam coverage range of existing ordinary patch antennas is narrow and cannot meet the needs of UWB car warning systems to monitor the entire range around the vehicle, resulting in blind spots and affecting the reliability of security.

[0004] Artificial magnetic conductors (AMCs) are artificial electromagnetic structures composed of periodically arranged metal units and a dielectric substrate. They possess the ability to control the phase of electromagnetic waves with zero reflection or a specific phase, unlike the 180° reflection characteristics of traditional metal ground planes. AMCs have important applications in antenna design, electromagnetic compatibility, and stealth technology, and are a key component for achieving wide beamwidth and high gain. Through proper design, AMCs can achieve in-phase reflection of vertically incident plane waves at a specific frequency, enabling electromagnetic functions that are impossible with traditional metal ground planes.

[0005] Therefore, there is an urgent need for a wide-beam antenna based on AMC design that is compatible with automotive sentry mode. Summary of the Invention

[0006] To address the issues of narrow beam coverage in conventional patch antennas, which fail to meet the requirements of UWB automotive surveillance systems for full-range monitoring of the vehicle's surroundings, and the presence of blind spots that affect security reliability, this invention provides a wide-bandwidth beamwidth artificial magnetic conductor monopole antenna.

[0007] This invention provides a widebandwidth beamwidth artificial magnetic conductor monopole antenna. A widebandwidth beamwidth artificial magnetic conductor monopole antenna, characterized in that it comprises: A dielectric substrate includes a first solder film layer, a first prepreg layer, a core layer, a second prepreg layer, and a second solder film layer stacked sequentially from top to bottom. A first metal layer is disposed between the first solder film layer and the first prepreg layer, a second metal layer is disposed between the first prepreg layer and the core layer, a third metal layer is disposed between the core layer and the second prepreg layer, and a fourth metal layer is disposed between the second prepreg layer and the second solder film layer. Radiation element, disposed on the first metal layer; and The AMC structure includes an AMC region and a plurality of AMC vertical vias. The AMC region is located at the position opposite to the radiating unit in the second metal layer. The AMC region includes a plurality of AMC metal units arranged in a periodic array. The AMC vertical vias penetrate the core layer along the thickness direction of the dielectric substrate. The top end of each AMC vertical via is connected to one of the AMC metal units, and the bottom end of each AMC vertical via is connected to the third metal layer.

[0008] In some alternative implementations, the top end of the AMC vertical through-hole extends to the top surface of the AMC metal unit, and the bottom end of the AMC vertical through-hole extends to the bottom surface of the third metal layer.

[0009] In some alternative implementations, the AMC structure further includes a bottom ground plane, with the third metal layer serving as the bottom ground plane.

[0010] In some alternative implementations, the AMC metal unit is square, circular, or polygonal.

[0011] In some alternative implementations, the AMC metal unit is designed for UWB channel 9.

[0012] In some alternative implementations, the radiating element is circular, elliptical, square, or polygonal.

[0013] In some alternative implementations, the first metal layer is divided into a first region and a second region, the radiating element is disposed in the first region, and the radiating element is connected to the side of the second region away from the first region via a feed line; the AMC region is disposed in the second metal layer at a position relative to the first region.

[0014] In some alternative implementations, the second region is provided with a grounding region, which is located on both sides of the feed line and is gapped to the feed line; the grounding region is provided with a vertical through hole, which penetrates the first metal layer, the first prepreg layer, the second metal layer and the core layer along the thickness direction of the dielectric substrate, the top end of the vertical through hole is connected to the grounding region and the bottom end of the vertical through hole is connected to the third metal layer.

[0015] In some alternative implementations, the top end of the vertical via extends to the top surface of the grounding region, and the bottom end of the vertical via is connected to the bottom surface of the third metal layer.

[0016] In some alternative implementations, the vertical through-hole is disposed on a first side of the grounding region opposite to the feed line and a second side away from the first region, the first side being adjacent to the second side.

[0017] Compared with the prior art, the present invention has the following advantages: This invention provides a widebandwidth beamwidth artificial magnetic conductor monopole antenna. This invention places the radiating element behind the AMC structure, adjacent to but not overlapping the AMC structure, with the radiating element's radiation direction facing the AMC region. Part of the electromagnetic wave from the radiating element propagates directly, while the other part is reflected by the AMC structure 30 to form coherent enhancement. This allows the input impedance of the monopole antenna to match that of subsequent circuits such as chips, ensuring that |S11| is below -10dB in the 2GHz band.

[0018] The radiating unit has wide beam radiation characteristics. Combined with the AMC structure located on the back, the reflected signal of the AMC structure is enhanced only in a specific direction. The azimuth beamwidth with a gain greater than 0 dBi is greatly widened to more than 120°, which meets the wide angle range requirements of the car sentry mode.

[0019] The above description is merely an overview of the technical solutions of the embodiments of the present invention. In order to better understand the technical means of the embodiments of the present invention and to implement them in accordance with the contents of the specification, and to make the above and other objects, features and advantages of the embodiments of the present invention more apparent and understandable, specific embodiments of the present invention are described below. Attached Figure Description

[0020] The accompanying drawings are for illustrative purposes only and are not intended to limit the invention. Furthermore, the same reference numerals denote the same parts throughout the drawings. In the drawings: Figure 1 This diagram illustrates the structure of a dielectric substrate for a wideband beam artificial magnetic conductor monopole antenna provided in an embodiment of the present invention.

[0021] Figure 2 This diagram illustrates the structure of a dielectric substrate for a wideband beam artificial magnetic conductor monopole antenna provided in an embodiment of the present invention.

[0022] Figure 3 for Figure 1 Sectional view of plane AA.

[0023] Figure 4 for Figure 3 Enlarged schematic diagram of part B in the diagram.

[0024] Figure 5 for Figure 3 Enlarged schematic diagram of part C in the diagram.

[0025] Figure 6 This diagram illustrates a structure of a wideband beam artificial magnetic conductor monopole antenna with the first solder layer removed, according to an embodiment of the present invention.

[0026] Figure 7 This image shows a perspective view of a wideband beam artificial magnetic conductor monopole antenna provided in an embodiment of the present invention.

[0027] Figure 8 This diagram illustrates a comparison of the S-parameters of a wide-bandwidth beam artificial magnetic conductor monopole antenna and a patch antenna provided in an embodiment of the present invention.

[0028] Figure 9 This diagram illustrates a comparison of the azimuth radiation patterns of a wide-bandwidth beam artificial magnetic conductor monopole antenna and a patch antenna provided in an embodiment of the present invention.

[0029] Figure 10 This diagram illustrates a comparison of the elevation patterns of a wideband beam artificial magnetic conductor monopole antenna and a patch antenna provided in an embodiment of the present invention.

[0030] Marked in the image: 10. Dielectric substrate; 11. First solder mask layer; 12. First prepreg layer; 13. Core layer; 14. Second prepreg layer; 15. Second solder film layer; 16. First metal layer; 17. Second metal layer; 18. Third metal layer; 19. Fourth metal layer; 20. Radiation unit; 21. Feeder cable; 22. Grounding area; 23. Vertical through hole; 30. AMC structure; 31. AMC metal unit; 32. AMC vertical through hole. Detailed Implementation

[0031] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. The described embodiments are some, but not all, of the embodiments of the present invention.

[0032] Therefore, the following detailed description of the embodiments of the invention provided in the accompanying drawings is not intended to limit the scope of the claimed invention, but merely to illustrate selected embodiments of the invention. All other embodiments obtained by those skilled in the art based on the embodiments of the invention without inventive effort are within the scope of protection of the invention.

[0033] To address the issues of narrow beam coverage in conventional patch antennas, which fail to meet the requirements of UWB automotive surveillance systems for full-range monitoring of the vehicle's surroundings, and the presence of blind spots that affect security reliability, this invention provides a wide-bandwidth beamwidth artificial magnetic conductor monopole antenna.

[0034] This invention provides a widebandwidth beamwidth artificial magnetic conductor monopole antenna, such as... Figure 1-7 As shown, it includes: a dielectric substrate 10, a radiating unit 20, and an AMC structure 30.

[0035] The dielectric substrate 10 includes a first solder film layer 11, a first prepreg layer 12, a core layer 13, a second prepreg layer 14, and a second solder film layer 15 stacked sequentially from the top to the bottom. A first metal layer 16 is disposed between the first solder film layer 11 and the first prepreg layer 12. A second metal layer 17 is disposed between the first prepreg layer 12 and the core layer 13. A third metal layer 18 is disposed between the core layer 13 and the second prepreg layer 14. A fourth metal layer 19 is disposed between the second prepreg layer 14 and the second solder film layer 15. Radiation element 20 is disposed on the first metal layer 16.

[0036] The AMC structure 30 includes an AMC region and a plurality of AMC vertical vias 32. The AMC region is located at the position opposite to the radiating unit 20 on the second metal layer 17. The AMC region includes a plurality of AMC metal units 31 arranged in a periodic array. The AMC vertical vias 32 penetrate the core layer 13 along the thickness direction of the dielectric substrate. The top end of each AMC vertical via 32 is connected to an AMC metal unit 31, and the bottom end of the AMC vertical via 32 is connected to the third metal layer 18.

[0037] In this embodiment, the dielectric substrate 10 adopts a structure design of five dielectric layers combined with four metal layers. The radiating unit 20 is disposed on the first metal layer 16. The AMC structure 30 includes a plurality of AMC metal units 31 arranged in a periodic array on the second metal layer 17. Combined with the AMC vertical through-hole 32 penetrating the core layer 13 and the ground plane of the third metal layer 18, a wide bandwidth beam characteristic is achieved.

[0038] The monopole antenna provided in this embodiment is designed with the radiating element 20 backing onto the AMC structure 30. The 0° reflection phase of the electromagnetic wave by the AMC structure 30 and the signal directly radiated by the radiating element 20 form coherent enhanced interference. The azimuth beamwidth with a gain greater than 0 dBi is widened to more than 120°, and the elevation plane covers ±60°, realizing large-angle range monitoring around the vehicle in the car sentry mode, which is adapted to the core scenario requirements of the car sentry mode.

[0039] The monopole antenna itself has ultra-wideband characteristics and omnidirectional transmission. Combined with the AMC structure, the 30-phase reflection is effective within a range of ±90°, making the monopole antenna |S11| less than -10dB in the 2GHz band. It covers the 9th channel of UWB 7.737-8.236GHz and the extended band, which far exceeds the 400MHz bandwidth of traditional patch antennas. It is compatible with multiple systems and does not require antenna replacement.

[0040] The coherent enhancement effect improves the gain of the monopole antenna by about 8dB over a large azimuth angle of ±80 degrees. Compared with patch antennas, it has a wider signal transmission angle and stronger resistance to environmental noise, ensuring the detection accuracy of the car sentry mode.

[0041] The symmetrical structure design of the dielectric substrate 10 enables the monopole antenna to support both embedded and external deployment methods, adapting to the installation space requirements of the car body without affecting the vehicle's appearance and aerodynamic performance.

[0042] The structural design of the monopole antenna in this embodiment solves the problems of existing patch antennas, such as narrow beam coverage leading to monitoring blind spots, insufficient bandwidth making them unable to adapt to UWB channel 9, and low gain resulting in weak anti-interference capability.

[0043] Preferably, the top end of the AMC vertical via 32 extends to the top surface of the AMC metal unit 31, and the bottom end of the AMC vertical via 32 extends to the bottom surface of the third metal layer 18, ensuring full-contact electrical connection between the AMC vertical via 32, the AMC metal unit 31, and the third metal layer 18. This avoids reflection phase shift caused by insufficient contact, ensures the stability of the 0° reflection phase of the AMC structure 30 in the target frequency band, maintains the coherent enhancement effect, and reduces the risk of beam distortion.

[0044] More preferably, the central axis of the AMC vertical through-hole 32 coincides with the central axis of the AMC metal unit 31, thereby forming a current loop and regulating the reflection phase.

[0045] The AMC metal unit 31 is square, circular, or polygonal in shape. The AMC metal unit is designed for UWB Channel 9 to ensure 0° reflection phase in the target frequency band and avoid bandwidth reduction or beam shift caused by size deviation.

[0046] The spacing between two adjacent AMC metal units 31 is designed for UWB channel 9. This ensures uniform reflection of electromagnetic waves in the AMC area, avoids phase cancellation, makes the azimuth beam coverage more uniform, and further eliminates monitoring blind spots.

[0047] In this embodiment, the AMC structure 30 also includes a bottom ground plane, and the third metal layer 18 serves as the bottom ground plane, so that the monopole antenna in this embodiment does not need to be provided with an additional independent ground plane, which simplifies the monopole antenna structure, reduces interlayer redundancy, and lowers manufacturing costs.

[0048] The third metal layer 18 is located between the core layer 13 and the second prepreg layer 14, and is directly connected to the metal unit 31 of the AMC structure 30 through the AMC vertical through-hole 32, which shortens the current loop path, reduces signal loss, and further improves the gain of the monopole antenna.

[0049] In this preferred embodiment, the radiating unit 20 is circular, elliptical, square, or polygonal; it can be a regular shape or an irregular shape.

[0050] In this embodiment, the shape of the radiating element 20 is not limited to the shape described above, and may also be other monopole antenna shapes.

[0051] The first metal layer 16 is divided into a first region and a second region. The radiating unit 20 is disposed in the first region and is connected to the side of the second region away from the first region via the feed line 21. The AMC region is disposed in the second metal layer 17 at a position relative to the first region.

[0052] The radiating unit 20 is positioned opposite to the AMC region, so that the electromagnetic wave energy of the radiating unit 20 can be projected onto the surface of the AMC metal structure 30 to the maximum extent, thereby enhancing the coherence enhancement effect and further widening the beamwidth.

[0053] The second region is provided with a grounding region 22, which is located on both sides of the feed line 21 and is gappedly connected to the feed line 21. A vertical through hole 23 is provided on the grounding region 22. The vertical through hole 23 penetrates the first metal layer 16, the first prepreg layer 12, the second metal layer 17 and the core layer 13 along the thickness direction of the dielectric substrate. The top end of the vertical through hole 23 is connected to the grounding region 22 and the bottom end of the vertical through hole 23 is connected to the third metal layer 18.

[0054] Preferably, the top end of the vertical through hole 23 extends to the top surface of the grounding region 22, and the bottom end of the vertical through hole 23 is connected to the bottom surface of the third metal layer 18.

[0055] More preferably, the vertical through hole 23 is disposed on a first side of the grounding region 22 opposite to the feed line 21 and a second side away from the first region, with the first side and the second side being adjacent to each other.

[0056] In this embodiment, the gapped distribution of the grounding region 22 and the feed line 21 forms a grounded coplanar waveguide (GCPW) structure, which optimizes the input impedance of the monopole antenna, ensures the impedance consistency between the monopole antenna and subsequent circuits, such as the UWB chip, and further broadens the bandwidth; the vertical via 23 realizes the electrical connection between the grounding region 22 and the bottom ground plane, enhances the grounding effect, suppresses the radiation interference of the feed line 21, and avoids affecting the reflection phase of the AMC structure 30.

[0057] In this embodiment, the monopole antenna is designed such that the radiating element 20 is placed against the AMC structure 30, adjacent to but not overlapping the AMC region of the AMC structure 30. The radiation direction of the radiating element 20 faces the AMC region. Part of the electromagnetic wave from the radiating element 20 propagates directly, while the rest is reflected by the AMC structure 30 to form coherent enhancement. Through optimization of the width and spacing of the GCPW transmission lines, the input impedance of the monopole antenna is matched with subsequent circuitry such as chips, ensuring that |S11| is below -10dB in the 2GHz band. Figure 8 As shown.

[0058] In this embodiment, as Figure 9-10 As shown, in the target frequency band (7.737–8.236 GHz), the reflection phase of the electromagnetic wave vertically incident on the AMC structure 30 pairs of radiating elements 20 is 0°, which is consistent with the phase of the signal directly radiated by the monopole antenna, forming coherent enhanced interference. This improves the gain of the monopole antenna at a large angle of ±80 degrees on the elevation plane by 8dB compared to the patch antenna.

[0059] Even if the reflection phase exceeds 0°, as long as it is within ±90°, the coherence enhancement effect is still effective. Therefore, the AMC structure 30 can continue to function in the 2GHz wideband, balancing the bandwidth reduction problem after integrating the monopole antenna with the AMC structure 30.

[0060] The monopole antenna itself has 360° azimuth radiation capability. The AMC region of the AMC structure 30 is only distributed on the side of the monopole antenna. The reflected signal of the AMC structure 30 only enhances the radiation in a specific direction, rather than omnidirectional reflection. Combined with the full radiation characteristics of the monopole antenna, the azimuth beamwidth of the monopole antenna with a gain greater than 0 dBi is greatly widened to more than 120°, and the elevation plane covers ±60°, which meets the large-angle range monitoring requirements of the vehicle in the car sentry mode.

[0061] In addition, the AMC structure 30 in this embodiment optimizes the size of the metal unit 31 and the spacing between two adjacent metal units 31. Combined with the fact that the monopole antenna itself is an ultra-wideband structure, the effective reflection phase range (±90°) of the AMC structure 30 covers the entire frequency band of the 9th channel of UWB. This avoids excessive bandwidth reduction caused by the AMC structure 30, and ultimately achieves a bandwidth of 2GHz with |S11|<-10dB, which far exceeds the 400MHz bandwidth of traditional patch antennas.

[0062] In this invention, unless otherwise explicitly specified and limited, the terms "installation," "connection," "linking," and "fixing," etc., should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral part; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal communication of two components or the interaction between two components. Those skilled in the art can understand the specific meaning of the above terms in this invention according to the specific circumstances.

[0063] In the description of this invention, it should be noted that the terms "center," "upper," "lower," "left," "right," "vertical," "horizontal," "inner," and "outer," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings, or the orientation or positional relationship commonly used when the product of this invention is in use. They are only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of this invention. In addition, the terms "first," "second," "third," etc., are only used to distinguish descriptions and should not be construed as indicating or implying relative importance.

[0064] Furthermore, terms such as "horizontal," "vertical," and "sag" do not imply that components must be absolutely horizontal or suspended, but rather that they can be slightly tilted. For example, "horizontal" simply means that its direction is more horizontal relative to "vertical," and does not mean that the structure must be completely horizontal, but can be slightly tilted.

[0065] In this invention, unless otherwise expressly specified and limited, "above or below" a first feature may include direct contact between the first and second features, or contact between the first and second features through another feature between them. Furthermore, "above," "over," and "on" the first feature includes the first feature directly above or diagonally above the second feature, or simply indicates that the first feature is at a higher horizontal level than the second feature. "Below," "below," and "under" the first feature includes the first feature directly below or diagonally below the second feature, or simply indicates that the first feature is at a lower horizontal level than the second feature.

[0066] Although the description of the invention has been given in conjunction with the specific embodiments described above, it will be apparent to those skilled in the art that many substitutions, modifications, and variations can be made based on the foregoing. Therefore, all such substitutions, modifications, and variations are included within the spirit and scope of the appended claims.

Claims

1. A widebandwidth beamwidth artificial magnetic conductor monopole antenna, characterized in that, include: The dielectric substrate (10) includes a first solder film layer (11), a first prepreg layer (12), a core layer (13), a second prepreg layer (14), and a second solder film layer (15) stacked sequentially from the top to the bottom. A first metal layer (16) is disposed between the first solder film layer (11) and the first prepreg layer (12), a second metal layer (17) is disposed between the first prepreg layer (12) and the core layer (13), a third metal layer (18) is disposed between the core layer (13) and the second prepreg layer (14), and a fourth metal layer (19) is disposed between the second prepreg layer (14) and the second solder film layer (15). Radiation element (20) is disposed on the first metal layer (16); and The AMC structure (30) includes an AMC region and a plurality of AMC vertical vias (32). The AMC region is disposed at the position of the second metal layer (17) relative to the radiating unit (20). The AMC region includes a plurality of AMC metal units (31) arranged in a periodic array. The AMC vertical vias (32) penetrate the core layer (13) along the thickness direction of the dielectric substrate. The top end of each AMC vertical via (32) is connected to one of the AMC metal units (31), and the bottom end of the AMC vertical via (32) is connected to the third metal layer (18).

2. The wideband beam artificial magnetic conductor monopole antenna according to claim 1, characterized in that, The top end of the AMC vertical through hole (32) extends to the top surface of the AMC metal unit (31), and the bottom end of the AMC vertical through hole (32) extends to the bottom surface of the third metal layer (18).

3. The wideband beam artificial magnetic conductor monopole antenna according to claim 1, characterized in that, The AMC structure (30) also includes a bottom ground plane, and the third metal layer (18) serves as the bottom ground plane.

4. A widebandwidth beam artificial magnetic conductor monopole antenna according to claim 1, characterized in that, The AMC metal unit (31) is square, circular or polygonal.

5. A widebandwidth beam artificial magnetic conductor monopole antenna according to claim 1, characterized in that, The AMC metal unit (31) is designed for UWB channel 9.

6. A widebandwidth beam artificial magnetic conductor monopole antenna according to claim 1, characterized in that, The radiating unit (20) is circular, elliptical, square or polygonal.

7. A widebandwidth beam artificial magnetic conductor monopole antenna according to claim 1, characterized in that, The first metal layer (16) is divided into a first region and a second region. The radiation unit (20) is disposed in the first region and is connected to the side of the second region away from the first region via a feed line (21). The AMC region is disposed in the second metal layer (17) at a position relative to the first region.

8. A widebandwidth beam artificial magnetic conductor monopole antenna according to claim 7, characterized in that, The second region is provided with a grounding region (22), which is located on both sides of the feed line (21) and is gappedly connected to the feed line (21); the grounding region (22) is provided with a vertical through hole (23), which penetrates the first metal layer (16), the first prepreg layer (12), the second metal layer (17) and the core layer (13) along the thickness direction of the dielectric substrate. The top end of the vertical through hole (23) is connected to the grounding region (22), and the bottom end of the vertical through hole (23) is connected to the third metal layer (18).

9. A widebandwidth beam artificial magnetic conductor monopole antenna according to claim 8, characterized in that, The top end of the vertical through hole (23) extends to the top surface of the grounding area (22), and the bottom end of the vertical through hole (23) is connected to the bottom surface of the third metal layer (18).

10. A widebandwidth beam artificial magnetic conductor monopole antenna according to claim 8, characterized in that, The vertical through hole (23) is disposed on a first side of the grounding area (22) opposite to the feed line (21) and a second side away from the first area, the first side being adjacent to the second side.

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