Patent Application
20240063547
Embodiments of the present invention relate in general to an enhanced antenna module and antenna array for wireless communication systems.
Utilization of smart antenna array solutions is increasing rapidly in various wireless communication systems such as 5G networks, Wireless Local Area Networks, WLANs, and satellite communication networks. For example, massive Multiple-Input Multiple-Output, MIMO, systems may be used in 5G/NR base stations. Obviously, antenna solutions should not be too complex, heavy or expensive. It is also desirable to have antenna solutions that are not too complicated to manufacture. Scarcity of available frequency spectrum is an issue as well for various wireless communication networks and hence it is important to use the limited radio resources as effectively as possible to provide sufficient communication capacity.
In general, millimetre-wave signals refer to a frequency range from about 30 to about 300 GHz, i.e., signals having a wavelength from 10 to 1 millimetre. At this frequency range antenna structures with radiating elements and ground plane phasing comparable to a quarter wavelength may be manufactured on a Printed Circuit Board, PCB, though manufacturing complex structures may be challenging when narrow lines and gaps become too small to be produced using standard PCB technology. At low frequencies, say sub 6 GHz 5G bands, other manufacturing methods than standard PCB process may be used.
According to some aspects, there is provided the subject-matter of the independent claims. Some embodiments are defined in the dependent claims.
According to a first aspect of the present invention, there is provided an antenna module comprising a Radio Frequency, RF, component electrical connection platform, a dipole antenna on top of, or buried in, the platform, wherein the dipole antenna is arranged to transmit and/or receive an RF signal. The distance between a ground at a bottom of the platform and arms of the dipole antenna is about a quarter of a wavelength of the RF signal. The antenna module further comprises a pair of via holes comprising a first via hole and a second via hole extend through the platform, from the ground of the platform to the arms of the dipole antenna. The first via hole is coupled to an RF feed and to a first arm of the dipole antenna and the second via hole is coupled to the ground at the bottom of the platform and to a second arm of the dipole antenna. The RF signal may be a millimetre wave signal for example.
According to a second aspect of the present invention, there is provided an antenna array comprising multiple antenna modules according to the first aspect.
According to a third aspect of the present invention, there is provided a wireless device, such as a base station, an access point, a relay, a satellite or a wireless terminal like a user equipment, comprising the antenna array of the second aspect.
Embodiments of the present invention relate to an antenna module and an antenna array for transmitting/receiving Radio Frequency, RF, signals, such as millimetre-wave signals. More specifically, in some embodiments, at simplest, the antenna module comprises an RF component electrical connection platform, such as a Printed Circuit Board, PCB, a radiating dipole antenna, a pair of via holes, ground plane and antenna feed. The dipole antenna may be manufactured on the top of the platform. One dipole arm may be connected electrically with a via hole to the antenna feed at the bottom of the platform while the other arm is connected electrically with another via hole directly to antenna ground.
The dimensions of the pair of via holes, used as an antenna feed, are important for proper operation. Via hole length defines the distance between the arms of the dipole antenna and ground metal to be about a quarter wavelength inside the platform, as at this length the grounded antenna module sees high impedance against the ground. Horizontal distance between the via holes and the diameter further define the feed impedance. Thus the pair of via holes is arranged to work as a balanced feed and as a balun, and as an impedance transformer for the dipole antenna about a quarter wavelength of an RF signal, like a millimetre-wave signal, above ground.
The antenna module is compact, cheap and easy to manufacture, especially standard PCB manufacturing processes can be used. No special structures, like cavities, metal walls etc., are needed for the antenna module. As the pair of via holes goes through the dipole antenna spacing substrate, i.e., through the substrate layer between the antenna module and the bottom layer, the via holes may be done by drilling the holes with a laser for example, thereby making manufacturing easy. If the platform has a stacked multi-level structure, the drilling of small via holes becomes even easier.
The antenna module may also comprise another pair of via holes for another dipole antenna forming a crossed dipole structure, where the dipole antennas can be used alternatively as a dual linear polarized set of isolated dipole antennas or in circular polarization mode by providing the two dipole antennas with 90 degree phase shift. According to some embodiments of the present invention, this phase shift may be achieved using antenna module integrated phase shifters. Two solutions are introduced for the phase shifter.
In some embodiments, two types of circularly polarized crossed dipole antennas are presented for millimetre-wave signals. The antenna module may comprise two dipole antennas and have two separate ports with 90 degree phase shift, e.g., for left and right hand circular polarizations. Both of the dipole antennas may be printed on top of, or buried in (i.e. on an inner layer of the PCB stack), the platform while a bottom of the platform acts as an antenna ground reflector. Both dipole antennas may comprise a pair of via-holes which form a balanced feed line to the dipole antennas.
If the dipole antenna is buried inside the structure, for example in a layer under the top layer of the stack, the advantage is that the top layer protects the dipole antenna (110) from weathering, making the dipole antenna (110) invisible. Top layer thickness may be used as a design parameter in matching the dipole antenna (110) for a desired operation band. Thus, the dipole antenna may be buried to the platform (102) and the antenna module (100) may further comprise a dielectric layer above the dipole antenna (110), the substrate layer being arranged to be used as a radome protecting the dipole antenna (110) from environmental corrosion, to hide the dipole antenna (110) under protective surface and to be used as an impedance matching element. That is to say, the dipole antenna (110) may be buried into the structure such that the dielectric layer is on the top of arms (112, 114) of the dipole antenna (110) and RF feed lines or a part of a feeding network may be in between the dipole antenna and the ground at the bottom (104) of the antenna module.
If the platform (102) is a PCB substrate, normal PCB-process may be used for cheap production of antenna modules, for example for large antenna arrays. The PCB substrate is a general term, which can be used for any suitable material than can be used when manufacturing (printed) circuit boards. For example, millimetre-wave platform technologies such as Low Temperature Co-fired Ceramics, LTCC, and thin-film substrates (quartz and silicon) may be used for electric connection of RF components. Furthermore, in some embodiments on-chip antenna technology may be utilized, e.g., at very high frequencies.
The distance between the bottom, i.e., the antenna ground (104), of the platform (102) and the dipole antenna (110) refers to a vertical distance. The expression “vertical” means a direction, which is perpendicular to the plane of the bottom (104) of the platform (102). The plane of the bottom or the antenna ground (104) of the platform (102) is denoted by x and y while the vertical direction is denoted by z in
The horizontal dipole antenna (110) further comprises a first arm (112) and a second arm (114), which may be referred to as branches of the dipole antenna (110) as well. The first arm (112) and the second arm (114) of the dipole antenna (110) may be referred to as conductive elements in general.
Antenna module (100) also comprises a pair of via holes. The pair of via holes comprises a first via hole (116) and a second via hole (118) extending through the platform (102), from the bottom (104) of the platform (102) to the dipole antenna (110), wherein the first via hole (116) is coupled to an RF feed (117) and to a first arm (112) of the dipole antenna (110) and the second via hole (118) is coupled to the ground at the bottom (104) of the platform (102) and to a second arm (114) of the dipole antenna (110).
Horizontal dipole antenna (110) is thus above the ground (104). The pair of via holes (116, 118) may be arranged to work as a balanced feed and as a balun for the dipole antenna (110). Alternatively, or in addition, the pair of via holes (116, 118) may be arranged to work as an impedance transformer for the dipole antenna (110).
The first via hole (116) and the second via hole (118) are separated by a distance from each other in horizontal direction such that a desired impedance of the dipole antenna (110) is generated, wherein the impedance of the dipole antenna (110) is observed at the bottom (104) of the platform (102) at the RF feed (117). The distance between the first via hole (116) and the second via hole (118) in horizontal direction may be adjusted to match a desired frequency of the millimetre-wave signal. Alternatively, or in addition, frequency adjustment may be performed by adjusting a length and/or width of the dipole antenna (110).
The impedance of the dipole antenna input (110) depends on several factors. As said, for proper via-balun operation, this distance (antenna height from ground) should anyway be close to a quarter-wave length inside the platform. A dielectric layer may be added on top of the top antenna layer (i.e., the dipole antenna 110) forming together platform (102). The first via hole (116) and the second via hole (118) preferably have symmetrical structures, for making manufacturing more efficient. For example, the radius of the first via hole (116) and the second via hole (118) may be the same so that the same drill can be used. The horizontal distance between the first via hole (116) and the second via hole (118) can be varied to adjust the impedance of the dipole antenna (110). That is to say, for instance the impedance of the dipole antenna (110) may be decreased by increasing the radius of the first via hole (116) and the second via hole (118), and vice versa. Alternatively, or in addition, the impedance of the dipole antenna (110) may be increased by increasing the distance between the via holes (116) and (118).
In typical case, but not always, the radius of the via holes (116, 118) is the same, not only as they can be drilled with one tool, but also as symmetry in antenna structure is preferred for obtaining symmetric radiation patterns. However, different diameters may be used as the via-holes are not radiating elements. Impedance tuning may be also done varying the distance of the bottom (104) of the platform (102) and the dipole antenna (110), i.e., the distance in a vertical direction (z-direction in
Further, a dielectric layer in the antenna module (100), on top of the dipole antenna (110) can be used to find good matching range for the antenna and the impedance may depend on parameters of the dielectric layer material and thickness above the antenna. The dielectric layer may be an extra PCB layer for example. As for example, suitable dielectric materials with dielectric constant (εr) less than 4 could be Megtron7™ by Panasonic for multilayer structures and RT Duroid™ by Rogers Corporation. The dielectric layer, when applied above the antenna may be thin, for example one tenth of a quart length thickness, such as 50-150 μm.
When the thickness of the platform (102), not including the possible top layer, is about a quarter of a wavelength in the PCB substrate with dielectric of, e.g., a millimetre-wave signal, the second via hole (118) contacting the ground at the bottom (104) of the platform (102) is seen as open at the contacting dipole arm, i.e., the second arm (114) of the dipole antenna (110) in
According to some embodiments of the present invention, the dependencies between the parameters shown in
The antenna module (400) of
In some embodiments, the dipole antenna (110) and said another dipole antenna (120) may be arranged to generate signals with opposite polarizations simultaneously, said opposite polarizations comprising LHCP and RHCP, thereby enhancing communication capacity. Alternatively, the dipole antenna (110) and said another dipole antenna (102) may be arranged to generate signals with opposite polarizations at different times in a pseudorandom way, thereby improving security.
In the example of
Circular polarization is provided by arranging the connecting lines (132, 134) so that the first connecting line (132) lets current flow from the first via hole (116) of the first arm (112) of the dipole antenna (110) to the first arm (122) of said another dipole antenna (120) with 90 degree phase shift, thereby making the antenna circularly polarized. That is to say, when the first port is excited, the first connecting line (132) lets current flow from the first via hole (116) of the dipole antenna (110) to excite said another dipole antenna (120) with 90 degree phase shift. Opposite polarization is obtained when the second port connected to the first arm (122) of the dipole antenna (120) is excited. Thus, connecting lines (132, 134) between arms of the dipole antennas may be arranged to provide the 90 degree phase shift, but in opposite polarization compared to the case with the first port excitation. Both RF-ports (116) and (126) are isolated in this configuration.
If only one type of circular polarization (LHCP or RHCP) is enough for the communication system, only one pair of via holes is needed, the other pair can either be omitted from the structure or left unused. That is to say, when the antenna module (400) is arranged to generate one-handed circular polarization using only the two via holes of a feeding dipole antenna, like the dipole antenna (110), the via holes of the other dipole antenna, like said another dipole antenna (120), may be omitted, shorted to ground (104), left open or matched to load, as feeding ports of the dipoles antennas (110, 120) are RF-isolated.
The length of the connecting lines (132, 134) may be tuned such that a signal may be induced from the dipole antenna (110) to said another dipole antenna (120) with 90 degree phase difference and said two connecting lines (132, 134) are identical at length, width and contact points at the two dipoles connecting opposite dipole arms together, i.e., have 180 degree rotational symmetry around the crossed dipole axis. When the connecting lines (132, 134) are moved towards the end of the dipoles, the length of the line increases and consequently the phase shift between the two dipole antennas increases. When the phase difference is 90 degrees, circular polarization is obtained. This tuning affects antenna impedance matching, and has to be compensated with feed geometry adjustment, e.g. by adjusting the via hole geometry in
The circuit (810) may be a 3 dB/90 deg hybrid power splitter for example. Connections (820, 822) connect the circuit (810) to the dipole feed connections/pads (816, 818) at the first via holes (116, 126). The structure of the circuit (810) is compact and therefore a compact antenna module comprising the circuit (810) can be provided as well.
In some embodiments, pads (816, 818) may be coupled to antenna feeds, i.e., the feeds may be connected directly to via holes (116, 126) in
The first port (824) may provide right hand circular polarization (RHCP) and the second port (826) may provide left hand circular polarization (LHCP). The first port (824) and the second port (826) may be used simultaneously. In some embodiments, the hybrid coupling circuit (810) may be made compact by placing the dipole antenna (110), and possibly said another dipole antenna (120), with the via holes on top of the hybrid circuit (810) so that edges of the dipole antenna(s) and the antenna module (100) fit within edges of the circuit (810) as shown in
Alternatively, or in addition, the hybrid circuit (810) may be on a PCB-layer which shares a common ground with the antenna ground on the bottom (104) of the platform (102). This PCB-layer either may be under the bottom (104) of the platform (102) or above the bottom (104) on stacked antenna structure, i.e. buried inside the platform (102). The hybrid circuit (810) can thus be integrated with the antenna and manufactured with same process without occupying extra space.
So the circuit (810) makes use of a branch line coupler with feeding ports defined as (824, 826) and ports with 90 degree phase difference as (828, 830). Further, port (828) is connected to port (816) and, port (830) is connected to port (818) with transmission lines (820, 822) turned inside the circuit (810) to make contact with the via holes, i.e., the first via hole (118) of the first dipole antenna (110) and the first via hole (128) of said another dipole antenna (120). As the transmission lines (820, 822) can be turned inside the circuit (810), the structure is compact enough to be inserted to an antenna module. A transmission line is a line which transfers power only, but does not cause a phase shift.
The architecture shown in
In
It is common, that a via hole diameter has to be in order of the substrate thickness at minimum for reliable hole plating (copper filling). As antenna structure is generally thick, the core layer (1016) thickness should be of the order of the via hole diameter used in antenna design. Say, a 1 mm thick antenna-ground separation with 100 μm via holes would require one core layer of 100 μm thickness and 9 prepreg layers of same thickness. The antenna vias may have to extend through all these layers and need connection pads in between to make contact with the via holes between different layers.
In some embodiments, these “extra” layers can be used as a part of the component layer when RF-bridges with crossing RF-lines such as for RF distribution net are needed. Also the hybrid coupler circuit (810) can be manufactured on the opposite side of the ground plane under the component layer.
However, for cost efficient manufacturing unnecessary layers should be avoided. Thick substrates with thin via holes up to 1/10 via hole diameters to substrate thicknesses ratio can be manufactured using anode plate and pulse reverse plating technology.
It is to be understood that the embodiments of the invention disclosed are not limited to the particular structures, process steps, or materials disclosed herein, but are extended to equivalents thereof as would be recognized by those ordinarily skilled in the relevant arts. It should also be understood that terminology employed herein is used for the purpose of describing particular embodiments only and is not intended to be limiting.
Reference throughout this specification to one embodiment or an embodiment means that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment of the present invention. Thus, appearances of the phrases “in one embodiment” or “in an embodiment” in various places throughout this specification are not necessarily all referring to the same embodiment. Where reference is made to a numerical value using a term such as, for example, about or substantially, the exact numerical value is also disclosed.
As used herein, a plurality of items, structural elements, compositional elements, and/or materials may be presented in a common list for convenience. However, these lists should be construed as though each member of the list is individually identified as a separate and unique member. Thus, no individual member of such list should be construed as a de facto equivalent of any other member of the same list solely based on their presentation in a common group without indications to the contrary. In addition, various embodiments and example of the present invention may be referred to herein along with alternatives for the various components thereof. It is understood that such embodiments, examples, and alternatives are not to be construed as de facto equivalents of one another, but are to be considered as separate and autonomous representations of the present invention.
Furthermore, the described features, structures, or characteristics may be combined in any suitable manner in one or more embodiments. In the preceding description, numerous specific details are provided, such as examples of lengths and widths as electrical dimensions (i.e., as a function of a used wavelength), shapes, etc., to provide a thorough understanding of embodiments of the invention. One skilled in the relevant art will recognize, however, that the invention can be practiced without one or more of the specific details, or with other methods, components, materials, etc. In other instances, well-known structures, materials, or operations are not shown or described in detail to avoid obscuring aspects of the invention.
While the forgoing examples are illustrative of the principles of the present invention in one or more particular applications, it will be apparent to those of ordinary skill in the art that numerous modifications in form, usage and details of implementation can be made without the exercise of inventive faculty, and without departing from the principles and concepts of the invention. Accordingly, it is not intended that the invention be limited, except as by the claims set forth below.
The verbs “to comprise” and “to include” are used in this document as open limitations that neither exclude nor require the existence of also un-recited features. The features recited in depending claims are mutually freely combinable unless otherwise explicitly stated. Furthermore, it is to be understood that the use of “a” or “an”, that is, a singular form, throughout this document does not exclude a plurality.
At least some embodiments of the present invention find industrial application in wireless communication networks. Examples of wireless communication networks comprise 5G/NR, WLAN and satellite communication networks.
| Number | Date | Country | Kind |
|---|---|---|---|
| 20215020 | Jan 2021 | FI | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/FI2022/050013 | 1/5/2022 | WO |
