Technical Field

The invention relates to a radiofrequency signal distribution network, an antenna with such a distribution network as well as a mobile communication base station comprising such an antenna.

Background

Radiofrequency signal distribution networks are a vital part of each antenna, in particular for mobile communication. The distribution networks have to be electrically and mechanically attached to the radiators of the antenna to provide the functionality of receiving and transmitting the signals to and from the radiators.

Antennas with such networks are known, for example, from CN 107819198 A and US 10 553 958 B2.

It is known in the art to use a metal sheet parallel to a substrate to form a distribution network, wherein the metal sheet in a form of a printed circuit board (PCB) is fixed in a defined distance to a reflector or to a ground by means of separate spacers. The ground of the PCB or special grounding points of the distribution networks of the metal may be galvanically connected to the ground. Solutions are known that use guide rails for the PCB or separate spacers to precisely define the distance between the PCB and the metal sheet. These solutions are, however, mechanically complex

Summary

It is thus the object of the invention to provide a radiofrequency signal distribution network, an antenna as well as a base station which can be manufactured more efficiently without loss in quality.

For this purpose, a radio frequency signal distribution network, in particular for a mobile communication antenna, is provided. The distribution network comprising a substrate with a printed circuit and at least one metal sheet, wherein the metal sheet is a single piece of metal comprising a flat base body and a plurality fixation portions for fixing the substrate relative to the base body. The fixation portions are located from the base body towards the substrate and are resiliently connected to the base body.

Thus, the location of substrate with respect to the metal sheet is fixed, in particular by fixation portions. By providing fixation portions that extend toward the substrate and that are resiliently connected to the base body, it is possible to revert to adhesive bonding, soldering or welding for manufacturing. This may be done as the resiliency of the fixation portions with respect to the base body compensates for manufacturing tolerances as well as the difference in the coefficient of thermal expansion between metal and the substrate. Adhesive bonding, soldering and welding provide quicker and thus more efficient ways than a rail system or attaching a separate spacer so that the radiofrequency signal distribution network can be manufactured more efficiently.

In particular, the base body and the fixation portion are a single piece, for example a stamped part. The fixation portions may be located separate from the conductors of the printed circuit.

In an aspect, the substrate and the base body of the metal sheet are parallel to each other and/or the fixation portion and the base body are parallel to each other, providing reliable signal quality.

For example, the substrate with the printed circuit is a printed circuit board, further reducing manufacturing costs. The board may be a FR-4 board.

The substrate with the printed circuit may also be a plastic with metal sheets or a molded interconnect device (MID), reducing the CO2 footprint of the distribution network.

In an embodiment, the metal sheet comprises a plurality of resilient portions, wherein each fixation portion is connected to the base body by at least one, in particular two of the resilient portions, providing a very reliable resilient connection between the fixation portion and the base body.

The two resilient portions may engage the fixation portion at opposite sides. The fixation portions and the corresponding at least one resilient portions may be aligned with one another.

To improve the resilience, in a top view of the metal sheet, the base body may comprise a plurality of cutouts in each of which one of the fixation portions is provided, wherein for each cutout the corresponding fixation portion, particularly also the corresponding at least one resilient portion, may extend in a first direction of the cutout.

The cutouts may also be designed to allow visual inspection of the fixation portion for defects.

The first direction is in particular the longitudinal direction of the cutout and the second direction is the traverse direction of the cutout. In an aspect, in the top view of the metal sheet, at least one edge of each of the cutouts is spaced apart from the corresponding fixation portion, particularly also from the corresponding at least one resilient portion, in a second direction of the cutout. This setup increases the resilience further.

The second direction is in particular perpendicular to the first direction.

For further improved resilience, two opposing edges of each cutout may be spaced apart from the corresponding fixation portion, particularly also from the corresponding at least one resilient portion.

In an embodiment, two neighboring ones of the fixation portions are spaced apart from one another by a distance smaller than one quarter of the wavelength of the average wavelength of the design frequency range of the radio frequency signal distribution network. This way, the line of fixation portions serves as a shielding, reliably containing the radiofrequency signal.

The distance refers in particular to fixation portions of the same group of fixation portions.

In an aspect, the fixation portion is attached to the substrate by adhesive bonding, soldering and/or welding, further reducing manufacturing costs.

For achieving low loss signal transmission, the metal sheet may provide a ground plane for conductors of the printed circuit, in particular wherein the metal sheet and the conductors form an air transmission line, particularly an air stripline or an air micro strip line.

For example, the stripline's central conductor or the microstrip's signal line is realized as part of the printed circuit on the substrate. In this case, the air stripline and air microstrip line is understood as stripline or microstrip line with the majority of the electrical field propagating in air. In an embodiment, the radio frequency signal distribution network comprises two of the substrates with a printed circuit, wherein the metal sheet is arranged between the two substrates, wherein of the fixation portions of the metal sheet, a first group of fixation portions extend toward one of the substrates and a second group of fixation portions extend toward the other one of the substrates. This way, the metal sheet may serve as a common ground for two substrates, reducing the number of parts.

The fixation portions of the first and/or the second group are, for example, attached to the respective substrate.

The fixation portions of first and second group may be arranged altematingly.

In a further embodiment, the radio frequency signal distribution network comprises two metal sheets, wherein the substrate is arranged between the two metal sheets, particularly wherein the metal sheets each provide a ground plane for conductors of the printed circuit of the substrate. This setup allows to provide air cavity waveguides.

For ease of manufacture, the fixation portions of the two metal sheets may be attached to the substrate by adhesive bonding, soldering and/or welding, in particular wherein the substrate comprises at least one via electrically connecting at least one of the fixations portions of one of the metal sheets with at least one of the fixations portions of the other one of the metal sheets.

In a further embodiment, in a top view, the fixation portions of the two metal sheets are at the same locations so that one fixation portion of one of the metal sheets and the fixation portions of the other metal sheet at the same locations form a pair of fixation portions. The substrate comprises cutouts at locations corresponding to the locations of the pairs of fixation portions, wherein one or both fixation portions of the corresponding pair of fixation portions extend through each cutout, wherein the fixation portions of the same pair of fixation portions are attached to one another, in particular by adhesive bonding, soldering and/or welding. This way, the substrate is fixed relatively to the base body of metal sheets even though not directly attached to metal sheets, further improving tolerance for different coefficients of thermal expansion.

For above mentioned purpose, further an antenna, in particular for a mobile communication base station, is provided. The antenna comprises a plurality of radiators and a radio frequency signal distribution network as described above, in particular wherein the metal sheet is a reflector for the radiators and/or the radiators are mechanically attached to the metal sheet and electrically connected to the printed circuit of the substrate.

The features and advantages discussed with respect to the radio frequency distribution network also apply to the antenna and vice versa.

Further, a mobile communication base station is provided for above mentioned purpose, the mobile communication base station comprising an antenna as described above and/or a radio frequency signal distribution network as described above.

The features and advantages discussed with respect to the radio frequency distribution network and/or the antenna also apply to the mobile communication base station and vice versa.

Brief Description of the Drawings

Further features and advantages will be apparent from the following description as well as the accompanying drawings, to which reference is made. In the drawings

Figure 1: shows a mobile communication base station according to the invention with an antenna according to the invention schematically, Figure 2: shows the antenna of Figure 1 in a sectional view with a radiofrequency signal distribution network according to the invention,

Figure 3: shows the distribution network of Figure 2 in an exploded view,

Figure 4: shows a metal sheet of the distribution network of Figure 3 in a perspective view,

Figures 5, 6: show the region of a fixation portion of the metal sheet in a side view and top view, respectively,

Figure ?: shows a second embodiment of a radiofrequency signal distribution network in a cross-section,

Figure 8: shows a cross-section of a third embodiment of a radiofrequency signal distribution network according to the invention,

Figure 9: shows a perspective view of the metal sheet of the distribution network of Figure 8, and

Figure 10: shows a perspective sectional view of a fourth embodiment of a radiofrequency signal distribution network according to the invention.

Detailed Description

Figure 1 shows a mobile communication base station 10 schematically. The base station 10 has at least two antennas 12.

Figure 2 shows one of the antennas 12 in a sectional view. The antenna 12 comprises a plurality of radiators 14 and a radiofrequency signal distribution network 16 for supplying the radiators 14 with a signal and receiving signals from the radiators 14. The radiators 14 are mounted to the distribution network The radiators 14 and thus the radiofrequency signal distribution network 16 are designed to work in a frequency range lying in the range between 500 MHz to 6 GHz. For example, the design frequency range of the radiators 14 and thus of the radiofrequency signal distribution network 16 lies between 1.7 GHz to 2.7 GHz.

Figure 3 shows an exploded view of the radiofrequency signal distribution network 16.

The distribution network 16 comprises a metal sheet 18 and a substrate 20.

The substrate 20 has a printed circuit 22 applied to at least one surface of it, wherein the printed circuit 22 is applied to the substrate 20 in a manner per se known in the art.

For example, the substrate 20 is made of FR-4 so that the substrate 20 and the printed circuit 22 are a printed circuit board (PCB) as commonly known in the art.

The substrate 20 may also be a plastic and the printed circuit 22 may be of metal sheets attached to the plastic.

It is also conceivable that the substrate 20 with the printed circuit 22 is a molded interconnect device (MID).

The printed circuit 22 comprises, for example, conductors forming signal lines and phase shifter.

The radiators 14 are mechanically attached to the metal sheet 18 and electrically connected to the printed circuit 22 in a manner per se known in the art.

The substrate 20 may comprise a printed circuit 22 on both of its surfaces, in particular the printed circuit 22 on the different surfaces may be identical in the sense that in a top view on one of the surfaces, the projections of the printed circuits 22 completely overlap.

The metal sheet 18 has, in the shown embodiment, a size of about 5 cm times 50 cm.

The metal sheet 18 comprises a base body 24, a plurality of fixation portions 26 and a plurality of resilient portions 28.

The metal sheet 18 is made out of a single piece meaning that the base body 24, the fixation portions 26 and the resilient portions 28 are also made of the single piece. For example, the metal sheet 18 is a stamped metal sheet.

The base body 24 is flat, being in particular the remaining unstamped part of the metal sheet.

In the shown embodiment, the fixation portions 26 are arranged in two lines along the edge of the base body 24, wherein the distance between adjacent fixation portions, in particular of the same line, is smaller than one quarter of the wavelength of the average wavelength of the design frequency range of the radiofrequency signal distribution network 16. The distance may also be smaller than one eighth or one tenth of the design frequency range of the radiofrequency signal distribution network 16.

Figure 4 shows an enlarged perspective view of the metal sheet and Figures 5 and 6 show a further enlarged view of one of the fixation portions 26 in a side view and top view, respectively.

The base body 24 has a plurality of cutouts 30 in which the resilient portions 28 and the fixation portions 26 are located.

The cutouts 30 are in particular created in the same stamping step as the fixation portions 26 and the resilient portions 28. In the shown embodiment, the cutouts 30 have a rectangular shape with a first direction Fl, being the longitudinal direction of the cutout 30, and a second direction F2 being the transverse direction of the cutout 30. The first direction Fl perpendicular to the second direction F2.

In each of the cutouts 30 one of the fixation portions 26 is provided, which is connected to the base body 24 by two of the resilient portions 28.

As best seen in Figure 5, the fixation portion 26 extends parallel to the base body 24 and is located offset to the base body 24, namely in the direction towards the substrate 20.

On both of the opposite ends of the fixation portion 26 in the first direction Fl, the resilient portions 28 abut. The resilient portions 28 extent to the traverse edge of the cutout 30.

The resilient portions 28 and the fixation portion 26 are aligned with one another forming a straight line.

As seen in a top view, for example the top view of Figure 6, the fixation portion 26 and the corresponding resilient portions 28 are spaced apart from the longitudinal edge of the cutout 30 extending in the first direction Fl. As such, a void is present between the longitudinal edges and the resilient portions 28 or the fixation portion 26, respectively.

Turning back to Figure 1, the base body 24 and the substrate 20 are arranged parallel to each other and the fixation portions 26 are in physical contact with the substrate 20.

The fixation portions 26 make contact with the substrate 20 in particular in regions without conductors of the printed circuit 22.

The fixation portions 26 are attached to the substrate 20 by welding, soldering or by adhesive bonding, using an adhesive. The adhesive may be conductive or non-conductive. This way, the substrate 20 is fixed to the metal sheet 18 and thus its location with respect to the metal sheet 18 is fixed.

The fixation of the substrate 20 to the metal sheet 18, precisely the base body 24, is not rigid, but resilient due to the resilient portions 28.

The resilient portions 28 are resilient in a way that they allow movement of the fixation portion 26 in an upwards direction of the cutout 30 as well as in the first direction Fl and/or the second direction F2 on a limited scale. This limited scale is, however, sufficient to compensate for manufacturing tolerances as well as differences in the coefficient of thermal expansion of the metal sheet 18 and the substrate 20, in particular while exposed to high temperatures during the curing of the adhesive, during welding or during soldering.

The resilience in the second direction F2 is, in particular, supported by the void between the fixation portions 26 and the resilient portions 28 and the respective edge of the cutout 30.

This way, a defined and fixed location of the substrate 20, in particular of the printed circuit 22 with respect to the base body 24 and thus the radiators 14 is achieved, leading to a very reliable radio frequency signal distribution network 16. At the same time, the distribution network 16 is efficiently manufactured as no complex rails or separate spacers have to be used.

The metal sheet 18, in particular the base body 24 provides a ground plane for the conductors of the printed circuit 22, in particular the signal lines of the printed circuit 22. Thus, air microstrip transmission lines having low losses are formed by the printed circuit 22 in conjunction with the base body 24. In this way, a radiofrequency signal distribution network with very low losses is provided.

Further, due to the distance between neighboring fixation portions 26 smaller than one quarter of the wavelength, the cavity formed between the metal sheet 18 and the substrate 20 is shielded from adverse influences. In particular, if several of the distribution networks 16 are located one beside the other, no interference between the distribution networks 16 is present.

At the same time, the metal sheet 18, in particular the base body 24 may serve as the reflector for the radiators 14, thus providing two functions at the same time.

Figures 7 to 10 show further embodiments of the radiofrequency signal distribution network 16 corresponding substantially to the first embodiment. Thus, only the differences are discussed in the following and the same and functionally the same components are labeled with the same reference signs.

Figure 7 shows a cross-section of a second embodiment of the radiofrequency signal distribution network 16.

In this embodiment, the distribution network 16 comprises two metal sheets 18 each having fixation portions 26 and resilient portions 28 as discussed with respect to the first embodiment.

The substrate 20 is provided between the two metal sheets 18 and the fixation portions 26 of the metal sheets 18 are in contact with both of the surfaces of the substrate 20.

In particular, the fixation portions 26 are attached to the surfaces of the substrate 20 by adhesive bonding, soldering or welding.

By providing metal sheets 18 above and below the substrate 20, an air stripline with low losses can be provided.

The conductors, namely the signal lines of the printed circuit 22 and the metal sheets 18 may also form an air cavity waveguide. To this end, the substrate 20 comprises a via 32 at the locations of contact of the fixation portions 26 of the metal sheet 18. By this via 32, the two metal sheets 18 are connected electrically so that they form a common ground.

In case of adhesive bonding, the adhesive may be conductive to provide a galvanic connection. If the adhesive is not conductive, a capacitive connection between the via 32 and their respective fixation portion 26 is achieved.

The via 32 and possible conductors connected to the via 32 do not form not part of the printed circuit 22 in the sense of this disclosure, even though they might be printed to the substrate 20.

It is also conceivable that the fixation portions 26 of the different metal sheets 18 are not located at the same location in a top view, so that a conductor connected to the via 32 is necessary to provide the electric connection between the metal sheets 18.

Furthermore, it is conceivable that for a small thicknesses of the substrate 20 the electrical connection is provided through capacitive coupling, e.g. overlapping metal areas on both surfaces of the substrate 20.

A third embodiment of the radiofrequency signal distribution network 16 is shown in a cross-section in Figure 8. In this third embodiment, the radio frequency signal distribution network 16 comprises two substrates 20 and one metal sheet 18.

The metal sheet 18 is provided between the substrates 20, wherein the substrates 20 and the metal sheet 18 are parallel to each other.

By providing the substrates 20 above and below the metal sheet 18, two air microstrip lines with low losses can be provided. The versatility of the distribution network 16 is thus improved. A central conductor of the air stripline or the signal line of the microstrip line can be realized on one surface or on both surfaces of the substrate 20.

Figure 9 shows a perspective view of the metal sheet 18, in which the difference to the first embodiment becomes apparent.

In this third embodiment, the metal sheet 18 comprises two groups of fixation portions 26, namely a first group 34 and a second group 36. The fixation portions 26 of the different groups extend in opposite directions.

Turning back to Figure 8, it can be seen that the fixation portions 26 of the first group 34 extend upwards towards the upper substrate 20 and the fixation portions 26 of the second group 36 extend downwards towards to the other one of the substrates 20, namely the lower substrate 20.

The fixation portions 26 of the first group 34 and the second group 36 are in contact and attached to the respective substrate 20 as discussed with respect to the first embodiment.

The fixation portions 26 of the first group 34 and of the second group 36 are arranged in alternating fashion, in particular along the edge of the metal sheet 18.

To achieve the shielding effect discussed with respect to the first embodiment, the distance between neighboring fixation portions 26 has to be smaller than one quarter of a wavelength. This applies to the fixation portions 26 of the same group 34, 36.

In this third embodiment, a single metal sheet 18 can be used to provide the ground plane for the printed circuits 22 on the two substrates 20, thus forming two air microstrip transmission lines using a single metal sheet 18.

Figure 10 shows a perspective view of a section of a fourth embodiment of a radiofrequency signal distribution network 16. The fourth embodiment is similar to the second embodiment in the fact that two metal sheets 18 are provided and that the substrate 20 is located between the two metal sheets 18.

In this embodiment, if the metal sheets 18 were seen in a top view, the fixation portions 26 of both metal sheets 18 are provided at the same locations. In other words, in a projection perpendicular to the substrate 20, the fixation portions 26 overlap.

The fixation portions 26 of the different metal sheets 18 that are provided at the same locations form a pair 38 of fixation portions.

Further in difference to the second embodiment, the substrate 20 comprises cutouts 40 at the locations of the pairs 38 of fixation portions 26.

In the shown embodiment, both of the fixation portions 26 of the same pair 38 extend into the cutout 40 and are attached to one another within the cutout 40.

Attaching the fixation portions 26 of the same pair 38 may be performed by adhesive bonding, soldering and or welding.

A conductive adhesive may be used, providing a galvanic connection between the two metal sheets. The adhesive may also be non-conductive so that a capacitive connection between the metal sheets 18 is formed at the fixation portions 26.

In this shown fourth embodiment, the substrate 20 itself is not attached to the pair 38 of fixation portions 26 directly by an adhesive, weld, solder or the like. In fact, the substrate is free-floating between the two metal sheets 18 but its location relative to the metal sheets 18 is nevertheless fixed by the pair of fixation portions 26 that extend through the cutout 40 of the substrate 20. Thus, also in this embodiment, the fixation portions 26 serve to fix the substrate 20 relative to the base body 24. Regardless whether the attachment is done by an adhesive, soldering or welding, the adhesive, solder or the weld, respectively, may be present only between the fixation portions 26.

It is also conceivable that the adhesive, solder or the weld is present not only between the fixation portions 26 but also contacts the edges of the cutout 40 of the substrate 20. In this case, the substrate 20 may also be mechanically fixed to the fixation portions 26.

Further, in this scenario a metallization of the substrate 20 may also be electrically connected to the metal sheets 18 by the adhesive, solder or weld, thus providing a grounding.

Moreover, in this scenario additional fixation portions, extending from the base body 24 towards the substrate 20, are conceivable. For example, the additional fixation portions define the distance between the substrate 20 and the metal sheets 18 further. In this case, the additional fixation portions can be realized as shown in Figure 7, without the need to touch the metallization of substrate 20 and without the need to be bonded together with the metal sheets 18.