The invention relates to an RF component for a coaxial cable network.

Background of the invention

Radio Frequency (RF) passive components have traditionally been designed such that their manufacturing requires fine-tuning during production phases. Such manufacturing naturally requires a significant amount of labor, and therefore products are typically produced in countries with low labor cost.

For example, RF isolators for cable television networks (CATV) may be manufactured by providing the component housing with a metal shaft through which a communication wire is installed. Cylindrical ferrites are slid over the shaft and additional capacitors are soldered while assembling and fine-tuning the isolator. Therefore, assembling the isolator is carried out manually, wherein one person completes the isolator in one production stroke, and fine-tuning is based on the individual skills of the person. Moreover, the small size of the housing makes it very difficult to solder all components inside the housing without the risk of damaging the components and/or the housing.

Another way to manufacture an RF isolator is to use cylindrical capacitors, which are slid over the metal shaft in the same way as the ferrites. This reduces labor time and dependency of individual skills and increases product quality and repeatability. One example of such isolator is disclosed in EP 2658137. Nevertheless, also this isolator involves the drawback that it must be assembled manually from a plurality, i.e. dozens, of pieces during the manufacturing.

Brief summary of the invention

Now, an improved arrangement has been developed to reduce the above-mentioned problems. As aspects of the invention, we present an RF component for a coaxial cable network and a printed circuit board (PCB) adaptable in such RF component, which are characterized in what will be presented in the independent claim.

The dependent claims disclose advantageous embodiments of the invention.

According to an aspect of the invention, there is provided an RF component for use in a coaxial cable network, the component comprising a multilayer printed circuit board (PCB) having an outer form with an elongated rod, the rod of the PCB comprising a grounded bottom layer; a middle layer embodying a signal track; a grounded top layer; and a plurality of via holes at both sides of the elongated rod extending from the bottom layer through the middle layer to the top layer.

According to an embodiment, the PCB has a plurality of elongated rods, wherein a first rod of the PCB comprises said signal track and is the middlemost rod, and a second rod and a third rod are arranged parallel to and at predetermined distance from the first rod.

According to an embodiment, the via holes encapsulate the signal track on both sides to establish a transmission path for high frequency RF signals.

According to an embodiment, the component further comprises a connecting point for connecting the signal track to a further component, said connecting point being arranged at the end of the elongated rod insulated from the top layer and extending into the middle layer.

According to an embodiment, the top layer comprises a silkscreen layer on its outer surface, wherein one or more predetermined locations of the top layer lacks the silkscreen layer.

According to an embodiment, said RF component is an isolator.

According to an embodiment, one or more of said predetermined locations of the top layer lacking the silkscreen layer are located in the second and/or the third rod and comprise a connecting point for a capacitor.

According to an embodiment, the PCB comprises further circuitry for implementing one or more filters of the isolator.

The other aspects, embodiments and advantages will be presented later in the detailed description of the invention.

Brief description of the drawings

The invention will now be described in more detail in connection with preferred embodiments with reference to the appended drawings, in which:

Fig. 1a shows an example of a schematic outline design of the RF component according to an embodiment;

Fig. 1 b shows a schematic cross-sectional view of a layer-wise structure of a rod of the PCB; and

Figs. 2a, 2b, 2c show an example of a layer-wise structure of the RF component according to an embodiment.

Detailed description of the embodiments

In the following, a new RF component for use in a coaxial cable network is introduced, the component comprising a multilayer printed circuit board (PCB) having an outer form with at least one elongated rod, the rod of the PCB comprising a grounded bottom layer; a middle layer embodying a signal track; a grounded top layer; and a plurality of via holes at both sides of the elongated rod extending from the bottom layer through the middle layer to the top layer.

Thus, the RF component may be implemented using stripline technology in order to provide a transmission line for high frequency RF signals. The multiple layer printed circuit board (PCB) is designed with tracks within a substrate to guide the RF signals and is the support, upon which the production process of the RF component is based. This combination of functions for the PCB significantly simplifies the production process, since individual wires and the need for fine- tuning is avoided. This allows the manufacturing of the circuitry to be separated from the phase of assembling the circuitry into the housing.

Figure 1a shows an example of a schematic outline design of the RF component according to an embodiment. The dimensions of the layers in Figure 1a are not in scale. The RF component 100 is implemented as a multilayer PCB 102. The PCB 102 is designed to form at least one elongated rod 104.

According to an embodiment, the PCB has a plurality of, such as three, elongated rods, wherein a first rod of the PCB comprises said signal track and is the middlemost rod, and a second rod and a third rod are arranged parallel to and at predetermined distance from the first rod. Figure 1 shows the RF component according to the embodiment, wherein the first rod 104 is the middlemost rod comprising the signal track, and the second rod 106 and the third rod 108 are arranged parallel to and at predetermined distance from the first rod. Thus, there is a gap without PCB between first rod 104 and both of the second 106 and third rod 108. The structure, benefits and further embodiments relating to the second and third rod are described more in detail further below.

Figure 1 b shows a schematic cross-sectional view of the first rod 104. The first rod comprises a top layer 120 and a bottom layer 122. A signal track 124 preferably in a form of a flat metal strip is embodied in a substrate of a middle layer 126 made of an insulating material, thereby forming a dielectric. An appropriate characteristic impedance of the strip may be obtained by adjusting the width of the strip, the thickness of the substrate and/or the relative permittivity of the substrate.

According to an embodiment, the via holes encapsulate the signal track on both sides to establish a transmission path for high frequency RF signals. The top layer 120 and the bottom layer 122 are grounded and shorted together through via holes 128, 130 at both sides of the first rod extending through substrate of the middle layer. The grounded top and bottom layer enable to prevent the propagation of unwanted modes, and the structure is less vulnerable to noise caused e.g. by radiated RF emissions, similarly to the coaxial cable.

It is noted that contrary to schematic view of Figure 1 b, the strip 124 does not necessarily need be equally spaced between top layer 120 and the ground layer 122. Depending on the desired characteristic impedance of the strip, the strip 124 may locate closer to either top layer 120 or the bottom layer 122. Moreover, different substrate materials may be used above and below the strip 124.

Figures 2a, 2b and 2c show an example of a layer-wise structure of the RF component according to an embodiment. Figure 2a shows an example illustration of the bottom layer 122 of the PCB. The bottom layer is implemented as a thin foil, typically made of copper, which is laminated onto the substrate of the middle layer with heat and adhesive. Thus, the first rod 104 comprises an electrically conductive plating. The first rod 104 comprises two rows of via holes 128, 130 on both sides of the rod. Figure 2b shows an example of the middle layer 126. The strip 124, i.e. the signal track, is located such that it is encapsulated by the rows of the via holes 128, 130 on both sides of the rod.

According to an embodiment, the component further comprises a connecting point for connecting the signal track to a further component, said connecting point being arranged at the end of the elongated rod insulated from the ground of outer layers and extending into the middle layer. Figure 2b shows how the strip 124 extends to a connecting point 132 by a via locating within the substrate.

Figure 2c, showing an example of the top layer topology, also illustrates the location of the connecting point 132. The top layer is implemented similarly to the bottom layer, i.e. as a thin foil, typically made of copper. As shown, the surface of the connecting point 132, which may be made e.g. from copper, is separate and insulated from the electrically conductive plating of the top layer. Thus, the connecting point 132 extends from the top layer into the substrate of the middle layer such that the transmission line of the signal track 124 can be extended to a further component or a coaxial cable.

Figure 2c further illustrates rows of the via holes 128, 130 on both sides of the rod as on the bottom layer. A soldermask is overlaid onto the copper of the top layer to insulate the copper traces from accidental conductive contacts and allocate place to the user to solder components at the proper places and prevent solder jumpers.

According to an embodiment, the top layer comprises a silkscreen layer on its outer surface, wherein one or more predetermined locations of the top layer lacks the silkscreen layer. A silkscreen layer is thus applied onto the soldermask, as typical for PCBs, but one or more predetermined locations of the top layer are left without the silkscreen layer, thereby providing fixed positions for connecting various PCB components and ground points upon assembling the RF component into the housing. Hence, there is no need for fine tuning upon the assembly phase, but the necessary PCB components and grounding points can be connected directly to the fixed positions.

According to an embodiment, said RF component is an isolator. While the overall principle underlying the embodiments can be applied to any passive RF components suitable for coaxial networks, the achieved benefits are especially obvious upon manufacturing an isolator. As described above, the traditional methods for manufacturing isolators are slow and laborious and prone to many types of errors. For the isolator according to the embodiment, the PCB circuitry may be manufactured separately, and the assembly phase of the isolator is thereby significantly fasted and made less dependent on the individual skills. Also, when carrying out tests for traditional isolators and isolators manufactured with the stripline technology, it has turned out that the RF performance of the strip line isolators in terms of isolation and transmission performance are far better than with a traditional metal shaft. According to an embodiment, one or more of said predetermined locations of the top layer lacking the silkscreen layer are located in the second and/or the third rod and comprise a connecting point for a capacitor. As described above, the implementation of an isolator comprises one or more capacitors. Now the PCB circuitry may be implemented such that the one or more capacitors are positioned in the side rods, i.e. in the second and/or the third rod, of the PCB, and their locations on the PCB are lacking the silkscreen layer. Thus, they provide fixed positions for coupling the top layer of the first rod to the capacitors in a straightforward manner, without any fine tuning.

The dimensions of the PCB, and especially those of the second and the third rod, as shown in Figure 1a, may be adjusted according to the housing to be used. Thus, the PCB may be dimensioned such that its outline conforms substantially tightly to the inner surface of the housing, thereby enabling the PCB to be placed into the housing firmly and with only simple manual work. Herein, the design of the second and the third rod play a significant role in securing the PCB firmly into the housing. The interior of the housing may have further support points, such as screws or connector bases, and the rods may be designed to fit against such support points, as illustrated by the roundings at the end of rods. It is noted that while the PCB shown in Figure 1a is intended for a rectangular housing, any other form of the housing and the PCB may be used, as well.

According to an embodiment, the PCB comprises further circuitry for implementing one or more filters of the isolator. As described above, the implementation of an isolator may comprise one or more filters to be connected to the isolator. Now the need for additional parts for separate filters is avoided and the filters may be implemented on the same PCB circuitry.

As becomes evident from what has been described above, the RF component according to the embodiments may provide significant advantages over RF components assembled in a conventional manner. For example, a significant advantage is obtained through the easiness and the repeatability of assembling the RF component. Instead of mounting and tuning every part separately inside the housing, the PCB may be mounted apart from the housing and simply plugged inside the housing as one piece. Further, this allows to spare lot of time in production, to reduce the cost of production due to mass production of the PCBs and to avoid the repetitive tuning of every RF component. Moreover, as a result of using the strip line technology for an isolator, the RF performance exhibit a better isolation and transmission performance than with a traditional metal shaft. It will be obvious for a person skilled in the art that with technological developments, the basic idea of the invention can be implemented in a variety of ways. Thus, the invention and its embodiments are not limited to the above-described examples, but they may vary within the scope of the claims.