TECHNICAL FIELD The present invention relates to an attachment system of a replaceable radio unit (RRU), and in particular to individual components of the attachment system. That is, the present invention relates in particular to an antenna holder and to an RRU holder, respectively. The present invention further relates to a method for mounting a RRU to an antenna. BACKGROUND

As shown in Fig 1 in (a), a conventional Active Antenna System (AAS) comprises an antenna 101 and at least one Radio Unit (RU) 102, which is typically integrated at least partly into the antenna 101. The antenna 101 is further mounted to a mast 103 by at least one bracket 104. Due to the integration of the at least one RU 102, the conventional AAS has fewer units and fewer interconnections than even older systems, and can consequently receive more capacity, consumes less energy, and requires a shorter installation time. Since in the conventional AAS the at least one RU 102 is partly inside of the antenna 101, it cannot be easily replaced.

As a consequence, no matter which or how many of such non-replaceable RUs 102 in a conventional AAS fail, the whole antenna 101 has to be replaced. Since RUs 102 are damaged rather easily, the antenna 101 of the AAS has to be replaced with a relatively high likelihood. That means more maintenance costs for the AAS. It is therefore desirable to provide an AAS with at least one RRU, in order to lower the maintenance costs.

As shown in Fig. 1 in (b), conventional RRUs 112 are normally mounted to the back of an antenna 111 with a bracket 114. The mounting and dismounting of the RRUs 112 must thus be done on the tower of the AAS. The conventional RRUs 112 are mounted hanging on a back support 116 of the antenna 111, and are fixed with screws 117. The work of replacing such conventional RRUs 112 requires at least two persons, which need to work together on the tower of the AAS including the antenna 111, since the weight of the RRUs 112 is rather high. Due to this fact, a system with conventional RRUs 112 requires more operating space 115 between a mast 113 of the tower and the antenna 111 than the space 105 required for a system with non-replaceable RUs 102 (see Fig. 1 in (a)). That also means that the distance between the antenna 111 and the mast 113 needs to be larger than with non-replaceable RUs 102, which leads to a higher lateral wind- load torque that is potentially exhibited by the antenna 111 , as illustrated in Fig. 2.

In Fig. 2 Fl denotes the lateral wind- load acting on the antenna 111, and L denotes the distance from the mast 113 to the antenna 111. Since this distance L is larger than for a system with non-replaceable RUs 102 due to the required operating space 115, also the wind load torque M, which is Fl multiplied by L, is larger, and challenges the antenna brackets 114 holding the RRUs 112.

SUMMARY In view of the above-mentioned disadvantages of systems with non-replaceable RUs and systems with conventional RRUs, the present invention aims to improve the state of the art. In particular, the present invention has the object to provide a mounting solution between an antenna and a RRU, which allows a reduction of the operating space between a mast and the antenna. Consequently, the present invention aims to reduce the lateral wind-load torque, which challenges the antenna brackets. Furthermore, the present invention desires to provide a method of mounting a RRU to an antenna, which can be carried out faster and easier. In particular, the mounting method should be performable by a single person, and should require less operating space. The above-mentioned object of the present invention is achieved by the solution provided in the enclosed independent claims. Advantageous implementations of the present invention are further defined in the respective dependent claims.

In particular the present invention proposes an attachment system between an antenna and a RRU, which employs a sliding mechanism. The sliding mechanism enables one worker alone to handle the RRU on the tower with one hand. Due to the sliding mechanism, the attachment system also requires less installation space, and specifically a shorter distance from mast to antenna. Accordingly, brackets of the attachment system are challenged less by wind-load torque. A first aspect of the present invention provides an antenna holder for engaging with a RRU holder, the antenna holder comprising a guiding part and a receiving part, wherein the guiding part is configured to receive and guide a protruding part of the RRU holder to a receiving part, and wherein the receiving part is configured to receive the protruding part of the RRU holder in an engagement position of the two holders.

By means of the guiding part and the receiving part, the RRU holder can be mounted to the antenna holder in a sliding manner, which allows one worker alone to mount and demount the RRU from the antenna. Furthermore, due to the sliding mechanism used for mounting the RRU holder to the antenna, a required operating space between the antenna and the mast can be reduced. Accordingly, the antenna brackets are challenged less by wind-load torque.

In a first implementation form of the antenna holder of the first aspect, the guiding part comprises a notch.

A notch presents a particular easy implementation of a guiding part, in which the protruding part of the RRU holder can slide in a controlled manner and with low resistance.

In a second implementation form of the antenna holder according to the first implementation form of the first aspect, the receiving part comprises a cut-out in the notch.

A cut-out in a notch is a specifically simple realization of a receiving part, and is cost sensitive since it requires no additional material.

In a third implementation form of the antenna holder according to the first aspect as such or according to any of the previous implementation forms of the first aspect, the antenna holder further comprises a protruding part, which extends from the guiding part and is configured to intrude into a receiving part of the RRU holder in an engagement position of the two holders. By means of the protruding part of the antenna holder can be guaranteed that in the engagement position the antenna holder and the RRU holder are securely mounted to each other. A second aspect of the present invention provides a RRU holder for engaging with an antenna holder, the RRU holder comprising a protruding part configured to be inserted into and guided in a guiding part of the antenna holder, wherein the protruding part is configured to intrude into a receiving part of the antenna holder in an engagement position of the two holders.

By means of the protruding part, the RRU holder can be easily mounted in a sliding manner to the antenna holder, and can be firmly secured in the engagement position. The sliding mechanism not only enables an easier mounting solution of the two holders, but also enables a reduction of the operating space between mast and antenna.

In a first implementation form of the RRU holder of the second aspect, the RRU holder further comprises a receiving part configured to receive a protruding part of the antenna holder in the engagement position of the two holders. By means of the receiving part, the RRU holder and the antenna holder are more securely locked in the engagement position.

In a second implementation form of the RRU holder according to the second aspect as such or according to the first implementation form of the second aspect, the RRU holder further comprises a guiding part configured to grasp the guiding part of the antenna holder in the engagement position of the two holders.

Due to the grasping engagement of the two guiding parts, the RRU holder is well stabilized in the engagement position with the antenna holder, and is fully supported by its weight.

A third aspect of the present invention provides an attachment system including an antenna holder according to the first aspect as such or according to any previous implementation form of the first aspect, an RRU holder according to the second aspect as such or according to any implementation form of the second aspect, wherein the receiving part of the antenna holder is configured to engage with the protruding part of the RRU holder, when the receiving part of the RRU holder is engaged with the protruding part of the antenna holder.

The attachment system achieves the above-mentioned advantages of the antenna holder and the RRU holder, respectively, namely that the RRU can be mounted to the antenna in a sliding manner, which is easy to apply, and which allows to reduce the operating space between mast and antenna.

In a first implementation form the attachment system according to the third aspect, the guiding part of the antenna holder is configured to engage with the guiding part of the RRU holder, when the receiving parts are respectively engaged with the protruding parts. Thereby, the antenna holder and the RRU holder are securely mounted to each other.

A fourth aspect of the present invention provides an antenna comprising an antenna holder according to the first aspect as such or an implementation form of the first aspect, wherein the antenna holder is attached to or is part of a housing of the antenna.

The antenna achieves all the advantages described above for the antenna holder.

A fifth aspect of the present invention provides a RRU comprising a RRU holder according to the second aspect as such or according to any implementation form of the second aspect, wherein the RRU holder is attached to or is part of a housing of the RRU.

The RRU achieves all the advantages described above for the RRU holder.

A sixth aspect of the present invention provides a method for mounting a RRU unit to an antenna, the method comprising guiding a protruding part of an RRU holder into and along a guiding part of an antenna holder, until a receiving part of the antenna holder receives the protruding part of the RRU holder. Since the method employs a sliding mechanism for mounting the antenna holder to the RRU holder, it can be carried out easier than conventional mounting methods. In particular, it can be carried out by a single person, and requires less working space between mast and antenna. Thus, the mounted antenna is also less endangered by wind- load torque.

In a first implementation form of the method according to the sixth aspect, the method further comprises before the guiding step, lifting and positioning the RRU, until the RRU holder is over the antenna holder, lowering the RRU, until the protruding part of the RRU holder is received by the guiding part of the antenna holder, and lowering the RRU, until a guiding part of the RRU holder is horizontally aligned with the guiding part of the antenna holder.

The specific mounting method provided by the first implementation form allows a fast and easy installation of the RRU at the antenna, and can be carried out by a single person.

In a second implementation form of the method according to the sixth aspect as such or according to the first implementation form of the sixth aspect, the method further comprises releasing the RRU, when the guiding parts of the two holders are aligned with another, so that the RRU holder falls into an engagement position with the antenna holder, and is stabilized by the weight of the RRU.

Since the RRU is stabilized by its weight on the antenna, no specific attachment means, like screws, are required. However, according to a further implementation form, the RRU can be additional fixed to the antenna, e.g. using screws.

In a third implementation form of the method according to a sixth aspect as such or according to any previous implementation form of the sixth aspect, a receiving part of the RRU holder receives a protruding part of the antenna holder in the engagement position of the two holders, or a guiding part of the RRU holder grasps the guiding part of the antenna holder in the engagement position of the two holders.

Thereby, the RRU holder can be mounted securely to the antenna holder, and thus also the RRU is securely attached to the antenna. It has to be noted that all devices, elements, units and means described in the present application could be implemented in the software or hardware elements or any kind of combination thereof. All steps which are performed by the various entities described in the present application as well as the functionalities described to be performed by the various entities are intended to mean that the respective entity is adapted to or configured to perform the respective steps and functionalities. Even if, in the following description of specific embodiments, a specific functionality or step to be full formed by eternal entities is not reflected in the description of a specific detailed element of that entity which performs that specific step or functionality, it should be clear for a skilled person that these methods and functionalities can be implemented in respective software or hardware elements, or any kind of combination thereof.

BRIEF DESCRIPTION OF DRAWINGS

The above described aspects and implementation forms of the present invention will be explained in the following description of specific embodiments in relation to the enclosed drawings, in which Fig. 1 shows in (a) a conventional system with non-replaceable RUs, and shows in (b) a conventional system with replaceable RRUs.

Fig. 2 explains how lateral wind-load acts on an antenna provided in a conventional system with replaceable RRUs.

Fig. 3 shows an antenna holder and an RRU holder according respectively to embodiments of the present invention.

Fig. 4 shows a first mounting step of a method according to an embodiment of the present invention.

Fig. 5 shows a second mounting step of a method according to an embodiment of the present invention. Fig. 6 shows a third and a fourth mounting step of a method according to an embodiment of the present invention.

Fig. 7 shows a fifth mounting step of a method according to an embodiment of the present invention.

DETAILED DESCRIPTION OF EMBODIMENTS

Fig. 3 shows an antenna holder 301 according to an embodiment of the present invention. Fig. 3 also shows a RRU holder 302 according to an embodiment of the present invention. The antenna holder 301 is configured to engage with the RRU holder 302 and vise versa. The antenna holder 301 and the RRU holder 302 form together an attachment system 300 according to an embodiment of the present invention. The antenna holder 301 comprises at least a guiding part 305 and a receiving part 304. The RRU holder 302 comprises at least a protruding part 307. The guiding part 305 of the antenna holder 301 is configured to receive the protruding part 307 of the RRU holder 302, and to guide the protruding part 307 to the receiving part 304. The receiving part 304 is further configured to receive the protruding part 307, so that the antenna holder 301 and the RRU holder 302 can engage with another in an engagement position.

The guiding part 305 of the antenna holder 301 preferably comprises or is a notch. The protruding part 307 of the RRU holder 302 may be accordingly configured and dimensioned to be introduced in a sliding manner into the notch 305. In this case, the receiving part 304 of the antenna holder 301 is preferably a cut-out in the notch 305. The cut-out is designed and dimensioned to receive the protruding part 307 of the RRU holder 302, preferably in a fitting manner.

Preferably, also the antenna holder 301 comprises a protruding part 303, which preferably protrudes from the guiding part 305. At the same time, preferably also the RRU holder 302 comprises a receiving part 308. In this case, the protruding part 303 of the antenna holder 301 is configured to intrude into the receiving part 308 of the RRU holder 302 in the engagement position of the two holders 301 and 302. That means, when the protruding part 307 is received in the receiving part 304, the protruding part 303 can be received in the receiving part 308, given that the two holders are aligned with another in a certain way, preferably with their guiding parts.

Preferably, also the RRU holder 302 comprises a guiding part 309, which preferably is or comprises a notch, and which can grasp the guiding part 305 of the antenna holder 301 in the engagement position of the two holders 301 and 302, in order to provide a more secure connection, and to allow the RRU holder 302 to be engaged stably with the antenna holder 301 through the weight of the RRU. Preferably, the protruding part 307 extends from the guiding part 309.

Preferably, the antenna holder 301 has an attachment portion 310 for attaching it to an antenna. Preferably the RRU holder 302 has an attachment portion 311 for attaching it to a RRU. As shown in Fig. 3, the attachment portions 310 and 311 can be respectively designed as flat panels, which have for example openings for screws or bolts. However, any other suitable attachment portion is possible.

The antenna holder 301 and the RRU holder 302 are each preferably formed as an integral pieced. Preferably, each holder 301 and 302 is made of metal. However, also other materials may be used, as long as the material and design of the holders 301 and 302 is sufficient for holding the weight of at least one RRU. In the shown embodiments, the antenna holder 301 and the RRU holder 302 are designed differently, as shown in Fig.3. For instance, the RRU 302 holder may have a larger attachment portion 311 than the antenna holder. However, it is also possible to have identical antenna and RRU holders 301 and 302, in order to save production costs.

In a mounting method according to a basic embodiment of the present invention, the protruding part 307 of the RRU holder 302 is guided into and along the guiding part 305 ofthe antenna holder 301, until the receiving part 304 ofthe antenna holder 301 receives the protruding part 307 of the RRU holder 302.

The Figs. 4 to 7 show a mounting method according to a specific embodiment of the present invention, which extends the basic embodiment. In particular, Fig. 4 shows a first mounting step of the method, in which a RRU 402 including a RRU holder 302 (not shown) is lifted over the antenna holder 301 of an antenna 401, which is mounted by at least one bracket 405 to a mast 404. The lifting of the RRU 402 can be carried out, for example, by using a rope 403 or the like.

Fig. 5 shows a second mounting step of the method, wherein in the second mounting step the RRU 402 is lowered (see (b)), until the protruding part 307 of the RRU holder 302 is received by the guiding part 305 of the antenna holder 301 of the antenna 401 (as can be seen in (a) and (c)). Preferably, for lowering the RRU 402, the RRU 402 is roped down.

Fig. 6 shows a third mounting step of the method, in which the RRU 402 is lowered further (see (b)), until a guiding part 309 of the RRU holder 302 is horizontally aligned. Preferably, the guiding part 309 is at the same time aligned with the guiding part 305 of the antenna holder 301 (as can be seen in (a) and (c)).

Fig. 6 also shows a fourth mounting step of the method, in which the RRU 402 is moved horizontally against the antenna 401 (see (b)), whereby the protruding part 307 of the RRU holder 302 slides preferably horizontally along the guiding part 305 of the antenna holder 301 (as indicated by the arrow), until the protruding part 307 of the RRU holder

302 is received by the receiving part 304 of the antenna holder 301 (as can be seen in Fig. 7 (a) and (c)). At the same time, preferably the protruding part 303 of the antenna holder 301 intrudes the receiving part 308 of the RRU holder 302. Fig. 7 shows a fifth mounting step of the method, in which, after the protruding parts

303 and 307 have engaged with the receiving parts 308 and 304, respectively, and the guiding parts 305 and 309 of antenna holder 301 and RRU holder 302, respectively, have grasped each other (see (a)), the RRU 402 is released (see (b)), so that the RRU holder 302 falls into the engagement position with the antenna holder 301, and is stabilized by the weight of the RRU 402 (see (a) and (c)).

After carrying out the above-described five mounting steps, the RRU 401 is mounted securely to the antenna 402, without any further attachment means required. However, according to a further embodiment, after carrying out the described method steps, the RRU holder 302 and the antenna holder 301 can be further fixed using one or more fixing elements such as screws or bolts.

Furthermore, the mounting method, which employs a sliding mechanism and preferably lifting and moving of the RRU 402 by a rope, can be easily carried out by a single person. Moreover, the method requires less operating space between the mast 404 and the antenna 401, and thus the final arrangement is less challenged by wind- load torque, and is therefore less easily damaged. Additionally, even in case of damage, the RRU 402 can be easily replaced, because the method is easily revertible.

Specifically, for dismounting the RRU 402 from the antenna 401, the RRU 402 only needs to be lifted, for instance by rope, so that the protruding parts 303 and 307 disengage with the receiving parts 308 and 304, respectively, and then can be moved horizontally, for instance, in the opposite direction as it was moved horizontally for sliding it into the engagement position. Therefore, also for dismounting the RRU 402, only a single person is required.

The present invention has been described in conjunction with various embodiments as examples as well as implementations. However, other variations can be understood and effected by those persons skilled in the art and practicing the claimed invention, from the studies of the drawings, this disclosure and the independent claims. In the claims as well as in the description the word "comprising" does not exclude other elements or steps and the indefinite article "a" or "an" does not exclude a plurality. A single element or other unit may fulfill the functions of several entities or items recited in the claims. The mere fact that certain measures are recited in the mutual different dependent claims does not indicate that a combination of these measures cannot be used in an advantageous implementation.