TRANSMITTER UNIT AND BASE STATION

Abstract: The present invention relates to a transmitter unit for transmitting radio frequency signals, the transmitter unit comprising: an input for receiving signals to be transmitted, signal processing means for transferring signals to be transmitted on a predetermined frequency level, and amplifier means (2) for amplifying and feeding signals to be transmitted to antenna means of the transmitter unit. For minimizing power losses, the antenna means comprise an antenna element (ANT) attached with an attachment means (3) to an amplifier (2) in the antenna means for forwarding radio signals fed by the amplifier.

Description: TRANSMITTER UNIT AND BASE STATION The invention relates to a transmitter unit for transmitting radio frequency signals, the transmitter unit comprising: an input for receiving signals to be transmitted, signal processing means for transferring the signals to be transmitted to a predetermined frequency channel, and amplifier means for amplifying and feeding the signals to be transmitted to antenna means of the transmitter unit. The invention further relates to a radio system base station comprising transmitter means and antenna means for transmitting radio signals to receiver units in the coverage area of the base station. The invention relates especially to the base station of a cellular radio system, although it can also be applied in other connections. In the following, the invention will be described with reference to the base station of a cellular radio system. In known base stations of cellular radio systems the base station is usually physically located at a distance from the antenna used by it, i.e. usually at the foot of the antenna mast. In such a known base station an output stage (the last amplifier stage) by which signals to be transmitted are amplified to a desired level is arranged inside the transmitters of the base station. The signals fed by the transmitters are then supplied to the antenna line, from where they pass through a combiner, a circulator element and an antenna cable to the antenna in the antenna mast, the antenna being composed of several antenna elements. In some cases the same signals are fed simultaneously to several antenna elements in the antenna mast. One significant problem relating to the known base station de- scribed above are losses occurring in the antenna line. Assuming the antenna mast comprises four antenna elements by which the same signals are transmitted simultaneously and that a power of 0.75 W is desired to said antenna elements, then a power of 3 W is required in the antenna mast. For accomplishing this, a power of 6 W has typically to be supplied from the base station to the antenna cable. To get an output power of 6 W from the base station a power of at least 12 W is usually needed before the combiner, but, in practice, because of losses caused by filters and cables, even higher powers, e.g. 15 W, are usually needed. To get an output power of 15 W from the transmitter of the base station, the power of the output stage of the transmitter must be con- siderably higher, e.g. 30 W. Thus, to get a power of 0.75 W to each antenna element in the above described known base station, an amplifier of about 30 W is typically required in the amplifier of the base station. In addition to causing a considerable waste of energy, the above losses also bring about a cooling problem. Power losses generally cause heating of the base station, and consequently, attention must be paid to cool the base station components at the planning stage. The object of the present invention is to solve the aforementioned problem and provide a method for minimizing power losses. This object is achieved by a transmitter of the invention, characterized in that the transmitter unit comprises branching means for feeding signals to be transmitted to several similar amplifiers, each comprising means for amplifying and feeding the signals to be transmitted to an amplifier-specific antenna element, and that at least one amplifier comprises a separate antenna element attached to it with attachment means for forwarding radio signals fed by the corresponding am- plifier. The invention also relates to a base station wherein the transmitter according to the invention can be utilized. The base station of the invention is characterized in that the base station comprises branching means for branching signals fed by a transmitter unit of the base station to at least two amplifi- ers which comprise amplifier-specific antenna elements for amplifying and forwarding signals to be transmitted simultaneously by said antenna elements, and that at least one of said amplifier-specific antenna elements is attached with attachment means to the amplifier for forwarding the signals fed by the amplifier. The invention is based on the idea that when signals to be transmitted are branched to at least two amplifiers which comprise amplifier-specific antenna elements for amplifying and forwarding signals to be transmitted simultaneously by at least two different antenna elements, the transmitter unit can utilize amplifiers with lower power, the amplifiers being also simpler and, often, more inexpensive. The known base station described above requires an about 30-W amplifier for supplying a power of 0.75 W to four antenna elements, whereas the solution of the invention enables the utilization of four about 2-W amplifiers for achieving the same transmission power (four amplifier-antenna elements). Consequently, power gain is significant, and, in addi- tion, the thermal power generated will be distributed among several components, whereby providing adequate cooling will not bring about problems. In addition, if an individual antenna element (e.g. a folded dipole) is directly fastened to the amplifier of the transmitter, preferably to the last output stage, and the output stage is allowed to feed signals directly to the antenna element without the use of separate transmission cables, a significantly better effi- ciency is achieved than in known solutions. Losses common in conventional solutions where a transmission-powered signal is being transferred via cables are thus avoided. In consequence of the loss reduction, as high an amplification as before is not required of the amplifier, but it can feed signals with a lower power level also resulting in less need for cooling. Thus, the most sig- nificant advantages of the solution of the invention are a better efficiency, less need for cooling, the possibility of using simpler and more inexpensive amplifiers, and savings in space and weight. When the transmitter of the invention is utilized, e.g. in the base station of a cellular radio system, the receiver unit corresponding to the trans- mitter unit can be implemented in a manner fully known per se, i.e. the base station can comprise an individual receiving antenna, the signals of which are applied via antenna cabling to a branching element, from where they are branched to each receiver unit of the base station. Alternatively, a corresponding amplifier-antenna element utilized at the transmitting side can also be utilized at the receiving side. In a preferred embodiment of the transmitter of the invention, an antenna element attached to an amplifier provides a cooling element of the transmitter unit, the attachment means being made of a heat conductive material, and the antenna element being designed to conduct thermal energy from the amplifier to the surroundings. Thus, no separate cooling fins, or the like, are required in connection with the amplifier, but the cooling fins can function both as signal conductors and as attachment means of the antenna element and thus conduct the thermal energy generated in the amplifier through the antenna element to the surroundings. In another preferred embodiment of the base station of the invention, the antenna means of the base station comprise antenna elements composed of conductive areas on the surface of a circuit board, amplifiers in the transmitter means of the base station being adapted directly on said circuit board in connection with the corresponding antenna element and attached by means of attachment means to said corresponding antenna element. This embodiment of the invention provides a very compact antenna element allow- ing a considerable part of several transmitters and receivers of the base station to be arranged on the same individual circuit board. The preferred embodiments of the transmitter and base station of the invention are disclosed in the attached dependent claims 2 to 4, and 6 to 11. The invention will be described in more detail by way of example by means of some preferred embodiments with reference to the attached figures, of which Figure 1 illustrates a first preferred embodiment of the transmitter of the invention, Figure 2 shows a block diagram of a preferred embodiment of the base station of the invention, and Figure 3 illustrates a second preferred embodiment of the transmitter of the invention. Figure 1 illustrates a first preferred embodiment of the transmitter of the invention. Figure 1 shows only the last output stage 2 of the transmitter and a transmitter antenna ANT. The antenna element ANT is attached by attachment means 3 to an amplifier 2 of the transmitter, the antenna element ANT and the amplifier 2 constituting an integrated amplifier-antenna element 1. The attachment means 3 constitute cooling fins of the amplifier 2, and they also function as antenna conductors. Consequently, the attachment means are made of a material with good heat (and electrical) conductivity. Thus, the thermal energy from the amplifier 2 can be conducted through the attachment means to the antenna element ANT which is also the main cooling element of the amplifier. Thus, the antenna element is designed to conduct the thermal energy transmitted from the amplifier to the surroundings. Primarily this means that the surface area of the antenna element is sufficient in proportion to the thermal energy generated by the amplifier 2 being used. Since the antenna element ANT is fastened directly to the amplifier 2 in the case in Figure 1 , the transmitter does not require a special antenna cable for forwarding a transmission-powered signal from the amplifier 2 to the antenna ANT. Consequently, losses commonly caused by antenna cabling are avoided. The amplifier 2 is preferably a very linear amplifier not necessarily requiring a filter in connection with it, but the signals from its output can be fed directly to the antenna element. If, however, the properties of the amplifier require a filter to be used in connection with it, said filter can be preferably integrated with the antenna element or the amplifier (not shown in Figure 1). Figure 2 shows a block diagram of a preferred embodiment of the base station of the invention. The base station in Figure 2 can be e.g. a base station of the GSM cellular radio system (Groupe Special Mobile). Figure 2 shows only one transmitter/receiver pair of the base station, although the base station can naturally also include other transmitters/receivers. The base station in Figure 2 comprises four amplifier-antenna ele- ments 1 as in Figure 1 utilized for transmitting the same radio signals. The signals to be transmitted are fed to an input 6 of the transmitter in Figure 2, from where they are in transferred to a predetermined frequency channel by a mixer 4 and a local oscillator in block 11. Next, the RF signals to be transmitted are amplified by a pre-amplifier 7 and fed to a branching element 8. The branching element 8 distributes the signals to be transmitted to four transmission branches, each comprising a phase processing element 9. The phase processing elements 9 provide a phase deviation between the signals to be transmitted through different branches, the phase deviation enabling the antenna pattern of the transmitter to be adjusted in a desired manner. In other words, by adjusting the phase processing elements, the maximum and minimum points of the field provided by the transmitter can be adjusted in a desired manner. The RF signals to be transmitted from the outputs of the phase processing element 9 are fed to the amplifier-antenna elements 1 where they are first amplified to the desired power level and then forwarded. The amplifier- antenna elements 1 in Figure 2 may have a mutually different amplification, which helps to provide the desired antenna pattern. By amplifying the signals to be transmitted to the desired power level immediately before they are fed to the antenna elements, a transmitter with significantly better efficiency will be obtained than if the last amplifier would be located e.g. before the branching element 8. Loss reductions also enable the transmitter to use amplifiers with lower amplification, and to produce less thermal energy than before. The base station in Figure 2 also comprises four antenna-receiver elements 13 for receiving radio signals. Said antenna-receiver elements 13 correspond to the solution presented in Figure 1 in other respects except that in reception, an amplifier 19 is naturally used for the amplification of the signals from an antenna 18 before they are fed to phase processing elements 14. The phase processing elements 14 enable the adjustment of the pattern of a receiving radiation lobe in such a way that a phase deviation will be provided for the signals received by different reception branches. Signals from the outputs of the phase processing elements 14 are summed with a combiner element 15, after which the summed signal is conducted to signal processing means which, in the case of Figure 2, comprise a mixer 16 and an oscillator 17. Figure 3 illustrates a second preferred embodiment of the transmitter of the invention. In the case in Figure 3, the antenna means of the transmitter comprise antenna elements ANT, e.g. printed folded dipoles, made of a conductive film and arranged on the surface of a circuit board 12, or the like. Figure 3 shows six such antenna elements ANT. On the surface of the circuit board 12 in connection with each antenna element ANT, the last output stage i.e. an amplifier 2' corresponding to that antenna element is adapted. Attachment means which connect the antenna elements and amplifiers together are, thus, composed of connectors or connections by which the amplifiers are attached onto the circuit board. The components adapted on the circuit board 12 in Figure 3 are connected to block 10 (cf. Figure 2) comprising for instance a branching element, a pre-amplifier, a phase processing element 9 etc. When required, the components of block 10 can also be adapted on the circuit board 12. In case filters are required in connection with the amplifiers 2', the filters can, corre- spondingly, be adapted on the circuit board in connection with each amplifier and/or antenna element. Consequently, most components of the transmitter unit have been mounted on the same base. The surface area of the antenna elements ANT, or even the surface area of the entire circuit board 12 can function as a cooling element, whereby suitable cooling of the transmitter can be ensured by increasing the surface area of the circuit board or the antenna elements. The solution in Figure 3 provides a very compact base station with a construction suitable for indoor installation. The antenna means of the base station can consist of e.g. a board which can be hung on the wall and on which a significant part of the transmitter components can be arranged, and which, when required, can be flexible. Naturally, it is also possible to arrange receiver components on the same board. Consequently, there are fewer components to be installed in the case of the actual base station, whereby a less space taking case will be provided. Another advantage of such a widely spread antenna curtain is also that the field strength remains low even very close to the antenna, whereby it is very suitable for indoor use. It is obvious that the above description and the related figures are only intended to illustrate the present invention. A variety of modifications and variations will be apparent to those skilled in the art without deviating from the scope and spirit of the invention disclosed in the appended claims.

Claims: CLAIMS: 1. A transmitter unit for transmitting radio frequency signals, the transmitter unit comprising: an input (6) for receiving signals to be transmitted, signal processing means (4, 5) for transferring the signals to be transmitted to a predetermined frequency channel, and amplifier means (2, 2", 7) for amplifying and feeding the signals to be transmitted to antenna means of the transmitter unit, characterized in that the transmitter unit comprises branching means (8) for feeding the signals to be transmitted to several similar amplifiers (2, 2') each comprising means for amplifying and feeding the signals to be transmitted to an amplifier- specific antenna element (ANT, ANT), and that at least one amplifier (2, 2') comprises a separate antenna element (ANT, ANT) attached to it with attachment means for forwarding radio signals fed by the corresponding amplifier. 2. A transmitter unit as claimed in claim 1, characterized in that the transmitter unit comprises phase processing means (9) for processing the signals to be fed to said several amplifiers (2, 2') in order to provide a phase deviation between the signals to be fed to different amplifiers. 3. A transmitter unit as claimed in any one of claims 1 to 2, c h a r - acterized in that filter means are integrated with the amplifier means (2, 2') and/or the antenna element for filtering signals to be transmitted before forwarding them by the antenna element (ANT, ANT). 4. A transmitter unit as claimed in any one of the preceding claims, characterized in that the transmitter unit has a cooling element which consists of the antenna element (ANT, ANT) of said at least one amplifier to which the antenna element is attached by attachment means (3) being made of a heat conductive material and the antenna element being designed to conduct thermal energy from the amplifier to the surroundings. 5. A radio system base station comprising transmitter means and antenna means (ANT, ANT) for transmitting radio signals to receiver units located in the coverage area of the base station, characterized in that the base station comprises branching means (8) for branching signals fed by a transmitter unit of the base station to at least two amplifiers (2, 2') which comprise amplifier-specific (2, 2') antenna elements (ANT, ANT) for amplifying and forwarding the signals to be transmitted simultaneously by said antenna elements, and that at least one of said amplifier-specific antenna elements (ANT, ANT) is attached with attachment means (3) to the amplifier (2, 2') for forwarding the signals fed by the amplifier. 6. A base station as claimed in claim 5, characterized in that filter means have been integrated with said at least one antenna element (ANT, ANT') and/or amplifier (2, 2') for filtering signals to be transmitted before they are forwarded by the antenna element (ANT, ANT). 7. A base station as claimed in claim 5 or 6, characterized in that the base station comprises phase processing means (9) for processing signals fed by the branching means (8) to the different amplifiers (2, 2') in order to provide a phase shift between signals transmitted by the different antenna elements (ANT, ANT). 8. A base station as claimed in any one of claims 5 to 7, characterized in that the antenna means of the base station comprise antenna elements (ANT) composed of conductive areas on the surface of a circuit board (12), and the amplifiers (2') in the transmitter means of the base station have been adapted on said circuit board (12) in connection with the antenna element (ANT) corresponding to the amplifiers, the amplifiers being attached with attachment means to said antenna element corresponding to the amplifier. 9. A base station as claimed in any one of claims 5 to 8 comprising a receiver unit for receiving radio frequency signals, the receiver unit comprising: antenna means (13) for receiving radio signals, amplifier means (13) for amplifying and forwarding signals received by the antenna means, and signal processing means (16-17) for processing amplified signals in a predetermined manner, characterized in that the antenna means comprise an antenna element (18) attached by attachment means to an amplifier (19) in the amplifier means for amplifying and forwarding signals received by the antenna element (18) to the signal processing means (16-17). 10. A base station as claimed in claim 9, characterized in that the amplifier means comprise several similar amplifiers (19), an amplifier- specific antenna element (18) is fastened to each amplifier for amplifying and forwarding signals received by each antenna element to the signal processing means (16-17), and that the base station comprises summing means (15) for combining and forwarding signals fed by the different amplifiers (19) to the signal processing means (16-17). 11. A base station as claimed in claim 10, c h a r a c t e r i z e d in that the base station comprises phase processing means (14) for providing a phase shift between signals received from different amplifiers before feeding the signals to the summing means (15).

Inventors: AHOSOLA RAIMO, AHOSOLA, RAIMO
Applicants: AHOSOLA RAIMO, NOKIA TELECOMMUNICATIONS OY, AHOSOLA, RAIMO
Application year: 1997
Main classification: H04B1
IPC codes: H01Q9, H01Q21, H01Q23, H04B1, H04Q7