Abstract:
A multicarrier linear RF power amplifier incorporating an improved signal splitter and an improved signal combiner is disclosed. The amplifier comprises a plurality of wedge-shaped amplifier modules. When such modules are radially disposed and abutted against one another, the inwardly facing edges of the modules collectively define a central or axially-located opening. An improved signal splitter, signal combiner, or dual splitter/combiner is advantageously disposed in the axially-located opening. The signal splitter or signal combiner is a conductor arrangement comprising a plurality of equal length conductors radially disposed on a dielectric substrate. The conductor arrangement is advantageously disposed within a suitably-configured housing. The housing is disposed within the axially-located opening.

Description:
FIELD OF THE INVENTION 
     The present invention relates generally to telecommnunications. More particularly, the present invention relates to an a combiner-splitter for use in conjunction with a multicarrier RF amplifier. 
     BACKGROUND OF THE INVENTION 
     FIG. 1 depicts a schematic diagram of a portion of a typical wireless communications system in the prior art. Such a system provides wireless telecommunications service to a number of wireless terminals (e.g. wireless terminals 101-1 through 103-1) that are situated within a geographic region. 
     The heart of a typical wireless telecommunications system is Wireless Switching Center (&#34;WSC&#34;) 120, which may also be known as a Mobile Switching Center (&#34;MSC&#34;) or a Mobile Telephone Switching Office (&#34;MTSO&#34;). Typically, WSC 120 is commented to a plurality of base stations (e.g., base stations 103-1 through 103-5) that are dispersed throughout the geographic area serviced by the system. Additionally, WSC 120 is connected to local-and toll-offices (e.g., local-office 130, local-office 138 and toll-office 140). WSC 120 is responsible for, among other things, establishing and maintaining calls between wireless terminals and between a wireless terminal and a wireline terminal, which is connected to the system via the local and/or long-distance networks. 
     The geographic area serviced by a wireless telecommunications system is partitioned into a number of spatially-distinct areas called &#34;cells.&#34; As depicted in FIG. 1, each cell is schematically represented by a hexagon; in practice, however, each cell usually has an irreguilar shape that depends on terrain topography. Typically, each cell contains a base station, which comprises radios and antennae that the base station uses to communicate with the wireless terminals in that cell and also comprises the transmission equipment that the base station uses to communicate with WSC 120. 
     For example, when wireless terminal 101-1 desires to communicate with wireless terminal 101-2, wireless terminal 101-1 transmits the desired information to base station 103-1, which relays the information to WSC 120. Upon receiving the information, and with the knowledge that it is intended for wireless terminal 101-2, WSC 120 then returns the information back to base station 103-1, which relays the information, via radio, to wireless terminal 101-2. 
     The manner in which the information received from WSC 120 is processed within base station 103-1 is depicted in FIG. 2. Such information is transmitted from WSC 120 to base station 103-1 as multiplexed signal 202. Such a signal comprises a multiplicity of constituent signals, which, in the context of present discussion, are RF carrier signals. Each one of such constituent RF carrier signals differs from all other of such signals in accordance with a particular multiplexing scheme used (e.g., time-division-multiplexing, frequency-division-multiplexing, code-division-multiplexing, etc.). 
     When received by base station 103-1, signal 202 is de-multiplexed into its constituent RF carrier signals 202 i ,i=l,N in demultiplexer 204. Each one of the N constituent RF carrier signals is routed to a corresponding one of N radios 206 i ,i=l,N. Each radio 206 is operable to modulate a message signal onto the one constituent signal 202 i  that it receives in accordance with a particular modulation scheme (e.g., time-division-multiple-access, code-division-multiple-access, etc.). A modulated RF carrier signal 208 i  generated by each radio is delivered to summing device 210 wherein such modulated carrier signals are summed to generate multicarrier RF signal 212. 
     As the modulated RF carrier signals 208 i  generated by the radios are very low power signals, multicarrier RF signal 212 must be routed to amplifier 214, typically a feedforward multicarrier linear RF power amplifier (&#34;FMLRF power amp&#34;), to boost signal strength for transmission from the base station to various wireless terminals, such as 101-2. A FMLRF power amp can usually amplify all RF carrier signals in use within a given cell. The design and operation of such amplifiers are familiar to those skilled in the art. See, for example. U.S. Pat. No. 5,304,945, incorporated by reference herein. 
     Within FMLRF power amp 214, multicarrier RF signal 212 is divided by splitter 216 into J equal power signals 212 i  and delivered to J identical amplifier modules 218 i . Each one of the signals 212 i  is amplified to a set output power in the amplifier modules. J amplified signals 220 i  from the amplifier modules are combined to form modulated multicarrier RF signal 224 in combiner 222. The signal 224 is routed to antenna 226 for transmission, such as to wireless terminal 101-2. 
     Ever-increasing wireless traffic results in a need to increase the calling capacity of such wireless systems. One way to increase calling capacity is to increase the number of cells within a given geographic area. Such an increase results in smaller cells, and, of course, more base stations. Increasing the number of cells results in a decrease in signal transmission power requirements (due to a smaller coverage area), thus enabling use of smaller, lower power FMLRF power amps. 
     Past splitter and combiner designs for conventional high power FMLRF power amps have utilized cavities of a specific size and geometry well-matched to such larger FMLRF power amps. With the decreasing size requirements of such power amps, a new more compact design for a power splitter and power combiner are needed. 
     SUMMARY OF THE INVENTION 
     A multicarrier linear RF power amplifier incorporating an improved signal splitter and an improved signal combiner is disclosed. The amplifier comprises a plurality of wedge-shaped amplifier modules. When such modules are radially disposed and abutted against one another, the inwardly facing edges of the modules collectively define a central or axially-located opening. An improved signal splitter, signal combiner, or dual splitter/combiner in accordance with an illustrative embodiment of the present invention is advantageously disposed in the axially-located opening. 
     In some embodiments, a signal splitter or signal combiner is a conductor arrangement comprising a plurality of equal length conductors radially disposed on a suitable dielectric surface. The conductor arrangement is advantageously disposed within a suitably-configured housing. The housing is disposed within the axially-located opening. 
     Each conductor within the arrangement has a length λ/4, where λ is the center frequency of the multicarrier signal. The impedance of each conductor is given by: Z=Z o  n 1/2 , where Z o  is the desired impedance of the lines external to the splitter or the combiner, typically 50 ohms, and n is the number of conductors in the plurality. 
     In some embodiments, each conductor is advantageously &#34;suspended&#34; within the housing, thereby minimizing signal loss. In some embodiments, that is achieved by locating the conductors in cylindrical cavities formed within the interior of the housing. Each conductor is &#34;suspended&#34; within the cavity on the dielectric surface. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 depicts a schematic diagram of a prior art wireless telecommunication system; 
     FIG. 2 depicts a simplified diagram of the manner in which a multiplexed signal received from a wireless switching center is processed in a prior art base station; 
     FIG. 3 depicts a top view of a portion of a multicarrier linear amplifier in accordance with an illustrative embodiment of the present invention; 
     FIG. 4 depicts a perspective view of the portion of the multicarrier linear amplifier of FIG. 3 with several amplification modules removed to show a splitter housing and a combiner housing; 
     FIG. 5 depicts a conductor arrangement in accordance with an illustrative embodiment of the present invention, 
     FIG. 6 depicts grooves formed in plates of a combiner or splitter housing in accordance with an illustrative embodiment of the present invention; 
     FIG. 7 depicts a perspective view of a combiner or splitter housing incorporating cylindrical cavities formed by abutting the grooved plates of FIG. 6; and 
     FIG. 8 depicts a dual splitter/combiner in accordance with an illustrative embodiment of the present invention. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     FIG. 3 is a top view of a portion of illustrative multicarrier linear amplifier 314 showing eight wedged-shaped, equal-sized, radially arranged amplifier modules 318 1  -318 8 . The amplifier modules 318 i  are suitably dimensioned so that when disposed in abutting relation as shown in FIG. 3, octagonally-shaped perimeter 322 is defined, collectively, by outwardly-facing edge 320 of each module. Additionally, when arranged as shown in FIG. 3, octagonally-shaped region 326 is defined, collectively, by inwardly-facing edge 324 of each module. 
     FIG. 4, which depicts a perspective view of the FIG. 3 (with several amplifier modules removed for clarity of illustration), shows splitter housing 416 and combiner housing 422 advantageously axially aligned within region 326 formed by the amplifier modules 318 i . Positioning a signal splitter, signal combiner, or both, in such manner is known in the art. When such devices are so aligned, equal length signal paths are readily obtained for each of i unamplified &#34;split&#34; signals traveling from the splitter to each of n amplifier modules, and for each of n amplified signals traveling from each amplifier module to the combiner. Such equal length signal paths are required to maintain phase relations between each of the n unamplified signals generated by the splitter and each of the n amplified signals delivered to the combiner. 
     Splitter housing 416 includes axially-aligned port 430 for receiving a low power multicarrier RF signal from a summer (See FIG. 2). Combiner housing 422 likewise includes axially-aligned port 432 to which an amplified multicarrier RF signal is delivered. Splitter housing 416 further includes eight output ports (not shown) for delivering each one of the eight split signals to one of the eight amplifier modules 318 i . Likewise, combiner housing 422 includes eight input ports (not shown) for receiving each one of eight amplified signals from the eight amplifier modules. Each amplifier module 318 i  has an input port and an output port (not shown) for receiving and delivering respective unamplified and amplified signals. The eight output ports on splitter housing 416 and the eight input ports on amplifier modules 318 i  are disposed in a uniform manner so that the path length for each of the eight split signals are identical. The eight input ports on combiner housing 422 and the eight output ports on the amplifier modules are arranged to similar effect. 
     FIG. 5 depicts a conductor arrangement 500 in accordance with an illustrative embodiment of the present invention suitable for functioning as a splitter or combiner. Such a conductor arrangement is located within splitter and combiner housings 416, 422. Eight conductors 504 1  -504 8  having the same length are equiangularly disposed in radial fashion on insulating surface 502. In some embodiments, the insulating surface 502 is a dielectric material. The length,l, of each conductors 504 i  is λ/4, where λ is the center frequency of multicarrier signal being processed. 
     The impedance of the lines external to the splitter or combiner is typically 50 ohms. To achieve impedance match, the impedance of each conductor 504 i  must be: 
     
         Z=Z.sub.o n.sup.1/2,                                       [1] 
    
     where: Z o  is 50 ohms and n is the number of conductors. For example, if there are eight conductors, then the impedance of each conductor 504 i  is 50(8) 1/2  =141 ohms. It is known to those skilled in the art how to design a conductor to have a specific impedance (e.g., 141 ohms) by appropriately selecting line width, dielectric, and the like. 
     To minimize signal loss, each conductor 504 i  is advantageously &#34;suspended&#34; within housings 416, 422. In some embodiments that may be accomplished by forming semicircularly-shaped grooves 619 and 622 within respective upper and lower portions 618 (FIG. 6a) and 621 (FIG. 6b) of illustrative splitter or combiner housing 620. FIG. 7 depicts upper and lower portions 618, 621 of housing 620 joined. Conductor arrangement 500 is disposed between the joined portions. Conductors 504 i  are &#34;suspended&#34; on a dielectric surface, such as is used for forming printed circuit boards, within cylindrical cavities 724. Note that for such a suspended conductor, a dielectric constant is estimated that accounts for the fact that there is dielectric material surrounded by air. 
     In the illustrative embodiment depicted in FIGS. 3-5, the multicarrier linear RF amplifier 314 was assumed to be comprised of eight amplifier modules. It should be appreciated that in other embodiments for other applications such an amplifier may be comprised of other numbers of amplifier modules. If a different number of amplifier modules is used, splitter and combiner housings 416, 422 (FIG. 4) will typically have a different shape consistent with such different number of modules. And, of course, the number of conductors will change directly with the number of amplifier modules. For example, if six amplifier modules are used, the region 326 (FIG. 3) will typically have a hexagonally-shaped perimeter such that the splitter and combiner housings are advantageously hexagonally-shaped. Moreover, if six amplifier modules are used, then six conductors should be used. 
     In the illustrative embodiments described above, the splitter and the combiner were disposed in separate housings. In other embodiments, the splitter and combiner are advantageously disposed in a single housing. Such a dual splitter/combiner requires two separator conductor arrangements, one to function as a splitter, the other as the combiner. FIG. 8 depicts a perspective view of a dual splitter/combiner 800 including three-piece housing 820 and first and second conductor arrangements 802. 804 in accordance with the present invention. One of the conductor arrangements functions as a splitter, and the other conductor arrangement functions as a combiner. It should be understood that such functionality is determined based on the way a conductor arrangement is integrated with the rest of the amplifier. That is, if a signal is delivered to the center of a conductor arrangement, it will functions as a splitter; if signals are delivered to the end of each conductor of the arrangement, the arrangement will function as a combiner. Each of the conductor arrangements includes a number, n, of conductors (not shown). As previously described, the particular number, n, of conductors in the conductor arrangements is dictated by the number of amplifier modules. 
     Three piece housing 820 comprises lower plate 822, middle plate 826 and upper plate 832. Upper surface 822b of lower plate 822 advantageously includes n semicircularly-shaped grooves 824, one for each conductor 802 i  of first conductor arrangement 802. Lower surface 826a of middle plate 826 advantageously includes n semicircularly-shaped grooves 828. Grooves 824 in lower plate 822 and grooves 828 on lower surface 826a of middle plate 826 are complimentarily located relative to one another so that when the lower and middle plates are placed in abutting relation, grooves 824 and 828 align forming a first group of n cylindrical cavities 840 for receiving a like number n of conductors from first conductor arrangement 802. 
     Upper surface 826b of middle plate 826 includes n semicircularly-shaped grooves 830. And, lower surface 832a of upper plate 832 includes n semicircularly-shaped grooves 834. When upper plate 832 and middle plate 826 are placed in abutting relation, grooves 830 and 834 align forming a second group of n cylindrical cavities 842 for receiving the n conductors from second conductor arrangement 804. The middle plate advantageously provides shielding between first conductor arrangement 802 and second conductor arrangement 804. 
     In the dual splitter/combiner 800 depicted in FIG. 8, grooves 824 in the lower plate and grooves 828 in the lower surface of the middle plate are advantageously offset from grooves 830 in the upper surface of the middle plate and grooves 832 of the upper plate. Such an offset results in thinner plates and results in a natural offset between a first set of ports/interfaces (required for electrical connection between the conductor arrangement functioning as a splitter and the amplifier modules) and a second set of ports/interfaces (required for electrical connection between the amplifier modules and the conductor arrangement functioning as a combiner). 
     The unamplified multicarrier RF signal is delivered, via axially-aligned port 836 through upper plate 832 to one of the conductor arrangements. Due to the equal signal path lengths between the center of the conductor arrangement and the input of each amplifier module, the multicarrier RF signal is split into n equal power signals traveling along the n conductors. The amplified signals returning from the amplifier modules are delivered to the conductors in the other conductor arrangement, and are combined into a single amplified multicarrier RF signal at the center of that conductor arrangement. The amplified multicarrier RF signal leaves the combiner through an axially-aligned port (not shown) extending through bottom plate 822. It should be understood that the configuration of the splitter/combiner can be reversed, wherein the unamplified input is received at the port in the bottom plate and the amplified output is delivered to port 836 through the top plate. 
     Although specific embodiments of this invention have been shown and described herein, it is to be understood that these embodiments are merely illustrative of the many possible specific arrangements that can be devised in application of the principles of the invention. Numerous and varied other arrangements can be devised in accordance with these principles by those of ordinary skill in the art without departing from the scope and spirit of the invention. It is therefore intended that such other arrangements be included within the scope of the following claims and their equivalents.