AN ARRANGEMENT IN AN ELECTRONICS SYSTEM

Abstract: The present invention relates to a RF connector arrangement. A 90 degree hybrid circuit is applied at each side of the connector to divide a signal into two paths. If the connector is disconnected, signals reflected in each path will cancel each other since they are 180 degrees out of phase. This is useful, for instance, in base transceiver stations with empty transceiver slots since no reflection occurs in these slots even though no terminating circuit is used.

Description: AN -f-R-R-f-NGEMENT IN AN ELECTRONICS SYSTEM TECHNICAL FIELD OF THE INVENTION The present invention relates to a connector arrangement and a connector unit for an electronics system, preferably operating at radio frequency. DESCRIPTION OF RELATED ART A mobile radio base transceiver station normally comprises a number of transceivers, typically around ten to twenty units. Each transceiver unit performs transmission and reception of radio signals associated with a downlink channel and an uplink channel. By means of a combiner the transceiver units may share a common antenna unit. In order to achieve flexibility, the transceiver units are detachably connected to the other parts of the base transceiver system. A transceiver card slot may thus be empty. This allows transceiver units to be added or removed in order to increase or reduce the capacity of the system. It furthermore allows a defect transceiver unit to be quickly replaced, without necessarily interrupting transmission processes performed by other transceiver units. When a transceiver slot is empty, however, radio frequency signals travelling towards the connector of the slot will be reflected back towards the system, where they may cause disturbances. Therefore, it is a normal procedure to place a matching, terminating circuit in each empty slot. The terminating circuit substantially absorbs all incoming signals, at least in a relevant frequency band. Thus, reflections are avoided. The introduction of terminating circuits, however, is costly and sometimes cumbersome . The use of a terminating circuit thus, is not a favourable solution. Moreover, if a transceiver unit is replaced by a terminating unit when the base station is operating, reflections will still occur during a short time period, since disconnection and connection cannot normally be done simultaneously. The same is true if, for instance, a first transceiver unit, which may perhaps be defect, is replaced by a second transceiver unit. SUMMARY OF THE INVENTION In accordance with a first aspect of the invention an object is therefore to provide an arrangement in a radio frequency equipment for detachably connecting a first conductor, connected to one unit in the equipment, to a second conductor, connected to another unit in the equipment, with improved radio frequency performance. Another object is to provide a connector arrangement that is easy to use and inexpensive to build. These objects are met by a connector arrangement for detachably connecting a first conductor to a second conductor where the first conductor is connected to a port of a first hybrid element and the second conductor is connected to a port of a second hybrid element. Each of the hybrid elements are designed so that a signal inputted at the port from the conductor is split equally and transmitted to two other ports of the respective hybrid. The signal transmitted to one of these ports is phase shifted an odd multiple of 90 degrees more than the signal appearing at the other port. The same is true in the opposite direction, since the hybrid element is reciprocal. These four ports, respectively, are connected to connector elements. The connector elements of the first hybrid mates with the connector elements of the second hybrid in such a manner that a signal travelling from the first to the second conductor is split into signal components that are added in- phase at the second conductor. If the connector elements are disconnected and a signal is inputted from the first connector, signals reflected at the connector elements will return to the port of the conductor 180 degrees out of phase and therefore no reflected energy will reach the conductor. Instead, this energy is terminated in a resistive element in or close to the hybrid element. This technique results in a connector arrangement where no separate terminating circuits need to be used and where reflections nevertheless are completely avoided in the relevant frequency band. As seen from the first conductor the connector arrangement is matched regardless of whether the second conductor is connected or not. Preferably, the first and second hybrid elements are 90 degree hybrid circuits. This results in a simple connector arrangement with suitable bandwidth that may be realised by means of inexpensive standard components. It is also preferable if the first hybrid and/or the second hybrid element has fourth port connected to a resistive element terminating any signals reflected at the connector elements. This allows the reflected energy to be absorbed at a distance from the hybrid element. In a preferred embodiment the first or second hybrid element is devised as a microstrip branchline hybrid. This results in a cost effective arrangement that is relatively simple to manufacture. In another preferred embodiment the first or second hybrid element is devised as a stripline branchline hybrid. Such a circuit radiates very little energy to surrounding circuits. In yet another preferred embodiment the first or second hybrid element is devised as a waveguide hybrid. This allows the arrangement to be used at high frequencies and with low losses . In yet another preferred embodiment the first hybrid element is devised as a Wilkinson divider having a splitter input and two splitter outputs, wherein the splitter input is connected to the first port, a first splitter output is connected to a second port and the second splitter output is connected to a third port via a λ/4 phase shifting unit. Such an arrangement requires little space and presents very low losses as long as the connection is matched. In accordance with a second aspect of the invention an object is to provide a connector unit with improved radio frequency characteristics. This object is met by a connector unit for detachably connecting a conductor to a functional unit, involving a hybrid element with first, second and third ports. A radio frequency signal within a predetermined frequency band, inputted at the first port is outputted with substantially equal signal strength at the second port and at the third port. The signal outputted at the third port is phase shifted an odd multiple of 90 degrees more than the signal outputted at the second port when said conductor is connected to and matched with the functional unit. The first port is connected to the conductor, the second port is connected to a first connector element and the third port is connected to a second connector element. The first and second connector elements mates with connectors of said functional unit. This results in a connector unit automatically terminating reflections when it is disconnected. The connector unit is matched as seen from the conductor regardless of whether it is connected to another unit or not. The connector arrangement is the characterised as it appears from the characterising portions of claims 1-7. The connector unit is then characterised as it appears from the characterising portion of claim 8. DESCRIPTION OF THE DRAWINGS Figure 1 illustrates a number of transceiver units connected to a base station system in accordance with prior art. Figure 2 illustrates transceiver units connected to a base station system in accordance with the invention. Figure 3 illustrates a microstrip branchline design of a 90 degree hybrid circuit. Figure 4 illustrates, schematically, a Wilkinson divider devised as a 90 degree hybrid circuit. Figure 5 illustrates a waveguide design of a 90 degree hybrid circuit. DESCRIPTION OF PREFERRED EMBODIMENTS Figure 1 illustrates a number of transceiver units connected to a base station system in accordance with prior art. The transceiver units are coupled to a common combiner network 102 and may therefore share a common antenna unit 103, as is well known in the art. In this illustration the combiner network 102 is designed to accommodate seven transceiver units. Since only six units lOla-lOlf are needed one transceiver slot is instead provided with a terminating unit 104, connected via a connector arrangement 105. Figure 2 illustrates, schematically, two transceiver units 201a, 201b connected to a base station system 202 by means of connector arrangements in accordance with the invention. It should be noted that the scope of the invention is not limited to this particular application. A connector arrangement in accordance with the invention, as well as a connector unit suitable for such a connector arrangement, is useful at numerous RF applications where a conductor is detachably connected to a functional unit and where reflections should be avoided. Depicted is a situation wherein a signal is sent from a first conductor 203 situated in the base station system 202 to a second conductor 204 situated in a transceiver unit 201a. However, the connector arrangement 202 may be considered as completely reciprocal and thus functions similarly if the direction of transmission is reversed. The term conductor should in the scope of this invention be given a broad interpretation. A conductor is then generally a means for transporting electrical energy, such as a pair cable, a coaxial cable, a microstrip, a stripline or a waveguide . The first conductor 203 is then connected to a first port 205 of a first hybrid element 206. The signal thus applied is equally split and transmitted to second and third ports 207, 208 of the first hybrid element 206. Since the hybrid element in this case is a 90 degrees hybrid circuit, the signal appearing at the third port 208 of the hybrid element 206 will be phase shifted λ/4=90 degrees more, vis-a-vis the input signal, than the signal appearing at the second port 207. Then λ is the wavelength of the inputted signal, which should be within a frequency band for which the hybrid element 206 is designed. Though this is a preferred embodiment, other embodiments are conceivable, where the phase shift between the outputs is WO 00/79695 η PCT/SEOO/01281 another odd multiple of 90 degrees such as 270 degrees. This will, however, lead to reduced bandwidth. The second port 207 is connected to a first connector element 209, which mates with a third connector element 211, belonging to the a transceiver unit 201a. The third port 208 is connected to a second connector element 210, which similarly mates with a fourth connector element 212 belonging to the same transceiver unit 201a. A second hybrid element 213 is placed in the transceiver unit 201a. It has a first port 214 connected to the second conductor 204, a second port 215 connected to the fourth connector element 212 and a third port 216 connected to the third connector element 211. Signals inputted at the second and third ports 215, 216 will be added to each other at the first port 214. Before this occurs, however, they are phase shifted. The signal originating from the third port 216 is phase shifted 90 degrees more than the signal originating from the second port 212. Thus, a signal inputted at the first port 205 of the first hybrid element 206 is equally split into two signal components, which are transmitted over two separate branches and which are added in-phase at the first port 214 of the second hybrid element. A first resistive element 217 is connected to a fourth port 218 of the first hybrid element 206 and a second resistive element 219 is connected to a fourth port 220 of the second hybrid element 213. In this case, however, if impedances in the circuit are matched no energy will be terminated in the resistive elements 217, 219. As will be shown there are embodiments where such resistive elements are integrated into the hybrid, which results in a three-port hybrid. Depicted in figure 2 is also a case when a transceiver slot 221 is empty. Then a signal is inputted from a third conductor 222 to a first port 223 of a third hybrid element 224. The signal is equally split and transmitted to the second and third ports 225, 226, where it is fully reflected at the associated connector elements 227, 228. At the first port 223 these reflections are added out of phase, since the difference in phase between them is now 180 degrees. Therefore no reflected component is transmitted to the third conductor 222. At a fourth port 230, however, the reflected components are added in phase, and the reflected energy is therefore terminated in a resistive element 228 connected to this port. Figure 3 illustrates a microstrip branchline design of a 90 degree hybrid circuit 300. The circuit is then devised as an etched pattern on top of a dielectric medium. On the opposite side of this dielectric medium a ground plane is formed. This hybrid circuit 300 is reciprocal. For clarity reasons it is nevertheless useful to define one port 301 of the hybrid as the input port. If the circuit is utilised in a manner according to the invention a first output port 302 is connected to a first connector element (not shown) as mentioned above. Similarly a second output port 303 is connected to a second connector element (not shown) . An isolated port 304 should be connected via a resistive element 305 to ground. In order to operate in a matched manner the ports should have a width adjusted so that they have a characteristic impedance Z 0 , corresponding to the characteristic impedance of associated transmission lines. A first bridge element 306 interconnects the first and the second ports 301, 302 and a second bridge element 307 interconnects the third and fourth ports 303, 304. These elements should be somewhat wider so that their characteristic impedance is Z 0 /V2. They should have a length corresponding to λ/4, where λ is the wavelength of the signal that is to be transmitted. A third bridge element 308 interconnects the first and the fourth ports 301, 304 and a fourth bridge element 309 interconnects the third and second ports 303, 302. These elements should have a width so that their characteristic impedance is Z 0 . They should have a length corresponding to λ/4. If a signal with the wavelength λ is inputted at the input port 301 this signal appears on both outputs 302, 303. The signal outputted at the second output 303, however, is phase shifted λ/4 more than the signal outputted at the second output 302. Such a microstrip circuit is relatively simple to manufacture. It is also possible to produce a branchline circuit in stripline technique, which results in very little energy radiated from the circuit during operation. This involves among other things introducing an extra earth-plane in the circuit as is well known to the person skilled in the art . Figure 4 illustrates, schematically, a Wilkinson divider devised as a 90 degree hybrid circuit 400. This embodiments involves a splitter input port 401, a first splitter output port 402 and a second splitter output port 403. A delay element 404 is applied at the first output port 402, that phase-shifts signals passing therethrough 1/4 wavelength. An internal resistor 405 is connected between the branches of the divider in order to render the divider matched. When a Wilkinson divider is used in a connector arrangement in accordance with the invention this resistor 405 terminates all reflected energy when the connector elements are disconnected. Figure 5 illustrates a waveguide design of a 90 degree hybrid circuit 500. In order to facilitate the description of this embodiment, an opening is provided in the top of the hybrid. The hybrid involves an input port 501 , a first output port 502 and a second output port 503. In order to achieve an even energy distribution between the output ports, recesses 504, 505 are formed in the respective waveguides and the wall 506 between them involves an opening 507. A terminated port 508 is provided with a resistive element 509, absorbing any energy reflected at the outputs. The hybrid is also provided with a connector 510 at the output ports 502, 503. Although the present invention and its advantages have been described in detail, it should be understood that various changes, substitutions and alterations can be made therein without departing from the spirit and scope of the invention as defined by the appended claims. Other embodiments are conceivable, for instance, where the conductors used are coaxial cables. Other hybrid circuits such as Lange- couplers, which may be build in stripline or microstrip techniques, are known in the art and may be used in connection with the invention. The same applies for low frequency hybrids, constituted by discrete inductors and capacitances.

Claims: CLAIMS 1. A connector arrangement for detachably connecting a first conductor (203) to a second conductor (204), c h a r a c t e r i s e d in -a first hybrid element (206) having a first (205), a second (207) and a third port (208), wherein a radio frequency signal within a predetermined frequency band, inputted at said first port (205) is outputted with equal signal strength at said second port (207) and at said third port (208) and wherein the signal outputted at the third port (208) is phase shifted an odd multiple of 90 degrees more in relation to the inputted signal than the signal outputted at the second port (207); said first port(205) being connected to said first conductor (203), said second port(207) being connected to a first connector element (209) and said third port (208) being connected to a second connector element (210) ; -a second hybrid element (213) having a first (214), a second (216) and a third port (215), wherein radio frequency signals within a predetermined frequency band, inputted at said second and third ports (215, 216) are added and outputted at said first port (214) whereby the signal inputted at the second port (216) is phase shifted an odd multiple of 90 degrees more than the signal inputted at the third port (215) ; said first port (214) being connected to said second conductor (204), said second port (216) being connected to a third connector element (211) and said third port (215) being connected to a fourth connector element (212) ; where said first connector element (209) mates with said third connector element (211) and where said second connector element (210) mates with said fourth connector element (212 ) , so that a signal transmitted from the first to the second conductor is sent over two separate branches. 2. A connector arrangement as claimed in claim 1 c h a r a c t e r i s e d in that said first and second hybrid elements are 90 degree hybrid circuits. 3. A connector arrangement as claimed in claim 1 or 2 c h a r a c t e r i s e d in that said first hybrid element (206) has a fourth port (218) connected to a first resistive element (217) terminating any signals reflected at said first and second connector elements (209, 210) and/or in that said second hybrid element (213) has a fourth port (220) connected to a second resistive element (219) terminating any signals reflected at said third and fourth connector elements (211, 212). 4. A connector arrangement as claimed in claim 3 c h a r a c t e r i s e d in that said first or said second hybrid element is devised as a microstrip branchline hybrid. 5. A connector arrangement as claimed in claim 3 c h a r a c t e r i s e d in that said first or said second hybrid element is devised as a stripline branchline hybrid. 6. A connector arrangement as claimed in claim 3 c h a r a c t e r i s e d in that said first or said second hybrid element is devised as a waveguide hybrid. 7. A connector arrangement as claimed in claim 1 or 2 c h a r a c t e r i s e d in that said first hybrid element is devised as a Wilkinson divider having a splitter input and two splitter outputs, wherein the splitter input is connected to the first port, a first splitter output is connected to the second port and the second splitter output is connected to the third port via a λ/4 phase shifting unit . 8. A connector unit for detachably connecting a conductor to a functional unit, c h a r a c t e r i s e d in a hybrid element having a first, a second and a third port, wherein a radio frequency signal within a predetermined frequency band, inputted at said first port is outputted at said second port and at said third port and wherein the signal outputted at the third port is phase shifted an odd multiple of 90 degrees more than the signal outputted at the second port when said conductor is connected to and matched with said functional unit; said first port being connected to said first conductor, said second port being connected to a first connector element and said third port being connected to a second connector element, said first and second connector elements mating with connectors of said functional unit.

Inventors: OLSSON MAGNUS, OLSSON, MAGNUS
Applicants: ERICSSON TELEFON AB L M, OLSSON MAGNUS, OLSSON, MAGNUS, TELEFONAKTIEBOLAGET LM ERICSSON (PUBL)
Application year: 2000
Main classification: H04B1
IPC codes: H01P5, H03H11, H04B1