MXPA99006157A - Method for integrating antennas in a distributed antenna system - Google Patents

Abstract

A method and arrangement for integrating antennas in a distributed antenna system. A remote RF unit in a distributed antenna system includes a substantially weatherproof housing, and multiple directional patch antennas are mounted on one or more surfaces of the housing. The antennas are preferably mounted flush with the surfaces of the housing, and can be easily made weatherproof by covering the antennas with radomes. The antenna are integrated by circuitry contained within the weatherproof housing, which includes RF combining circuits and RF dividing circuits.

Description

METHOD FOR INTEGRATING ANTENAS IN A DISTRIBUTED ANTENNA SYSTEM Field of the invention The present invention relates generally to transmission systems employing distributed antennas. More particularly, the present invention focuses on a method and arrangement for integrating antennas into a distributed antenna system. BACKGROUND OF THE INVENTION Referring now to Figure 1, an exemplary distributed antenna system is shown. Said system can be used, for example, to distribute wireless carrier signals to and from remote locations through the use of a cable television transmission network. The system includes a central distribution unit 10 and a plurality of remote RF units 12. The remote units 12 perform an RF signal processing and associate with radiation elements (antenna) to propagate the processed signals. Preferably, the system is designed in such a way that each antenna provides an efficient coverage to a desired coverage area, without coverage gaps and without splicing (i.e. causing interference) with neighboring coverage areas. To obtain a sufficient antenna gain and a sufficient coverage area in a typical system of distributed antennas, an external element, such as a monopoly or dipolio antenna, is provided in each RF unit. Such external ones are typically fed through a coaxial cable. Exemplary remote units having external antennas 14 are illustrated in Figures 2A-B. Remote RF units are typically placed in public and / or external locations. Due to their locations, environmental factors such as rain, ice, and wind are important considerations in the design of a unit. For units located in public areas, aesthetic considerations are also important. Since external antennas in conventional units on out of the unit, are subjected to severe environmental conditions and are generally considered as aesthetically undesirable. In addition, dipole and monopole antennas generally have a limited azimuthal directivity. Accordingly, their propagation paths are not easily controllable to provide efficient coverage in a desired area. Thus, in distributed antenna systems (systems made from several units connected to a central combiner), the remote units, preferably: a) provide coverage in a desired area, without coverage gaps or interference with neighboring coverage areas; b) are weatherproof; c) they are aesthetic; and d) they are integrated efficiently. As described above, known remote units employ external dipole or monopole antennas connected to a coaxial cable. Such remote units do not meet any of the aforementioned criteria. Accordingly, it would be desirable for a remote unit in a distributed antenna system to efficiently provide coverage in a desired coverage area, without coverage gaps or interference with neighboring coverage areas. It would also be desirable for a remote unit to have weather resistance characteristics, and for a remote unit to take aesthetic considerations into account. It would also be desirable for a remote unit to have efficiently integrated antennas. SUMMARY OF THE INVENTION In order to overcome the aforementioned problems, and to provide other advantages, the present invention offers a method and arrangement for integrating several antennas into a distributed array of antennas. In accordance with the method of the present invention, a plurality of antennas in a distributed antenna communication system are integrated by the provision of a plurality of antennas on one or more surfaces of a frame. Each antenna can provide signal propagation in a desired direction. The plurality of antennas inside the rack are integrated provide one or several internal RF combination circuits, and one or several internal RF division circuits. Each combining circuit combines signals received from two or more of the antennas, and each division circuit divides signals to propagate from a signal source into at least two signals for propagation from at least 2 antennas. In accordance with the arrangement of the present invention, the integrated antenna unit includes a plurality of antennas provided on one or more surfaces of a frame. Each antenna can provide a signal propagation in a desired direction. The array also includes one or several internal RF combining circuits and one or more internal RF division circuits. Each combining circuit combines signals received from two or more of the antennas and each division circuit divides signals to propagate from a signal source into at least two signals for propagation from at least two antennas. As a result of the method and arrangement in accordance with the present invention, a remote distributed antenna system unit can be developed which provides efficient coverage in one or more desired areas, which has a substantial resistance to weathering, which can be easily adapted to desired aesthetic criteria, and where the antennas are integrated efficiently. BRIEF DESCRIPTION OF THE DRAWINGS The features and advantages of the present invention can be more fully understood by reading the following detailed description of the preferred embodiments in combination with the accompanying drawings, where similar reference numerals refer to similar elements, and wherein: Figure 1 is a block diagram of an exemplary system of distributed antennas wherein the present invention can be implemented; Figures 2A-B show conventional remote RF units that can be employed in the system of Figure 1; Figure 3 is a diagram of a remote RF unit, covered by a frame, employing an exemplary method and arrangement for the integration of antennas in accordance with the present invention; Figures 4A-B are diagrams of the internal combiner and divider circuit, respectively, of the remote RF unit of Figure 3; Figures 5A-B are detailed circuit diagrams showing an exemplary implementation of the circuit of Figures 4A-B. Figures 6A-B are diagrams comparing the coverage areas of a conventional distributed antenna system with the coverage areas of a system incorporating the method and arrangement of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring now to Figure 3, a remote RF unit according to one embodiment of the present invention is shown. As shown, the remote RF unit 12 includes directional temporary connection antennas 14 mounted on each side of the RF unit 12. The directional temporary connection antennas 14 each face a desired direction of signal propagation. The temporary connection antennas can each provide, for example, 5dBi of gain in the vertical plane. Diversity reception antennas can be of opposite polarity (vertical and horizontal), and spatially separated to decrease the correlation. The remote RF unit 12 is preferably covered with a frame 16. The frame 16 can be mounted on a cable television cable 18, as shown, or it can be mounted on a telephone pole, wall, or on another structure . According to one embodiment of the present invention, the frame 16 can have a height of approximately 9 inches by a depth of 3 inches and a length of 20 inches, and the entire unit housed can have a weight of approximately 12 pounds. The frame can be made of cast aluminum coated or of other suitable materials. The antennas 14 are preferably mounted substantially flush with the surfaces of the frame 16.

As a result of the flush mounting of the antennas 14, the antennas can be covered with protective domes to provide environmental protection and to improve the aesthetic appearance of the unit 12. The antennas are integrated, as will be discussed below, to feed the antennas towards and from receiver and transmitter ports. Unit 12 is a remote RF unit that can be used in distributed antenna communication systems. For example, as a remote antenna interface that extracts a PCS carrier (personal communication system) from a downlink CATV network, and transmits the extracted carrier on an air interface. In an uplink path, the remote unit 12 receives two instances of diversities of a single PCS carrier, converts the received cases to different link CATV frequencies, and transmits the converted frequencies to a cable processor (not shown) in the cable television transmission network. With reference to Figures 4A-B, a circuit diagram of an exemplary device for integrating the antennas 14 is shown. Specifically, Figure 4A shows a diagram of an exemplary combiner circuit wherein two of the antennas 14 are connected to a summing circuit 18. In the circuit of Fig. 4A the antenna 14 receives signals, the received signals are combined in the summing circuit 18, and the output of the summing circuit is provided to a receiver port 20. Fig. 4B shows a diagram of an exemplary divider circuit wherein the output of a transmit port 22 is provided to a divider element 24, and the output of the divider element 24 is provided to two of the antennas 14. It will be observed in the combiner and divider devices of Figures 4A-B can be modified to allow the combination or division of more than two antennas. Referring now to FIGS. 5A-B, detailed circuit diagrams of exemplary implementations of the combiner / divider circuits of FIGS. 4A-B are shown. The circuit receiver position of Figure A will be written below. The receiver circuit shown includes receiving antennas RxAl, RxA2, RxBl, and RxB2 for receiving signals, and combiners 100A and 100B. The 100A and 100B combiners of this mode are Wil Inson combiners. It will be noted that other suitable passive combiner devices (eg quadrature hybrids, resistive ones, etc.) can be employed, according to considerations such as power handling, cost, space, etc. The outputs of the combiners 100A and 100B are fed to amplifiers 102A and 102B, respectively, and filters 104A and 104B, respectively. The filters 104A and 104B are, in accordance with a preferred embodiment of the present invention, bandpass filters having a bandwidth of about 1850-1910 MHz. The combined, filtered and amplified received signals are mixed with a signal of Oscl oscillator in mixers 106A and 106B as shown. The Oscl oscillator is preferably an oscillator operating at approximately 1580-1640 MHz. The modulated output is amplified in amplifiers 108A and 108B. The outputs of amplifiers 108A and 108B are filtered in bandpass filters 110A and 110B, respectively. The filters 110A and 110B, in accordance with a preferred embodiment, have a bandwidth of approximately 270 MHz. The output of the filters 110A is mixed with an oscillator signal Osc5 in the mixer 112A, and amplified by a gain amplifier. variable VGA2. The output of the filter 110B is mixed with an oscillator signal Osc6 in the modulator 112B and amplified by a variable gain amplifier VGA3. The gain of each of the variable gain amplifiers is preferably established based on the received signal strength indication RSSI of the received signal, in accordance with that determined with a circuit not illustrated. Certain implementations of such a scheme are described in the co-owned US patent application serial number 08/683, 187, "System and Method for Controlling the Level of Signals Output to Transmission Media in a Distributed Antenna Network" (system and method to control the output level of signals to transmission media in a network of distributed antennas), which is incorporated here for reference. The outputs of variable amplifiers 112A and 112B are combined in the combiner 114 and the combined signal is filtered in a low pass filter 116, and the filtered signal is supplied to a common cable 118 through combiner / splitter 200. The filter 116 it is preferably a filter that passes low signals of a frequency of about MHz. It will be noted that the separate receive paths for RxA and RxB provide a diversity of reception. The transmission portion of the circuit of Figure 5A will be described below. The signal to be transmitted supplies from a common cable 118 to the combiner / divider 200. The combiner / divider 200 divides the signal to be transmitted into two signals, a first signal that is filtered in a band pass filter 202. In accordance with In a preferred embodiment of the present invention, the bandpass filter 202 passes signals within a range of about 402 to 750 MHz. This signal is mixed with an oscillator signal Osc2 in the mixer 204. The modulated signal is amplified in the amplifier 206, and the amplified signal is filtered in a bandpass filter 208 having, in this example, a bandwidth of about 350 MHz. The filtered signal is mixed with the oscillator signal Oscl in the mixer 210, amplified by the variable gain amplifier VGA1 and by the amplifier 212. The amplified signal is provided to a connector 214, which generates a first RF detection signal and a second signal which is supplied to a Isolator 216. The first RF detection signal is used to adjust the gain of a VGAl variable gain amplifier. The isolated signal is filtered in a low pass filter 218, which passes signals having a frequency of less than about 2000 MHz in this mode. The filtered signal is divided by the divider 220, and the divided signals are transmitted from the antennas TX1 and TX2. The splitter 220, in this mode is a hybrid connector; however, it can be seen that other suitable devices (for example, Wilkinson, quadrature hybrid, resistive, etc.) can be used. It will be noted that in the embodiment of Figure 5A, a standard transceiver architecture is employed, and the mode is therefore economical. In this embodiment, the divider loss occurring in the divider 220 is preferably compensated for by the reduction in the link margin contemplated. Figure 5B shows an alternative embodiment of the antenna integration circuit. In the embodiment of Figure 5B, each transmitter antenna Txl, Tx2 has a separate chain of associated transmitter amplifier and each receiving antenna RxAl, RxA2, RxBl and RxB2 has a separate associated noise amplifier under 102A1, 102A2, 102B1, and 102B2. In this mode, the transmitter division occurs at a point in the transmission path where the loss caused by the division can be compensated for by the VGAl and 212A and 212B amplifiers. In addition, the reception combination occurs at a point in the reception path where the loss caused by the combination can be compensated for by an appropriate selection or adjustment of the noise amplifiers under 102A1-102B2. This modality allows a better performance than the modality of Figure 5A, but said modality is generally more expensive and complex. It will be noted that Figures 5A-B show two circuit modalities for the integration of antennas, and that the circuit components illustrated and described can be modified as necessary depending on design considerations such as power handling capacity, cost, space, etc. Referring now to Figures 6A-B, a comparison of the coverage areas of a conventional distributed antenna system and a distributed antenna employing the method and arrangement of the present invention is illustrated. In Figure 6A a suburban application of a distributed antenna system is illustrated where they employ omnidirectional remote RF antennas 12a and 12b. A remote omnidirectional RF antenna 12a provides coverage to the houses 54a and 54d, and the omnidirectional antenna 12b provides coverage to the houses 54c and 54f. However, since the antennas 12a and 12b are omnidirectional, the coverage provided to the houses 54b and 54e is subject to interference. This does not provide efficient coverage in the desired area. In contrast, the use of directional antennas 12a 'and 12b' is illustrated in Figure 5B. Directional antennas allow coverage of houses 54a-f without interference, thus covering the desired area more efficiently. While the above description includes many details and specificities, it is understood that these details and specificities are for illustration and explanation purposes only. Many modifications can be made to the described modalities, which do not depart from the spirit or scope of the invention as defined in the appended claims and their legal equivalents.

Claims (10)

1. CLAIMS A method for integrating a plurality of antennas in a distributed antenna communication system, comprising the steps of: providing a plurality of antennas on one or more surfaces of a remote RF link, each antenna is capable of providing a propagation of signal in a desired direction; and integrating the plurality of antennas by providing one or several internal RF combining circuits, each combining circuit combines signals received from two or more of the antennas, and by supplying one or several internal RF division circuits, each circuit of division divides signals to propagate from a signal source into at least two signals for propagation from at least two antennas.
2. The method of claim 2, further comprising the step of covering the remote RF unit with a frame.
3. The method of claim 2, wherein at least one of the antennas is a temporary directional connecting antenna.
4. The method of claim 3, wherein the antennas are mounted substantially flush with one or more surfaces of the frame.
5. The method of claim 4, wherein each antenna is covered with a protective dome.
6. The method of claim 1, wherein the frame is substantially weatherproof.
7. The method of claim 1, wherein each combination circuit and each division circuit includes a Wilkinson device.
8. 8. An integrated antenna unit, comprising: a frame; a plurality of antennas mounted substantially flush with one or more surfaces of the frame, each antenna is capable of providing a signal propagation in a desired direction; one or several internal RF combination circuits, each combination circuit combines signals received from two or more of the antennas; and one or more internal RF division circuits, each division circuit divides signals to be propagated from a signal source into at least two signals for propagation from at least 2 antennas.
9. The unit of claim 8, wherein at least one of the antennas is a temporary directional connecting antenna.
10. 10. The unit of claim 9, wherein each antenna is covered with a protective dome. The unit of claim 8, wherein the frame is substantially weatherproof. The unit of claim 8, wherein each combination circuit and each division circuit includes a Wilkinson device.