Abstract:
Repeater apparatus for conveying a radio-frequency (RF) signal into an environment closed-off to the RF signal, including a master transceiver unit having a master port which receives the RF signal, a local oscillator (LO), which generates a LO signal at a LO frequency, and a frequency divider which divides the LO frequency of the LO signal by an integer to produce a divided LO signal. The master transceiver unit also includes a master mixer coupled to the master port and the divider which generates an intermediate-frequency (IF) signal responsive to the RF signal and the LO signal. The apparatus includes one or more slave transceiver units, each unit positioned within the environment closed-off to the RF signal and including a frequency multiplier which generates a recovered LO signal at the LO frequency by multiplying the frequency of the divided LO signal by the integer, a slave mixer coupled to the multiplier which generates a recovered RF signal responsive to the recovered LO signal and the IF signal, and a slave port coupled to the slave mixer which receives the recovered RF signal therefrom and transmits the recovered RF signal into the closed-off environment. The apparatus further includes one or more cables coupled between the master transceiver unit and the one or more slave transceiver units which convey the IF signal and the divided LO signal between the master transceiver unit and the one or more slave transceiver units.

Description:
RELATED APPLICATIONS  
       [0001]    This Application is a continuation of U.S. patent application Ser. No. 09/431,434, filed on Nov. 1, 1999, Attorney Docket No. 990519. 
     
    
     
       FIELD OF THE INVENTION  
         [0002]    The present invention relates generally to transmission of electromagnetic signals, and specifically to automatic amplification and retransmission of the signals.  
         DESCRIPTION OF THE RELATED ART  
         [0003]    Electronic repeaters, wherein a received electromagnetic signal is automatically amplified and then retransmitted, are well known in the art. Use of a repeater enables a relatively low-power original signal, such as that from a mobile telephone unit, to be transmitted with a power orders of magnitude greater than the original signal.  
           [0004]    [0004]FIG. 1 illustrates a repeater system  10 , as is known in the art. A first antenna  12  receives a signal from a first transmitter  13 , for example a cellular base transceiver station (BTS). The signal is transferred on a coaxial cable  14  to a repeater  16 , wherein the signal is amplified and transferred on a coaxial cable  18  to a second antenna  20 , which transmits the “repeated” signal generated by repeater  16 . Similarly, a signal received by antenna  20  from a second transmitter  15 , such as a mobile telephone, traverses a reverse path through system  10 , being amplified in repeater  16  and retransmitted by antenna  12 . Overall power gains typically required for the signals, from antenna to antenna, are of the order of 90 dB.  
           [0005]    Since antennas  12  and  20  are operating on the same frequencies and are both positioned within range of both transmitters, it is important to isolate the antennas one from another in order to avoid interference effects. In order to achieve stability, the antennas need to be isolated by a factor of the order of 110 dB. Typically the antennas are partially isolated by carefully aiming each antenna so that significant radiation from one antenna is not incident on the other antenna, and so that each antenna mainly receives signals from either transmitter  13  or  15 , but not both. In practice, sufficient isolation can only be achieved by having the antennas separated by a relatively large physical distance, of the order of at least 30 m. Thus, cable  14  and cable  18  need to be as long as possible.  
           [0006]    Lengthening cables  14  and  18  introduces some deleterious effects into system  10 . The longer the cables, the higher the noise level of the signals received by repeater  16  from the antennas. To overcome the increased noise, filters are introduced into the repeater. The longer cables also attenuate signals transmitted therein, necessitating increased gain of power amplifiers within the repeater to compensate for the attenuation. At frequencies of the order of 1 GHz, such as those used by cellular telephone systems, leakage of radiation from the cables may be significant, although the leakage is typically limited by using densely-sheathed coaxial cable or even doubly-shielded cable.  
           [0007]    Repeaters which separate the functions performed by repeater  16  into two or more separate systems are also known in the art. U.S. Pat. No. 5,404,570, to Charas et al, which is incorporated herein by reference, describes a repeater system used between a base transceiver station (BTS) and a closed environment, such as a tunnel, which is closed off to transmissions from the BTS. The system down-converts a high radio-frequency (RF) signal from the BTS to an intermediate frequency (IF) signal, which is then radiated by a cable and an antenna in the closed environment to a receiver therein. The receiver up-converts the IF signal to the original RF signal. Systems described in the patent serve a vehicle moving in a tunnel, so that passengers in the vehicle who would otherwise be cut off from the BTS are able to receive signals.  
           [0008]    U.S. Pat. No. 5,603,080, to Kallandar et al., which is incorporated herein by reference, describes a plurality of repeater systems used between a plurality of BTSs and a closed environment, which is closed off to transmissions from the BTSs. Each repeater system down-converts an RF signal from its respective BTS to an IF signal, which is then transferred by a cable in the closed environment to one or more respective receivers therein. Each receiver up-converts the IF signal to the original RF signal. Systems described by the inventors serve a vehicle moving between overlapping regions in a tunnel, each region covered by one of the BTSs via its repeater system.  
           [0009]    U.S. Pat. No. 5,765,099, to Georges et al., which is incorporated herein by reference, describes a system and method for transferring an RF signal between two or more regions using a low-bandwidth medium such as twisted-pair cabling. In a first region the RF signal is mixed with a first local oscillator to produce a down-converted IF signal. The IF signal is transferred to a second region via the low-bandwidth medium, wherein the signal is up-converted to the original RF signal using a second local oscillator. The local oscillators are each locked by a phase locked loop (PLL) in each region to generate the same frequency, the locking being performed in each loop by comparing the local oscillator frequency with a single low-frequency stable reference signal generated in one region. The reference signal is transferred between the regions via the low-bandwidth medium.  
         SUMMARY OF THE INVENTION  
         [0010]    It is an object of some aspects of the present invention to provide an improved method and apparatus for repeating of electromagnetic signals.  
           [0011]    In preferred embodiments of the present invention, a split repeater comprises a master transceiver unit and a slave transceiver unit coupled together by a connecting cable. Each unit is able to receive and transmit radio frequency (RF) electromagnetic signals via a respective antenna. The antennas are preferably positioned in a common environment, i.e., there are substantially no electromagnetic barriers between the antennas, but are independently positionable due to the use of the connecting cable.  
           [0012]    Operating the repeater as two separate units connected by a cable gives a number of significant advantages over systems having one unit:  
           [0013]    There is more flexibility in positioning the antennas of each of the units.  
           [0014]    Each unit may be positioned close to its antenna, improving the noise characteristics of signals received by both antennas.  
           [0015]    Because signals are transmitted within the cable at intermediate frequencies, there is less loss in the cable, and less leakage radiation from the cable. Any loss that does incur occur is easily compensated for by intermediate frequency amplification, which does not add significant noise to the original signals.  
           [0016]    In some preferred embodiments of the present invention, the connecting cable carries intermediate frequency (IF) signals. The master unit receives a RF signal on its antenna, down-converts the received signal to a forward intermediate frequency (IF-FWD) signal, and transfers the IF-FWD signal by the cable to the slave unit. The IF-FWD signal is up-converted and then transmitted by the antenna of the slave unit. Similarly, a signal received by the slave unit on its antenna is down-converted to a reverse intermediate frequency (IF-REV) signal, which IF-REV signal is transferred via the cable to the master unit. The IF-REV signal is up-converted and transmitted by the master unit antenna. By utilizing intermediate frequencies to transfer the signals, significantly greater isolation between signals received by the master and the slave units can be incorporated into the system. Preferably, in generating the intermediate frequencies, filters are used in both units, which filters may also be adjusted to serve the function of substantially reducing or eliminating unwanted and/or interfering signals received by the master and slave antennas, particularly signals outside a certain communication channel or set of channels that is to be repeated.  
           [0017]    In some of these preferred embodiments, the master unit generates a local oscillator (LO) signal which is mixed with the signal from the antenna of the master unit to generate the IF-FWD signal. Most preferably, the local oscillator signal is also used to regenerate an original signal from the IF-REV signal received from the slave unit. Preferably, the frequency of the LO signal is divided by an integer, thus generating a lower-frequency signal. The lower-frequency signal is transmitted on the connecting cable to the slave unit, where its frequency is multiplied by the integer to regenerate the LO signal. In the slave unit, the regenerated LO signal is used both to regenerate the master signal from the IF-FWD signal received from the master unit, and as a local oscillation for producing the IF-REV signal transmitted to the master unit. Alternatively, the LO signal generated by the master unit is transmitted to the slave unit in an undivided form. Using the same LO signal in the two units eliminates in a simple fashion problems caused by having a separate local oscillator in each unit. Furthermore, since the same LO signal is used in both units for up- and down-conversion, there is no need for the local oscillator to be particularly stable, so that phase-locked loops, which are used to stabilize the LO frequency in repeaters known in the art, are not needed.  
           [0018]    In other preferred embodiments of the present invention, the master transceiver unit amplifies a master RF signal received on its antenna without down-conversion to an intermediate frequency. The amplified signal is transferred via the connecting cable to the slave transceiver unit, wherein it is further amplified then transmitted from the antenna of the slave unit. Similarly, a RF signal received by the slave unit on its antenna is amplified without down-conversion, then transferred via the cable to the master unit, wherein it is further amplified then transmitted by the master unit antenna.  
           [0019]    In some preferred embodiments of the present invention, a power supply located in or near the master unit produces DC voltage to power the master unit. The DC voltage is transferred via the connecting cable to the slave unit, in order to also power the slave unit. Alternatively, the power supply may be located in or near the slave unit to power the slave unit, and DC voltage transferred via the cable to the master unit.  
           [0020]    In some preferred embodiments of the present invention, the master unit comprises a remote control unit, whereby control and monitoring of the master and/or slave unit may be performed by an operator remote from one or both of the units. Most preferably, the remote control unit operates by transmitting signals between the master unit and the remote operator.  
           [0021]    In some preferred embodiments of the present invention, operation of the slave unit is controlled from the master unit, via a modulated signal such as an FSK signal, transmitted from the master unit to the slave unit.  
           [0022]    There is therefore provided, in accordance with a preferred embodiment of the present invention, a radio-frequency (RF) repeater, including:  
           [0023]    a master antenna, positioned to receive an RF master signal;  
           [0024]    a master unit, including:  
           [0025]    a master RF port, coupled to receive the RF master signal from the master antenna;  
           [0026]    a local oscillator, which generates a master local oscillator signal at a local oscillation frequency; and  
           [0027]    a master mixer which mixes the RF master signal and the master local oscillator signal to generate an intermediate frequency (IF) signal;  
           [0028]    a cable which is coupled to the master unit so as to receive therefrom the IF signal and a reference signal at a reference frequency, derived from the local oscillator signal;  
           [0029]    a slave antenna, positioned in a common environment with the master antenna; and  
           [0030]    a slave unit, coupled to receive the IF signal and the reference signal from the cable, the slave unit including:  
           [0031]    a slave mixer which mixes the IF signal and a slave local oscillator signal at the local oscillation frequency, derived from the reference signal, so as to recover the received RF master signal; and  
           [0032]    a slave RF port, which is coupled to convey the recovered RF master signal to the slave antenna for transmission thereby.  
           [0033]    Preferably, the master port is a two-way port, and the slave RF port is a two-way port through which the slave unit receives an RF slave signal from the slave antenna and downconverts the RF slave signal by mixing it with the slave local oscillator signal to produce a slave IF signal which is conveyed by the cable to the master unit, wherein the slave RF signal is recovered and is conveyed by the master port to the master antenna for transmission thereby.  
           [0034]    Preferably, the reference frequency is substantially less than the local oscillator frequency.  
           [0035]    Preferably, the master unit includes a frequency divider which divides the local oscillation frequency by an integer to derive the reference frequency, and the slave unit includes a frequency multiplier which multiplies the reference frequency by the integer to regenerate the local oscillation frequency.  
           [0036]    Alternatively, the master unit includes a DC power supply which generates a DC level that is conveyed by the cable to power the slave unit.  
           [0037]    Preferably, the repeater includes a controller in one of the slave or master units which controls the operation of both units.  
           [0038]    Preferably, the repeater includes a remote control unit which transfers control signals between the controller and an operator of the repeater.  
           [0039]    Alternatively, the controller generates modulated control signals which are conveyed by the cable between the master and the slave units.  
           [0040]    Preferably, the repeater operates in a communications network at frequencies in the range 450 MHz to 30 GHz.  
           [0041]    Alternatively, the repeater operates in a cellular communications network at frequencies in the range 800 MHz to 1900 MHz.  
           [0042]    Preferably, the frequency of the IF signal is substantially less than the frequency of the RF signal.  
           [0043]    Preferably, the frequency of the IF signal is substantially less than the local oscillation frequency.  
           [0044]    Preferably, the IF signal corresponds to one or more predetermined channels of a multiple access communications network.  
           [0045]    There is further provided, in accordance with a preferred embodiment of the present invention, a radio-frequency (RF) repeater, including:  
           [0046]    a master unit, including:  
           [0047]    a master RF port, coupled to receive an RF signal from a master antenna;  
           [0048]    a local oscillator, which generates a master local oscillator signal at a local oscillation frequency; and  
           [0049]    a master mixer which mixes the RF signal and the master local oscillator signal to generate an intermediate frequency (IF) signal;  
           [0050]    a cable which is coupled to the master unit so as to receive therefrom the IF signal and a reference signal at a reference frequency substantially less than the local oscillation frequency, which reference signal is derived from the local oscillator signal; and  
           [0051]    a slave unit, coupled to receive the IF signal and the reference signal from the cable, the slave unit including:  
           [0052]    a slave mixer which mixes the IF signal and a slave local oscillator signal at the local oscillation frequency, derived from the reference signal, so as to recover the received RF signal; and  
           [0053]    a slave RF port, which is coupled to convey the recovered RF signal to a slave antenna.  
           [0054]    Preferably, the master port is a two-way port, and the slave port is a two-way port through which the slave unit receives an RF slave signal from the slave antenna and downconverts the RF slave signal by mixing it with the slave local oscillator signal to produce a slave IF signal which is conveyed by the cable to the master unit, wherein the slave RF signal is recovered and is conveyed by the master port to the master antenna for transmission thereby.  
           [0055]    Preferably, the master unit includes a frequency divider which divides the local oscillation frequency by an integer to derive the reference frequency, and the slave unit includes a frequency multiplier which multiplies the reference frequency by the integer to regenerate the local oscillation frequency.  
           [0056]    Alternatively, the master unit includes a DC power supply which generates a DC level which is conveyed by the cable to power the slave unit.  
           [0057]    Preferably, the repeater includes a controller in one of the slave or master units which controls the operation of both units.  
           [0058]    Preferably, the IF signal corresponds to one or more predetermined channels of a multiple access communications network.  
           [0059]    There is further provided, in accordance with a preferred embodiment of the present invention, a method for repeating a radio-frequency (RF) signal, including:  
           [0060]    receiving the RF signal from a first antenna at a first location;  
           [0061]    generating at the first location a first local oscillator signal having a local oscillation frequency;  
           [0062]    mixing the RF signal with the first local oscillator signal at the first location to produce an intermediate frequency (IF) signal;  
           [0063]    deriving a reference signal having a reference frequency from the first local oscillator signal at the first location;  
           [0064]    transferring the IF and reference signals over a cable to a second location in a common environment with the first location;  
           [0065]    processing the reference signal at the second location to reconstruct the local oscillator signal at the local oscillation frequency;  
           [0066]    mixing the IF signal and the local oscillator signal at the second location to recover the RF signal; and  
           [0067]    transferring the recovered RF signal to a second antenna at the second location for transmission of the signal thereby.  
           [0068]    Preferably, the method includes:  
           [0069]    receiving a slave RF signal at the second antenna;  
           [0070]    mixing the slave RF signal and the local oscillator signal at the second location to produce a slave IF signal;  
           [0071]    transferring the slave IF signal over the cable to the first location;  
           [0072]    recovering the slave RF signal by mixing the slave IF signal with the first local oscillator signal; and  
           [0073]    transmitting the slave RF signal from the first antenna.  
           [0074]    Preferably, deriving the reference signal includes dividing the local oscillation frequency by an integer, and processing the reference signal includes multiplying the reference signal frequency by the integer to regenerate the local oscillation frequency.  
           [0075]    Preferably, the reference frequency is substantially less than the local oscillator frequency.  
           [0076]    Preferably, transferring the IF and reference signals over the cable includes transferring a DC level over the cable.  
           [0077]    Preferably, the method includes providing a controller in one of the slave or master units which controls the operation of both units.  
           [0078]    Alternatively, the method includes providing a remote control unit which transfers control signals between the controller and an operator of the repeater.  
           [0079]    Preferably, the method includes generating modulated control signals at the control unit and conveying the modulated control signals over the cable between the master and the slave units.  
           [0080]    Preferably, receiving the RF signal includes receiving a communications transmission at a frequency in the range 450 MHz to 30 GHz.  
           [0081]    Alternatively, receiving the RF signal includes receiving a cellular communications transmission at a frequency in the range 800 MHz to 1900 MHz.  
           [0082]    Preferably, mixing the RF signal to produce the IF signal includes producing an IF signal having a frequency substantially less than the frequency of the RF signal.  
           [0083]    Preferably, mixing the RF signal to produce the IF signal includes producing an IF signal having a frequency substantially less than the local oscillation frequency.  
           [0084]    Preferably, mixing the RF signal includes producing the IF signal to correspond to one or more predetermined channels of a multiple access communications network.  
           [0085]    There is further provided, in accordance with a preferred embodiment of the present invention, a method for repeating a radio-frequency (RF) signal, including:  
           [0086]    receiving the RF signal from a first antenna at a first location;  
           [0087]    generating at the first location a first local oscillator signal having a local oscillation frequency;  
           [0088]    mixing the RF signal with the first local oscillator signal at the first location to produce an intermediate frequency (IF) signal;  
           [0089]    deriving a reference signal having a reference frequency substantially less than the local oscillation frequency, which reference signal is derived from the first local oscillator signal at the first location;  
           [0090]    transferring the IF and reference signals over a cable to a second location in a common environment with the first location;  
           [0091]    processing the reference signal at the second location to generate a second local oscillator signal at the local oscillation frequency;  
           [0092]    mixing the IF signal and the second local oscillator signal at the second location to recover the RF signal; and  
           [0093]    transferring the recovered RF signal to a second antenna for transmission of the signal thereby.  
           [0094]    Preferably, the method includes:  
           [0095]    receiving a slave RF signal at the second antenna;  
           [0096]    mixing the slave RF signal and the second local oscillator signal at the second location to produce a slave IF signal;  
           [0097]    transferring the slave IF signal over the cable to the first location;  
           [0098]    recovering the slave RF signal by mixing the slave IF signal with the first local oscillator signal; and  
           [0099]    transmitting the slave RF signal from the first antenna.  
           [0100]    Preferably, deriving the reference signal includes dividing the local oscillation frequency by an integer, and processing the reference signal includes multiplying the reference signal frequency by the integer to regenerate the local oscillation frequency.  
           [0101]    Preferably, transferring the IF and reference signals over the cable includes transferring a DC level over the cable.  
           [0102]    Preferably, mixing the RF signal to produce the IF signal includes producing an IF signal corresponding to one or more predetermined channels of a multiple access communications network.  
           [0103]    There is further provided, in accordance with a preferred embodiment of the present invention, a radio-frequency (RF) repeater, including:  
           [0104]    a master unit, including:  
           [0105]    a master RF port, coupled to receive an RF signal from a master antenna; and  
           [0106]    at least one amplifier which generates a first amplified RF signal responsive to the RF signal;  
           [0107]    a cable which is coupled to the master unit so as to receive therefrom the first amplified RF signal; and  
           [0108]    a slave unit, coupled to receive the first amplified RF signal from the cable, the slave unit including:  
           [0109]    at least one amplifier which generates a second amplified RF signal responsive to the RF signal; and  
           [0110]    a slave RF port, which is coupled to convey the second amplified RF signal to a slave antenna.  
           [0111]    Preferably, the master port is a two-way port, and the slave port is a two-way port through which the slave unit receives an RF slave signal from the slave antenna and amplifies the RF slave signal to produce a first amplified slave IF signal which is conveyed by the cable to the master unit, wherein the first amplified slave RF signal is amplified and is conveyed by the master port to the master antenna for transmission thereby.  
           [0112]    Preferably, the first amplified RF signal has an RF frequency substantially equal to the frequency of the RF signal received by the master RF port.  
           [0113]    Preferably, the master and slave units are independently positionable in locations that are physically separated from one another.  
           [0114]    There is further provided, in accordance with a preferred embodiment of the present invention, a method for repeating a radio-frequency (RF) signal, including:  
           [0115]    receiving the RF signal from a first antenna at a first location;  
           [0116]    amplifying the RF signal at the first location to produce a first amplified RF signal;  
           [0117]    transferring the first amplified RF signal over a cable to a second location;  
           [0118]    amplifying the first amplified RF signal at the second location to produce a second amplified RF signal;  
           [0119]    transferring the second amplified RF signal to a second antenna at the second location for transmission of the signal thereby.  
           [0120]    Preferably, the method includes:  
           [0121]    receiving a slave RF signal at the second antenna;  
           [0122]    amplifying the slave RF signal at the second location to produce a first amplified slave RF signal;  
           [0123]    transferring the first amplified slave RF signal over the cable to the first location;  
           [0124]    amplifying the first amplified slave RF signal at the first location to produce a second amplified slave RF signal; and  
           [0125]    transmitting the second amplified slave RF signal from the first antenna.  
           [0126]    Preferably, the first location is physically separated from the second location.  
           [0127]    Preferably, the first amplified RF signal has a RF frequency substantially equal to the frequency of the RF signal received from the first antenna.  
           [0128]    The present invention will be more fully understood from the following detailed description of the preferred embodiments thereof, taken together with the drawings, in which: 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0129]    [0129]FIG. 1 schematically illustrates a repeater system, as is known in the art;  
         [0130]    [0130]FIG. 2 schematically illustrates a split repeater system, according to a preferred embodiment of the present invention;  
         [0131]    [0131]FIG. 3 is a schematic block diagram of a master unit in the split repeater system illustrated in FIG. 2, according to a preferred embodiment of the present invention;  
         [0132]    [0132]FIG. 4 is a schematic block diagram of a slave unit in the split repeater system illustrated in FIG. 2, according to a preferred embodiment of the present invention;  
         [0133]    [0133]FIGS. 5A and 5B are schematic frequency diagrams showing frequency bands used by the split repeater system illustrated in FIG. 2, according to a preferred embodiment of the present invention;  
         [0134]    [0134]FIG. 6 schematically illustrates a split repeater system, according to an alternative preferred embodiment of the present invention;  
         [0135]    [0135]FIG. 7 is a schematic block diagram of a master unit in the split repeater system illustrated in FIG. 6, according to a preferred embodiment of the present invention; and  
         [0136]    [0136]FIG. 8 is a schematic block diagram of a slave unit in the split repeater system illustrated in FIG. 6, according to a preferred embodiment of the present invention.  
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0137]    Reference is now made to FIG. 2, which schematically illustrates a split repeater system  20 , according to a preferred embodiment of the present invention. A master antenna  22  receives a master electromagnetic radio-frequency (RF) signal from a first remote transmitter  23 . Transmitter  23  is preferably a transmitter comprised in a base transceiver station (BTS) of a cellular telephone system, although any other suitable transmitter could also be used. The master RF signal is transferred from antenna  22  to a master unit  26  in substantially the same location as the antenna via an RF-signal conductor  24 . Most preferably, the length of conductor  24  is as short as possible, so that noise introduced by the conductor is as small as possible, and so that radiation from the conductor is also as small as possible. Most preferably, conductor  24  comprises a standard coaxial cable having one or more dense sheathings and/or a low-loss dielectric in order to reduce radiation from and attenuation in the cable, as are known in the art.  
         [0138]    Master unit  26  receives the master RF signal from conductor  24  and down-converts the signal to a forward intermediate frequency (IF-FWD) signal, so that master unit  26  functions as a frequency conversion unit. The IF-FWD signal is transferred via a cable  30  to a slave unit  32 , wherein the IF-FWD signal is up-converted to a “repeated” master RF signal corresponding to the RF signal received by master unit  26 . Cable  30  is preferably a standard coaxial cable, although any other cable capable of transferring signals generated within master unit  26  and slave unit  32  may be used. Slave unit  32  thus also functions as a frequency conversion unit. The up-converted RF signal is transferred via a conductor  34 , the conductor most preferably having similar characteristics to those described above for conductor  24 , to a slave antenna  36  in substantially the same location as the slave unit, which antenna radiates the repeated master RF signal.  
         [0139]    Antenna  36  also receives a slave RF signal from a second transmitter  25 . Transmitter  25  preferably comprises a transmitter of a cellular telephone, although any other suitable transmitter could be used. Slave unit  32  down-converts the slave RF signal to a reverse intermediate frequency (IF-REV) signal. The IF-REV signal is transferred via cable  30  to master unit  26 , wherein the IF-REV signal is up-converted to a repeated slave RF signal. The up-converted slave RF signal is transferred via conductor  24  to master antenna  22 , which radiates the repeated slave RF signal.  
         [0140]    In installing system  20 , antenna  36  and antenna  22  are placed in relatively close physical proximity, so that the signal level from either of remote transmitters  23  or  25  is substantially similar at the position of both of the antennas. However, the system has sufficient flexibility so that the antennas and their associated units can be positioned and oriented such that even with antenna-antenna gains of the order of 90 dB, isolation of 110 dB or better between the antennas is easily achievable. The operations of unit  26  and of unit  32  are explained in detail hereinbelow.  
         [0141]    [0141]FIG. 3 is a schematic block diagram of master unit  26 , according to a preferred embodiment of the present invention. An RF duplexer  40  receives the master RF signal from antenna  22  via conductor  24 . Duplexer  40  acts as a port and separates a path  41  of the master signal from a path  43  of the received slave signal, by methods which are known in the art. The master RF signal is transferred, via an isolator  42  which prevents RF radiation back to duplexer  40 , to a low noise RF amplifier  44 . Amplifier  44  acts as a first stage of amplification in path  41 , and is most preferably constructed from very-low-noise components, as are known in the art.  
         [0142]    The amplified signal from amplifier  44  is input to a mixer  46 . Mixer  46  also receives a local oscillator signal, most preferably generated by a local oscillator frequency synthesizer  56 , via a splitter  58 . Preferably, a controller  88  sets the frequency generated by synthesizer  56 . Mixer  46  uses the local oscillator signal to generate mixed signals comprising intermediate frequency (IF) side-bands, which mixed signals are amplified in a second-stage amplifier  48 . The amplified mixed signals are then filtered in a band-pass filter  50  which passes one intermediate frequency band centered on a frequency herein termed IF-FWD, and rejects other bands generated in mixer  46 . Preferable choices for the local oscillator frequency, and the corresponding IF-FWD frequency, are described in detail below.  
         [0143]    The output of filter  50  is input to a final-stage amplifier  52  and attenuator  54 , which together adjust a level of the IF-FWD signal to a value suitable for reception by unit  32 , and which supply the adjusted signal to a triplexer  64 . Preferably, attenuator  54  is a digital attenuator whose attenuation is set by controller  88 .  
         [0144]    Preferably, synthesizer  56  also supplies a local oscillator signal via splitter  58  to a frequency divider  63 , which divider is set to divide the frequency by an integer, which is typically in the range 2-16, although any other suitable value could be used. The divided local oscillator signal is input to an amplifier  60 . Alternatively, the local oscillator signal from splitter  58  is not divided, but is transferred directly to amplifier  60 . Amplifier  60  amplifies the received signal and transfers its output as a reference signal operating at a reference frequency to triplexer  64  via an isolator  62 , which isolator prevents intermediate frequency signals from triplexer  64  from leaking back to synthesizer  56 . Triplexer  64  combines the amplified local oscillator reference signal and the adjusted IF-FWD signal, and transfers the combined signal to a bias-T filter  66 .  
         [0145]    Filter  66  acts as a port and as a low-pass filter which biases the combined signal from triplexer  64  with a DC level generated by a power supply  68 . The DC level generated by supply  68  drives master unit  26 . Preferably, power supply  68  receives its driving power in the form of standard AC line power via a connector  28 . Alternatively, power supply  68  receives its driving power in any other suitable standard form, such as from a battery. Filter  66  transfers the combined signal at the DC bias level to cable  30 , which thus transmits the signal and the DC power to slave unit  32 .  
         [0146]    Master unit  26  receives the IF-REV signal generated in slave unit  32  in filter  66 , via cable  30 . The filter separates the signal from the DC level present in the cable. The AC component, i.e., the IF-REV signal, is transferred to triplexer  64 . Triplexer  64  directs the IF-REV signal along path  43  of unit  26 , to a first amplifier  70  and then to a band-pass filter  72 . The filtered amplified signal is then attenuated in an attenuator  74 , which attenuator is preferably a digital attenuator whose attenuation is controlled by controller  88 . Amplifier  70 , filter  72 , and attenuator  74  function so that attenuator  74  provides an output level to a mixer  76  according to an overall required repeater gain. Mixer  76  also receives the local oscillator signal from splitter  58 , and uses the two signals to regenerate the slave signal received by antenna  36  of slave unit  32 .  
         [0147]    The regenerated signal is passed along path  43  via a first amplifier  78  and a band-pass filter  80 , which together act to produce a preamplified low noise input for a power amplifier  82 . Amplifier  82  supplies a final output RF signal, corresponding to the input slave signal, via an isolator  84  and duplexer  40 , to antenna  22 , which then radiates the amplified slave signal. Most preferably, gains and attenuations of elements of master unit  26  described hereinabove are adjusted so that the overall signal gain, from port to port, for path  41  and for path  43  is of the order of 10-60 dB for each path.  
         [0148]    Optionally, master unit  26  comprises a remote control unit  86 , such as an “Amber” unit supplied by Qualcomm Inc. of San Diego, Calif., which unit supplies control commands to controller  88 . Remote control unit  86  preferably receives signals from an operator via a tap  25  on conductor  24 , so that operation of remote control unit  86  is generally independent of other elements comprised in master unit  26 . Remote control unit  86  is preferably able to monitor parameters such as the levels set by controller  88  to attenuators  54  and  74 , and forward and reverse receive and transmit gains, as well as the frequency generated by synthesizer  56 , and transmit values of the monitored parameters to the operator. Preferably, controller  88  operates unit  26  automatically according to instructions which are installed in the controller when unit  26  is initially set up. Most preferably, if remote control unit  86  is installed in unit  26 , the instructions operating controller  88  can be changed via the remote control unit.  
         [0149]    [0149]FIG. 4 is a schematic block diagram of slave unit  32 , according to a preferred embodiment of the present invention. Slave unit  32  comprises a bias-T filter  90 , which receives the IF-FWD signal, the local oscillator reference signal, and the DC level from cable  30 . Filter  90  acts as a port, splitting off the DC level to power slave unit  32 , and transferring the AC signals to a triplexer  92 . Triplexer  92  separates the AC signals into a path  91  followed by the IF-FWD signal, and a path  93  followed by the local oscillator signal.  
         [0150]    Preferably, path  93  comprises a frequency multiplier  111 , which multiplies the frequency of the divided local oscillator signal by the same integer value used by divider  63  of master unit  30 . Thus a local oscillator signal is reconstituted in slave unit  32 , which signal has a frequency identical to that of the local oscillator signal originally synthesized by synthesizer  56  of master unit  26 , and which is input to an amplifier  110 . Alternatively, if the local oscillator signal has not been divided in master unit  30 , path  93  does not comprise frequency multiplier  111 , and the local oscillator signal from triplexer  92  is input directly to amplifier  110  as a reconstituted signal. The reconstituted local oscillator signal is amplified in amplifier  110 , and passed through a band-pass filter  112  to a splitter  114 . Amplifier  110  and filter  112  together generate a local oscillator signal level which is suitable for use by a mixer  96  and a mixer  120 , which receive the local oscillator signal from splitter  114 .  
         [0151]    Path  91  comprises a band-pass filter  94 , which passes frequencies centered on IF-FWD to mixer  96 , and rejects other frequencies. Mixer  96  up-converts the IF-FWD signal received from filter  94 , using the reconstituted local oscillator signal, to regenerate the master RF signal received by master unit  26 . The up-converted RF signal is amplified in an RF pre-amplifier  98  and filtered in band-pass filter  102 , which together prepare an RF signal at a level suitable for inputting to an RF power amplifier  104 . Power amplifier  104  generates an RF power output signal corresponding to the original master signal received by the master unit, which power signal is transferred via an isolator  106  to increase the voltage standing wave ratio. The power signal is input to an RF duplexer  108  which acts as a port. Duplexer  108  routes the power signal via signal conductor  34  to slave antenna  36 , which radiates the RF power signal.  
         [0152]    As explained above, antenna  36  also receives a slave RF signal. The slave signal is routed via RF duplexer  108  along a path  95  to a low noise pre-amplifier  124 , which pre-amplifier is most preferably constructed from very-low-noise components by methods known in the art. An isolator  122  substantially eliminates any leakage of the reconstituted local oscillator signal to antenna  36 . A mixer  120  uses the reconstituted local oscillator signal received from splitter  114  and the output signal of pre-amplifier  124  to down-convert the slave RF signal to the intermediate frequency signal IF-REV. The IF-REV signal is amplified by an amplifier  118  feeding a band-pass filter  116 , which together operate to generate an IF-REV signal substantially free from unwanted sidebands, such as those produced in mixer  120 , and having a level suitable for transmission in cable  30 . The IF-REV signal output of filter  116  is routed by triplexer  92  and filter  90  to cable  30 , wherein it is transmitted to master unit  26 .  
         [0153]    Preferably, parameters affecting the operation of slave unit  32 , such as gains of amplifiers  98 ,  104 ,  110 ,  118 , and  124 , are preset when slave unit  32  is set up, so that slave unit  32  is able to operate independently. Most preferably, the overall signal gain, from port to port, for path  91  and for path  95  is set to be of the order of 10-60 dB for each path. In a preferred embodiment of the present invention, controller  88  of master unit  26  is able to control and/or monitor the operation of slave unit  32 , by transferring control signals to the slave unit on cable  30 . Most preferably, the control signals are in the form of a frequency and/or a phase and/or an amplitude modulated signal, such as a frequency shift key (FSK) signal, as are known in the art.  
         [0154]    [0154]FIGS. 5A and 5B are schematic frequency diagrams showing frequency bands used by system  20 , and examples of specific frequencies transmitted within the system, according to a preferred embodiment of the present invention. FIG. 5A shows frequencies used when system  20  operates as a repeater of signals in a frequency band  150  from approximately 800 MHz to 900 MHz. Such a band covers frequencies used by cellular telephone systems, wherein the forward and reverse signals are typically separated by a duplex separation of 45 MHz. In the example shown in FIG. 5A, the master signal received by master antenna  22  has a frequency of 885 MHz and the slave signal received by slave antenna  36  has a frequency of 840 MHz.  
         [0155]    Local oscillator synthesizer  56  most preferably generates a local oscillator signal having a frequency below the lowest frequency of band  150 , for example, at 750 MHz. With a local oscillator frequency of 750 MHz, intermediate frequencies in a frequency band  160  from approximately 50 MHz to 150 MHz are generated by the master and slave units. The frequency of the IF-FWD signal generated by mixer  46  from the master signal frequency of 885 MHz is 135 MHz. The frequency of the IF-REV signal generated by mixer  120  from the slave signal at 840 MHz is 90 MHz. Divider  63  in master unit  26  preferably divides the local oscillator frequency by an integer, for example  16 , giving a divided LO frequency of 46.875 MHz. Thus, frequencies transmitted on cable  30  for the example values given above are 46.875 MHz, 90 MHz, and 135 MHz. Alternatively, if divider  63  does not operate in master unit  26 , frequencies transmitted on cable  30  for the typical frequency values given above are 750 MHz, 90 MHz, and 135 MHz.  
         [0156]    [0156]FIG. 5B shows frequencies used when system  20  operates as a repeater of signals in a frequency band  170  from approximately 1800 MHz to 1900 MHz. Such a band covers frequencies used by personal communication systems (PCS) and/or cellular phones, wherein the forward and reverse signal frequencies are typically separated by a duplex separation of 70 MHz. In the example shown here, the master signal received by master antenna  22  has a frequency of 1880 MH, and the slave signal received by slave antenna  36  has a frequency of 1810 MHz. As described hereinabove, synthesizer  56  most preferably generates a local oscillator signal having a frequency below the lowest value of band  170 , for example, at 1750 MHz, thereby generating IF signals in a frequency band  180  from approximately 50 MHz to 150 MHz. The frequency of the IF-FWD signal generated by mixer  46  from the master signal frequency of 1880 MHz is 130 MHz. The frequency of the IF-REV signal generated by mixer  120  from the slave signal of 1810 MHz is 60 MHz. Assuming divider  63  divides the frequency by an integer  8 , for example, a divided LO frequency of 218.75 MHz is generated. Thus, frequencies transmitted on cable  30  for the example values given above are 60 MHz, 130 MHz, and 218.75 MHz. Alternatively, if divider  63  does not operate in master unit  26 , frequencies transmitted on cable  30  for the example values given above are 60 MHz, 130 MHz, and 1750 MHz.  
         [0157]    The frequency separation of the duplex channels, (45 MHz and 70 MHz in the examples described with reference to FIGS. 5A and 5B) remains the same during the down- and up-conversion stages. However, the ratio of the separation to the mean carrier frequency is significantly increased in the IF stages generated in the master and slave units. In the example described above with reference to FIG. 5A, where the mean radio frequency is 850 MHz and the mean intermediate frequency is 100 MHz, the ratio increases from 45/850 to 45/100. It will be appreciated that the increase in ratio enables significantly improved isolation of the duplex channels to be incorporated into the IF stages, by using standard bandpass design of at least some of filters  50 ,  72 ,  80 ,  94 ,  102 , and  116 , with no deleterious effect on the stages.  
         [0158]    Those skilled in the art will be able to determine other values of frequencies to be generated by system  20  and transmitted on cable  30 , for master and slave signals with frequencies other than those of the examples described above with reference to FIGS. 5A and 5B.  
         [0159]    Each of the intermediate frequency signals transmitted on cable  30  has a frequency substantially below the frequencies of the master and slave signals received by system  20 . The lower frequencies used, and the high levels introduced by the signal amplification in both the master and the slave unit, mean that there is practically no limitation on the length of cable  30 . Similar reasoning applies when the local oscillator signal is divided and then transmitted in cable  30 . When the local oscillator signal is not divided, it may be necessary to increase the signal levels of the local oscillator to compensate for attenuation in cable  30 . Thus, slave unit  32  and its associated antenna  36  may be positioned at substantially any desired distance from master unit  26  and its antenna  22 , enabling high gains to be utilized in one or both units without introducing interference in either unit.  
         [0160]    In some preferred embodiments of the present invention, some of filters  50 ,  72 ,  80 ,  94 ,  102 , and  116  and/or some of attenuators  54  and  74  are adjusted so that in addition to operating as described hereinabove, unwanted and/or interfering signals received by antenna  22  and antenna  36  are substantially reduced or eliminated. For example, when repeater system  20  is used as a repeater of multiple access signals in a cellular communication network, such as code division multiple access (CDMA) signals, which signals are transmitted in specific channels, the filters and/or attenuators may be adjusted to allow only signals in predetermined channels to be repeated.  
         [0161]    While the preferred embodiments described hereinabove utilize frequency bands corresponding to those used by cellular telephone systems, those skilled in the art will be able to apply the principles described above, wherein a radio-frequency signal is down-converted then up-converted to recover the signal, and wherein a single local oscillator signal is utilized in both conversions, to other frequency bands used in communications systems, for instance, bands from approximately 450 MHz to 30 GHz.  
         [0162]    By using a single local oscillator in system  20 , and transferring the local oscillation signal either directly throughout the system, or by dividing and then multiplying the frequency by an integer, problems such as differences in local oscillator frequencies within a repeater system are eliminated. Thus, it will be appreciated that the single local oscillator does not need to be a high-stability oscillator, such as a crystal-controlled and/or temperature-stabilized oscillator. Since drift in the frequency of oscillation will be transferred throughout the repeater system, there are virtually no special stability requirements for the local oscillator.  
         [0163]    [0163]FIG. 6 schematically illustrates a split repeater system  220 , according to an alternative preferred embodiment of the present invention. Except where otherwise stated hereinbelow, the operation of system  220  is generally similar to that of system  20 , whereby elements indicated by the same reference numerals in systems  20  and  220  are generally identical in operation and construction. System  220  comprises a master unit  226 , which is connected to and separated from a slave unit  232  by an RF coaxial cable  230 . Master unit  226  receives a master RF signal from antenna  22 , and amplifies and transmits the amplified RF signal to cable  230 , without down-converting the RF signal to a lower frequency, as described in more detail below. Cable  230  transfers the amplified RF signal to slave unit  232 , which further amplifies the signal and transmits the repeated amplified master RF signal from antenna  36 . Similarly, as described in more detail below, slave unit  232  receives a slave RF signal from antenna  36 , and the slave RF signal is amplified without down-conversion. The amplified slave RF signal is then transferred by cable  230  to master unit  226 , where it is further amplified and the amplified repeated slave RF signal is transmitted from antenna  22 .  
         [0164]    [0164]FIG. 7 is a schematic block diagram of master unit  226 , according to a preferred embodiment of the present invention. Master unit  226  receives an RF master signal from antenna  22  via conductor  24 , and the signal is transferred via RF duplexer  40  to low-noise-amplifier  44 , which operates substantially as described above for master unit  26 . The output of amplifier  44  is transferred to an RF band-pass filter  250 , most preferably a surface acoustic wave (SAW) filter, which passes frequencies transmitted by transmitter  23  and rejects other frequencies. The amplified master signal passed by filter  250  is input to a variable gain RF amplifier  252 , whose gain is preferably set when master unit  226  is initially installed. The gain setting of amplifier  252 , and of other variable gain amplifiers in system  220 , is described in more detail below. The output of amplifier  252  is input to an RF duplexer  264 , which routes the RF signal from amplifier  252  to a bias-T filter  266 .  
         [0165]    Master unit  226  preferably comprises a power supply  268  which receives input power via a connector  228 . The input power is preferably standard AC line power, or alternatively another standard power source such as a battery. Power supply  268  supplies DC power to operate unit  226 , and also supplies DC power to filter  266 , which acts as a port and wherein the DC power and received RF signal are combined and transferred to a coaxial RF cable  230 . Cable  230  is preferably a doubly-shielded coaxial cable, or alternatively is another standard form of coaxial cable capable of transmitting RF signals with low loss. Cable  230  transfers the combined DC power and amplified RF master signal to slave unit  232 .  
         [0166]    Filter  266  also receives an amplified RF slave signal from slave unit  232 , the generation of which signal is described below, and transfers the signal to duplexer  264 . Duplexer  264  routes the slave signal to a variable gain RF amplifier  278 , whose gain is preferably set at installation of unit  226 . Amplifier  278  transfers its output to a band-pass filter  280 , preferably a SAW filter which passes frequencies transmitted by transmitter  25  and rejects other frequencies. The output of filter  280  is transferred to power amplifier  82 , isolator  84  and duplexer  40 , which function substantially as described above for master unit  26 . Duplexer  40  transfers the amplified RF slave signal via conductor  24  to antenna  22 , which radiates the signal.  
         [0167]    [0167]FIG. 8 is a schematic block diagram of slave unit  232 , according to a preferred embodiment of the present invention. Slave unit  232  comprises a bias-T filter  290  which acts as a port and which is coupled to cable  230 . Filter  290  receives the combined DC power and amplified RF master signal from cable  230 , and separates the DC level to power unit  232 . The RF master signal is transferred to an RF duplexer  292 , which routes the signal to a variable gain amplifier  398  whose gain is preferably set when slave unit  232  is installed. The output of amplifier  398  is input to a band-pass filter  302 , preferably a SAW filter which passes frequencies transmitted by transmitter  23  and rejects other frequencies. The output of filter  302  is transferred via power amplifier  104 , isolator  106 , RF duplexer  108  and conductor  34  to antenna  36 , substantially as described above for slave unit  32 , and antenna  36  radiates the amplified RF master signal.  
         [0168]    Slave unit  232  also receives, substantially as described above for slave unit  32 , an RF slave signal from transmitter  25  via antenna  36 , conductor  34 , duplexer  108 , and low-noise amplifier  124 . The amplified RF slave signal, output from amplifier  124 , is fed to a band-pass filter  316 , which is preferably a SAW filter that passes frequencies transmitted by transmitter  25  and rejects other frequencies. Filter  316  inputs the filtered signal to a variable gain amplifier  318 , whose gain is preferably set when slave unit  232  is installed, and the amplified slave RF signal is routed by RF duplexer  292  to filter  290 , which transfers the signal to cable  230 .  
         [0169]    Most preferably, the gains of amplifiers  252 ,  278 ,  318 , and  398  are adjusted so that an overall gain for the master RF signal, and for the slave RF signal, are each of the order of 90 dB, the specific overall gains being set according to signal levels from transmitters  23  and  25 . The gains of the amplifiers are preferably set so as to minimize losses in and radiation from cable  230 , and so that the gains in the master unit and the slave unit are approximately equal.  
         [0170]    The preferred embodiments described above comprise master and slave units separated by a coaxial cable. It will be appreciated that the separation of the units and their respective antennas facilitate the placement and orientation of the antennas so that signals may be transmitted by each antenna substantially without being received by the other antenna.  
         [0171]    It will further be appreciated that the preferred embodiments described above are cited by way of example, and the full scope of the invention is limited only by the claims.