Abstract:
The invention discloses a DCS/WCDMA dual frequency multiplexer. On one hand, the multiplexer utilizes distributed parameter type capacitors in place of conventionally used capacitors. On the other hand, within the multiplexer, a direct circuit and a RF circuit are isolated from each other physically. All components including capacitors co-exist together physically. Similarly, the invention further discloses a dual frequency multiplexer with large application range. It also utilizes the distributed parameter type capacitors like the DCS/WCDMA dual frequency multiplexer. Because the invention has redesigned the entire construction of the multiplexer, it results good effects such as small size, less differential loss, large power capacity, as well as high isolation degree between circuits.

Description:
FIELD OF THE INVENTION 
       [0001]    The invention relates to a processing device for multiplexing a DCS system and a WCDMA system and more particularly, relates to a DCS/WCDMA dual frequency multiplexer. 
       BACKGROUND OF THE INVENTION 
       [0002]    With the rapid development of mobile communications, a scheme in which multiple systems share a common station as well as a common antenna feeder resource has gotten its population by more and more operators. By this way, advantage of sharing resource and reducing system device cost can be obtained. In DCS/WCDMA system sharing a common antenna feeder, dual frequency multiplexer is a necessary microwave component that mainly serves to multiplex/de-multiplex signals of different systems so as to save the length of feed cable, simplify system construction and reduce cost. In addition, power is supplied to the devices at base station tower via a radio frequency cable and accordingly, the multiplexer connected with the feed cable must have the ability of passing direct current there through. 
         [0003]    With reference to the schematic diagram of  FIG. 1 , a multiplexer is a microwave component having three ports, i.e., two direct current feed circuits and two RF signal circuits, wherein each direct current feed circuit is constructed by a lump parameter low pass filter, a switch and a lightning protection device. The low pass filter is used to suppress RF signal at high frequency such that control signal at certain frequency (such as 3 MHz) can pass the filter with ease. The switch serves to selectively conduct direct current there through. The RF signal circuit consists of a blocking capacitor and a band pass filter. The band pass filters of respective two RF signal circuits have their band pass range be set so as to be suited to frequency range of two signals to be multiplexed. During operation, the signal input from a common port Port 1  is shunted to Port 2  or Port 3  according to the frequency range. Alternatively, the signal input from ports Port 2  or Port 3  may also be combined and output via the port Port 1 . 
         [0004]    The RF signal frequency range of the system in which DCS/WCDMA sharing a common antenna feeder is 1710 MHz-1880 MHz and 1920 MHz-2170 MHz respectively. By now, to obtain such wide a work frequency band and capability of passing direct current, most multiplex products employ dielectric substrates and realize it by micro-strip circuits. The disadvantages of product of this type include large bulkage and low power capacity. Moreover, inactive inter-modulation is greatly depended on property of dielectric substrate material and therefore, it is difficult to control the dielectric substrate material during batch production. 
       SUMMARY OF THE INVENTION 
       [0005]    One object of the invention is to provide a DCS/WCDMA dual frequency multiplexer which can be minimized in size, reduce differential loss, obtain large power capacity, and have high isolation degree between direct current circuit and RF signal circuit. 
         [0006]    Another object of the invention is to provide a more general dual frequency multiplexer so as to extend application field of the invention, for example application of the invention into a system in which 2G and 3G share a common antenna feeder. 
         [0007]    To this end, the invention utilizes the following technical scheme. 
         [0008]    The DCS/WCDMA dual frequency multiplexer of the invention is used to perform multiplexation of two signals of different frequency, and includes a multiplexer port, a first port and a second port. The first and second ports are both connected with the multiplexer port through a RF (radio frequency) circuit and a direct current circuit respectively. Each RF circuit comprises a band pass filter and capacitors connected with the band pass filter at two sides thereof in series; the two band pass filters are coupled with the multiplexer port via a common capacitor; each direct circuit comprises a low pass filter and a discharging tube connected to the low pass filter electrically; and the two direct circuit are electrically connected to the multiplexer port through the low pass filter. 
         [0009]    The multiplexer also comprises a box including a base body, a circuit board and a cover body; the two band pass filters are disposed in the base body and separated from each other by a metal plate; the multiplexer port, first and second ports are positioned on lateral sides of the base body; the capacitors are contained in corresponding band pass filters; a plurality of support members are disposed on top portion of the base body; the low pass filters are supported on the support members; the discharging tube and switch are secured on the circuit board; the cover body is clamped together with the base body. 
         [0010]    The capacitors each are of distributed parameter capacitor. 
         [0011]    Each capacitor includes an inner conductor, an insulator and a sleeve; the insulator surrounds the inner conductor at outer perimeter thereof, while the sleeve surrounds the outer perimeter of the insulator; the sleeve serves to electrically connect to adjacent band pass filters; the inner conductor is used to connect electrically with adjacent direct current circuit so as to be connected with an adjacent port. 
         [0012]    The insulator is Polytetrafluoroethene film. 
         [0013]    Each band pass filter comprises a plurality of harmonic posts; and a ridge is formed between two adjacent harmonic posts for enhancement of coupling effect. 
         [0014]    The circuit board has several tuning screws corresponding to the two band pass filters, the tuning screws passing through the circuit board and extending into inside of the band pass filters for adjusting harmonic frequency and coupling degree. 
         [0015]    Inductive coupling is generated in the first band pass filter by creating openings in the filter, while capacitive coupling is generated in the second band pass filter by means of flying bars. 
         [0016]    The first and second band pass filters share a common harmonic post at a location adjacent the multiplexer port. 
         [0017]    The number of the harmonic posts of the band pass filter located between the first port and multiplexer port is seven, whereas the number of the harmonic posts of the band pass filter located between the second port and multiplexer port is eight. 
         [0018]    The direct circuit also comprises a switch; the printed circuit of the direct circuit has several discontinous locations where slots are defined, and metal magnetic beads are situated in the slots in order to open or close the direct circuit. 
         [0019]    A gap with a width not less than 0.2 mm is defined between the top surface of the support member and a bottom surface of the circuit board. 
         [0020]    The cover plate has a through hole defined therein on which a Gore permeable film is covered. 
         [0021]    A waterproof plate is placed on the through hole. 
         [0022]    The second object of the invention is obtained by the following technical solution. 
         [0023]    A general dual frequency multiplexer used to perform multiplexation of two signals with different frequency, comprising a multiplexer port, a first port, and a second port, wherein the first and second ports are both connected with the multiplexer port through a RF circuit and a direct current circuit respectively; each RF circuit comprises a band pass filter and capacitors connected with the band pass filter at two sides thereof in series; the two band pass filters are coupled with the multiplexer port via a common capacitor; each direct circuit comprises a low pass filter and a discharging tube connected to the low pass filter electrically; and the two direct circuit are electrically connected to the multiplexer port through the low pass filter; the capacitors each are of distributed parameter capacitor. 
         [0024]    Each capacitor includes an inner conductor, an insulator and a sleeve; the insulator surrounds the inner conductor at outer perimeter thereof, while the sleeve surrounds the outer perimeter of the insulator; the sleeve serves to electrically connect to adjacent band pass filters; the inner conductor is used to connect electrically with adjacent direct current circuit so as to be connected with an adjacent port. 
         [0025]    The insulator is Polytetrafluoroethene film. 
         [0026]    Each band pass filter comprises a plurality of harmonic posts; and a ridge is formed between two adjacent harmonic posts for enhancement of coupling effect. 
         [0027]    The circuit board has several tuning screws corresponding to the two band pass filters, the tuning screws passing through the circuit board and extending into inside of the band pass filters for adjusting harmonic frequency and coupling degree. 
         [0028]    Inductive coupling is generated in the first band pass filter by creating openings in the filter, while capacitive coupling is generated in the second band pass filter by means of flying bars. 
         [0029]    The first and second band pass filters share a common harmonic post at a location adjacent the multiplexer port. 
         [0030]    Compared with prior art, the invention can get the following good effects. The dual frequency multiplexer of the invention is implemented by band pass filters, thereby separating the direct circuit and RF circuit from each other. The utilization of distributed parameter type of capacitors brings size reduction of the product of the invention. Moreover, the invention has designed the entire construction, hence leading to good effects such as small size, less differential loss, large power capacity, as well as high isolation degree between circuits. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0031]      FIG. 1  illustrates a schematic diagram of the invention; 
           [0032]      FIG. 2  illustrates a perspective view of the product of the invention; 
           [0033]      FIG. 3  illustrates an enlarged view of portion A of  FIG. 2 ; 
           [0034]      FIG. 4  shows top plan view of a base body of the invention; and 
           [0035]      FIG. 5  shows a schematic view of a printed circuit of the direct current circuit of the circuit board of  FIG. 2 . 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0036]    With reference to  FIG. 1 , the DCS/WCDMA dual frequency multiplexer of the invention is mostly used to combine 2G signal and 3G signal together. 
         [0037]    As shown in  FIG. 2 , the multiplexer is of a box type, and is constructed by a base body  6 , a circuit board  2  and a cover body  4  collectively. 
         [0038]    A first port Port 2  and a second port Port 3  are provided at right side of the base body  6 , both of which are adapted to receive radio frequency (RF) signals with frequency of 1710-1880 MHz and 1920-2170 MHz respectively. A multiplexer port Port 1  is located at the left side of the base body  6 . The multiplexer port Port 1  is able to output RF signal multiplexed by the first and second ports (Port 2  and Port 3 ). Alternatively, a signal can be input into the multiplexer port Port 1  and then de-multiplexed through the first and second ports (Port 2  and Port 3 ). 
         [0039]    Two RF circuits, that is, a first RF circuit for transmitting DCS signal and a second RF circuit for transmitting WCDMA signal are integrated in the base body  6 . The first RF circuit is constructed by the first port Port 2 , a first capacitor  68 ′ (see  FIG. 4 ), a first band pass filter  610 , a third capacitor  68  and a multiplexer port Port 1 , all of which are electrically connected with each other in series. The second RF circuit is constructed by the second port Port 3 , a second capacitor  68  (see  FIG. 4 ), a second band pass filter  620 , a third capacitor  68  and the multiplexer port Port 1 , all of these components being connected with each other electrically. 
         [0040]    It is clear that each RF circuit includes an individual band pass filters ( 610  or  620 ), and shares the third capacitor  68 . 
         [0041]    Each of band pass filters  610  and  620  is constructed by coaxial harmonic chamber, and includes plural harmonic posts  611  and  621 . As illustrated in  FIGS. 2 and 4 , a compartment defined in middle portion of the base body  6  is divided into two parts by a metal plate  63 , these two parts being the first band pass filter  610  corresponding to the first RF circuit and the second band pass filter  620  corresponding to the second RF circuit. The separation effect caused by the metal plate  63  can result in higher isolation between the first and second RF circuits. Seven harmonic posts  611  are sequentially arranged in the first band pass filter  610 . A harmonic post  611  close to the first port Port 2  is electrically coupled to the first capacitor  68 ′ via a wire, thereby being further coupled with the first port Port 2 . Eight harmonic posts  621  are sequentially arranged in the second band pass filter  620 . A harmonic post  611  close to the second port Port 3  is electrically coupled to the second capacitor  68 ″ via a wire, thereby being further coupled with the second port Port 3 . A harmonic post  6012  located adjacent the multiplexer port Port 1  is shared by the first and second band pass filters  610  and  620 . In fact, the total number of the harmonic posts for the both band pass filters is fourteen. The harmonic post  6012  common to both filters may be used to transfer the signal of band pass filters  610  and  620  to the multiplexer port Port 1  through a wire  671  by means of electromagnetic resonance. 
         [0042]    As seen from  FIGS. 2 and 4 , the band pass filters  610  and  620  are not completely isolated by the metal plate  63  located between therebetween. 
         [0043]    To ensure isolation of the WCDMA RF circuit, two inductive couplings are formed in the first band pass filter  610  by creating openings on the band pass filter  610 , thereby resulting two suppression points at right side of the pass band and WCDMA band pass in total. 
         [0044]    To ensure isolation of the DCS RF circuit, two capacitive couplings are formed in the second band pass filter  620  by providing flying bars on the band pass filter  610 , thereby resulting two suppression points at left side of the pass band and DCS band pass in total. 
         [0045]    With reference to  FIGS. 2 ,  3  and  4 , the first and second capacitors  68  and  68 ″ have the same construction as the third capacitor  68 . The third capacitor  68  includes an inner conductor  683 , an insulator  682  and a sleeve  681 . The insulator  682  surrounds the inner conductor  683 , while the sleeve  681  surrounds the insulator  682 . The insulator  682  is implemented by medium film such as Polytetrafluoroethene (PTFE). The sleeve  681  is electrically coupled with the common harmonic post  6012  of the first and second band pass filters  610  and  620 , while the inner conductor  683  is coupled with the multiplexer port Port 1  directly. As such, the sleeve  681  and inner conductor  683  can be isolated from each other by the insulator  682  so as to construct distributed parameter capacitor. For two RF circuits, transmission of RF signal is carried out by coupling between the inner conductor  683  and sleeve  681 . For two direct current circuits, they are directly connected to the inner conductor  683  such that direct current is prohibited to pass through the sleeve  681 , hence direct current being blocked by the RF circuit. 
         [0046]    As described above, the first and second capacitors  68 ′ and  68 ″ employ the same construction as the third capacitor  68 . However, the sleeve of the first capacitor  68 ′ is connected only to a harmonic post  611  adjacent the first capacitor  68 ′, of the first band pass filter  610 , whilst the sleeve of the second capacitor  68 ″ is connected only to a harmonic post adjacent the second capacitor  68 ″, of the second band pass filter  620 . 
         [0047]    The inner conductors of corresponding capacitors are extended out of and electrically connected with the ports Port 1 , Port 2  and Port 3  respectively. 
         [0048]    Referring to  FIG. 2  again, the circuit board  2  has a printed circuit board supported thereon. The printed circuit is shown in  FIG. 5  and mainly located at two sides of the circuit board  2 . Direct circuits of the dual multiplexer are techniques of well known and description thereof is set forth below in brief. 
         [0049]    Referring to  FIGS. 1 ,  2  and  FIG. 5 , two direct current circuits, namely a first direct current circuit and a second direct current circuit are incorporated into the circuit board  2 . Each direct current circuit is mainly constructed of low pass filters  201 ,  202  and  203 , switches and lightning protection components  205 . Signals coming from the first/second ports Port 2 /Port 3  of the first/second direct current circuits are filtered by a first/second low pass filter  202 / 203 , then combined together and outputted to the third low pass filter  201 , and finally outputted to the multiplexer port Port 1 . The low pass filters  201 ,  202  and  203  serve mainly to suppress high frequency signal while permitting transmission of control signal with a frequency less than 3 MHz. Moreover, a switch may be provided between the two direct current circuits depending upon need to determine whether transmission of direct current is allowed. Lightning protection component  205  made of discharging tube may be further provided. 
         [0050]    The printed circuit diagram of  FIG. 5  shows three connection nodes  281 ,  282  and  283  of the low pass filters  201 ,  202  and  203 . The low pass filters  201 ,  202  and  203  are supported independently on three support members. As shown in  FIG. 2 , the three support members  641 ,  642  and  643  are disposed on top edges of the two band pass filters  610  and  620 , and are adjacent to respective ports Port 1 , Port 2  and Port 3  (see  FIG. 4 ). Each support member has respective low pass filters  201 ,  202  and  203  supported thereon. 
         [0051]    One ends of respective low pass filters  201 ,  202  and  203  are connected to capacitors of adjacent ports Port 1 , Port 2 , Port 3 . More specifically, one end of the third low pass filter  201  is electrically connected with the inner conductor  683  of the third capacitor  68 ; one end of the first low pass filter  202  is electrically connected with the inner conductor of the first capacitor  68 ′; while one end of the second low pass filter  203  is electrically connected with the inner conductor of the second capacitor  68 ″. The other ends of the low pass filters  201 ,  202  and  203  have predefined contact pads  26  which contact respectively with the connection nodes  281 ,  282  and  283  of the printed circuit board shown in  FIG. 5 . Corresponding to three contact pads  26 , three holes are defined in the circuit board  2 . Engagement of three holes defined in the circuit board  2  with three contact pads  26  ensures connection between the circuit board  2  and base body  6 . At this time, three connection nodes  281 ,  282  and  283  of the printed circuit board shown in  FIG. 5  contact with the contact pads  26  of three low pass filters  201 ,  202  and  203  of three support members respectively, thus resulting connection of the low pass filters  201 ,  202  and  203  with the direct current circuit. A gap with a width not less than 0.2 mm is defined between the top surface of the support member and the circuit board in order to maintain good electrical performance of the RF signal. 
         [0052]    The switches are implemented by some metal magnetic beads  204  welded onto the circuit board to suppress high frequency signal. Locations of the printed circuit where the magnetic beads are provided are discontinued. Here, slots can be further defined to engage the spherical surface of the magnetic beads. Disconnection can be established by removing the magnetic beads  204 , and resumption of connection can be obtained by placing the same thereon. 
         [0053]    As illustrated in  FIG. 2 , the third low pass filter  201  is electrically coupled with the multiplexer port Port 1  by means of connection of the wire  272  with the inner conductor  683  of the third capacitor  68 . The same principle applies to the second and third low pass filters  202  and  203 . By this way, it is realized that both the direct current circuit and RF circuit are coupled with the multiplexer port Port 1 . 
         [0054]    As illustrated again in  FIG. 2 , corresponding to two band pass filters  610  and  620  of the base body  6 , twenty-nine tuning screws  69  are located at two lateral sides of the circuit board  2 . When the circuit board  2  and the base body  6  are secured together, the screws  69  can pass through the circuit board  2  and then extended into the interior of the two band pass filters  610  and  620 . The screws  69  are used to adjust tuning frequency and coupling degree of the harmonic oscillators of the two band pass filters  610  and  620 . 
         [0055]    To achieve strong coupling among the harmonic posts  611 , a ridge  616  is formed between two adjacent harmonic posts  611  of the two band pass filters  610  and  620 . The height of various ridges  616  may vary and be regulated according to certain situation. A gap with a width preferably not less than 1.5 mm is defined between the harmonic posts and the circuit board  2  so as to meet power capacity requirement. 
         [0056]    With reference to  FIG. 2  again, which shows the cover body  4  used to cover the base body  6 , thereby protecting components inside the base body  6 . A rubber ring may be provided at the perimeter of the cover body  4  so as to enhance waterproof performance and protect the inner circuit. A Through hole may be defined in the surface of the circuit board  2 . A Gore permeable film  40  may be covered on the through hole to keep pressure balance between inside and outside of the base body  6 . In addition, a waterproof plate  41  is placed on the through hole to protect the Gore permeable film  40 . 
         [0057]    In addition, the inner surfaces of the two band pass filters  610  and  620  are coated with silver, thereby greatly reducing attenuation of RF signal transmission and keeping differential loss of the signal within the pass band less than 0.2 dB. 
         [0058]    The design of the invention is never limited to DCS/WCDMA antenna feeder sharing system. In addition, the invention can also be applied to systems such as 2G/3G antenna sharing system. In such systems, distributed parameter-type capacitors described above may be employed. Specific shape and layout of the cover body can be varied within the spirit of the invention. As such, the invention can also be adapted to dual frequency multiplexers of general purpose, as well as kinds of antenna feeder sharing systems. 
         [0059]    In summary, the invention has overcome drawbacks of prior art. The following advantages can be resulted after making suitable adjustment to electrical structure and physical structure of the multiplexer. 
         [0060]    The size of the dual frequency multiplexer of the invention can be reduced even to 218 mm*145.5 mm*51 mm. The sleeve typed coupling construction sufficiently utilizes a room through which the inner conductor of the multiplexer port Port 1  passes. Therefore, coupling of RF signal is obtained, and no additional space is necessary. Addition of the lump parameter low pass filters between the direct current circuit and RF circuit ensures isolation between the direct current circuit and RF signal circuit, and reduces largely the size of the printed circuit board on the circuit board. 
         [0061]    High isolation is realized. Because each RF circuit is of completely sealed waveguide chamber construction, isolation between the circuits is improved largely. The isolation provided by the first port Port 1  to RF signal at frequency of 1710-1880 MHz is larger than 50 dB, and the isolation provided by the second port Port 3  to RF signal at frequency of 1920-2170 MHz is also larger than 50 dB. 
         [0062]    Higher power capacity is realized. As a gap with sufficient width is defined between each harmonic post within the coaxial chamber and walls of the coaxial chamber, RF signal power support ability of the components is enhanced. Mean power supported by each port is up to 250 watts.