Abstract:
A low noise block down converter with integrated feedhorn (LNBF). A module frame provides an isolating structure and a first receiving portion, both disposed thereon. A first probe and insert element are disposed in the first receiving portion. A connector is mounted on the module frame. First and second printed circuit boards and the isolating structure are disposed in the module frame. The first printed circuit board is coupled to the second printed circuit board. A conducting wire passes through the isolating structure and connects the second printed circuit board to the connector.

Description:
BACKGROUND 
   The present invention relates to a down converter, and in particular to a low noise block down converter with integrated feedhorn (LNBF). 
     FIG. 1   a  is a schematic diagram showing a conventional LNBF. The LNBF  100  comprises a module frame  110 , a first probe  120 , a second probe  130 , a connector  140 , a first printed circuit board (not shown) and a second printed circuit board  155 . The module frame  110  provides a waveguide tube  111 , a first receiving portion  112  and a second receiving portion  113 . The waveguide tube  111  is disposed on the module frame  110 . The first and second receiving portions  112  and  113  are formed on the module frame  110 . The first printed circuit board is installed in the module frame  110  and electronically connected to the second printed circuit board  155  and then connected to the connector  140  by a conducting wire  151 . The first probe  120  is connected into the first receiving portion  112 , a groove. The second probe  130  is connected into the second receiving portion  113 .  FIG. 1   b  is a cross section of the first probe  120  connected into the first receiving portion  112 . The first probe  120  comprises a conducting wire  121  and an insulating material  122  wrapped around the conducting wire  121 . The first probe  120  further comprises an abutting portion  123  contacting an edge of the first receiving portion  112 . The first probe  120  is L-shaped. 
   The first receiving portion  112  is a groove to receive the L-shaped first probe  120 . However, such a groove interrupts the inner surfaces of the waveguide tube  111  (acting as a resonance chamber). As a result, a deep notch  160  is generated in frequency response in the 12.6-12.7 GHz range, as shown in  FIG. 1   c,  which reflects the signals received by the LNBF  100 . The deep notch  160  is near the frequency band of the satellite signals processed by the LNBF  100 , influencing the output of the LNBF  100 . 
   In  FIG. 1   a,  a height difference exists between the second printed circuit board  155  and the connector  140 , whereby the conducting wire  151  is necessarily exposed to the air to connect the connector  140 . Such an arrangement increases the large voltage standing wave rate (VSWR) beyond 4, thus significantly influence the received signals of the LNBF  100 . 
     FIG. 1   d  is a circuit diagram of a conventional LNBF. The down converter circuit comprises a radio frequency circuit  2100  and an intermediate frequency circuit  2200 . The frequency band of radio signals is between 10 GHz and 13 GHz. The frequency band of mid-frequency signals is between 900 MHz and 2500 MHz. The radio frequency circuit  2100  comprises an amplifier  210 , filters  220 ,  221  and  222 , a local oscillator  230 , and a mixer  240 . The intermediate frequency circuit  2200  comprises distribution units  261  and  262 , a switch  270 , and an amplifier  280 . Conventionally, a plurality of radio frequency circuits  2100  and intermediate frequency circuits  2200  are alternately arranged on the first printed circuit board  150  and the second printed circuit board  155 . To meet the requirements of radio frequency circuit  2100 , both the first printed circuit board  150  and the second printed circuit board  155  are fabricated using material such as PTFE or Rogers, with high costs, accordingly. 
   SUMMARY 
   An embodiment of the present invention provides a low noise block down converter with integrated feedhorn (LNBF). The LNBF comprises a module frame, a first probe, an insert element, a connector, a first printed circuit board, a second printed circuit board and a conducting wire. The module frame comprises an isolating structure and a first receiving portion. The first probe and the insert element are disposed in the first receiving portion. The connector is mounted on the module frame. The first printed circuit board and the second printed circuit board are disposed in the module frame and electronically connect to each other. The conducting wire passes through the isolating structure and connects the second printed circuit board and the connector. 
   According to the present invention, receiving condition of satellite signal can be improved using the insert element by reducing the resonance within the first receiving portion. The isolating structure also isolates the electromagnetic noise generated by conducting wire and reduces the VSWR below 2. The RF circuit is also separated from the lower-frequency circuit, and the two circuits are disposed on two different circuit boards. By reducing the usage of expensive RF circuit board, the present invention also reduces the cost of a LNBF. 
   A detailed description is given in the following with reference to the accompanying drawings. 

   
     DESCRIPTION OF THE DRAWINGS 
     The present invention can be more fully understood by reading the subsequent detailed description in conjunction with the examples and references made to the accompanying drawings, wherein: 
       FIG. 1   a  is a schematic diagram showing a conventional LNBF; 
       FIG. 1   b  is a local cross section of a first probe in a first receiving portion; 
       FIG. 1   c  is a schematic diagram showing received signals of the conventional LNBF; 
       FIG. 1   d  is a circuit-diagram of the conventional LNBF; 
       FIG. 2  is a schematic diagram showing a LNBF of an embodiment of the present invention; 
       FIG. 3   a  is a local cross section of an insert element connectorged in a first receiving portion; 
       FIG. 3   b  is a schematic diagram showing received signals of the LNBF of the embodiment of the present invention; 
       FIG. 4  is a partial schematic diagram showing a LNBF of the embodiment of the present invention; and 
       FIG. 5  is a schematic diagram of the modify hairpin filter. 
   

   DETAILED DESCRIPTION 
     FIGS. 2 and 4  show a LNBF  100  of an embodiment of the present invention, comprising a module frame  110 , a first probe  120 , a second probe  130 , an insert element  124 , a connector  140 , a first printed circuit board  150 , a second printed circuit board  155 , a board  153 , and a conducting wire. The module frame  110  comprises an isolating structure  152 , a first receiving portion  112 , a second receiving portion  113 , and a waveguide tube  111 . The isolating structure  152 , the first receiving portion  112 , and the second receiving portion  113  are formed on the module frame  110 . The waveguide tube  111  is disposed on the module frame  110 . The first receiving portion  112  interlinks the waveguide tube  111 . The first receiving portion  112  is a groove structure and provides a circular opening  1121 . In this embodiment, the diameter of the circular opening  1121  exceeds the width of the groove. The first probe  120 , disposed in the first receiving portion  112 , receives a first signal from the waveguide tube  111 . The insert element  124  is disposed in the first receiving portion  112  to improve the performance of the received signals, see  FIG. 3   a.  The second probe  130  is disposed in the second receiving portion  113  and receives a second signal from the waveguide tube  111 . A down converter circuit (not shown) is formed on the first printed circuit board  150  and the second printed circuit board  155  ( FIG. 4 ) for converting the first signal and the second signal to a first down-converted signal and a second down-converted signal. Since the first printed circuit board  150  is electronically connected to the second printed circuit board  155 , signals are transmitted between the first printed circuit board  150  and the second printed circuit board  155 . The conducting wire  154 , surrounded by an insulating coating, passes through the isolating structure  152  and connects the second printed circuit board  155  to the board  153 . As a result, the first and second down-converted signals at the second printed circuit board  155  are transmitted to connector  140  via the conducting wire  154  and the conducting strip on board  153 . 
     FIG. 3   a  is a schematic diagram showing the insert element  124  and the first probe  120  in the first receiving portion  112 , wherein the first receiving portion  112  is a groove structure. The first probe  120  comprises a first conducting wire  121  and a first insulating material  122 . The first conducting wire  121  is divided into a first part  1211  and a second part  1212  that perpendicular to the first part  1211 . The first insulating material  122  wraps around the first part  1211  of the conducting wire  121  to form a cylinder. An abutting portion  123  at one end of the first insulating material  122  contacts a fringe (not shown) of the first receiving portion  112 . When the first probe  120  is plugged into the first receiving portion  112 , the first part  1211  and the first insulating material  122  are located at the circular opening  1121  (shown in  FIG. 2 ). The second part  1212  is seated in the first receiving portion  112 , with the second part  1212  that perpendicular to the first part  1211 . The insert element  124  is disposed in the first receiving portion  112  opposite the circular opening  1121 . 
   The first receiving portion  112  may be a recess having different shape, and the insert element  124  may be a screw or other element that can adjust resonance effect of the receiving portion  112 .  FIG. 3   b  shows the received signals of the LNBF  100 . As a result, the deep notch formed between 12.6 GHz and 12.7 GHz of the prior-art LNBF, is eliminated. 
   In  FIG. 4 , the isolating structure  152  is rectangular with through holes  1521  formed therein. The conducting wire  154  passes through the through holes  1521  and electronically connects to the second printed circuit board  155 . The second printed circuit board  155  electronically connects to the first printed circuit board  150  via another conducting wire (not shown). An insulating material is formed around the conducting wire  154 . Another end of the conducting wire  154  connects to the board  153 , and the connector  140  connects to the board  153  as well. The conducting strip on board  153  interconnects conducting wire  154  and the connector  140 . Since the conducting wire  154  is wrapped with the insulating material and is embedded within the isolating structure  152 , the voltage standing wave rate (VSWR) of the LNBF  100  can be reduced to around or less than 2. The isolating structure  152  may comprise metal and can be integrated with the housing. 
   Referring to  FIG. 1   d,  the down converter circuit of the embodiment of the present invention comprises a radio frequency circuit  2100  and an intermediate frequency circuit  2200 . The radio frequency circuit  2100  comprises an amplifier  210 , filters  220 ,  221  and  222 , a local oscillator  230  and a mixer  240 . The first and the second signals are processed by the radio frequency circuit  2100  to generate a first down-converted signal and a second down-converted signal respectively. The intermediate frequency circuit  2200  comprises an amplifier  250 , distribution units  261  and  262 , a switch  270 , and an amplifier  280 . For producing multiple output, the first down-converted signal and the second down-converted signal are split by the intermediate frequency circuit  2200 . To reach better performance, the radio frequency circuit  2100  is disposed on the first printed circuit board  150  that is manufactured with good high-frequency characteristics, such as Rogers or PTFE. The intermediate frequency circuit  2200  is disposed on the second printed circuit board  155 . The second printed circuit board  155  is fabricated using low-cost epoxy resin material to reduce costs. Moreover, the second printed circuit board  155  can be a four-layer board. The intermediate frequency circuit  2200  is disposed on both sides of the second printed circuit board  155 . 
   In this embodiment, the first signal and the second signals can be RF signals with frequency between 10 GHz and 13 GHz. The frequency of the first down-converted signal and the second first down-converted signal are between 900 MHz and 2500 MHz. 
   The filter  221  is for filtering unwanted twofold frequency noises generated by the local oscillator  230 . The filter  221  can be an interdigital filter or a modified hairpin filter. The cycle of the interdigital filter is three times that of the base frequency.  FIG. 5  is a circuit structure of the modified hairpin filter. For technology of the modified hairpin filter please refer to a publication “Hairpin filters with tunable transmission zeros, IEEE”. 
   A discontinuous resonance generated from the receiving portion of the LNBF is eliminated by the insert element. Thus, the performance of the received signals is improved. isolating structure. By isolating the undesired electromagnetic emission, the isolating structure effectively reduced the VSWR of the LNBF to about or less than 2. To reduce costs, the radio frequency circuit and the intermediate frequency circuit of the LNBF are separately disposed on a first printed circuit board and a second printed circuit board of different material. 
   While the invention has been described by way of example and in terms of preferred embodiments, it is to be understood that the invention is not limited thereto. On the contrary, it is intended to cover various modifications and similar arrangements apparent to those skilled in the art. Therefore, the scope of the appended claims should be accorded the broadest interpretation so as to encompass all such modifications and similar arrangements.