Patent Publication Number: US-6981307-B2

Title: Manufacturing method for filter module

Description:
DETAILED DESCRIPTION OF THE INVENTION 
     1. Technical Field of the Invention 
     The present invention relates to a manufacturing method for a filter module containing a filter and a device except the filter. 
     2. Description of the Related Art 
     A filter module containing a filter and a low-noise amplifier (LNA) is disclosed in Japanese Unexamined Patent Application Publication No. 5-83147. In the filter module, the filter and the LNA are housed in the same case, and the LNA is directly connected to a coupling line of the output portion of the filter. 
     In this way, the characteristics of the filter and the LNA can be monitored and adjusted by using the coupling line. 
     However, in such filter modules having a filter and a device directly connected and housed in the same case, since the filter and the device are required to be adjusted together, there is a problem in that it takes time to adjust them. Furthermore, when the filter and the device are combined, since the characteristics of each of them are not known, it is not easy to adjust them. 
     SUMMARY OF THE INVENTION 
     Accordingly, it is an object of the present invention to provide a manufacturing method for a filter module in which the time for adjustment is shortened and the adjustment for obtaining fixed characteristics is made easy. 
     According to a manufacturing method for a filter module of the present invention, a device, characteristics measurement of which has been made, and a filter, characteristics adjustment of which is to be made, are provided to manufacture a filter module. 
     The required characteristics of the filter are first determined from the characteristics of the device and target characteristics of the filter module. 
     Then, the characteristics of the filter alone are measured. From the characteristics and the required characteristics, adjustment locations and adjustment amounts of the filter are determined so as to meet the required characteristics, and then the adjustment is carried out. 
     After the adjustment is carried out, the filter and the device are combined to form the filter module. 
     In the manufacturing method for a filter module according to the present invention, the connection between the filter and the device is preferably made by connecting a pin provided in the filter to a transmission line provided in the device, and the characteristics of the filter alone are measured by attachment of a connector adapter in which the pin constitutes a center conductor. 
     In a preferred manufacturing method for a filter module according to the present invention, the device is a circuit constructed on a substrate, and the filter is provided with a concave portion into which the substrate is fitted. 
     Furthermore, in the manufacturing method for a filter module according to the present invention, the device is preferably a low-noise amplifier and the filter is connected in a front stage or rear stage of the low-noise amplifier. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIGS. 1A and 1B  are block diagrams showing a filter module and a filter, respectively. 
         FIGS. 2A–2C  are perspective views showing the construction of a filter, device, and filter module. 
         FIGS. 3A–3D  are partial perspective views showing the construction of the connection portion between a filter and a device. 
         FIG. 4  is a flow chart showing the processes of a manufacturing method for a filter module. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Hereinafter, a manufacturing method for a filter module will be described with reference to the accompanying drawings. 
       FIG. 1A  is a block diagram showing the construction of a filter module at the time when the filter module and its characteristics are adjusted.  FIG. 1B  shows the construction of a filter  10  separated from a device  20 . As is shown in  FIG. 1A , the filter module is constructed such that the device  20  (LNA) is provided in a latter stage of the filter  10 . In the manufacturing method for a filter module according to the present invention, the device  20 , the characteristics of which are known, is used and the measurement and adjustment of the characteristics of the filter  10  alone are performed. 
       FIGS. 2A through 2C  are perspective views showing the construction of the filter, device, and filter module, respectively.  FIG. 2A  shows the construction of the filter alone. The filter  10  is provided with a connector  14  for connection to the outside. The filter  10  is also provided with a concave portion  11  into which a substrate constituting the device is fitted. A pin  12  for connection to a transmission line of the device is provided in the concave portion  11  of the filter  10 . This filter  10  can be used as a dielectric filter in which electrodes are provided inside and outside a dielectric block, or as a dielectric filter in which a dielectric resonator is disposed inside a cavity. Furthermore, the filter  10  is provided with a frequency adjustment screw (not shown) for adjusting a frequency as required. 
     In  FIG. 2A , reference numeral  13  represents a connector adapter. When the connector adapter  13  is attached to the pin  12 , a coaxial connector having the connector adapter  13  as an outer conductor and the pin  12  as a central conductor is constructed. In that state, the front end of the filter can be connected to the outside through the connector  14  and the rear end of the filter can be connected to the outside through the coaxial connector made up of the connector adapter  13  and the pin  12 . 
       FIG. 2B  shows how the device  20  is fitted into the filter  10 . The device  20  shown in  FIG. 2B  is formed as a circuit board. A connector  21  for connection to the outside is provided in the device  20 . The device  20  is electrically connected to the filter  10  by fitting the device  20  into the concave portion of the filter  10  and preferably soldering the pin  12  of the filter  10  to a transmission line of the device  20 . Reference numeral  30  represents a protective cover which covers the device  20 . Thus, a filter module  100  is constructed as shown in  FIG. 2C . 
       FIGS. 3A through 3D  show how the connector adapter  13  is attached to the pin  12  of the above filter, and how the device  20  is connected to the filter. In the filter alone, the connector on the output side of the filter is made such that the connector adapter  13  is attached to the pin  12  as shown in  FIG. 3A . After the characteristics of the filter alone has been measured and adjusted, the connector adapter  13  is removed as shown in  FIG. 3B , and the filter and the device are electrically connected such that the transmission line  22  is soldered to the pin  12  of the filter as shown in  FIGS. 3C and 3D . 
       FIG. 4  is a flow chart showing the processes of the manufacturing method for a filter module according to the present invention. In this invention, adjustments are preferably not performed for the variations in manufacture of the device (LNA) to be used in the filter module, but rather, the characteristics of the filter module are set to satisfy a fixed specification by adjustment of only the filter portion. 
     The required characteristics of the filter are determined from characteristics of the device and target characteristics of a filter module (n 1 ). Preferably, the characteristics of the filter module are normalized using S parameters. The S parameters of the device without the filter are measured using a network analyzer in advance. Then, by using a high-frequency simulator, the S parameters of the filter that satisfy the normalized S parameters of the filter module are determined from the normalized S parameters of the filter module and the S parameters of the device. 
     Next, the characteristics of the filter alone are measured, and adjustment locations and adjustment amounts of the filter are determined from the measured characteristics of the filter and the required characteristics of the filter (n 2  and n 3 ). Preferably, the upper limit and lower limit of each element (equivalent capacitance, inductance, etc.) constituting the filter is set in advance, and the value of each element constituting the filter is determined so as to meet the target S parameters of the filter by using the high-frequency simulator. Moreover, since each element of the filter practically has its own adjustable range different from each other, this is input in advance. 
     Next, the determined value of each element constituting the filter is input into a computer, the computer is connected to the network analyzer, and the filter is connected to the network analyzer. As commonly conducted in the field of filter designing, calculations are performed to determine what part of the filter is to be cut to what level, the frequency adjustment screw of which resonator is to be turned, etc., and they are adjusted so that the required S parameters may be satisfied (n 4 ). 
     Then, the filter and the device are assembled to produce a filter module (n 5 ). Thereafter, the characteristics of the filter module are measured, it is judged whether the characteristics are in a specified range or not, and whether the filter module passes and is accepted as a conforming filter module (n 6  and n 7 ). 
     According to the present invention, the device is not adjusted and the measurement and adjustment of the filter alone is made possible. Accordingly, the time required for adjustment is shortened and adjustment of the filter module characteristics can be easily made. 
     Furthermore, according to the present invention, since a filter can be connected to the outside in order to measure the characteristics of the filter at the portion of the filter where the a device is later connected, the measurement of the characteristics of the filter alone can be securely performed without being affected by any other element. Therefore, desired characteristics of a filter module can be easily obtained only by the adjustment of the filter. 
     Furthermore, according to the present invention, since a filter is provided with a concave portion into which a device constructed on a substrate is fitted, the filter and the device are easily assembled. 
     Furthermore, according to the present invention, since the device is a low-noise amplifier (LNA), a low-noise amplifier the transmission loss of which is low and which is of small size can be constructed. 
     Although the present invention has been described in relation to particular embodiments thereof, many other variations and modifications and other uses will become apparent to those skilled in the art. It is preferred, therefore, that the present invention be limited not by the specific disclosure herein, but only by the appended claims.