1/2 WAVELENGTH SIDE COUPLING FILTER

Abstract: In a 1/2 wavelength side coupling filter, a plurality of resonance lines (4) are arranged on a board (20) in parallel to each other in a staggered manner so that respective ends thereof have step portions. An input coupling line (3) is arranged in parallel to the plurality of resonance lines, with an input end (5) formed opposed to an intermediate position of the adjacent resonance line and one end portion (6) formed aligned with one end portion of the adjacent resonance line. An adjusting line (7) is formed extending from one end portion (6) on the input coupling line, and the filtering characteristics adjusted by the adjusting line.

Description: BACKGROUND OF THE INVENTION Field of the Invention The present invention relates to a 1/2 wave parallel-coupled-line filter and, more specifically, to a 1/2 wave parallel-coupled-line filter employed in, for example, a low noise converter for receiving satellite broadcasting. Description of the Prior Art Figs. 1 to 3 are patterns of microstrip lines in conventional 1/2 wave parallel-coupled-line filters. First, referring to Figs. 1 to 3, description will be given of a conventional 1/2 wave parallel-coupled-line filter. In Fig. 1, a plurality of resonance lines 4 are arranged on a printed board 20 in parallel to each other in the horizontal direction in a staggered manner. An input coupling line 3 is arranged adjacent to the resonance line 4 on one end. A signal input end 1 is formed extending from the input end 5 of the input coupling line 3, and signals are inputted to the signal input end 1. The end portion 6 of the input coupling line 3 is formed such that it is aligned with an intermediate position of the resonance line 4. Only the signal components in a prescribed band out of the signals inputted to the input end 1 are outputted from an output end 2 of the resonance line 4 of the last stage. The length from the input end 1 to the output end 2 of the 1/2 wave parallel-coupled-line filter structured as described above should be longer than a prescribed length. However, if other parts and the like are arranged in the x direction limiting the space, the arrangement of the pattern shown in Fig. 1 can not be employed. In the 1/2 wave parallel-coupled-line filter shown in Fig. 2, the input coupling line 3 and a plurality of zonal resonance lines are arranged in the vertical direction, with the input end of the input coupling line 3 bent by 90° in the horizontal direction, and the output end 2 of the resonance line 4 in the last stage bent by 90° in the horizontal direction. The 1/2 wave parallel-coupled-line filter of this pattern arrangement is advantageous when there is a limit in the x direction but not in the y direction in arranging the pattern on the board 20. However, if other parts are arranged in the y direction, it is disadvantageous if the space is taken into consideration. Since the limit of space makes it difficult to arrange the 1/2 wave parallel-coupled-line filters shown in Figs. 1 and 2, a pattern arrangement such as shown in Fig. 3 is supposed. In the example shown in Fig. 3, the input coupling line 3 and a plurality of resonance lines 4 are arranged with inclination, with the input end 1 and the output end 2 bent so as to be oriented in the horizontal direction. The 1/2 wave parallel-coupled-line filter having such pattern arrangement is more available than the examples shown in Figs. 1 and 2, even if the space is limited both in the x and y directions. However, the filter has the following disadvantage. The 1/2 wave parallel-coupled-line filter shown in Fig. 3 has its input coupling line 3 and the resonance lines 4 formed by etching. In order to make an original drawing for fabricating films for etching, the angle factors in the x and y directions are required, the check for each of the coordinate becomes complicated, and the check of modification of the dimension becomes difficult. IEEE Transactions on Microwave Theory and Techniques, October 1972, Vol. MTT-20 No. 10, pp 696-699 discloses a half-wave parallel-coupled-line filter in which the input and output lines each comprise a first line portion, aligned with the half of the adjacent line section which is not alongside part of the next-but-one line section, an end stub extending from the end of the first line portion furthest from the next-but-one line section, and an input or output line portion extending from the other end of the first line portion away from the adjacent line section at right angles to it. The end stubs are much thinner than the first line portions and the input and output line portions. No comment is made about the reasons for or results of this configuration of the input and output lines. US 4168479 discloses a diplexer comprising an input strip in the shape of a T, with the input at the stem of the T. Each arm of the T provides the input line to a half-wave parallel-coupled-line filter portion, having strip lines parallel to the arms of the T. The two filter portions have different passbands. The lengths of the arms of the T are adjusted so that each filter portion appears as an open circuit at the input of the other at the mid frequency of the other's passband. SUMMARY OF THE INVENTION According to the present invention there is provided a half-wave parallel-coupled-line filter provided on a board and having first and second outputs for providing respective signals having different respective passbands, and a common input, the filter comprising: power distributing means comprising microstrip lines for distributing signals from the input of the filter between outputs of the power distributing means; and two filter means having said different passbands and extending from respective outputs of said power distributing means with the spatial separation of the components of one said filter means from the components of the other said filter means increasing with the distance towards their outputs, characterised in that the power distributing means comprises a resistance arranged on the board and electrically coupled to the said outputs. Preferably, each said filter means comprises a plurality of zonal resonance lines parallel to each other and arranged in a staggered manner so that respective end portions thereof form successive steps. In a preferred embodiment, the power distributing means comprises: an input end to which said signals are input; and two output ends dividing said signals input to said input, with said resistance connected therebetween, and each said filter means comprises: a respective input coupling line arranged parallel to said plurality of resonance lines, having an input end connected to a respective output end of said power distributing means and opposed to an intermediate position of an adjacent resonance line, and one end formed aligned with one end portion of said adjacent resonance line; and adjusting lines provided to extend end portions of said input coupling lines serving as stubs for adjusting filtering characteristics. Embodiments of the present invention, given by way of non-limiting example, will now be described with reference to the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS Figs. 1, 2 and 3 are patterns of conventional 1/2 wave parallel-coupled-line filters; Fig. 4 is a pattern of a more compact 1/2 wave parallel-coupled-line filter; Fig. 5 is a pattern of a dual band 1/2 wave parallel-coupled-line filter in accordance with a first embodiment of the present invention; and Fig. 6 is a pattern of a dual band 1/2 wave parallel-coupled-line filter in accordance with a second embodiment of the present invention. DESCRIPTION OF THE PREFERRED EMBODIMENTS Fig. 4 is a pattern of a compact 1/2 wave parallel-coupled-line filter. Referring to Fig. 4, a plurality of resonance lines 4 are arranged in parallel with each other in the horizontal direction in a so-called staggered manner with end portions of the respective lines having steps in succession, in the similar manner as the conventional one shown in Fig. 1. An input coupling line 3 is provided adjacent to a resonance line 4 at one end, with one end portion of the input coupling line 3 formed aligned with one end portion of the adjacent resonance line 4, and an adjusting line 7 having the same width as the input coupling line 3 is provided extending from one end of the input coupling line 3. The adjusting line 7 serves as a stub for adjusting the filtering characteristics. An input end 5 is formed on the other end portion of the input coupling line 3 so as to be positioned on the intermediate position of the adjacent resonance line 4. A signal input end 1 is formed extending from the input end to the direction crossing the adjacent resonance line 4. Since the 1/2 wave parallel-coupled-line filter is structured as described above, only the adjusting line 7 is projected from the end surface of the resonance line 4, whereby the length in the x direction can be reduced and the space in the y direction can be also reduced compared with the conventional one shown in Fig. 1. It is clear that the original drawing for forming the pattern of the resonance lines 4 and the input coupling line 3 can be made easier compared with the example shown in Fig. 3. In addition, a prescribed band characteristics as the filtering characteristics can be obtained by adjusting the length of the adjusting line 7, thereby providing a filter of superior characteristics. The filter of Figure 4 is similar, but not identical, to the filter of IEEE Transactions MTT-20 No. 10 pp 696-699 referred to above. Meanwhile, a dual band low noise converter capable of receiving signals of two different input frequency bands is used as a low noise converter for receiving satellite broadcasting. In such dual band low noise converter, two 1/2 wave parallel-coupled-line filters are employed. In that case, the two 1/2 wave parallel-coupled-line filters can possibly be coupled to each other to cause ripples in the filtering characteristics of each filter. In order to prevent such bad influences, two filters each structured in a seprate unit and which are shielded should be used. Consequently, the circuit structure becomes complicated and expensive. Therefore, a dual band 1/2 wave parallel-coupled-line filter which is inexpensive and capable of preventing degradation of two filtering characteristics will be described in the following. Fig. 5 is a pattern of a dual band 1/2 wave parallel-coupled-line filter in accordance with a first embodiment of the present invention. Referring to Fig. 5, a y shaped power distributing portion 9 formed of microstrip lines is provided on a board 20. The power distributing portion 9 comprises an input end 8 and two branching ends 11a and 11b, with a terminated resistance connected between the branching ends 11a and 11b. 1/2 wave parallel-coupled-line filters 12a and 12b are respectively connected to the branching ends 11a and 11b with the distance between the filters widening toward the ends thereof. More specifically, as for the 1/2 wave parallel-coupled-line filter 12a, the input end 1a of the input coupling line 3a is connected to the branching end 11a, and a plurality of resonance lines 4a are provided in parallel to the input coupling line 3a. As for the other 1/2 wave parallel-coupled-line filter 12b, it is structured in the similar manner as the 1/2 wave parallel-coupled-line filter 12a, comprising an input coupling line 3b and a plurality of resonance lines 4b. Signals are inputted from a low noise amplifier, not shown, to the input end 8 of the power distributing portion 9. The signals are branched into the branching ends 11a and 11b to be outputted at the output ends 2a and 2b through the 1/2 wave parallel-coupled-line filters 12a and 12b, with respective signals inputted to mixer circuits, not shown. Fig. 6 is a pattern of a dual band 1/2 wave parallel-coupled-line filter in accordance with a second embodiment of the present invention. The embodiment shown in Fig. 6 is the same as the embodiment shown in Fig. 5 except the following points. Namely, one input coupling line 3a is formed in parallel to an adjacent resonance line 4a, an adjusting line 7a is formed protruding from one end 6a thereof, and a signal input end 1a is formed on an input end 5a of the input coupling line 3a extending in the direction crossing the input coupling line 3a and the branching end 11a. The other input coupling line 3b and the signal input end 1b are formed in the similar manner. As described above, since the signal input ends 1a and 1b are formed in the direction crossing the input coupling lines 3a and 3b, the space to be occupied in the x direction can be reduced. Although the present invention has been described and illustrated in detail, it is clearly understood that the same is by way of illustration and example only and is not to be taken by way of limitation.

Claims: 1. A half-wave parallel-coupled-line filter provided on a board and having first and second outputs for providing respective signals having different respective passbands, and a common input, the filter comprising: power distributing means (9) comprising microstrip lines for distributing signals from the input of the filter between outputs of the power distributing means; and two filter means (12a, 12b) having said different passbands and extending from respective outputs of said power distributing means with the spatial separation of the components of one said filter means from the components of the other said filter means increasing with the distance towards their outputs, characterised in that the power distributing means (9) comprises a resistance arranged on the board and electrically coupled to the said outputs. 2. A half-wave parallel-coupled-line filter according to claim 1, wherein each said filter means comprises a plurality of zonal resonance lines (4a, 4b) parallel to each other and arranged in a staggered manner so that respective end portions thereof form successive steps. 3. A half-wave parallel-coupled-line filter according to claim 2, wherein said power distributing means comprises: an input end (8) to which said signals are input; and two output ends (11a, 11b) dividing said signals input to said input, with said resistance connected therebetween, and each said filter means comprises: a respective input coupling line (3a, 3b) arranged parallel to said plurality of resonance lines, having an input end connected to a respective output end of said power distributing means and opposed to an intermediate position of an adjacent resonance line, and one end formed aligned with one end portion of said adjacent resonance line; and adjusting lines (7a, 7b) provided to extend end portions of said input coupling lines serving as stubs for adjusting filtering characteristics. 4. A half-wave parallel-coupled-line filter according to claim 3, wherein said adjusting line comprises a member formed to have the same width as said input coupling line.

Inventors: NAKAMURA, MAKIO
Applicants: SHARP KABUSHIKI KAISHA
Application year: 1988
Main classification: H01P1
IPC codes: H01P1