Microwave filter

Abstract: The present invention is directed towards an electric filter for use in a transmitter or receiver and more particularly, its object is to provide an improved filter capable of minimizing the transmission of noise. The filter includes an input electrode (15), an output electrode (16), and a resonator comprising a strip conductor (12a,13a,14a) and grounded conductors (17,117a...d) which are all disposed on a substrate (11) made of a dielectric substance. In addition, said strip conductor is electrically connected to the grounded conductors through capacitors (18-24). In the equipment employing the aforementioned filter, harmonic components of a signal will be attenuated effectively thus minimizing the transmission of noise.

Description: The present invention relates to an electric filter for use in various types of communication equipment, TV receivers, and the like. US Patent No. 2760169 relates to a simplified form of radio frequency filter which does not require the precision and exactness of previous filters comprising a conductive strip substantially one-quarter wavelength long and grounded at one end with capacity coupling between the strip and the input and output electrodes the filter is of a character which may be readily adapted fr the use printed circuit techniques. The structure of a further prior art filter based on the same principles as US 2760169 will be explained with the help of drawings. Fig. 14 is a schematic plan view showing the structure of a primary part of the prior art filter employing coplanar waveguide resonators. As shown in Fig. 14 there is provided a substrate 1 formed of a dielectric substance on which three coplanar waveguides 2 to 4, an input electrode, and an output electrode 6 are disposed in place. A strip conductor 2a of the coplanar waveguide 2 is coupled to the input electrode 5 through a capacitor 7. Similarly, a strip conductor 4a of the coplanar waveguide 4 is coupled to the output electrode 6 through a capacitor 8. A strip conductor 3a of the coplanar waveguide 3 is coupled to the strip conductor 2a of the coplanar waveguide 2 and the strip conductor 4a of the coplanar waveguide 4 through capacitors 9 and 10, respectively. This arrangement constructs a bandpass filter. The frequency response of the filter of the foregoing structure is illustrated in Fig. 13 in which A represents the limit of the required attenuation level, is of the specified center frequency, and 3f o , 5f o , and 7f o are ,its harmonic components. As apparent from Fig. 13, the harmonics 3f o , 5f o , and 7f o and other harmonic components representing odd multiples of the center frequency are not attenuated mostly, and their most parts pass through the filter. Hence, when the filter is assembled in a transmitter, it allows the harmonics also to be transmitted with a resultant problem of generating noises in other communication equipment. When the filter is installed in a receiver, it permits the receiver to receive unwanted harmonic components, resulting in a problem of developing noise. It is an object of the present invention to provide an electric filter in which harmonic components of the frequency of a signal are attenuated enough to prevent the transmission of noise. For this purpose, a filter according to the present invention comprises : a band pass filter of predetermined centre frequency comprising: a) a dielectric substrate having a first surface and a second surface; and b) a resonator having: an input electrode formed on said first surface of said dielectric substrate; an output electrode formed on said first surface of said dielectric substrate; a first ground conductor formed on at least one of said first surface and said second surface; at least one waveguide having a strip conductor shaped as a flat bar formed on said first surface of said dielectric substrate said strip conductor having one end connected to said first ground conductor and wherein said input electrode is capacitively coupled with said strip conductor by a first capacitance; and said strip conductor is capacitively coupled with said output electrode by a second capacitance said band pass filter being characterised by having: a second ground conductor formed on at least one of said first surface and said second surface; and wherein said strip conductor is capacitively coupled with said second ground conductor by at least one third capacitance wherein said strip conductor is shorter than the theoretical length associated with said predetermined centre frequency. According to the frequency response of the filter having the foregoing structure, the transmission level of the harmonic components of the center frequency will be attenuated significantly. As a result, in equipment using said filter the generation of noise due to such harmonic components will effectively be minimized. Fig. 1 is a schematic plan view to show the structure of a primary part of a filter described as a first exemplary embodiment (Example 1) of the present invention. Fig. 2 is a schematic plan view to show the structure of) a primary part of another filter described as a second exemplary embodiment (Example 2) of the present invention. Fig. 3 is a schematic plan view to show the structure of a primary part of a further filter described as a third exemplary embodiment (Example 3) of the present invention. Fig. 4 is a schematic plan view to show the structure of a primary part of a further filter described as a fourth exemplary embodiment (Example 4) of the present invention. Fig. 5 is a diagram showing the frequency response of the filter of Example 1. Fig. 6 is a schematic front view to show the structure of a primary part of a still further filter described as a fifth exemplary embodiment (Example 5) of the present invention. Fig. 7 is a cross sectional view taken along the line X-Y of Fig. 6. Fig. 8 is a schematic plan view to show the structure of a primary part of a still further filter described as a sixth exemplary embodiment (Example 6) of the present invention. Fig. 9 is a diagram showing the frequency response of the filter of Example 6. Fig. 10 is a schematic plan view to show the structure of a primary part of a still further filter described as a seventh exemplary embodiment (Example 7) of the present invention. Fig. 11 is a cross sectional view taken along the line X-Y of Fig. 10. Fig. 12 is an enlarged front view of the primary part of the filter illustrated in Fig. 11. Fig. 13 is a diagram showing the frequency response of a prior art filter. Fig. 14 is a schematic plan view to show the structure of a primary part of the prior art filter. The present invention will be described in more details according to exemplary embodiments. Example 1 A filter of Example 1 will be explained referring to Figs. 1 and 5. Fig. 1 is a schematic plan view showing the structure of a primary part of a filter employing coplanar waveguide resonators. As shown in Fig. 1, there is provided a substrate 11 of a dielectric substance on which coplanar waveguides 12, 13, and 14, an input electrode 15, an output electrode 16, and a second grounded conductor 17 all formed of copper foil are disposed in position. The coplanar waveguides 12, 13, and 14 have strip conductors 12a, 13a, and 14a of a flat bar shape respectively which are alternated with first grounded conductors 117a, 117b, 117c, and 117d. The strip conductor 12a of the coplanar waveguide 12 is electrically coupled to the input electrode 15 through a first capacitor 18. Similarly, the strip conductor 14a of the coplanar waveguide 14 is electrically connected to the output electrode 16 through a second capacitor 19. The first capacitor 18 and second capacitor 19 can be supplemented with the capacitance existing between electrodes when the distances between the input electrode 15 and the strip conductor 12a and between the output electrode 16 and the strip conductor 14a are considerably small. The strip conductor 13a of the coplanar waveguide 13 is electrically connected by fourth capacitors 20 and 21 to the strip conductors 12a and 14a respectively. The capacitors 20 and 21 may be supplemented with the capacitance existing between electrodes when the distances between the two strip conductors 13a and 12a and between the conductors 13a and 14a are significantly small. Furthermore, the strip conductors 12a, 13a, and 14a of their respective coplanar waveguides 12, 13, and 14 are electrically coupled to the second grounded conductor 17 through third capacitors 22, 23, and 24 respectively. The third capacitors 22, 23, and 24 may be supplemented by the capacitance existing between electrodes when the distance between the strip conductors 12a, 13a, and 14a and the second grounded conductor 17 is considerably small. A portion of the first grounded conductor 117b situated between the strip conductors 12a and 13a is extended towards the second grounded conductor 17 thus forming an extending grounded conductor 26. Similarly, a portion of the first grounded conductor 117c situated between the strip conductors 13a and 14a is extended towards the second grounded conductor 17 thus forming an extending grounded conductor 27. It is possible to build a structure wherein both the extending grounded conductors 26 and 27 are connected to the second grounded conductor 17. The strip conductors 12a, 13a, and 14a are adapted to have appropriate lengths so as to correct a shift of the center frequency caused by the presence of the third capacitors 22, 23, and 24 coupled between the strip conductors 12a, 13a, and 14a and the second grounded conductor 17. More particularly, the third capacitors 22, 23, and 24 offer an increase in the capacitive component thus causing the center frequency f o to shift to the lower. For correction of the shift of the center frequency, the inductive component is decreased by trimming the length of the strip conductors 12a, 13a, and 14a. Thus, the center frequency required of the filter can be preserved at optimum. The frequency response of the filter having the foregoing structure is illustrated in Fig. 5 where A represents the limit of desired attenuation level and B is a harmonic component of the center frequency. As apparent, the unwanted harmonics appear at a higher range as compared with the components 3fo, 5fo, and 7fo of the prior art filter and the harmonics transmitted are remarkably attenuated. This results from reduction of the inductive component by short ening the strip conductors 12a, 13a, and 14a. In particular, the resultant harmonics are shifted towards the higher, as shown by the harmonic B in Fig. 5, and will be drained through the third capacitors 22, 23, and 24 to the second grounded conductor 17. Accordingly, in a transmitter or receiver using this filter, a noise caused by the harmonic components of the frequency will be reduced remarkably. The extending grounded conductors 26 and 27 prevent the capacitive coupling between the coplanar waveguides 12 and 13 and between the coplanar waveguides 13 and 14 respectively, contributing to suppression of noises. The filter of Example 1 may contain only one coplanar waveguide. More specifically, it is possible to build a modified filter in which, according to Fig. 1, the two coplanar waveguides 12 and 13 out of the three of the coplanar waveguides 12 to 14, and the two capacitors 22 and 23 out of the third capacitors 22 to 24, and the fourth capacitors 20 and 21 are all eliminated. The effectiveness of such a modified- filter is equivalent to that of the filter shown .in Fig. 1 in avoiding the transmission of noise. Also, the filter of Example 1 may employ two or more than three of the coplanar waveguides. At the case, a corresponding number of the third and fourth capacitors are also provided in specified positions. As described above, a first form of the filter of the first exemplary embodiment of the present invention comprises a substrate formed of a dielectric substance and the like, an input electrode and an output electrode both disposed at specified locations on at least one surface of said substrate, a coplanar waveguide resonator which is disposed on at least one surface of said substrate and comprised of a strip conductor of a flat bar shape and a first grounded conductor located on both sides of said strip conductor, a second grounded conductor disposed at a specified loca-tion on said substrate, a first capacitor electrically connected between said input electrode and said strip conductor of the coplanar waveguide resonator, a second capacitor electrically connected between said strip conductor of the coplanar waveguide resonator and said output electrode, and a third capacitor electrically connected between said strip conductor of the coplanar waveguide resonator and at least one of said first and second grounded conductors. A second form of the filter of the first exemplary embodiment, unlike the first form, includes a plurality of the coplanar waveguide resonators. More particularly, two or more of the coplanar waveguide resonators are provided. The strip conductor of one of the coplanar waveguide resosnators is electrically connected by the first capacitor to the input electrode, and while the strip conductors of other coplanar waveguide resonators are elec trically connected by the second capacitor to the output electrode, a fourth capacitor is electrically connected between the strip conductors of each respective coplanar waveguide resonator. A third form of the filter of the first exemplary embodiment further includes an extending grounded conductor formed between the first and second grounded conductors. At least one of the input electrode, the output electrode, and the coplanar waveguide resonator may be disposed on the opposite surface of the substrate. It is also possible to eliminate the second grounded conductor when the strip conductor is coupled to the first grounded conductor through the third capacitor. The electrodes and grounded conductors may be made of silver or other conductive materials as well as copper foil. In the frequency response of the foregoing filters the transmission level of unwanted harmonic components is minimized and the transmission of noise in equipment using the filters will be reduced significantly. It is possible that the strip conductor is referred to as a center conductor. Example 2 Fig. 2 illustrates a primary part of the structure of a filter of the second exemplary embodiment. The second exemplary embodiment is distinguished from the first exemplary embodiment by the fact that the third capacitors are classified to two different capacitance types. More specifically, the third capacitor 23 is greater in the capacitance than the other third capacitors 22 and 24 and the strip conductor 13a of the coplanar waveguide 13 is proportionally reduced in the length. The frequency response of the foregoing filter will excellently ensure the marked reduction of noise in the same way as those of the filters of Example 1 do. Example 3 The third exemplary embodiment of the present invention defined in Claims 11 to 15 will be described. Fig. 3 illustrates a primary part of the structure of a filter of the third exemplary embodiment which employs strip line type resonators. As shown in Fig. 3, disposed at specified locations on one surface of a substrate 28 are three strip conductors 29, 30, and 31, an input electrode 32, an output electrode 33, and a second grounded conductor 34. The other surface of the substrate 28 (not shown in Fig. 3) is completely covered with an grounded conductor. The strip conductors 29, 30, and 31 and the second grounded conductor 34 are connected at respective proximal ends to the grounded conductor of the other surface of the substrate 28, thus forming resonators. Capacitors 18 to 24 are arranged in the same manner as of the first exemplary embodiment shown in Fig. 1. More particularly, the strip conductor 29 and the input electrode 32 are electrically connected with each other through the first capacitor 18 and the strip conductor 31 and the output electrode 33 are electrically connected with each other through the second capacitor 19. The first capacitor 18 and second capacitor 19 may be substituted with the inter-electrode capacitance when the distances between the strip conductor 29 and the input electrode 32 and between the strip conductor 31 and the output electrode 33 are considerably small. The strip conductors 30 is electrically connected with the strip conductors 29 and 31 by fourth capacitors 20 and 21 respectively. The capacitors 20 and 21 may also be substituted with the inter-electrode capacitance when the strip conductor 30 is spaced by a small distance from the strip conductors 29 and 31. The strip conductors 29, 30, and 31 are further connected electrically to the second grounded conductor 34 through the third capacitors 22, 23, and 24 respectively. Similarly, the third capacitors 22, 23, and 24 may be substituted with the inter-electrode capacitance when the strip conductors 29, 30, and 31 are distanced closely from the second grounded conductor 34. The filter of the third exemplary embodiment comprises a substrate formed of a dielectric substance, an input electrode and an output electrode disposed at specified locations respectively on at least one surface of said substrate, resonators formed of strip conductors of a flat bar shape and a grounded conductor connected to said strip conductors at respective proximal ends thereof and extended to cover the other surface of said substrate, a first capacitor electrically connected between said input electrode and one of said strip conductors, a second capacitor electrically connected between another of said strip conductors and said output electrode, and third capacitors electrically connecting said grounded conductor to the strip conductors. The frequency response of the foregoing filter will excellently ensure the marked reduction of noise in the same way as those of the filters of Example 1 do. The third exemplary embodiment is not limited to the structure employing three strip conductors and the number of conductors can be one, two, or more than three with equal success. Example 4 Fig. 4 shows a primary part of the structure of a filter of the fourth exemplary embodiment which is distinguished from the foregoing third exemplary embodiment by the fact that the third capacitors 22, 23, and 24 are classified into two different capacitance values. As apparent from Fig. 4, the third capacitor 23 is greater in capacitance than the other third capacitors 22 and 24 and the strip conductor 30 is shortened in the length proportionately. The frequency response of the foregoing filter will excellently ensure the marked reduction of noise in the same way as those of the filters of Example 1 do. Example 5 Figs. 6 and 7 illustrate a primary part of the structure of a filter of the fifth exemplary embodiment which has a plurality of substrates arranged in layers. Fig. 6 is a front view of said filter and Fig. 7 is a cross sectional view taken along the line X-Y of Fig. 6. As shown, strip conductors 29a, 30a, and 31a, an input electrode 32, and an output electrode 33 are disposed on the upper surface of a first substrate 28 made of a dielectric substance. The lower surface of said first substrate 28 is covered with a grounded conductor 35. A second substrate 36 made of a dielectric substance is placed on the upper surface of the first substrate 28. A grounded conductor 34a is formed on said second substrate 36 so that it extends across at least the approximate positions opposite to the distal ends of the strip conductors 29a, 30a, and 31a as denoted by the broken lines in Fig. 7. In other words, the grounded conductor 34a is separated by the second substrate 36 from the respective distal ends of the strip conductors 29a, 30a, and 31a. The filter of the foregoing exemplary embodiment has the electrodes, strip conductors, and grounded conductors put together with the layers of the dielectric substrate interposed. The frequency response of the filter even with the foregoing structure will excellently ensure the marked reduction in noise in the same way as those of the filters of Example 1 do. Although the number of the strip conductors of the filter of the fifth exemplary embodiment is three, it may be one, two, or more than three. Example 6 Fig. 8 is a plan view of a primary part of the structure of a 1/2 wavelength filter wherein the filters disclosed by the present invention are employed. In Fig. 8, an input electrode 40, an output electrode 41, and three coplanar waveguides 42, 43, and 44 are disposed on a substrate 39 made of a dielectric substance. Each of the coplanar waveguides 42. 43, and 44 comprises strip conductor 42a, 43a, or 44a of a flat bar shape and grounded conductors 45 and 46 disposed opposite to each other on both sides of said strip conductors. The input electrode 40 is electrically connected to one end of the strip conductor 42a through a first capacitor 47. Similarly, the output electrode 41 is electrically connected to one end of the strip conductor 44a through a second capacitor 48. The other end of the strip conductor 42a is electrically connected to one end of the strip conductor 43a through a fourth capacitor 49. The other end of the strip conductor 43a is electrically connected to the other end of the strip conductor 44a through another fourth capacitor 50. The strip conductors 42a, 43a, and 44a are also electrically connected at the both ends to the grounded conductors 45 and 46 situated in either side thereof respectively through twelve third capacitors 51, as shown in Fig. 8. Fig. 9 is a diagram of the frequency response of the foregoing 1/2 wavelength filter, in which A represents the limit of attenuation level and B is a harmonic component. As apparent, the harmonic B appears at a far higher range than the required center frequency fo and its transmission level is far lower than the attenuation limit A. The strip conductors 42a, 43a, and 44a are electrically connected at their both ends to the grounded conductors 45 and 46 through the third capacitors 51, whereby electrical phase stability will be preserved while the excellent frequency response shown in Fig. 9 being ensured. Conversely, the same frequency response as shown in Fig. 9 is theoretically attainable by connecting the strip conductors 42a, 43a, and 44a to either one of the grounded conductors 45 and 46 through the third capacitors 51. It was however found in reality that the electrical phase balance between the two sides of the strip conductors 42a, 43a, and 44a was lost thus impairing the otherwise excellent frequency response. Although the number of the strip conductors of the foregoing filter is three, it may be one, two, or more than three. It is possible that the strip conductor is referred to as a center conductor. Example 7 Figs. 10 to 12 illustrate a primary part of the structure of a 1/2 wavelength filter employing strip conductors. Fig. 10 is a schematic plan view of the primary part of the 1/2 wavelength filter, Fig. 11 is a cross sectional view taken along the line X-Y of Fig. 10, and Fig. 12 is an enlarged view of the primary part of Fig. 11. As shown, an input electrode 53, an output electrode 54, and three strip conductors 55, 56, and 57 are linearly disposed at specified intervals on the upper surface of a substrate 52 made of a dielectric substance. The substrate 52 has through holes 52a therein where both ends of each of the strip conductors 55, 56, and 57 are located. Each of the through holes 52a is communicated at lower end with a lower electrode 52b formed on the lower surface of the substrate 52. A corresponding number of grounded conductors 58 are disposed on the lower surface of the substrate 52 so as to seat opposite to the input electrode 53, the output electrode 54, and the strip conductors 55, 56, and 57 on the-upper surface while being spaced from the lower electrodes 52b. The input electrode 53 is electrically connected to one end of the strip conductor 55 through a first capacitor 59. The other end of the strip conductor 55 is electrically connected to one end of the next strip conductor 56 through a fourth capacitor 60. In succession, the other end of the strip conductor 56 is electrically connected to one end of the strip conductor 57 through another fourth capacitor 61. The other end of the strip conductor 57 is electrically connected to the output electrode 54 through a second capacitor 62. Each respective grounded conductor 58 and lower electrode 52b disposed on the lower surface of the substrate 52 are electrically connected to each other through a third capacitor 63. The frequency response of the filter of the foregoing structure will excellently ensure the marked reduction in noise in the same way as those of the filter of Example 6 do. Although the number of the strip conductors of the foregoing filter is three, it may be one, two, or more than three. It is possible that the strip conductor is referred to as a strip line. As set forth above, the filter of the present invention has the strip conductors and the grounded conductors connected electrically through the capacitors. Accordingly, the transmission level of the harmonic components of the center frequency will significantly be attenuated. More particularly, in electrical equipment using the filter of the present invention, the transmission of noise due to the harmonic components will be drastically reduced. It would be understood that other modifications and changes of the exemplary embodiments are possible. For example, one or more of the strip conductors are applicable together with a corresponding number of capacitors disposed in relevant relationship. The strip conductors, the grounded electrodes, the input electrodes, and the output electrodes are not limited to their shapes in the described exemplary embodiments and other shapes will be eligible without affecting the frequency response of the filter. The strip conductor may be expressed, if desired, as a center conductor or a strip line providing the same effects.

Claims: A band pass filter of predetermined centre frequency comprising: a) a dielectric substrate (11,28) having a first surface and a second surface; and b) a resonator having: an input electrode (15,32) formed on said first surface of said dielectric substrate (11,28); an output electrode (16,33) formed on said first surface of said dielectric substrate (11,28); a first ground conductor (117a,117b,117c or 117d) formed on at least one of said first surface and said second surface; at least one waveguide (12,13,14) having a strip conductor (12a,13a,14a,29,30,31) shaped as a flat bar formed on said first surface of said dielectric substrate (11,28) said strip conductor having one end connected to said first ground conductor and wherein said input electrode is capacitively coupled with said strip conductor by a first capacitance (18); and said strip conductor is capacitively coupled with said output electrode by a second capacitance (19) said band pass filter being characterised by having: a second ground conductor (17,34) formed on at least one of said first surface and said second surface; and wherein said strip conductor is capacitively coupled with said second ground conductor by at least one third capacitance (22,23 or 24) wherein said strip conductor is shorter than the theoretical length associated with said predetermined centre frequency. A band pass filter according to claim 1 wherein said input electrode (15), output electrode (16), said first ground conductor (117a,117b,117c or 117d) and said second ground conductor are all formed on the same surface of said dielectric substrate (11) and wherein said first ground conductor (117a,117b,117c,117d) is formed on said first surface of said dielectric substrate 11 to define an edge, said first ground conductor having a cavity extending inwardly from said edge of said first ground conductor, said cavity having an inner edge, and wherein, said waveguide (12,13,14) is a coplanar waveguide having said strip conductor (12a,13a or 14a) extending outwardly from said inner edge of said cavity, said strip conductor having an outer edge aligned in a straight line with said edge of said first ground conductor, A bandpass filter according to claim 2, wherein said first ground conductor 117a-117d has a plurality of cavities extending inwardly from said edge of said first ground conductor, each of said cavities having an inner edge, and a plurality of strip conductors (12a,13a,14a) each strip conductor extending outwardly from said inner edge of each cavity, said each strip conductors having an outer edge aligned in a straight line with said edge of said first conductor, thereby forming a plurality of coplanar waveguides (12,13,14), said first capacitance (18) electrically coupling said input electrode (15) and a first strip conductor (12a) of said plurality of strip conductors, said second capacitance 19 electrically coupling said output electrode (16) and a second strip conductor (14a) of said plurality of strip conductors, said third capacitance (22-24) includes a plurality of third capacitances, each of said plurality of third capacitances electrically coupling said second ground conductor and an end of said each strip conductor (12a,13a,14a), and further comprising, fourth capacitances (20,21), each of said capacitances electrically coupling mutually between said each of said plurality of strip conductors. A filter according to claim 3, wherein at least one or more from the input electrode, the output electrode, and one of said plurality of coplanar waveguides is or are disposed on the second surface of the substrate. A bandpass filter according to claim 3, wherein the inductive value of said each coplanar waveguide depends on the length of said each strip conductor and the desired center frequency of the filter, said length differing for at least two strip conductors of said plurality of strip conductors. A bandpass filter according to claim 3, wherein said each of said plurality of third capacitances electrically couples said each of said plurality of strip conductors and said second ground conductor. A bandpass filter according to claim 3, further comprising, an extending ground conductor (26 or 27) for each portion of said first ground conductor (117b,117c) formed between a pair of said plurality of strip conductors electrically coupling said each portion to said second conductor for preventing the transmission of noise and preventing the coupling capacitance between said pair of said plurality of strip conductors. A bandpass filter according to claim 7, wherein the length and width of said extending ground conductor (26, 27) depends on the desired amount of suppression of the harmonics of said predetermined frequency . A bandpass filter according to any of claims 3 to 8 wherein the capacitive value of said each third capacitance (22,23,24) is mutually different. A band pass filter according to any of the preceding claims wherein said input electrode (32), said output electrode (33), second ground conductor (34), and strip conductor (29,30 or 31) are formed on said first surface of a said dielectric substrate, and said first ground conductor is formed on said second surface of said dielectric substrate, said waveguide (12,13,14) is a microstrip waveguide having said strip conductor (29,30,31), said strip conductor extending from an edge of said first ground conductor. A bandpass filter according to claim 10, wherein, said microstrip waveguide includes a plurality of said microstrip waveguides, each waveguide of said plurality of microstrip waveguides having a strip conductor having a flat bar shape, each said strip conductor having one end connected to said first ground conductor, said first capacitance (18) electrically coupling said input electrode (32) and a first strip conductor (29) of said each strip conductor, said second capacitance (19) electrically coupling said output electrode 33 and a second strip conductor (31) of said each strip conductor, said third capacitance (22, 23, 24) including a plurality of capacitors, each of said plurality of capacitances electrically coupling said second ground conductor (34) and end of said each strip conductor (29, 30, 31), and further comprising, fourth capacitances, each of said fourth capacitances electrically coupling the other ends of a pair of said strip conductors. A filter according to Claim 10 or 11, wherein at least one or more from the input electrode, the output electrode, and one of the strip conductor is or are disposed on the second surface of the substrate. A bandpass filter according to any of claims 11 or 12, wherein the inductive value of said each microstrip waveguide depends on the length of said each strip conductor and the desired center frequency of the filter, said length differing for at least two strip conductors of said plurality of microstrip waveguides. A bandpass filter according to any of claims 1 to 13, wherein the capacitive value of said each third capacitance (22, 23, 24) is mutually different. A band pass filter according to claim 1 wherein said dielectric substrate has a first dielectric substrate (28) and a second dielectric substrate (36), said input electrode (32), output electrode (33), and wave guide (29a,30a,3 la) are formed on said first surface of said first dielectric substrate, said first ground conductor (35) is formed on said second surface of said first dielectric substrate, and wherein said second ground conductor (34a) is formed on a third surface of said second dielectric substrate 36 disposed over said first surface of said first dielectric substrate (28), said first surface of said first dielectric substrate (28) facing said third surface of said second dielectric substrate (36), wherein said second ground conductor (34a) is shaped as a bar formed on said third surface of said second dielectric substrate (36) and positioned above an end of the strip conductor (29a, 30a or 3 la) and wherein said waveguide is a microstrip waveguide having said strip conductor, and said strip conductor extending from an edge of said first ground conductor (35). A bandpass filter according to claim 15 wherein, said microstrip waveguide includes a plurality of said microstrip waveguides, each waveguide having a strip conductor shaped as a flat bar, each said strip conductor having one end terminating at said edge of said first surface of said first dielectric (28) and connected to said first ground conductor 35, said first capacitance (18) electrically coupling said input electrode 32 and the other end of a strip conductor (29a), said second capacitance (19) electrically coupling said output electrode (33) and the other end of another strip conductor (3 la), said third capacitance (22, 23, 24) including a plurality of capacitors, each of said plurality of capacitances electrically coupling said second ground conductor 34a and the other end of said strip conductor (29a, 30a, 3 la), and further comprising, fourth capacitances (22, 23, 24), each of said capacitances electrically coupling the other ends of a pair of said strip conductors. A bandpass filter according to claim 16, wherein the capacitive value of said each third capacitance is mutually different. A bandpass filter according to claim 16, wherein the inductive value of said each microstrip waveguide depends on the length of said each strip conductor and the desired center frequency of the filter, said length differing for at least two strip conductors of said plurality of microstrip waveguides. A bandpass filter according to claim 2, 10 or 15, wherein said third capacitance is an inter-electrode capacitance between said strip conductor and said second ground conductor. A bandpass filter according to claim 3, 11 or 16, wherein at least one of said first capacitance and said second capacitance is an inter-electrode capacitance between said strip conductor and said input electrode and between said strip conductor and said output electrode. A bandpass filter according to claims 2, 10 or 15, wherein said third capacitance is a capacitor connected between said strip conductor and said second ground conductors. A bandpass filter according to claims 3, 11 or 16 wherein at least one of said first capacitance and said second capacitance is a capacitor connected between said strip conductor and said input electrode and between said strip conductor and said output electrode.

Inventors: HIDEYUKI MIYAKE, JUNYA ISHI, YASUMASA NOGUCHI, YUKIHIRO TAKEDA, HIDEYUKI, MIYAKE, JUNYA, ISHI, YASUMASA, NOGUCHI, YUKIHIRO, TAKEDA
Applicants: MATSUSHITA ELECTRIC IND CO LTD, MATSUSHITA ELECTRIC INDUSTRIAL CO., LTD.
Application year: 1993
Main classification: H01P1
IPC codes: H01P3, H01P1