Impedance converting device with an electromagnetic shielding effect

Abstract: An impedance converting device comprises a tri-plate structure having a first grounded conductor member (21) a second grounded conductor member (22) apart from the first grounded conductor member so as to form a space between the first and the second grounded conductor members, and a line conductor member (23) located in the space for allowing a signal to pass therethrough. The impedance converting device comprises a varying section (31 to 37) for varying a terminative condition of the electric flux generated from the line conductor member. The varying section may be a window section (31 to 34) formed on the second grounded conductor member at a predetermined location. The varying section may include a metal portion (35, 36) and a slave window section (37). The window section is partially covered with the metal portion. The slave window section is connected to the window section.

Description: This invention relates to an impedance converting device and, more particularly, to an impedance converting device having a tri-plate structure. In general, an impedance converting device is known which comprises a microstrip line. The impedance converting device of the microstrip line will be called a first impedance converting device. The first impedance converting device comprises a grounded conductor member and a dielectric member located on the grounded conductor member. A microstrip line is formed on the dielectric member as a line conductor member which allows a signal to pass therethrough. The microstrip line has an open stub line including impedance converting section having an inductive reactance element and a capacitive reactance element. Furthermore, at least one metal portion may be attached to the microstrip line in order to adjust the reactance of the impedance converting section. However, an electromagnetic wave is inevitably irradiated from the microstrip line to outside of the impedance converting device on the basis of a high frequency signal passing through the microstrip line inasmuch as none is located above the microstrip line in the first impedance converting device. In addition, another electromagnetic wave may be applied from outside of the impedance converting device to the microstrip line. In order to shield the electromagnetic wave, it is necessary to cover the first impedance converting device by a metal cover. As a result, the first impedance converting device becomes large. Furthermore, the metal cover affects a high frequency characteristic of the microstrip line. On the other hand, an impedance converting device is known which comprises a strip line. The impedance converting device of the strip line will be called a second impedance converting device. The second impedance converting device is disclosed in Japanese Unexamined Publication Tokkai Sho 62-268202 (268202/1987). The second impedance converting device comprises a tri-plate structure having first and second grounded conductor members and the strip line which is located in a space formed between the first and the second grounded conductor members. The strip line may be called the line conductor member in the second impedance converting device. The strip line is supported by a dielectric member inserted in the space. The strip line comprises the impedance converting section having the inductive reactance element and the capacitive reactance element. Inasmuch as the strip line is located in the space formed by the first and the second grounded conductor members, it is possible for the second impedance converting device to shield the electromagnetic wave. Namely, the second impedance converting device has an electromagnetic shielding effect. However, it is difficult to vary the reactance of the impedance converting section in the second impedance converting device inasmuch as the strip line is located in the space formed by the first and the second grounded conductor members. Namely, it is difficult to vary an impedance converting characteristic of the second impedance converting device. US-A-2 896 177 discloses a high frequency transmission line tuning device for matching the impedance of a transmission line load to its characteristic impedance. In view of the above, it is an object of this invention to provide an impedance converting device capable of readily varying an impedance converting characteristic with an electromagnetic shielding effect. On describing the gist of this invention, it is possible to understand that an impedance converting device comprising a tri-plate structure having a first grounded conductor member, a second grounded conductor member apart from the first grounded conductor member so as to form a space between the first and the second grounded conductor members, and a line conductor member located in the space for allowing a signal to pass therethrough. The line conductor member generates electric flux in accordance with the signal. According to this invention, the impedance converting device comprises varying means for varying a terminative condition of the electric flux. Brief Description of the Drawings: Fig. 1 shows a perspective view of a first conventional impedance converting device having a microstrip line; Fig. 2 shows a perspective view of a second conventional impedance converting device having a strip line; Fig. 3A shows a perspective view of an impedance converting device according to a first embodiment of this invention; Fig. 3B shows a plane view of the impedance converting device illustrated in Fig. 3A; Fig. 4 shows a sectional view for describing a distribution of an electric field at a window of the impedance converting device illustrated in Fig. 3A; Fig. 5 shows a sectional view for describing a distribution of an electric field on locating a metal portion on the window illustrated in Fig. 3A; Fig. 6 shows a sectional view for describing a distribution of an electric field on forming an additional window on the impedance converting device illustrated in Fig. 3A; Fig. 7 shows a sectional view for describing a distribution of an electric field on inserting a metal portion in the window illustrated in Fig. 3A; Fig. 8 shows a perspective view of an impedance converting device according to a second embodiment of this invention; Fig. 9 shows a sectional view for describing a distribution of an electric field on locating a dielectric portion on the window illustrated in Fig. 8; Fig. 10 shows a sectional view for describing a distribution of an electric field on locating a dielectric portion having a metal case on the window illustrated in Fig. 8; Fig. 11 shows a sectional view for describing a distribution of an electric field on inserting a dielectric portion in the window illustrated in Fig. 8; and Fig. 12 shows a sectional view for describing a distribution of an electric field on inserting a dielectric portion having a metal case in the window illustrated in Fig. 8. Referring to Fig. 1, description will first be made as regards a first conventional impedance converting device for a better understanding of this invention. The illustrated impedance converting device 11 comprises a microstrip line 12 which has a line conductor portion. The microstrip line 12 has a transmission line 12a and an open stub line 12b. The open stub line 12b has an impedance converting section which comprises an inductive reactance element 121 and a capacitive reactance element 122. The impedance converting device further comprises a grounded conductor member 13 and a dielectric member 14 located on the grounded conductor member 13. The microstrip line 12 is formed on the dielectric member 14. In the example being illustrated, metal portions 14a and 14b are attached to the microstrip line 12 on the dielectric member 14 in order to make an impedance converting characteristic be a desired characteristic in the impedance converting device 11. However, an electromagnetic wave is inevitably irradiated from the microstrip line 12 to outside of the impedance converting device 11 on the basis of a high frequency signal passing through the microstrip line 12 inasmuch as none is located above the microstrip line 12 in the impedance converting device 11. In addition, another electromagnetic wave may be applied from outside of the impedance converting device 11 to the microstrip line 12. In order to shield the electromagnetic wave, it is necessary to cover the impedance converting device 11 by a metal cover (not shown). As a result, the impedance converting device 11 becomes large. Furthermore, the metal cover affects a high frequency characteristic of the microstrip line 12. Referring to Fig. 2, description will proceed to a second conventional impedance converting device. The illustrated impedance converting device 20 comprises a tri-plate structure having first and second grounded conductor members 21 and 22 and a line conductor member 23. The second grounded conductor member 22 is apart from the first conductor member 21 so as to form a space between the first and the second grounded conductor members 21 and 22. The line conductor member 23 is located in the space with being supported by a dielectric member 24. The line conductor member 23 will be called a strip line which comprises a transmission line 23a and an impedance converting section 23b having an inductive reactance element 231 and a capacitive reactance element 232. Inasmuch as the line conductor member 23 is located in the space formed by the first and the second grounded conductor members 21 and 22 in the impedance converting device 20, it is possible to shield the electromagnetic wave. Namely, the impedance converting device 20 has an electromagnetic shielding effect. However, it is difficult to vary or adjust the reactance of the impedance converting section 23b in the impedance converting device 20 inasmuch as the line conductor member 23 is located in the space formed by the first and the second grounded conductor members 21 and 22. Namely, it is difficult to adjust an impedance converting characteristic of the impedance converting device 20. Referring to Figs. 3A and 3B, description will proceed to an impedance converting device according to a first embodiment of this invention. The illustrated impedance converting device is different in structure from the impedance converting device 20 illustrated in Fig. 2 and is therefore designated afresh by a reference numeral 30. The impedance converting device 30 comprises similar parts which are designated by like references. The impedance converting device 30 comprises the tri-plate structure having the first and the second grounded conductor members 21 and 22 and the line conductor member 23. The second grounded conductor member 22 is apart from the first conductor member 21 so as to form the space between the first and the second grounded conductor members 21 and 22. The line conductor member 23 is located in the space with being supported by the dielectric member 24. In the example illustrated, the line conductor member 23 is located in the space. The dielectric member 24 is filled up in the space to support the line conductor member 23. The dielectric member 24 may be composed of at least two dielectric materials. In addition, the dielectric member 24 may occupy a part of the space. At any rate, the dielectric member 24 supports the line conductor member 23 in the space. The line conductor member 23 will be called the strip line. In the example being illustrated, the line conductor member 23 comprises the transmission line 23a and the impedance converting section 23b having the inductive reactance element 231 and a capacitive reactance element 232. The line conductor member 23 may have at least two impedance converting sections. The impedance converting device 30 comprises at least one window section which is formed on at least one of the first and the second grounded conductor members 21 and 22. In the example being illustrated, the impedance converting device 30 comprises first through fourth window sections 31 to 34. More particularly, the first through the fourth window sections 31 to 34 are formed on the second grounded conductor member 22 in correspondence with the line conductor member 23. Each of the first and the fourth window sections 31 and 34 is formed on the second grounded conductor member 22 in correspondence to the transmission line 23a. The second window section 32 is formed on the second grounded conductor member 22 in correspondence to the inductive reactance element 231. The third window section 33 is formed on the second grounded conductor member 22 in correspondence to the capacitive reactance element 232. Each of the first through the fourth window sections 31 to 34 has a window form which may be, for example, a rectangular form. As known in the art, electromagnetic wave is inevitably generated from the line conductor member 23 in accordance with a high frequency signal which passes through the line conductor member 23. Namely, the line conductor member 23 generates an electric flux in accordance with the high frequency signal. When the first through the fourth window sections 31 to 34 are formed on the second grounded conductor portion 22 as described above, a terminative condition of the electric flux is varied by the first through the fourth window sections 31 to 34. More particularly, a capacity is formed between the line conductor member 23 and the second grounded conductor member 22. The capacity is varied by the first through the fourth window sections 31 to 34. As a result, the reactance of the impedance converting section 23b is substantially varied as will be later described. Namely, it is possible to vary the impedance converting characteristic in the impedance converting device 30 by the first through the fourth window sections 31 to 34. Now, it will be assumed that the first through the fourth window sections 31 to 34 has first through fourth open areas, respectively. The first through the fourth open areas may be different from one another. It is possible to vary each of the first through fourth open areas by additional or slave window section or a metal portion. In the example being illustrated, the first window section 31 is partially covered with a first metal portion 35 so that the first open area becomes small. Similarly, the third window section 33 is partially covered with a second metal portion 36 so that the third open area becomes small. On the other hand, the slave window section 37 is formed on second grounded conductor member 22 to be connected to the second window section 32. As a result, the second open area substantially becomes large. As readily understood from the above description, it is possible to easily adjust the impedance converting characteristic in the impedance converting device 30 when the the area of the window section is varied by using the slave window or the metal portion. Referring to Figs. 4 to 7, description will proceed to an electric field in the impedance converting device 30. In Fig. 4, attention will be directed to the first window section 31. The electric flux designated by solid arrows is generated from the line conductor member 23 as described above. The electric flux mostly reaches to the first and the second grounded conductor members 21 and 22. The electric flux slightly passes through the first window section 31. This means that the electric field is varied in the impedance converting device 30 by the first window section 31. Similarly, the electric field is varied by each of the second through the fourth window sections 32 to 34 (Fig. 3A). As a result, the impedance converting characteristic is varied by the first through the fourth window sections 31 to 34. Inasmuch as the amount of the electric flux is very little which comes through the first through the fourth window sections 31 to 34, the electromagnetic shielding effect is hardly deteriorated in the impedance converting device 30. In Fig. 5, attention will be directed to the first window section 31. The first window section 31 is partially covered with the first metal portion 35. As a result, the first open area of the first window section 31 becomes small. Decrease occurs in the electric flux passing through the first window section 31. Therefore, it is possible to adjust the impedance converting characteristic of the impedance converting device 30 by the first metal portion 35. Similarly, the third window section 33 is partially covered with the second metal portion 36. By the second metal portion 36, the second open area of the third window section 33 becomes small. Decrease occurs in the electric flux passing through the third window section 33. Therefore, it is possible to adjust the impedance converting characteristic of the impedance converting device 30 by the third metal portion 36. In Fig. 6, the second window section 32 is connected to the slave window section 37 which is formed on the second grounded conductor member 22. By the slave window section 37, the second open area of the second window section 32 substantially becomes large. The electric flux passes through the second window section 32 and the slave window section 37. Therefore, it is possible to adjust the impedance converting characteristic of the impedance converting device 30 by slave window section 37. In Fig. 7, attention will be directed to the first window section 31. In the example being illustrated, the first metal portion 35 has a first projection portion 35a. The first projection portion 35a is inserted into the impedance converting device 30 through the first window section 31. In this case, the first window section 31 may be perfectly covered with the first metal portion 35. As shown in Fig. 7, the electric field is varied by the projection portion 35a. As a result, it is possible to adjust the impedance converting characteristic of the impedance converting device 30 by the first projection portion 35a. Although illustration is not made, the second metal portion may have a second projection portion which is inserted into the impedance converting device 30 through the third window section 33. Referring to Fig. 8, description will proceed to an impedance converting device according to a second embodiment of this invention. Although the line conductor member is not illustrated in Fig. 8, the illustrated impedance converting device is similar in structure to the impedance converting device 30 illustrated in Fig. 3A except the first and the second metal portions 35 and 36. In Fig. 8, the impedance converting device is designated afresh by a reference numeral 40. First and second dielectric bodies 41 and 42 are used instead of the first and the second metal portions 35 and 36 (Fig. 3A). In the example being illustrated, the first window section 31 is partially covered with the first dielectric body 41 composed of a dielectric material. The first open area of the first window section 31 is varied by the first dielectric body 41 in order to adjust the impedance converting characteristic of the impedance converting device 40. The first dielectric body 41 has a form of a rectangular solid. The third window section 33 is partially covered with a second dielectric body 42. The second dielectric body 42 is composed of a metal case 42a and a dielectric material 42b filled up in the metal case 42a. The metal case 42a has a form of a rectangular solid and has at least one opening surface. As a result, the dielectric material 42b is exposed from the metal case 42a at the opening surface. In order to adjust the impedance converting characteristic of the impedance converting device 40, the third open area of the third window section 33 is varied by the second dielectric body 42. In this event, the opening surface of the metal case 42a is directed to the third window section 33. Referring to Figs. 9 to 12, description will proceed to an electric field in the impedance converting device 40. In Fig. 9, attention will be directed to the first window section 31. The first window section 31 is partially covered with the first dielectric body 41. As a result, the first open area of the first window section 31 becomes small. Decrease occurs in the electric flux passing through the first window section 31. Furthermore, a part of the electric flux reaches in the first dielectric body 41 to be terminated in the first dielectric body 41. Therefore, it is possible to adjust the impedance converting characteristic of the impedance converting device 40 by the first dielectric body 41. The first window section 31 may be perfectly covered with the first dielectric body 41. In this case, the first dielectric body 41 terminates the electric flux passing through the first window section 31. In Fig. 10, attention will be directed to the third window section 33. The third window section 33 is partially covered with the second dielectric body 42. As a result, the second open area of the third window section 33 becomes small. Decrease occurs in the electric flux passing through the third window section 33. Furthermore, a part of the electric flux reaches in the second dielectric body 42 to be terminated in the second dielectric body 42. Therefore, it is possible to adjust the impedance converting characteristic of the impedance converting device 40 by the second dielectric body 42. The third window section 33 may be perfectly covered with the second dielectric body 42. In this case, the second dielectric body 42 terminates the electric flux passing through the third window section 33. In Fig. 11, the first dielectric body 41 has a projection portion 41a which is inserted from the first window section 31 into impedance converting device 40. The first window section 31 may be perfectly covered with the first dielectric body 41. As shown in Fig. 11, the first dielectric body 41 terminates the electric flux passing through the first window section 31. Inasmuch as the first dielectric body 41 has the projection portion 41a, it is possible to greatly vary the terminative condition of the electric flux passing through the first window section 31. In Fig. 12, the second dielectric body 42 has a projection portion 42c which is inserted from the third window section 33 into impedance converting device 40. The third window section 33 may be perfectly covered with the second dielectric body 42. As shown in Fig. 12, the second dielectric body 42 terminates the electric flux passing through the third window section 33. Inasmuch as the second dielectric body 42 has the projection portion 42c, it is possible to greatly vary the terminative condition of the electric flux lines passing through the third window section 33.

Claims: An impedance converting device comprising a tri-plate structure having a first grounded conductor member (21), a second grounded conductor member (22) apart from said first grounded conductor member so as to form a space between said first and said second grounded conductor members, and a line conductor member (23) located in said space for allowing a signal to pass therethrough, said line conductor member generating electric flux in accordance with said signal, characterized by said line conductor member having a transmission line (23a) and an impedance converting section (23b) which has an inductive reactance element (231) and a capacitive reactance element (232) a window section (32, 33) being formed on at least one of said first and said second grounded conductor members at a location corresponding to said impedance converting section, said window section varying a terminative condition of said electric flux to adjust reactances of said inductive reactance element and said capacitive reactance element. An impedance converting device as claimed in Claim 1, wherein said window section has a window form of a predetermined area; and said impedance converting device further comprising and altering means (36, 37, 42) for altering said predetermined area into an altered area. An impedance converting device as claimed in Claim 2, characterized in that said altering means comprises an additional window section (37) connected to said window section for altering said predetermined area into said altered area greater than said predetermined area. An impedance converting device as claimed in Claim 2, characterized in that said altering means comprises a metal portion (36) for covering said window section to alter said predetermined area into said altered area smaller than said predetermined area. An impedance converting device as claimed in Claim 4, characterized in that said metal portion comprises a projection portion (35a) which is inserted into said impedance converting device through said window section. An impedance converting device as claimed in Claim 5, characterized in that said altered area is equal to zero. An impedance converting device as claimed in Claim 2, characterized in that said altering means comprises a dielectric portion (42) for covering said window section to alter said predetermined area into said altered area smaller than said predetermined area. An impedance converting device as claimed in Claim 7, characterized in that said dielectric portion comprises a projection portion (42c) which is inserted into said impedance converting device through said window section. An impedance converting device as claimed in Claim 8, characterized in that said altered area is equal to zero. An impedance converting device as claimed in Claim 7 characterized in that said dielectric portion (42) is composed of a conductor case (42a) and a dielectric material (42b) filled up in said conductor case, said conductor case having at least one opening surface, the opening surface of said dielectric portion being directed to said window section.

Inventors: ISIDA MASATOSI, ISIDA, MASATOSI
Applicants: NIPPON ELECTRIC CO, NEC CORPORATION
Application year: 1995
Main classification: H01P3
IPC codes: H01P5, H01P3