BALUN

Abstract

A balun includes a first transforming part (30) and a second transforming part (40). The first transforming part includes a first coupled line (32), a first transmission line (34), a second transmission line (36), and a first capacitor (C1). The first transmission line includes a first balanced port (2). The second transmission line includes a second balanced port (3). The first capacitor connects the first balanced port and the second balanced port. The second transforming part includes a second coupled line (42), a third transmission line (44), a first line node (48), a second capacitor (C2), a fourth transmission line (46), a second line node (49), and a third capacitor (C3). The third transmission line includes an unbalanced port (1). The second capacitor connects the third transmission line and the first line node. The third capacitor connects the fourth transmission line and the second line node.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram of a conventional one-sixteenth ( 1/16) wavelength balun;

FIG. 2 is a schematic diagram of a balun of an exemplary embodiment of the present invention;

FIG. 3 is a graph of simulated results showing an insertion loss and a return loss from balanced ports to an unbalanced port of the balun of FIG. 2;

FIG. 4 is a graph of simulated results showing a phase difference between an input signal and an output signal of the balun of FIG. 2; and

FIG. 5 is a graph of test results showing a phase difference at balanced ports of the balun of FIG. 2.

Claims

1. A balun, comprising: a first transforming part, comprising: a first coupled line, comprising a first end and a second end;a first transmission line, connected to the first end, comprising a first balanced port;a second transmission line, connected to the second end, comprising a second balanced port; anda first capacitor, for connecting the first balanced port and the second balanced port; anda second transforming part, comprising: a second coupled line, comprising a third end and a fourth end;a third transmission line, connected to the third end, comprising an unbalanced port;a first line node;a second capacitor, for connecting the third transmission line and the first line node;a fourth transmission line, connected to the fourth end;a second line node; anda third capacitor, for connecting the fourth transmission line and the second line node.

2. The balun as claimed in claim 1, wherein the second capacitor is aligned with the third capacitor.

3. The balun as claimed in claim 1, wherein the first line node comprises a ground via.

4. The balun as claimed in claim 3, wherein the second line node comprises a ground via.

5. The balun as claimed in claim 1, wherein the first transforming part is symmetrical with respect to a central line thereof.

6. The balun as claimed in claim 5, wherein the second transforming part is symmetrical with respect to a central line thereof.

7. The balun as claimed in claim 1, wherein the first transmission line, the first coupled line, and the second transmission line are connected in series, forming a first resonator.

8. The balun as claimed in claim 7, wherein the third transmission line, the second coupled line, and the fourth transmission line are connected in series, forming a second resonator.

9. The balun as claimed in claim 1, wherein the first balanced port and the second balanced port are used for inputting signals, and the unbalanced port is used for outputting signals.

10. The balun as claimed in claim 1, wherein the unbalanced port is used for inputting signals, and the first balanced port and the second balanced port are used for outputting signals.

11. The balun as claimed in claim 1, matching impedances at the first balanced port, the second balanced port, and the unbalanced port are substantially 50 ohm.

12. The balun as claimed in claim 1, lengths of the first coupled line and the second coupled line are substantially one-sixteenth of a working wavelength of the balun.

13. The balun as claimed in claim 1, wherein the first coupled line is parallel to the second coupled line.

14. The balun as claimed in claim 1, wherein a width of the first coupled line is less than that of first transmission line and that of the second transmission line.

15. The balun as claimed in claim 14, wherein a width of the second coupled line is less than that of the third transmission line and that of the fourth transmission line.

16. A balun assembly comprising: a substrate; anda balun disposed on said substrate and comprising a first transforming part and a second transforming part neighboring said first transforming part and spaced therefrom, said first transforming part comprising a first coupling line extending beside and spaced from said second transforming part, and a first transmission line and a second transmission line respectively extending out of said first coupling line and away from said second transforming part in order to electrically connect with a corresponding balanced port, said second transforming part comprising a second coupling line extending beside and spaced from said first coupling line, and a third transmission line and a fourth transmission line respectively extending out of said second coupling line and away from said first transforming part, extending ends of said third and fourth transmission lines electrically connectable with at least one unbalanced port and spaced from each other, a capacitor electrically connectable with each of said extending ends of said third and fourth transmission lines at one side of said capacitor and disposed between said extending ends of said third and fourth transmission lines, the other side of said capacitor being grounded.

17. The balun assembly as claimed in claim 16, wherein said capacitor is electrically connected with a line node at said other side thereof and said line node is grounded.

18. A balun assembly comprising: a substrate; anda balun disposed on said substrate and comprising two transforming parts neighboring and spaced from each other, one of said two transforming parts electrically connectable with two balanced ports and the other of said two transforming parts electrically connectable with at least one unbalanced port, said other of said two transforming parts comprising two transmission lines extending away from said first transforming part, respectively, and extending ends of said two transmission lines spaced from each other to electrically connect with said at least one unbalanced port, at least one grounded line node disposed between said extending ends of said two transmission lines and electrically connectable with at least a selective one of said extending ends of said two transmission lines via a capacitor.

19. The balun assembly as claimed in claim 18, wherein said at least grounded line node comprises two spaced grounded line nodes disposed between said extending ends of said two transmission lines, each of said two spaced line nodes is electrically connected with a corresponding one of said extending ends of said two transmission lines via a corresponding one of said capacitor.