Compact balun with rejection filter for 802.11a and 802.11b simultaneous operation

1. A balancing/unbalancing (balun) structure for operating at frequency f 1 and rejecting a frequency f 2 comprising:

a printed circuit board (PCB);

a balun on the PCB comprising:

first and second input ports for coupling to a differential signal,

a third port connected to ground through a resistance,

a fourth port for coupling to a single-ended signal corresponding to the differential signal, and

a plurality of traces on the PCB connecting the first and second input ports, the third port and a tap point to the fourth port;

a first λ 2 /4 element connected to the fourth port;

a second λ 2 /4 element connected to the tap point and wrapped around the balun; and

a third λ 2 /4 element connecting the tap point to the fourth port.

2. The balun structure of claim 1 , wherein the first and second input ports and the fourth port are on opposite sides of the balun structure.

3. The balun structure of claim 1 , wherein the third λ 2 /4 element is oriented in a direction generally perpendicular to a direction from the first and second input ports to the fourth port.

4. The balun structure of claim 1 , wherein the balun is a 180° hybrid.

5. The balun structure of claim 1 , wherein a transmission distance from the first input port to the tap point is λ 1 /4.

6. The balun structure of claim 1 , wherein the first λ 2 /4 element is oriented in a direction generally corresponding to a direction from the first and second input ports to the fourth port.

7. A balancing/unbalancing (balun) structure for operating at frequency f 1 and rejecting a frequency f 2 comprising:

a printed circuit board (PCB);

a balun on the PCB comprising:

first and second input ports for coupling to a differential signal,

a third port connected to ground through a resistance,

a fourth port for coupling to a single-ended signal corresponding to the differential signal, and

a plurality of traces on the PCB connecting the first and second input ports, the third port and a tap point to the fourth port;

a first λ 2 /4 element connected to the fourth port;

a second λ 2 /4 element connected to the tap point; and

a third λ 2 /4 element connecting the tap point to the fourth port,

wherein the first and second input ports and the fourth port are on the same side of the balun structure.

8. A balancing/unbalancing (balun) structure for operating at frequency f 1 and rejecting a frequency f 2 comprising:

a printed circuit board (PCB);

a balun on the PCB comprising:

first and second input ports for coupling to a differential signal,

a third port connected to ground through a resistance,

a fourth port for coupling to a single-ended signal corresponding to the differential signal, and

a plurality of traces on the PCB connecting the first and second input ports, the third port and a tap point to the fourth port;

a first λ 2 /4 element connected to the fourth port;

a second λ 2 /4 element connected to the tap point; and

a third λ 2 /4 element connecting the tap point to the fourth port,

wherein the PCB includes two substrate layers, two tracing layers and a ground layer, and

wherein the plurality of traces that comprise the balun and the λ 2 /4 elements are formed on the two tracing layers and are folded over each other.

9. A balancing/unbalancing (balun) structure for operating at frequency f 1 and rejecting a frequency f 2 comprising:

a printed circuit board (PCB);

a balun on the PCB comprising:

first and second input ports for coupling to a differential signal,

a third port connected to ground through a resistance,

a fourth port for coupling to a single-ended signal corresponding to the differential signal, and

a plurality of traces on the PCB connecting the first and second input ports, the third port and a tap point to the fourth port;

a first λ 2 /4 element connected to the fourth port;

a second λ 2 /4 element connected to the tap point; and

a third λ 2 /4 element connecting the tap point to the fourth port,

wherein distance between adjacent traces is approximately twice PCB thickness.

10. An f 1 balun with an integrated f 2 rejection filter comprising:

a printed circuit board (PCB);

a plurality of transmission lines on the PCB forming the balun and connecting a first and second input ports, an isolation port and an output port,

wherein the f 2 rejection filter is wrapped around the plurality of transmission lines.

11. The f 1 balun of claim 10 , wherein the plurality of transmission lines includes a plurality of folded λ 1 /4 elements.

12. The f 1 balun of claim 10 , wherein the first and second input ports and the fourth port are on opposite sides of the balun.

13. The f 1 balun of claim 10 , wherein the first and second input ports and the fourth port are on the same side of the balun.

14. The f 1 balun of claim 10 , wherein the balun is a 180° hybrid.

15. The f 1 balun of claim 10 , wherein a transmission distance from a first input port of the two ports to a tap point is λ 1 /4.

16. The f 1 balun of claim 10 , wherein the f 2 rejection filter includes a first folded element that is oriented in a direction generally corresponding to a direction from the first and second input ports to the fourth port.

17. The f 1 balun of claim 16 , wherein the f 2 rejection filter includes a second folded element that is oriented in a direction generally perpendicular to a direction from the first and second input ports to the fourth port.

18. The f 1 balun of claim 10 , wherein distance between adjacent transmission lines is approximately twice PCB thickness.

19. The f 1 balun of claim 10 , wherein the at least one transmission line element includes a first folded element having a transmission length of λ 2 /4 and connected to the fourth port.

20. The f 1 balun of claim 19 , further including a second folded element having a transmission length of λ 2 /4 and connected to the tap point.

21. The f 1 balun of claim 20 , wherein the second folded element is wrapped around the plurality of transmission lines.