received by the International Bureau on 21 June 2016 (21.06.2016)

1. A balun circuit comprising:

a substrate;

an output stripline having coplanar first and second branches formed on a first surface of the substrate;

an input stripline formed on the first surface of the substrate;

one or more slotlines formed in a ground plane on a second surface of the substrate, the one or more slotlines forming a transmission path between the input stripline and the first and second output stripline branches; and

a triangular metallization formed on the ground plane, wherein at least a portion of the first branch is positioned in line with a first edge of the metallization, and at least a portion of the second branch is positioned in line with a second edge of the metallization.

2. The balun circuit of claim 1, wherein the first and second branches of the output stripline are adapted to provide a characteristic impedance of about 200 ohms and an impedance transformation ratio of about 1 :4.

3. The balun circuit of claim 2, wherein the balun circuit is adapted to operate at a frequency greater than about 11 GHz.

4. The balun circuit of claim 2, wherein the balun circuit is adapted to operate at any frequency between about 5 GHz and about 30 GHz.

5. The balun circuit of claim 1, wherein each of the first and second branches of the output stripline is of a uniform width.

6. The balun circuit of claim 1, wherein the second branch of the output stripline is arranged symmetrical with the first branch.

7. The balun circuit of claim 1, wherein each of the first and second branches of the output stripline, and the input stripline, includes a termination point with an open end discontinuity.

8. The balun circuit of claim 1, wherein the one or more slotlines comprises two slotlines formed in the ground plane in parallel with each other, a first of said two slotlines forming a transmission path between the input stripline and the first branch of the output stripline, and a second of said two slotlines forming a transmission path between the input stripline and the second branch of the output stripline.

9. The balun circuit of claim 8, wherein the distance between the two parallel slotlines is between about 50 microns and about 100 microns.

10. The balun circuit of claim 9, wherein each end of each of the first and second slotlines includes a termination point with an open end discontinuity.

11. The balun circuit of claim 10, wherein said termination points are radial stubs.

12. The balun circuit of claim 10, wherein each of the first branch of the output stripline, the second branch of the output stripline, and the input stripline includes a termination point with an open end discontinuity, and wherein the radial stubs at the termination points of the input striplines, first and second slotlines, and first and second branches of the output stripline are not equal in dimensions with one another.

13. A balun circuit comprising:

a substrate;

a first output stripline formed on a first surface of the substrate;

a second output stripline formed on the first surface of the substrate;

an input stripline formed on the first surface of the substrate; and

28 a slotline formed on a second surface of the substrate opposite the first surface, the slotline having first and second ends, each end including a stub, the first end overlapping the first output stripline and the second end overlapping the second output stripline, and the input stripline overlapping the slotline midway between the first end and the second end, thereby forming a microstrip-to-slotline cross junction transition with each of the microstrip input and output lines,

wherein at least one of the input stripline, the first output stripline, and the second output stripline extends from a side of the substrate to its respective microstrip-to-slotline cross junction transition along a straight line, and

wherein the first output stripline and a second output stripline are substantially rotationally symmetrical with one another.

14. The balun circuit of claim 13, wherein the first and second output striplines are adapted to provide a characteristic impedance of about 70 ohms and a differential impedance of about 140 ohms.

15. The balun circuit of claim 14, wherein the balun circuit is adapted to operate at a frequency greater than about 1 1 GHz.

16. The balun circuit of claim 14, wherein the balun circuit is adapted to operate at a range of frequencies between about 5 GHz and about 45 GHz.

17. The balun circuit of claim 14, wherein the balun circuit is adapted to operate at a range of frequencies between about 5 GHz and about 1 10 GHz.

18. The balun circuit of claim 13, wherein each of the first output stripline, the second output stripline, the input stripline, and each end of the slotline includes a radial stub.

19. The balun circuit of claim 13, wherein each of the first output stripline, the second output stripline, the input stripline, and each end of the slotline includes a termination

29 point, and wherein the slotline overlaps the first output stripline at a respective root of the termination points of each of the first end and the first output stripline, and wherein the slotline overlaps the second output stripline at a respective root of the termination points of each of the second end and the second output stripline.

20. The balun circuit of claim 13, wherein each of the first and second output striplines is straight, and the input stripline is bent at an approximately 90 degree angle.

21. The balun circuit of claim 20, wherein each of the first and second output striplines is of a non-uniform width that gradually widens in the direction moving away from the slotline, and wherein the input stripline is of a uniform width.

22. The balun circuit of claim 13, wherein each of the first and second output striplines is bent at an approximately 90 degree angle, and the input stripline is straight.

23. The balun circuit of claim 13, wherein the first output stripline extends between the slotline and a first end of the substrate, the second output stripline extends between the slotline and a second end of the substrate opposite the first end, and the input stripline extends between the slotline and a third end of the substrate between the first and second ends.

24. A double balanced mixer circuit comprising:

a first balun circuit according to claims 13;

a second balun circuit also according to claim 13; and

a switch coupled to each of the first and second balun circuits and operative to mix the respective output frequencies of the first and second balun circuits.

25. The double balanced mixer of claim 24, wherein the switch comprises a crossover quad diode ring.

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26. The double balanced mixer circuit of claim 24, wherein the double balanced mixer circuit is formed on a single substrate, and

wherein the input stripline of each of the first and second balun circuits is straight, and wherein the input stripline of the first balun circuit extends between the slotline of the first balun circuit and a first end of the substrate, and the input stripline of the second balun circuit extends between the slotline of the second balun circuit and a second opposite end of the substrate.

27. The double balanced mixer circuit of claim 24, wherein the double balanced mixer circuit is formed on a single substrate, and wherein the first and second balun circuit are rotationally symmetrical with one another.

28. A balun circuit formed on a substrate, the balun circuit comprising:

an input stripline;

coplanar first and second output striplines; and

one or more coplanar slotlines connecting the input stripline and the coplanar first and second output striplines,

wherein the first and second output striplines are adapted to have a distance between each other that provides an impedance transformation ratio of greater than 1 : 1.

29. The balun circuit of claim 28, wherein the balun circuit is adapted to provide a characteristic impedance of about 200 ohms and an impedance transformation ratio of about 1 :4.

30. The balun circuit of claim 28, wherein the balun circuit is adapted to provide a characteristic impedance of about 150 ohms.

31. The balun circuit of claim 28, wherein the balun circuit is adapted to operate at a frequency greater than 11 GHz.

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32. The balun circuit of claim 28, wherein the balun circuit is adapted to operate at any frequency between about 5 GHz and about 45 GHz.

33. The balun circuit of claim 28, wherein the balun circuit is adapted to operate at any frequency between about 5 GHz and about 110 GHz.

34. The balun circuit of claim 28, wherein the balun circuit is adapted to operate at any frequency between about 5 GHz and about 200 GHz.

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