Wide band directional coupler

1. A wide band directional coupler, comprising:

a main transmission line connected between an input port and an output port; and

a coupling transmission line having a first length and connected between a coupling port and an isolation port, wherein the coupling transmission line is coupled to the main transmission line through a coupling capacitive connection and a mutual inductive connection;

wherein at least a distance between the main transmission line and the coupling transmission line varies along the first length of the coupling transmission line such that any one of a capacitance value of the capacitive connection and an inductance value of the inductive connection is characterized by a relatively low value;

wherein a coupling factor of the wide band directional coupler remains substantially constant throughout an operating frequency band of the wide band directional coupler;

wherein a width of at least the coupling transmission line varies along the first length, and wherein the main transmission line and the coupling transmission line are placed in a configuration such that the lines are shifted relative to each other in a horizontal direction, such that there is a partial overlap between the main transmission line and the coupling transmission line;

wherein the coupling transmission line includes a plurality of sub coupling-lines, wherein the wide band directional coupler further comprises a substrate, wherein each of the sub coupling-lines is placed in a different layer of the substrate of the wide band directional coupler, wherein the sub coupling-lines are connected through vias; and

wherein at least one of a width of each of the sub coupling-lines and a length of each of the sub coupling-lines is distinct.

2. The wide band directional coupler of claim 1 , wherein the main transmission line partially overlaps the coupling transmission line.

3. The wide band directional coupler of claim 2 , wherein a placement of the main transmission line is shifted relative to a placement of the coupling transmission line.

4. The wide band directional coupler of claim 2 , wherein the wide band directional coupler further comprises any one of: a single metal plate coupled between the main transmission line and the coupling transmission line, and two metal plates coupled between the main transmission line and the coupling transmission line.

5. The wide band directional coupler of claim 4 , wherein the any one of the single metal plate and the two metal plates are coupled to allow partial overlapping between the main transmission line connected to the coupling transmission line.

6. The wide band directional coupler of claim 2 , wherein the wide band directional coupler further comprises a metal core inserted between the main transmission line and the coupling transmission line.

7. The wide band directional coupler of claim 1 , wherein the main transmission line includes a plurality of sub main-lines, wherein each of the sub mainlines is placed in a different layer of the substrate, wherein the sub main-lines are connected through vias.

8. The wide band directional coupler of claim 1 , wherein at least one of a width of each of the sub main-lines and a length of each of the sub main-lines is distinct.

9. The wide band directional coupler of claim 1 , wherein a distance between each of the sub main-lines and each of the sub coupling-lines is distinct.

10. The wide band directional coupler of claim 1 , wherein the sub mainlines and the sub coupling-lines partially overlap.

11. The wide band directional coupler of claim 1 , wherein the wide band directional coupler is a miniature coupler.

12. The wide band directional coupler of claim 11 , wherein each of the main transmission line and the coupling transmission line is any one of: a strip-line and micro-strip.

13. The wide band directional coupler of claim 1 , wherein the operating frequency band is between 3 Giga Hertz (GHz) and 7 GHz, wherein the operating frequency band includes a plurality of distinct frequency bands.

14. A wide band directional coupler, comprising:

a main transmission line connected between an input port and an output port, wherein the main transmission line includes at least one sub main-line placed in at least one layer of a substrate of the wide band directional coupler; and

a coupling transmission line connected between a coupling port and an isolation port, wherein the coupling transmission line includes a plurality of sub coupling-lines, wherein each of the sub coupling-lines is placed in a different layer of the substrate;

wherein the coupling transmission line is coupled to the main transmission line through a coupling capacitive connection and a mutual inductive connection, wherein any one of a capacitance value of the capacitive connection and an inductance value of the inductive connection is characterized by a relative low value, wherein a width of at least the coupling transmission line varies along the first length, and wherein the main transmission line and the coupling transmission line are placed in a configuration such that the lines are shifted relative to each other in a horizontal direction, such that there is a partial overlap between the main transmission line and the coupling transmission line;

wherein the plurality of sub coupling-lines are connected through vias, wherein at least one of a width of each of the plurality of sub coupling-lines and a length of each of the plurality sub coupling-lines is distinct.

15. The wide directional coupler of claim 14 , wherein a coupling factor of the wide band directional coupler remains substantially constant throughout an operating frequency band of the wide directional coupler.

16. The wide band directional coupler of claim 14 , wherein each of the at least one sub main-line is placed in a different layer of the substrate and connected through vias, wherein at least one of a width of each of the at least one sub main-lines and a length of each of the least one sub main-lines is distinct.

17. The wide band directional coupler of claim 14 , wherein the at least one sub main-line and the sub coupling-lines partially overlap.

18. The wide band directional coupler of claim 14 , wherein the operating frequency band is between 3 Giga Hertz (GHz) and 7 GHz, wherein the operating frequency band includes a plurality of distinct frequency bands.