Hollow waveguide directional coupler

1. A directional coupler, comprising: two hollow waveguide sections connected to each other by a plurality of coupling openings formed in a wall extending between the hollow waveguide sections, two adjacent coupling openings of said plurality having a distance of (2n+1) λ g /4 from each other, wherein λ g is a wavelength of a nominal center frequency of an operating frequency range of the directional coupler, wherein n is an integer, and wherein the two adjacent coupling openings are separated from each other by a wall portion having a length of more than λ g /4.

2. The directional coupler according to claim 1 , in that n equals 1.

3. The directional coupler according to claim 1 , in that the hollow waveguide sections have rectangular cross-sections, and in that the wall forms a narrow side-wall of the hollow waveguide sections.

4. The directional coupler according to claim 1 , in that the hollow waveguide sections have rectangular cross-sections, and in that the wall forms a broad side-wall of the hollow waveguide sections.

5. The directional coupler according to claim 1 , in that at least one of the coupling openings has a dimension in a longitudinal direction of the hollow waveguide sections of λ g /8.

6. The directional coupler according to claim 5 , wherein the dimension is on the order of λ g /4.

7. The directional coupler according to claim 1 , in that each coupling opening has a dimension in a longitudinal direction of the hollow waveguide sections of at least λ g /8.

8. The directional coupler according to claim 1 , in that each coupling opening has a length that decreases from a center towards an end of the directional coupler.

9. The directional coupler according to claim 1 , wherein the length is on the older of λ g /2.