The invention relates to a multi-port directional coupler (100) for broadband communication applications, comprising: a half-mirror (110), comprising: a first dielectric slab (101) and a second dielectric slab (102); wherein the first dielectric slab (101) and the second dielectric slab (102) are arranged adjacently in a first plane, and wherein the first dielectric slab (101) and the second dielectric slab (102) each comprise at least one port.
1. Multi-port directional coupler (100) for broadband communication applications, comprising: a half-mirror (110), comprising: a first dielectric slab (101) and a second dielectric slab (102); wherein the first dielectric slab (101) and the second dielectric slab (102) are arranged adjacently in a first plane, and wherein the first dielectric slab (101) and the second dielectric slab (102) each comprise at least one port. 2. Multi-port directional coupler (100, 200) according to claim 1, wherein the permittivity of the first dielectric slab (101) is equal to the permittivity of the second dielectric slab (102) or wherein the permittivity of the first dielectric slab (201) is different from the permittivity of the second dielectric slab (202). 3. Multi-port directional coupler (900) according to one of the preceding claims, wherein a gap (905), e.g. an air gap, is formed between a first side (901a) of the first dielectric slab (901) and a first side (902a) of the second dielectric slab (902), and wherein the multi-port directional coupler (900) further comprises a third dielectric slab (903) that is arranged such that it passes through the gap (905) and wherein said third dielectric slab (903) has an orientation that is perpendicular to the first dielectric slab (901) and the second dielectric slab (902). 4. Multi-port directional coupler (100, 200) according to claim 1 or claim 2, further comprising: a first rod (103) arranged in a second plane and a second rod (104) arranged in a third plane; wherein the first plane and the second plane and the third plane are parallel to each other and wherein the first plane lies between the second plane and the third plane; and wherein a longitudinal axis (103a) of the first rod and a longitudinal axis (104a) of the second rod are arranged parallel and opposite to each other; and wherein said longitudinal axes (103a, 104a) of the first rod and the second rod are arranged parallel to and opposite to a longitudinal axis (105a) lying between a first side (101a) of the first dielectric slab and a first side (102a) of the second dielectric slab. 5. Multi-port directional coupler (100) according to claim 4, wherein a gap (105), e.g. an air gap, is formed between a first side (101a) of the first dielectric slab and a first side (102a) of the second dielectric slab and wherein the longitudinal axes (103a, 104a) of the first rod and the second rod are arranged parallel to and opposite to a longitudinal axis (105a) lying in the gap or a multi-port directional coupler (100) according to claim 1 or claim 2, wherein no gap or nearly no gap is formed at an interface (205) between a/the first side (201a) of the first dielectric slab and a/the first side (202a) of the second dielectric slab. 6. Multi-port directional coupler (200) according to one of the preceding claims 1 or 2 or 4, wherein no gap or nearly no gap is formed at an interface (205) between a/the first side (201a) of the first dielectric slab and a/the first side (202a) of the second dielectric slab and wherein the longitudinal axes (203a, 204a) of the first rod and the second rod are arranged parallel to and opposite to a longitudinal axis (205a) lying along the interface between the first side (201a) of the first dielectric slab and the first side (202a) of the second dielectric slab, and wherein the permittivity of the first dielectric slab (201) can be different from the permittivity of the second dielectric slab (202). 7. Multi-port directional coupler (100, 200) according to one of the preceding claims 3 to 6, wherein the first rod and the second rod have a cylindrical shape and/or wherein the material of the first rod and the material of the second rod comprises a conductive material, e.g. a metallic material. 8. Multi-port directional coupler (100, 200, 500, 600) according to one of the preceding claims, wherein the first dielectric slab and the second dielectric slab are planar slabs and have a rectangular shape, and/or wherein the operating frequency of the multi-port directional coupler lies in the range of 1 GHz to 1 THz, and/or wherein the at least one port of the exemplary multi-port directional coupler is configured as a dielectric rod waveguide, or wherein all ports of the exemplary multi-port directional coupler are configured as dielectric rod waveguides. 9. Multi-port directional coupler (300, 400, 500, 600) according to one of the preceding claims, wherein the multi-port directional coupler is configured as a four-port directional coupler comprising four ports, wherein each of the two adjacent dielectric slabs comprises two ports, and wherein a first port is configured as input port, a second port is configured as transmitted port, a third port is configured as coupled port and a fourth port is configured as isolated port. 10. Multi-port directional coupler (800) according to one of the preceding claims 1 to 8, wherein the permittivity of the first dielectric slab (801) is different from the permittivity of the second dielectric slab (802), and wherein the first dielectric slab comprises a first port that is configured as input port (811) and a second port (812) that is configured as transmitted port, and wherein the second dielectric slab comprises at least two further ports that are configured as coupled ports (813, 813', 813"). 11. Multi-port directional coupler (300, 400, 500, 600, 800) according to one of the preceding claims, further comprising a plurality of signal launchers, wherein each signal launcher is spatially associated to one specific port of the multi-port directional coupler and wherein at least one signal launcher is configured for collimating electromagnetic wave signals received from external sources and wherein said at least one signal launcher is further configured for injecting the received electromagnetic wave signals into at least one of the dielectric slabs, wherein, in particular, the at least one signal launcher is configured for injecting the received electromagnetic wave signals into at least one of the dielectric slabs in the form of a single two-dimensional beam for all operating frequencies. 12. Multi-port directional coupler (300, 400, 500, 600, 800) according to the preceding claim, wherein the first dielectric slab and the second dielectric slab are planar slabs and have a rectangular shape, and wherein the multi-port directional coupler comprises a plurality of ports, with each port having a signal launcher, and wherein the signal launchers and ports are located at or near the corners of the dielectric slabs, wherein said corners are the corners of the dielectric slabs that are located not on the first side of the first dielectric slab and not located on the first side of the second dielectric slab; and/or wherein at least one port is configured as a dielectric rod waveguide port. 13. Multi-port directional coupler (300, 400, 500, 600, 800) according to one of claims 11 or 12, wherein the signal launchers are of one of the following types: total internal reflection reflectors, e.g. total internal reflection parabolic reflectors, planar elliptic or flat mirrors, and/or tapered dielectric rod waveguides. 14. Multi-port directional coupler (300, 400, 500, 600, 800) according to one of the preceding claims, wherein the first dielectric slab and the second dielectric slab have the same size and the same dimensions, or a multi-port directional coupler (300, 400, 500, 600, 800) according to one of claims 3 to 13 wherein the first rod and the second rod have the same size and the same dimensions and wherein the first dielectric slab and the second dielectric slab have the same size and the same dimensions. 15. Device for broadband communication applications comprising at least one multi-port directional coupler according to one of the preceding claims, wherein the device can be, for example, of one of the following types: a network analyzer, e.g. a vector network analyzer, a transceiver a spectrometer or an image detector.