This invention relates generally to a hybrid coupler and, more specifically but not necessarily exclusively, to a 180° hybrid coupler for use in, for example, an antenna arrangement. The invention also relates to antenna arrangements incorporating one or more hybrid couplers and associated methods of operating a hybrid coupler, with particular, but not necessarily exclusive, reference to microwave hybrid couplers.

A 4-port 180° hybrid coupler is a type of power divider or combiner. It can also be used as a balun. Baluns are well-known passive electrical devices. The term “balun” is derived from the abbreviation of the two terms ‘balanced’ and ‘unbalanced’. Baluns are 3-port devices which convert signals from an unbalanced transmission line to a balanced transmission line, and vice versa. In general, the two balanced ports of a balun should provide a signal equal in amplitude with a 180° phase difference.

Microwave balun devices can be implemented in various ways, such as in transformer-type arrangements, coupled transmission lines and transmission line junctions. It is known from US2005/0105637 how to implement baluns using microwave techniques involving microstrips and slotlines.

A 4-port 180° hybrid coupler has the property that, from two inputs, the common or even mode will output from one port (the Σ or sum port), while the differential or odd mode will appear at a different port (the Δ or difference port). A four-port 180° hybrid coupler can be made into a 180° power divider (effectively a three-port balun) by terminating the sum port with a matched load, such that the load on the sum port absorbs some or all of the common-mode signal received at the output ports.

However, known 180° hybrid couplers tend to be relatively narrowband. It would, therefore, be desirable to improve the characteristics of these devices. In particular, it would be desirable to achieve a wider frequency range over which useful operation of the device can be achieved.

The present invention, in at least some of its embodiments, addresses the above described problems and desires.

According to a first aspect of the present invention, there is provided a hybrid coupler for dividing an input electrical signal to produce first and second output electrical signals which are substantially out of phase, the hybrid coupler including:

a first port comprising an input port for receiving the input electrical signal; an input line for coupling the input electrical signal to a slotline; and an output line for coupling the first and second output electrical signals to, respectively, second and third ports comprising, respectively, a first output port and a second output port, the output line having a junction with the slotline; wherein the slotline couples the input electrical signal to the junction, and the junction acts as a divider to produce the first and second electrical signals;

wherein the hybrid coupler further comprises:

an input section including said input line and an output section including said output line, and wherein the slotline is terminated at the output section by an output open circuit termination;

a pair of ground planes, between which said input line and said output line are located;

and wherein:

on one of the ground planes, the slotline transitions at said output section into a first end of a Co-Planar Waveguide, said Co-Planar Waveguide being electrically connected to said output line, said Co-Planar Waveguide defining, at a second, opposing end thereof, a sum port configured to divert common mode signals received at said first and second output ports to said second end thereof.

In an exemplary embodiment, the second end of said Co-Planar Waveguide may be connected, or otherwise coupled, to a matched load, a connector, or another form of transmission line interface.

The slotline may also be terminated at the input section by an input open circuit termination.

In a preferred embodiment, the Co-Planar Waveguide may comprise a generally central track having a first elongate portion extending in a direction from said input section toward said output open circuit termination, said first elongate portion being of a first width, an intermediate portion extending across said output open circuit termination and having a second width, different to said first width, and a second elongate portion extending beyond said output open circuit termination and having a third width different to said second width. Optionally, the first elongate portion of said Co-Planar Waveguide is nearest to the input section, said Co-Planar Waveguide extending from said first elongate portion in a direction toward said output ports, wherein said second portion of said Co-Planar Waveguide may be located between said first and second elongate portions, the sum port optionally being located at a distal end of said second elongate portion of said Co-Planar Waveguide.

In an exemplary embodiment, the first elongate portion may have a first impedance (e.g. 100Ω to match the transmission line) and the second elongate portion may have a second, different impedance (e.g. 50Ω to match a connector), and the widths of said first and second elongate portions may be different so as to transition from said first impedance to said second impedance within said Co-Planar Waveguide. This transition may, for example, be achieved by stepping or tapering the second elongate portion.

The distal end of said first elongate portion of the Co-Planar waveguide may be tapered to a point.

In an exemplary embodiment, the electrical connection between the Co-Planar Waveguide and the output line may comprise a blind via; and the co-planar waveguide may be substantially symmetrical about the slotline. In the latter case, the electrical connection between the Co-Planar Waveguide and the output line may be located generally centrally on the output line. Indeed, in an exemplary embodiment, the output line is beneficially symmetrical and may (optionally but not necessarily) be substantially U-shaped and the electrical connection between the Co-Planar Waveguide and the output line may be located generally centrally at the curved portion of the substantially U-shaped output line.

In an exemplary embodiment of the invention, at least one of the input line, slotline and output line has a width and a length and the width may vary over the length.

A hybrid coupler according to an exemplary embodiment of the present invention may be in the form of a microwave laminate structure.

According to a second aspect of the present invention, there is provided an antenna arrangement including an antenna which is fed electrical signals from a hybrid coupler substantially as described above.

According to a third aspect of the present invention, there is provided a method of operating a hybrid coupler substantially as described above, including: inputting an input electrical signal to the hybrid coupler, and outputting from the hybrid coupler first and second output electrical signals which are substantially out of phase.

According to a fourth aspect of the present invention, there is provided a method of operating a hybrid coupler substantially as described above, including: inputting an input electrical signal to the hybrid coupler, and outputting from the hybrid coupler first and second output electrical signals which are substantially of equal phase.

Whilst the invention has been described above, it extends to any inventive combination of the features set out above, or in the following description, drawings or claims.

