Dual-Polarisation Four-Way Power Divider

Description:

The present invention originated as a means to reduce the length of radiating elements in space-segment feed systems for GEO satcom applications, including passive multiple beam reflector antennas and active arrays, where radiating elements typically have an aperture in the range of 2 to 3 wavelengths. This aperture size is constrained by the wish to reduce the number of elements for a given array aperture size while maintaining grating lobes outside of the field of view. A typical horn design with high aperture efficiency has a length of about 2 to 3 times its aperture diameter. For Ku-band applications, this results in a rather bulky radiating element. A possible way to shorten this radiating element is to divide the aperture in smaller elements and combine them using a suitable beamforming network. This requires compact power dividers, preferably operating in dual-polarisation. 

There have been various developments on this topic showing that that there is no simple solution fitting the need for dual-polarisation four-way power dividers, with element spacing below one wavelength.

The present invention shows a simpler solution starting from a combination of four 2-probe junctions. The main difference with respect to the prior-art comes in the way those 4 junctions are connected. E-plane junctions are used between facing ports of adjacent 2-probe junctions without any matching transitions, keeping the design very compact. An additional novelty when compared to existing designs is to use offset twists to change the direction of the common ports of the T junctions, enabling their combination with a turnstile junction in a compact way.

This has the advantage of providing the right phase conditions for using this component in a 2x2 array antenna with a much simpler design and implementation than some of the prior art solutions. 

The various layers of the invention are illustrated in Figure 1. The top left figure illustrates the arrangement of the 2-probe junctions and the connection between them. Following the E-plane T-junctions, the top right figure illustrates the arrangement of the T junction common ports. The bottom left figure illustrates the twists that enable rotating the four common ports, while the bottom right figure illustrates the connection of those ports through a turnstile junction. A key for an extremely compact array spacing is in the T-junctions which require no bending and in the twists that enable to offset the ports to provide sufficient space for the turnstile junction.

A prototype of the proposed dual-polarization four-way power divider has been designed and manufactured to operate over the portion of the K-band allocated to broadband satcom down-link (17.7– 20.2 GHz).

A very good agreement between simulation and measurement has been achieved in relation to the return loss and port-to-port isolation of the array and CP OMT assembly. Further details are available upon request.

Innovations and advantages:

• More compact and simpler than existing solutions, and easily scalable to larger arrays.
• Four 2x2 arrays may be combined using the very same four-power divider (only 1) thanks to the fact that the common port of the four-way power divider is a dual-mode waveguide. Hence, it may be used to design small or large arrays.
• The invention could be combined with 3D printing techniques for further size and mass reduction.

Domain of application:

This solution is applicable in the field of passive and active arrays and it may also be used as feed system in a reflector antenna: 

• At Ku-band, this solution could lead to a significant reduction of the passive RF section.
• Active antennas (typically Ku and Ka band products) with cluster spacing in the range of 3/4 wavelengths as well as passive arrays, mainly for ground segment (mechanically steered passive array). 

Outside the space field, this invention could find application as a compact probe for RF measurement facilities, particularly at frequencies in Ku-band and below where the reference probes can be quite bulky.   

IP Status

EP patent application has been filed.