Active antenna system comprising coupling paths between feed networks
Embodiments described herein relate to an active antenna system. The active antenna system comprises an antenna array wherein the antenna array comprises a plurality of sub-arrays; a plurality of feed networks configured to couple respective signals from the plurality of sub-arrays to respective radio chains; and at least one coupling path configured to provide coupling between a first feed network and a second feed network, wherein the first feed network is coupled to a first sub-array and the second feed network is coupled to a second sub-array, wherein the coupling is of a higher magnitude than a lowest magnitude of mutual aperture couplings occurring between antenna elements in the first sub-array and the second sub-array.
1. An active antenna system comprising:
an antenna array wherein the antenna array comprises a plurality of sub-arrays;
a plurality of feed networks configured to couple respective signals from the plurality of sub-arrays to respective radio chains; and
at least one coupling path configured to provide coupling between a first feed network and a second feed network, wherein the first feed network is coupled to a first sub-array and the second feed network is coupled to a second sub-array,
wherein the coupling is of a higher magnitude than a lowest magnitude of mutual aperture couplings occurring between antenna elements in the first sub-array and the second sub-array.
2. The active antenna system as claimed in claim 1 wherein the coupling is used in a calibration measurement path in a mutual coupling based antenna calibration function to calibrate phase settings and/or amplitude settings of a first radio chain coupled to the first feed network and a second radio chain coupled to the second feed network.
3. The active antenna system as claimed in claim 1 , wherein the coupling has a magnitude x, wherein −50 dB≤x≤−15 dB.
4. The active antenna system as claimed in claim 1 wherein the plurality of feed networks comprises two feed networks for each of the plurality of sub-arrays.
5. The active antenna system as claimed in claim 1 , wherein a first coupling path of the at least one coupling path is realized by arranging the first feed network and the second feed network to provide a directional coupler between the first feed network and the second feed network.
6. The active antenna system as claimed in claim 1 , wherein a second coupling path of the at least one coupling path comprises:
a first directional coupler coupled to the first feed network;
a second directional coupler coupled to the second feed network; and
a signal path between the first directional coupler and the second directional coupler.
7. The active antenna system as claimed in claim 6 wherein the first antenna element and the second antenna element are the same.
8. The active antenna system as claimed in claim 1 , wherein a third coupling path of the at least one coupling path comprises a T-split signal path between the first feed network and the second feed network.
9. The active antenna system as claimed in claim 1 , wherein the at least one coupling path is configured to couple a first section of the first feed network to a second section of the second feed network, wherein the first section of the first feed network is coupled to only a first antenna element and the second section of the second feed network is coupled to only a second antenna element.
10. The active antenna system as claimed in claim 9 wherein the first plurality of antenna elements and the second plurality of antenna elements are the same.
11. The active antenna system as claimed in claim 1 , wherein the at least one coupling path is configured to couple a third section of the first feed network to a fourth section of the second feed network, wherein the third section of the first feed network is coupled to a first plurality of antenna elements and the fourth section of the second feed network is coupled to a second plurality of antenna elements.
12. The active antenna system as claimed in claim 1 , wherein the first feed network and second feed network, are coupled to sub-arrays that are positioned next to each other within the antenna array.
13. The active antenna system as claimed in claim 12 wherein the at least one coupling path is configured to couple a first sub-array to a second sub-array adjacent to the first sub-array in the first direction.
14. The active antenna system as claimed in claim 12 wherein the at least one coupling path is configured to couple a first sub-array to a second sub-array adjacent to the first sub-array in a second direction perpendicular to the first direction.
15. The active antenna system as claimed in claim 1 , wherein the at least one coupling path is positioned to couple together signals from antenna elements that have mutual aperture coupling that is lower than an expected antenna coupling.
16. The active antenna system as claimed in claim 1 , wherein the plurality of sub-arrays are each arranged with a number of antenna elements stacked in a first direction.
17. The active antenna system as claimed in claim 1 , wherein the plurality of sub-arrays each comprise four antenna elements.