Calibration of active antenna arrays for mobile telecommunications
In order to calibrate in amplitude and phase the individual transceiver elements ( 4 ) of an active antenna array for a mobile telecommunications network, each transceiver element including a transmit and a receive path ( 8, 10 ) coupled to an antenna element ( 12 ), each transceiver element includes a comparator ( 100 ) for comparing phase and amplitude of transmitted or received signals with reference signals in order to adjust the characteristics of the antenna beam. In order to provide an accurate means of reference signal distribution, a feed arrangement distributes the reference signals and includes a waveguide ( 50 ) of a predetermined length which is terminated at one end ( 52 ) in order to set up a standing wave system along its length, and a plurality of coupling points ( 56 ) at predetermined points along the length of the waveguide, which are each coupled to a comparator of a respective transceiver element.
1. An active antenna array for a mobile telecommunications network, comprising a plurality of radio elements including a transmit and/or a receive path coupled to a respective antenna element, and including a comparator configured to compare phase of transmitted or received signals with reference values in order to adjust the characteristics of the antenna beam, and including a feed arrangement configured to supply reference signals of phase, the feed arrangement including a waveguide of a predetermined length, which is coupled to a reference signal source, and which is terminated at one end in order to set up a standing wave system along its length, and a plurality of coupling points at predetermined points along the length of the waveguide, which are coupled to a comparator of a respective said radio element.
2. An array as claimed in claim 1 , wherein said waveguide comprises a length of coaxial cable.
3. An array as claimed in claim 2 , wherein said coupling points comprise capacitive coupling ports.
4. An array as claimed in claim 3 , wherein the capacitive coupling ports are adjustable in order to adjust the coupling coefficient with the central conductor of the coaxial cable.
5. An array as claimed in claim 2 , wherein the coaxial cable has a dielectric filling which may be adjusted in characteristics to alter an electromagnetic wave in a line.
6. An array as claimed in claim 1 , wherein the coupling points are spaced apart by a distance of equal to or less than 1λ, where λ is the wavelength in free space of the reference signal.
7. An array as claimed in claim 6 , wherein the coupling points are spaced apart by a distance of about 0.9λ, where λ is the wavelength in free space.
8. An array as claimed in claim 1 , wherein the waveguide comprises a plurality of waveguide sections of predetermined length, interconnected by releasable couplings.
9. An array as claimed in claim 1 , wherein the coupling points are located at or adjacent a voltage maximum or minimum in the standing wave system.
10. An array as claimed in claim 1 , wherein the coupling points are spaced from the terminated end by a distance d=(Nλ+λ/4), where λ is the wavelength in the waveguide.
11. An array as claimed in claim 1 , wherein the terminated end comprises a short circuit.
12. An array as claimed in claim 1 , wherein the couplings points are connected to a comparator by a coupling length of waveguide which is short in relation to the predetermined waveguide length.
13. An array as claimed in claim 1 , wherein the array is two dimensional and includes a further plurality of waveguides, wherein at least one waveguide of said further plurality has an end which is not terminated coupled to a respective coupling point of said first-mentioned waveguide, said first mentioned waveguide extending in a different direction to that of said further plurality of waveguides.
14. An array as claimed in claim 1 , wherein the feed arrangement includes a second waveguide of a predetermined length which is terminated at one end in order to set up a standing wave system along its length, and a plurality of coupling points at predetermined points along the length of the waveguide, which are coupled to a comparator of a respective said radio element, wherein the waves in the first and second waveguides have predetermined time phase difference.
15. An array as claimed in claim 1 , wherein the coupling points of the waveguide are symmetrically arranged about the mid-point of the length of the waveguide.