Multi-element antenna calibration technique
Antenna system having an antenna array with multiple sub-arrays, each having one or more antenna elements, is calibrated using a distributed calibration antenna element, such as a leaky coaxial cable, that spans across at least two and possibly all of the sub-arrays. To calibrate the transmit (TX) paths of the sub-arrays, TX calibration test signals are transmitted by the sub-arrays, captured by the distributed calibration element, and processed by a corresponding calibration radio. To calibrate the receive (RX) paths of the sub-arrays, an RX calibration test signal is generated by the calibration radio, transmitted by the distributed calibration element, captured by the sub-arrays, and processed by their corresponding radios. Cross-correlation between the calibration and captured signals is performed to derive the complex gain of each sub-array transmitter and receiver, which provides information for aligning the gain, phase, and delay of the different TX and RX paths of the antenna array.
1. An antenna system comprising:
an antenna array comprising a plurality of sub-arrays, each sub-array having one or more antenna elements;
a radio for each sub-array, each radio comprising one or more transceivers;
a distributed calibration antenna element distributed across at least two sub-arrays of the antenna array; and
a calibration radio for the distributed calibration antenna element, the calibration radio comprising:
a transmit path configured to generate a receive calibration signal for transmission from the distributed calibration antenna element to the antenna array to calibrate receive paths of the antenna system;
a receive path configured to process a transmit calibration signal captured by the distributed calibration antenna element from the antenna array to calibrate transmit paths of the antenna system.
2. The invention of claim 1 , wherein the distributed calibration antenna element is distributed across all of the sub-arrays of the antenna array.
3. The invention of claim 1 , wherein the calibration radio further comprises
a switch matrix configured to selectively connect the distributed calibration antenna element to either the transmit path or the receive path of the calibration radio.
4. The invention of claim 1 , wherein the distributed calibration antenna element is a leaky coaxial cable.
5. A method of calibrating transmit (TX) paths of an antenna system comprising (i) an antenna array with a plurality of sub-arrays, each sub-array having one or more antenna elements, and (ii) a radio for each sub-array, each radio comprising one or more transceivers, the method comprising:
(a) transmitting one or more TX calibration test signals from one or more of the sub-arrays;
(b) capturing a TX received signal corresponding to the one or more TX calibration test signals using a distributed calibration antenna element that is distributed across at least two sub-arrays of the antenna array;
(c) processing the TX received signal using a calibration radio for the distributed calibration antenna element to generate TX digital signals; and
(d) processing the TX digital signals to calibrate the TX paths of the antenna system.
6. The method of claim 5 , further comprising:
(e) transmitting an RX calibration test signal from the distributed calibration antenna element;
(f) capturing one or more RX received signals corresponding to the RX calibration test signal using one or more of the sub-arrays of the antenna array;
(g) processing the one or more RX received signals using the corresponding radios for the one or more sub-arrays to generate RX digital signals; and
(h) processing the RX digital signals to calibrate RX paths of the antenna system.
7. The method of claim 5 , wherein the distributed calibration antenna element is distributed across all of the sub-arrays of the antenna array.
8. The method of claim 5 , wherein the distributed calibration antenna element is a leaky coaxial cable.
9. A method of calibrating receive (RX) paths of an antenna system comprising (i) an antenna array with a plurality of sub-arrays, each sub-array having one or more antenna elements, and (ii) a radio for each sub-array, each radio comprising one or more transceivers, the method comprising:
(a) transmitting an RX calibration test signal from a distributed calibration antenna element that is distributed across at least two sub-arrays of the antenna array;
(b) capturing one or more RX received signals corresponding to the RX calibration test signal using one or more of the sub-arrays of the antenna array;
(c) processing the one or more RX received signals using the corresponding radios for the one or more sub-arrays to generate RX digital signals; and
(d) processing the RX digital signals to calibrate the RX paths of the antenna system.
10. The method of claim 9 , wherein the distributed calibration antenna element is distributed across all of the sub-arrays of the antenna array.
11. The method of claim 9 , wherein the distributed calibration antenna element is a leaky coaxial cable.
12. The method of claim 5 , wherein transmitting one or more TX calibration test signals from one or more of the sub-arrays comprises concurrently transmitting unique and linearly independent TX calibration test signals from the one or more of the sub-arrays.
13. The method of claim 5 , wherein processing the TX digital signals to calibrate the TX paths of the antenna system comprises cross-correlating the TX calibration test signals with the TX digital signals to calibrate the TX paths of the antenna system.
14. The method of claim 5 , wherein at least one TX calibration test signal is transmitted while non-calibration signals are processed by the antenna system.
15. The method of claim 12 , wherein the distributed calibration antenna element is distributed across all of the sub-arrays of the antenna array, wherein the distributed calibration antenna element is a leaky coaxial cable, wherein processing the TX digital signals to calibrate the TX paths of the antenna system comprises cross-correlating the TX calibration test signals with the TX digital signals to calibrate the TX paths of the antenna system, and wherein at least one TX calibration test signal is transmitted while non-calibration signals are processed by the antenna system.