In-device characterization of antenna coupling
A wireless communication device is provided with an in-device capability of characterizing the coupling between a pair of antennas. The wireless communication device determines the coupling through an operating gain measurement and through calibration gain measurements obtained through test ports.
1 . An apparatus for wireless communication, comprising:
a plurality of antennas including a first antenna and a second antenna;
a first antenna tuner coupled to the first antenna;
a second antenna tuner coupled to the second antenna;
a transmitter;
a receiver;
an antenna switch array having a first configuration in which the transmitter is coupled through the antenna switch array to drive the first antenna through the first antenna tuner and in which the second antenna tuner is coupled to a receiver node and having a second configuration in which the transmitter is coupled through the antenna switch array to drive the second antenna through the second antenna tuner and in which the receiver node is coupled to the first antenna tuner;
a first switch coupled between the receiver node and a receive path in the receiver; and
a second switch coupled between the receiver node and a first terminal of a matched load having a second terminal coupled to ground, the second switch configured to selectively couple the receiver node to the matched load.
2 . The apparatus of claim 1 , further comprising:
a controller configured to adjust the second antenna tuner through a plurality of load values while the antenna switch array is in the first configuration, the first switch is open, and the second switch is closed to determine a first coupling factor between the first antenna and the second antenna; and
a directional coupler coupled to a transmit path of the transmitter and configured to sample a forward signal directed through the transmit path towards the antenna switch array and further configured to detect a reverse signal directed through the transmit path from the antenna switch array.
3 . The apparatus of claim 2 , wherein the controller is further configured to determine the first coupling factor while the antenna switch array is in the first configuration responsive to a ratio of the reverse signal to the forward signal at a first load value in the plurality of load values.
4 . The apparatus of claim 3 , wherein the plurality of load values comprises three load values.
5 . The apparatus of claim 2 , wherein the controller is further configured to adjust the first antenna tuner to a load value that matches an impedance of the first antenna tuner to an impedance of the transmitter.
6 . The apparatus of claim 1 , wherein the apparatus comprises a user equipment.
7 . The apparatus of claim 2 , wherein the controller is further configured to adjust the first antenna tuner through a plurality of load values while the antenna switch array is in the second configuration to determine a second coupling factor between the first antenna and the second antenna.
8 . The apparatus of claim 7 , wherein the controller is configured to average the first coupling factor with the second coupling factor.
9 . The apparatus of claim 1 , further comprising:
a transmission line, wherein the receiver includes a receive path and the transmitter includes a transmit path, and wherein the antenna switch array is further configured in the first configuration to couple the second antenna to the receive path through the transmission line, and wherein the antenna switch array is configured in the second configuration to isolate the transmission line from the transmit path and from the receive path.
10 . The apparatus of claim 9 , further comprising:
a controller configured to measure a calibration gain between the transmit path and the receive path while the antenna switch array is in the first configuration and configured to measure an operating gain between the transmit path and the receive path while the antenna switch array is in the second configuration.
11 . The apparatus of claim 10 , further comprising:
a directional coupler coupled to the transmit path and configured to sample a forward signal directed through the transmit path towards the antenna switch array and further configured to detect a reverse signal directed through the transmit path from the antenna switch array.
12 . The apparatus of claim 11 , wherein the controller is further configured to calculate a coupling factor between the first antenna and the second antenna based upon a ratio of the reverse signal to the forward signal, the calibration gain, and the operating gain.
13 . An apparatus for wireless communication, comprising:
a plurality of antennas including a first antenna and a second antenna;
a first antenna tuner coupled to the first antenna;
a second antenna tuner coupled to the second antenna;
a transmitter;
a receiver;
an antenna switch array having a first configuration in which the transmitter is coupled through the antenna switch array to drive the first antenna through the first antenna tuner and in which the second antenna tuner is coupled to a receiver node and having a second configuration in which the transmitter is coupled through the antenna switch array to drive the second antenna through the second antenna tuner and in which the receiver node is coupled to the first antenna tuner;
a first switch coupled between the receiver node and a receive path in the receiver;
a second switch coupled between the receiver node and a first terminal of a matched load having a second terminal coupled to ground; and
a controller configured to adjust the first antenna tuner to a load value that matches an impedance of the first antenna tuner to an impedance of the transmitter.