Dynamic real-time calibration for antenna matching in a radio frequency receiver system
Real-time calibration of a tunable matching network that matches the dynamic impedance of an antenna in a radio frequency receiver system. The radio frequency receiver system includes two non-linear equations that may be solved to determine the reflection coefficient of the antenna. The tunable matching network is repeatedly perturbed and the power received by the antenna is measured after each perturbation at the same node in the matching network. The measured power values are used by an optimizer in converging to a solution that provides the reflection coefficient of the antenna. The reflection coefficient of the antenna may be used to determine the input impedance of the antenna. The elements of the matching circuit are then adjusted to match the input impedance of the antenna.
1. A radio frequency (RF) receiver comprising:
an antenna having a feed point;
a tunable matching network connected to the antenna feed point to receive RF signals from the antenna;
power detector, connected to point to the RF receiver, to measure at the single node power levels of the received RF signals output from said feed point; and
a control system that calculates values of tuning elements of the tunable matching network to match an input impedance of the antenna at the feed point by using at least three power level measurements simultaneously in two non-linear equations, the at least three power level measurements being detected at said single node by said power detector, wherein a first non-linear equation of the two non-linear equations is formulated as:
P
L
(
1
)
P
L
(
0
)
=
S
22
(
1
)
2
1
-
S
22
(
0
)
Γ
L
2
1
-
Γ
A
Γ
in
(
0
)
2
S
21
(
0
)
2
1
-
S
22
(
1
)
Γ
L
2
1
-
Γ
A
Γ
in
(
1
)
2
,
wherein
P
L
(
1
)
P
L
(
0
)
is the ratio of power received by the reactive elements of the matching network; S 22 (1) is a scattering matrix parameter that represents an output reflection coefficient of a 50 ohm terminated input after a first perturbation of the matching network; S 22 (0) is a matrix parameter that represents an output reflection coefficient of a 50 ohm terminated input in a previous tuning period; S 21 (0) is a scattering matrix parameter which represents the forward transmission coefficient of a 50 ohm terminated output in a previous tuning period; Γ L is a reflection coefficient of the load, and Γ in (0) is an input reflection coefficient of the matching network as seen from the antenna in a previous tuning period; Γ in (2) is an input reflection coefficient of the matching network as seen from the antenna after a first perturbation of the matching network; and Γ A is a reflection coefficient of the antenna.
2. The receiver of claim 1 , wherein the control system calculates a complex value of the input impedance.
3. The receiver of claim 1 , wherein a first non-linear equation includes a reflection coefficient of the antenna and scattering parameters of the matching network.
4. The receiver of claim 1 , wherein a first of said three power level measurements is detected after a first perturbation of a number of reactive elements in the matching network.
5. The receiver of claim 1 wherein a second of said three power level measurements is detected after a second perturbation of a number of reactive elements in the matching network.
6. The receiver of claim 1 wherein a third of said three power level measurements is detected after a third perturbation of a number of reactive elements in the matching network.
7. The receiver of claim 1 , wherein a second non-linear equation of the two non-linear equations is formulated as:
P
L
(
2
)
P
L
(
0
)
=
S
21
(
2
)
2
1
-
S
22
(
0
)
Γ
L
2
1
-
Γ
A
Γ
in
(
0
)
2
S
21
(
0
)
2
1
-
S
22
(
2
)
Γ
L
2
1
-
Γ
A
Γ
in
(
2
)
2
,
wherein
P
L
2
P
L
(
0
)
is the ratio of power received by the reactive elements of the matching network; S 22 (1) is a scattering matrix parameter that represents an output reflection coefficient of a 50 ohm terminated input after a second perturbation of the matching network; S 22 (0) is a matrix parameter that represents an output reflection coefficient of a 50 ohm terminated input in a previous tuning period; S 21 (0) is a scattering matrix parameter which represents the forward transmission coefficient of a 50 ohm terminated output in a previous tuning period; S 21 (2) is a scattering matrix parameter which represents the forward transmission coefficient of a 50 ohm terminated output after a second perturbation of the matching network; Γ L is a reflection coefficient of the load, and) Γ in (0) is an input reflection coefficient of the matching network as seen from the antenna in a previous tuning period; Γ in (2) is an input reflection coefficient of the matching network as seen from the antenna after a second perturbation of the matching network; and Γ A is the reflection coefficient of the antenna.
8. A method of matching an input impedance of an antenna to a receiver, the method comprising:
connecting a tunable matching network in an RF signal path from a feed point of the antenna to the receiver;
detecting at a single node in the RF signal path power levels of received RF signals; and
calculating values of tuning elements of the tunable matching network to match an input impedance of the antenna by use of at least three different power levels simultaneously in two non-linear equations, the at least three power level measurements being measured at said single node detected by said power detector, wherein a first non-linear equation of the two non-linear equations is formulated as:
P
L
(
1
)
P
L
(
0
)
=
S
22
(
1
)
2
1
-
S
22
(
0
)
Γ
L
2
1
-
Γ
A
Γ
in
(
0
)
2
S
21
(
0
)
2
1
-
S
22
(
1
)
Γ
L
2
1
-
Γ
A
Γ
in
(
1
)
2
,
wherein
P
L
(
1
)
P
L
(
0
)
is the ratio of power received by the reactive elements of the matching network; S 22 (1) is a scattering matrix parameter that represents an output reflection coefficient of a 50 ohm terminated input after a first perturbation of the matching network; S 22 (0) is a matrix parameter that represents an output reflection coefficient of a 50 ohm terminated input in a previous tuning period; S 21 (0) is a scattering matrix parameter which represents the forward transmission coefficient of a 50 ohm terminated output in a previous tuning period; Γ L is a reflection coefficient of the load, and Γ in (0) is an input reflection coefficient of the matching network as seen from the antenna in a previous tuning period; Γ in (2) is an input reflection coefficient of the matching network as seen from the antenna after a first perturbation of the matching network; and Γ A is a reflection coefficient of the antenna.
9. The method of claim 8 , including using the three power level to solve two non-linear equations to calculation the values of the tuning elements.
10. The method of claim 8 , wherein said calculating calculates a complex value of the input impedance.
11. The method of claim 8 , including using a reflection coefficient of the antenna and scattering parameters of the matching network in a first of the two non-linear equations.
12. The method of claim 8 , including perturbing a number of reactive elements in the matching network before detecting a first of said three power levels.
13. The method of claim 12 , including perturbing a second number of reactive elements in the matching network before detecting a second of said three power levels.
14. The method of claim 12 , including perturbing a third number of reactive elements in the matching network before detecting a third of said three power levels.
15. The method of claim 8 , wherein a second non-linear equation of the two non-linear equations is formulated as:
P
L
(
2
)
P
L
(
0
)
=
S
21
(
2
)
2
1
-
S
22
(
0
)
Γ
L
2
1
-
Γ
A
Γ
in
(
0
)
2
S
21
(
0
)
2
1
-
S
22
(
2
)
Γ
L
2
1
-
Γ
A
Γ
in
(
2
)
2
,
wherein
P
L
2
P
L
(
0
)
is the ratio of power received by the reactive elements of the matching network; S 22 (1) is a scattering matrix parameter that represents an output reflection coefficient of a 50 ohm terminated input after a second perturbation of the matching network; S 22 (0) is a matrix parameter that represents an output reflection coefficient of a 50 ohm terminated input in a previous tuning period; S 21 (0) is a scattering matrix parameter which represents the forward transmission coefficient of a 50 ohm terminated output in a previous tuning period; S 21 (2) is a scattering matrix parameter which represents the forward transmission coefficient of a 50 ohm terminated output after a second perturbation of the matching network; Γ L is a reflection coefficient of the load, and Γ in (0) is an input reflection coefficient of the matching network as seen from the antenna in a previous tuning period; Γ in (2) is an input reflection coefficient of the matching network as seen from the antenna after a second perturbation of the matching network; and Γ A is the reflection coefficient of the antenna.