Automatic phase calibration

1. A method of calibrating a test platform to establish a phase relationship between copies of a signal at a measurement location within the test platform, comprising:

manipulating phase relationships of the copies of the signal traversing signal paths and ending at the measurement location; and

analyzing vector signal addition from the copies of the signal at the measurement location as the phase relationships are manipulated to find a phase offset adjustment that establishes a particular phase relationship between the signal paths.

2. The method of claim 1 , comprising:

repeating said manipulating and said analyzing using a changed signal source and a changed signal path within the test platform.

3. The method of claim 1 , comprising:

applying said manipulating and said analyzing to versions of a signal generated by a pair of signal sources and transmitted through the signal paths.

4. The method of claim 1 , wherein said manipulating includes using one or more phase offsets for the signal paths.

5. The method of claim 4 , comprising determining the phase offsets to reduce destructive signal addition from the copies of the signal.

6. The method of claim 1 , comprising:

using a switching network with balanced signal paths to direct copies and versions of signals from a pair of signal sources within the test platform.

7. The method of claim 1 , said manipulating comprising:

keeping a first copy of the signal at an initial phase offset;

setting a second copy of the signal to each phase offset in a set of phase offsets; and

measuring combined power resulting from vector signal addition of the first copy and the second copy of the signal at the measurement location as the second copy is set to the each phase offset.

8. The method of claim 7 , said analyzing comprising:

deriving a first unknown phase offset θ 1 from:

φ 1 =θ 1 −arc-cosine( P (θ 1 −φ)− P 1 −P 2 )/(2×square-root( P 1 ×P 2 ));

and

deriving a second unknown phase offset φ 2 from:

φ 2 =θ 2 −arc-cosine( P (θ 2 −φ)− P 1 −P 2 )/(2×square-root( P 1 ×P 2 )),

wherein θ 1 and θ 2 are first and second phase offsets in the set of phase offsets, P(θ 1 −φ) is a first measurement of the combined power when the second copy is set to the first phase offset θ 1 , P(θ 2 −φ) is a second measurement of the combined power when the second copy is set to the second phase offset θ 2 , P 1 is a first single-copy measurement of power at the measurement location from only the first copy of the signal, and P 2 is a second single-copy measurement of power at the measurement location from only the second copy of the signal.

9. The method of claim 8 , wherein the first unknown phase offset includes two results, and the second unknown phase offset includes two other results, comprising:

identifying a first result from the two results of the first unknown phase offset, and a second result from the two other results of the second unknown phase offset, wherein the first result and the second result are closer to each other than to other results of the first unknown phase offset and the second unknown phase offset; and

averaging the first result and the second result to find the phase offset adjustment.

10. The method of claim 1 , comprising:

measuring power at the measurement location from only a first copy of the signal to obtain a first single-copy measurement of power; and

measuring power at the measurement location from only a second copy of the signal to obtain a second single-copy measurement of power.

11. A test platform for calibrating a phase relationship between copies of a signal at a measurement location within the test platform, whether over the air or cabled, comprising:

signal paths transmitting the copies of the signal from a signal source to the measurement location;

phase settings in the signal paths for manipulating phase relationship of the copies of the signal; and

circuitry to analyze vector signal addition from the copies of the signal at the measurement location as the phase relationships are manipulated to find a phase offset adjustment that establishes a particular phase relationship between the signal paths.

12. The test platform of claim 11 , comprising:

a changed signal path transmitting different copies of the signal from a changed signal source within the test platform.

13. The test platform of claim 11 , comprising:

a pair of signal sources generating versions of a signal transmitted through the signal paths.

14. The test platform of claim 11 , wherein:

the phase settings are configured with one or more phase offsets for the signal paths.

15. The test platform of claim 14 , wherein:

the phase offsets are determined to reduce destructive signal addition from the signal copies.

16. The test platform of claim 11 , comprising:

a switching network with balanced signal paths to direct copies and versions of signals from a pair of signal sources through the test platform.