Antenna system calibration

1. A method for calibrating an antenna system having electronics and a pair of passive antennas for connection to the electronics in which modification control is applied to the electronics based upon a pilot signal injected into the electronics through a pair of signal interfaces when the electronics is being operated, the method comprising:

receiving a signal with the passive antennas and determining amplitude and phase differences in the received signal between the first and second passive antennas;

injecting a test signal to one of the signal interfaces and then the other and determining the amplitude and phase differences in the test signal between when it is injected to the one of the signal interfaces and the other; and

determining a calibration offset that is equal to the determined amplitude and phase differences in the test signal between when it is injected to the one of the signal interfaces and the other, subtracted from the determined amplitude and phase differences in the received signal between the passive antennas.

2. The method of claim 1 , further comprising:

operating the electronics with the calibration offset determined in said determining a calibration offset in the absence of input from the antennas;

injecting a pilot signal having a first frequency;

applying modification control;

ceasing modification control;

changing the pilot signal to a second frequency offset from the first frequency and switching the pilot signal from one signal interface to the other;

determining the amplitude and phase differences at an output of the electronics between when the pilot signal with the second frequency is switched from the one signal interface to the other; and

using these differences resulting from said determining the amplitude and phase differences as the calibration offset.

3. The method of claim 1 , further comprising repeating said receiving a signal, said supplying a pilot signal, and said determining a calibration offset over a plurality of frequencies.

4. The method of claim 3 , wherein the plurality of frequencies range from 10.70 GHz to 12.75 GHz inclusively.

5. The method of claim 2 , wherein the electronics include an active mode and a passive mode and said switching the pilot signal is performed in the passive mode.

6. The method of claim 5 , wherein the signal is received over a range of frequencies from 10.70 GHz to 12.75 GHz inclusively.

7. The method of claim 1 , wherein said receiving a signal is performed with the passive antennas in an anechoic environment without the passive antennas connected to the electronics.

8. A method for calibrating an antenna system having a first passive antenna and a second passive antenna and first and second signal interfaces, the method comprising:

supplying a signal to the passive antennas and determining amplitude and phase differences between transmissions of the first and second antennas;

passing a test signal through one of the signal interfaces and then the other and determining the amplitude and phase difference in the test signal between when it is passed through the one of the signal interfaces and the other;

determining a calibration offset that is equal to the determined amplitude and phase difference in the test signal between when it is passed through the one of the signal interfaces and the other, subtracted from the determined amplitude and phase difference in the transmissions between the first and second antennas.

9. The method of claim 8 , wherein each passive antenna is for connection to electronics in which modification control is applied to the electronics based upon a pilot signals injected into the electronics and passing through the signal interfaces when the electronics is being operated, the method further comprising:

operating the electronics with the calibration offset determined in said determining a calibration offset in the absence of input from the antennas;

injecting a pilot signal having a first frequency;

applying modification control;

ceasing modification control;

changing the pilot signal to a frequency offset from the first frequency;

determining the amplitude and phase differences between when the pilot signal with the second frequency passes through the electronics and the first signal interface and the electronics and the second signal interface; and

using the differences resulting from said determining the amplitude and phase differences as the calibration offsets.

10. The method of claim 8 , further comprising repeating said supplying a signal, said passing a test signal, and said determining a calibration offset over a plurality of frequencies.

11. The method of claim 10 , wherein the plurality of frequencies range from 14 GHz to 14.5 GHz inclusively.

12. The method of claim 9 , wherein the electronics include an active mode and a passive mode and said switching the pilot signal is performed in the passive mode.

13. The method of claim 9 , wherein the offset is approximately 50 MHz.

14. The method of claim 9 , wherein the second frequency is offset downward form the first frequency.

15. The method of 8 , wherein said supplying a signal is performed in an anechoic environment.

16. The method of claim 9 , wherein said determining the amplitude and phase differences includes switching the input into a signal measurement apparatus from one signal interface to another.