Imbalance correction of in-phase and quadrature phase return signals

• US 5,369,411 A
• Filed: 06/01/1993
• Issued: 11/29/1994
• Est. Priority Date: 06/01/1993
• Status: Expired due to Fees

• Current Assignee: Northrop Grumman Corporation
• Original Assignee: Westinghouse Electric Company LLC (Brookfield Asset Management Incorporated)
• Inventors: Lisle, Thomas K. Jr.
• Primary Examiner(s): Sotomayor, John B.
• Application Number:
  US08/069,499
• Time in Patent Office: 546 Days
• Field of Search: 342/160, 342/161, 342/162, 342/194, 342/195, 342/151, 342/174
• US Class Current: 342/194
• CPC Class Codes: G01S 7/2886 using I/Q processing
• CPC Class Codes: G01S 7/358 using I/Q processing
• CPC Class Codes: G01S 7/4021 of receivers

Abstract

A method of correcting phase and amplitude imbalances of I and Q components using digital correction coefficients. The amplitude Gc and phase coefficient Pc obtained solely in the time domain from a pilot signal. The I and Q components of the pilot signal are sampled over at least one integer cycle after which the number of samples taken during an integer number of cycles is determined for the samples of the component with the steepest slope. The sums of self and cross products are used to calculate the coefficients.

Claims

1. A method for correcting phase and amplitude imbalances between in-phase (I) and quadrature (Q) phase components of a return radiant energy signal, comprising:

converting each of the (I) and (Q) phase components of the return signal into digital data;

calculating solely in time domain, phase and amplitude coefficients for correcting digital data of the (Q) phase component of the return signal in accordance with the number and amplitude of samples taken from a selected one of the I and Q components of a pilot tone during an integer cycle of at least one cycle of the pilot tone;

multiplying the digital data of the (I) component by the phase coefficient to obtain a first product;

multiplying the digital data of the Q component by the amplitude coefficient to obtain a second product; and

adding the first and second products to obtain a corrected Q component having a phase and amplitude substantially corresponding to the quadrature phase and amplitude of the (I) component.

2. The method of claim 1 wherein the step of calculating the phase and amplitude coefficients, comprises the substeps of determining the total number of time samples of the selected one of the I and Q components taken during the at least one integer cycle;

and

calculating the amplitude and phase coefficients in accordance with the determined total number of time samples.

3. The method of claim 2 wherein the step of calculating the phase and amplitude coefficients comprises the substeps of

calculating the mean value in accordance with the sum of all the determined total number of samples to obtain a DC offset value;

find self product and cross product terms of the determined number of samples; and

calculating the amplitude coefficient in accordance with the self product and cross product terms.

4. The method of claim 3 wherein the substep of calculating the amplitude coefficient in accordance with the product terms comprises the substeps of

calculating the phase coefficient in accordance with the amplitude coefficient and the cross products terms.

5. The method of claim 3 further comprising the step of

adding the DC offset values to the I and Q components of the radiant energy signal.

6. A method of calculating image correction coefficients for I and Q components of a radiant energy signal, comprising:

generating I and Q components of a pilot signal, having a selected frequency, at times when the radiant energy signal is not being transmitted or received;

sampling N time samples of both the I and Q components of the generated pilot signal;

selecting the N time samples of one of the I and Q components having the steepest slope;

determining the total number of time samples of the selected component taken during an integer cycle of at least one complete cycle of the sampled pilot signal;

calculating the average value of each of the corresponding samples of the I and Q components of the pilot signal;

calculating the sums of the products of each of corresponding determined number of samples of the I and Q components of the pilot signal; and

calculating the amplitude and phase image correction coefficients in accordance with the calculated sums of the products of the average value of the determined number of samples.

7. The method of claim 6 wherein the step of determining the total number of time samples includes determining the total number of samples taken during a plurality of integer complete cycles of the pilot signal.

8. A system for correcting phase and amplitude imbalances between in-phase (I) and quadrature (Q) phase components of a return radiant energy signal, comprising:

means for converting each of the (I) and (Q) phase components of the return signal into digital data;

means for calculating solely in time domain, phase and amplitude coefficients for correcting digital data of the (Q) phase component of the return signal in accordance with the number and amplitude of samples taken from a selected one of the I and Q components of a pilot tone during an integer cycle of at least one cycle of the pilot tone;

means for multiplying the digital data of the (I) component by the phase coefficient to obtain a first product;

means for multiplying the digital data of the Q component by the amplitude coefficient to obtain a second product; and

means for adding the first and second products to obtain a corrected Q component having a phase and amplitude substantially corresponding to the 90 degree phase and amplitude of the (I) component.

9. The method of claim 8 wherein means for calculating the phase and amplitude coefficients, comprises

means for determining the total number of time samples of the selected one of the I and Q components taken during the at least one integer cycle;

and

means for calculating the amplitude and phase coefficients in accordance with the determined total number of time samples.

10. The system of claim 9 wherein the means for calculating the phase and amplitude coefficients comprises

means for calculating the means value in accordance with the sum of all the determined total number of samples to obtain a DC offset value;

means for determining self product and cross product reigns of the predetermined number of samples; and

means for calculating the amplitude coefficient in accordance with the self product and cross product terms.

11. The system of claim 10 wherein the means for calculating the amplitude coefficient in accordance with the product terms comprises

means for calculating the phase coefficient in accordance with the amplitude coefficient and the cross products terms.

12. The system of claim 10 further comprising

means for adding the DC offset values to the I and Q components of the radiant energy signal.

13. A system for calculating image correction coefficients for I and Q components of a radiant energy signal, comprising:

means for generating I and Q components of a pilot signal, having a selected frequency, at times when the radiant energy signal is not being transmitted or received;

means for sampling N time samples of both the I and Q components of the generated pilot signal;

means for selecting the N time samples of one of the I and Q components having the steepest slope;

means for determining the total number of time samples of the selected component taken during an integer cycle of at least one complete cycle of the sampled pilot signal;

means for calculating the average value of each of the corresponding samples of the I and Q components of the pilot signal;

means for calculating the sums of the products of each of corresponding determined number of samples of the I and Q components of the pilot signal; and

means for calculating the amplitude and phase image correction coefficients in accordance with the calculated sums of the products of the average value of the determined number of samples.

14. The system of claim 13 wherein the means for determining the total number of time samples includes means for determining the total number of samples taken during a plurality of integer complete cycles of the pilot signal.

15. A method of determining solely in the time domain phase and gain coefficients for correcting imbalances between (I) in-phase and (Q) quadrature phase components of a received radiant energy signal, comprising:

applying I and Q components of a pilot signal to an analog to digital converter means,

sampling the amplitude of the pilot signal for an integer of at least one complete cycle,

determining the total number of samples for the integer of at least one complete cycle,

calculating the sums of the determined total number of samples to obtain the means of the samples corresponding to DC offsets for the received signals;

calculating the sums of the product means, and

calculating the amplitude and phase coefficients in accordance with the sums of the product means and the DC offsets.