RF FEED ELEMENT DESIGN OPTIMIZATION USING SECONDARY PATTERN

• US 20130006585A1
• Filed: 06/28/2011
• Published: 01/03/2013
• Est. Priority Date: 06/28/2011
• Status: Active Grant

• Current Assignee: Maxar Space LLC (Galileo Parent, Inc.)
• Original Assignee: Space Systems/Loral Incorporated (Loral Space and Communications Incorporated)
• Inventors: Simon, Peter S.
• Granted Patent: US 8,914,258 B2
• Time in Patent Office: Days
• US Class Current: 703/1
• CPC Class Codes: G06F 30/23 using finite element methods [FEM] or finite difference methods [FDM]
• CPC Class Codes: G06K 7/00 Methods or arrangements for sensing record carriers, e.g. for reading patterns methods or arrangements for marking the record carrier in digital fashion G06K1/00; pattern recognition G06F18/00; arrangements for image or video recognition or understanding G06V10/00; character recognition, recognising digital ink or document-oriented image-based pattern recognition G06V30/00
• CPC Class Codes: H01Q 13/0208 Corrugated horns waveguide mouth antenna with corrugated flange H01Q13/065; manufacturing details H01Q13/0283

Abstract

An RF feed element for an antenna system required to comply with a set of specified secondary pattern characteristics is designed by performing a quantitative optimization of the RF feed element directly with respect to the secondary pattern characteristics. The quantitative optimization may include pre-computing a plurality of partial secondary pattern complex field values. Each partial secondary pattern may be associated with an RF feed element modal beamlet. A value of at least one to-be-optimized feature is optimized by iteratively adjusting the value of the to-be-optimized feature(s) within an optimization loop that iteratively computes secondary pattern characteristics and compares them to the specified secondary pattern characteristics. The computed secondary pattern characteristics result from performing a linear superposition on the pre-computed partial secondary pattern complex field values, using complex modal coefficients of the RF feed element, determined taking into account current value(s) of the to-be-optimized feature(s).

Claims

1. A method for designing an antenna system to comply with a plurality of specified secondary pattern characteristics, the antenna system including an RF feed element and a reflector, the RF feed element characterized by a first geometric feature, and configured to exhibit a plurality of primary pattern characteristics, the method comprising:

computing a plurality of partial secondary pattern complex field values for the reflector, each partial secondary pattern characteristic being associated with an individual RF feed element mode;

storing the computed plurality of partial secondary pattern characteristics;

optimizing a value of at least a second, to-be-optimized, feature of the RF feed element, other than the selected first geometric feature, by executing, on a processor, at least two cycles of an optimization loop, the optimization loop comprising;

(i) determining a cost for a current value of the to-be-optimized feature, said cost resulting at least in part from a variance between a plurality of computed secondary pattern characteristics and the plurality of specified secondary pattern characteristics; and

(ii) determining, when the cost is not greater than a specified value, that the second feature is sufficiently optimized, and, when the cost is greater than the specified value, adjusting the current value of the to-be-optimized feature and repeating steps (i) and (ii);

wherein the computed secondary pattern characteristics are computed by performing a linear superposition on the stored computed plurality of partial secondary pattern complex field values, the linear superposition being performed using a set of complex modal coefficients of the RF feed element determined, for a selected number of radiating modes, taking into account the current value of the to-be-optimized feature.

2. The method of claim 1, further comprising determining the set of complex modal coefficients of the RF feed element by performing an analysis of electromagnetic properties of the RF feed element.

3. The method of claim 2, wherein the analysis comprises at least one of:

method of moments (MoM), finite difference time domain (FDTD), finite difference frequency domain (FDFD), finite elements (FE), and mode matching.

4. The method of claim 2, wherein the analysis comprises mode matching.

5. The method of claim 1, wherein the RF feed element is a horn.

6. The method of claim 5, wherein the horn has a longitudinal axis and a cross section of the horn is axially symmetric.

7. The method of claim 6, wherein the first geometric feature is a dimension of an aperture of the horn.

8. The method of claim 1, wherein the second feature is a geometric feature.

9. The method of claim 1, wherein the second feature is other than a geometric feature.

10. The method of claim 1, wherein the reflector has a known set of optical properties, said known set of optical properties comprising at least one of a number of reflecting surfaces and a type of reflecting surface.

11. The method of claim 1, wherein computing a plurality of partial secondary pattern characteristics comprises:

selecting a set of optimization stations at locations within the secondary pattern coverage area of interest; and

computing, for each of the selected number of aperture modes, and at each optimization station, a respective partial secondary pattern, said computing step assuming a radiation pattern emitted from the RF feed element resulting only from excitation of a single respective mode.

12. The method of claim 11, wherein the selected number of aperture modes comprises substantially all propagating modes and at least one additional, cutoff, mode.

13. The method of claim 12, wherein the selected number of aperture modes comprises approximately twenty cutoff modes.

14. The method of claim 11, wherein computing a plurality of partial secondary pattern characteristics comprises integrating physical optics currents induced on a surface of the reflector.

15. The method of claim 11, wherein computing a respective partial secondary pattern comprises using at least one of:

geometrical optics, physical optics, geometrical theory of diffraction (GTD) and physical theory of diffraction (PTD)

16. The method of claim 11, wherein each optimization station has a respective specification of at least one desired pattern characteristic.

17. The method of claim 11, wherein the computing step assumes a radiation pattern emitted from the RF feed element resulting only from excitation, with a unit excitation amplitude, of a respective single mode.

18. The method of claim 1, wherein the specified secondary pattern characteristics are selected from the group consisting of:

effective isotropic radiated power (EIRP), gain to noise temperature ratio (G/T), edge of coverage directivity, sidelobe suppression, polarization, far field amplitude, polarization purity, ratio of desired polarization/cross polarization (C/X), and cross polarization and co-polarization roll-off

19. The method of claim 1, wherein optimizing a value of the at least a second, to-be-optimized, feature of the RF feed element comprises executing, on the processor, at least one thousand cycles of the optimization loop.

20. The method of claim 1, wherein the cost results from a weighted sum of (i) the variance between the plurality of computed secondary pattern characteristics and the specified secondary pattern characteristics and (ii) a variance of at least one other property of the resulting feed geometry from a desired value.

21. The method of claim 21, wherein the at least one other property comprises at least one of feed return loss, physical length, and another property of interest that depends on the to-be-optimized feature.

22. An antenna system, comprising:

an RF feed element and a reflector, the RF feed element characterized by a first geometric feature, and configured to exhibit a plurality of primary pattern characteristics, wherein;

the antenna system is required to comply with a plurality of specified secondary pattern characteristics; and

a design feature of the RF feed element results from performing a quantitative optimization directly with respect to the specified secondary pattern characteristics.

23. The antenna system of claim 22, wherein the quantitative optimization comprises:

computing a plurality of partial secondary pattern complex field values for the reflector, each partial secondary pattern characteristic being associated with an individual RF feed element mode;

storing the computed plurality of partial secondary pattern characteristics;

optimizing a value of at least a second, to-be-optimized, feature of the RF feed element, other than the selected first geometric feature, by executing, on a processor, at least two cycles of an optimization loop, the optimization loop comprising;

(i) determining a cost for a current value of the to-be-optimized feature, said cost resulting at least in part from a variance between a plurality of computed secondary pattern characteristics and the plurality of specified secondary pattern characteristics; and

(ii) determining, when the cost is not greater than a specified value, that the second feature is sufficiently optimized, and, when the cost is greater than the specified value, adjusting the current value of the to-be-optimized feature and repeating steps (i) and (ii);

wherein the computed secondary pattern characteristics are computed by performing a linear superposition on the stored computed plurality of partial secondary pattern complex field values, the linear superposition being performed using a set of complex modal coefficients of the RF feed element determined, for a selected number of radiating modes, taking into account the current value of the to-be-optimized feature.

24. The antenna system of claim 23, wherein the cost results from a weighted sum of (i) the variance between the plurality of computed secondary pattern characteristics and the specified secondary pattern characteristics and (ii) a variance of at least one other property of the resulting feed geometry from a desired value.

25. The method of claim 24, wherein the at least one other property comprises at least one of feed return loss, physical length, and another property of interest that depends on the to-be-optimized feature.

26. A computer readable medium wherein computer instructions are stored, the instructions operable to cause a computer to perform steps of a method for designing an antenna system to comply with a plurality of specified secondary pattern characteristics, the antenna system including an RF feed element and a reflector, the RF feed element characterized by a first geometric feature, and configured to exhibit a plurality of primary pattern characteristics, the method comprising:

computing a plurality of partial secondary pattern complex field values for the reflector, each partial secondary pattern characteristic being associated with an individual RF feed element mode;

storing the computed plurality of partial secondary pattern characteristics;

optimizing a value of at least a second, to-be-optimized, feature of the RF feed element, other than the selected first geometric feature, by executing, on a processor, at least two cycles of an optimization loop, the optimization loop comprising;

(i) determining a cost for a current value of the to-be-optimized feature, said cost resulting at least in part from a variance between a plurality of computed secondary pattern characteristics and the plurality of specified secondary pattern characteristics; and

(ii) determining, when the cost is not greater than a specified value, that the second feature is sufficiently optimized, and, when the cost is greater than the specified value, adjusting the current value of the to-be-optimized feature and repeating steps (i) and (ii);

wherein the computed secondary pattern characteristics are computed by performing a linear superposition on the stored computed plurality of partial secondary pattern complex field values, the linear superposition being performed using a set of complex modal coefficients of the RF feed element determined, for a selected number of radiating modes, taking into account the current value of the to-be-optimized feature.