Satellite borne synthetic aperture radar

Patent metadata

Field	Value
Publication number	US-11442161-B2
Application number	US-201916577670-A
Country	US
Kind code	B2
Filing date	Sep 20, 2019
Priority date	Sep 20, 2019
Publication date	Sep 13, 2022
Grant date	Sep 13, 2022

Abstract

The example non-limiting technology herein provides a Synthetic Aperture Radar (SAR) solution on board a micro-satellite that provides global revisit within 1 month; a cost below US$ 10 million; and satellite mass lower than 100 kg. One solution uses an inflatable Cassegrain type antenna with a phased beam steering array in the 1.2 GHz band.

First claim

The invention claimed is:

1. A satellite borne Synthetic Aperture Radar (SAR) for surveying the earth's surface, comprising:
a geometrically-adjustable Cassegrain type antenna with aperture size in a range between 15 to 30 meters, comprising an inflatable balloon with a controlled pressure during orbit providing, during orbit, adjustable antenna geometry and characteristics for radar wavelengths larger than millimeters,
the geometrically-adjustable Cassegrain type antenna comprising a two-dimensional active antenna array enabling electronic beam steering in elevation and azimuth directions with in-orbit adjustable electronic beam steering range,
the Cassegrain type antenna comprising a sub-reflector that is centralized or offset for defining an illumination pattern on earth's surface with in-orbit adjustable geometry; and
a Power, Attitude and Orbit Control Subsystem comprising a pressure control of geometrically-adjustable Cassegrain antenna reflectors, a telemetry infrastructure and a real-time data down link enabling the satellite to be controlled by a satellite control center and to download acquired radar data to a ground station.

2. The satellite borne SAR as claimed in claim 1 , wherein the gain and beamwidth of the illumination beam of the geometrically adjustable inflatable Cassegrain type antenna can be modified in orbit by changing the shape of the main and secondary reflectors, wherein independent pressure control of first and second cavities are used to control the shapes of the main and secondary cavities to modify the antenna characteristics.

3. The satellite borne Synthetic Aperture Radar as claimed in claim 1 , wherein the geometrically adjustable inflatable Cassegrain type antenna has a large diameter enabling a transmission power lower than 100 watts, a total radar power consumption less than 100 W, and a total satellite weight less than 100 kilograms.

4. The satellite borne Synthetic Aperture Radar as claimed in claim 1 , wherein the geometrically adjustable inflatable Cassegrain type antenna is configured so that the illumination beam of the Cassegrain type antenna is electronically steerable on the earth's surface, so that an imaging swath width in the range up to several hundreds of kilometers can be reached by an orbit of around 500 km, achieving a global revisit time of 1 month with 10 meter resolution, wherein localization of the imaging swath of the earth's surface can vary beyond elevation and azimuth steering deflection limits by geometrically adjusting the geometry of the main and sub-reflectors of the inflatable Cassegrain antenna by respective pressure controls.

5. The satellite borne Synthetic Aperture Radar as claimed in claim 4 , wherein Global revisit time of one week is achieved by a constellation of 2 satellites with a resolution of 30 meters.

6. The satellite borne Synthetic Aperture Radar as claimed in claim 4 , wherein Global revisit time lower than one week and/or resolutions better than 10 m can be reached by a satellite constellation of more than 2 satellites.

7. The satellite borne Synthetic Aperture Radar (SAR) of claim 1 wherein the pressure control modifies the illumination beam gain and/or beamwidth provided by the geometrically-adjustable Cassegrain antenna reflectors.

8. The satellite borne Synthetic Aperture Radar (SAR) of claim 1 wherein the pressure control provides a controllable amount of inflation that defines the geometry of the two-dimensional active antenna array and thereby focusses the RF radiation beam pattern of the array.

9. An orbital platform comprising:
a housing;
a SAR radar system comprising an inflatable geometrically adjustable Cassegrain antenna mounted to the housing, the antenna comprising a two-dimensional steerable active antenna array, a sub-reflector and a main reflector, the antenna array emitting microwave pulses that the sub-reflector reflects to the main reflector and the main reflector reflects to the target; and
solar panels mounted to the housing;
wherein the solar panels provide sufficient energy to enable substantially continuous operation of the SAR radar system.

10. The orbital platform of claim 9 wherein the SAR radar system consumes less than 100 watts.

11. The orbital platform of claim 9 wherein the orbital platform has a total mass of less than 100 kg.

12. The orbital platform of claim 9 wherein the SAR radar system achieves a global revisit time of 1 month with 10 meter resolution; one week when operating in a constellation of two satellites with a resolution of 30 meters; and less than one week and/or resolution better than 10 meters when operating in a constellation of more than two satellites.

13. An orbital platform comprising:
a housing;
a SAR radar system comprising an inflatable Cassegrain antenna mounted to the housing, the antenna comprising a two-dimensional steerable active antenna array, a sub-reflector and a reflector, the antenna array emitting microwave pulses that the sub-reflector reflects to the reflector and the reflector reflects to the target; and
solar panels mounted to the housing;
wherein the solar panels provide sufficient energy to enable substantially continuous operation of the SAR radar system,
wherein the gain and beamwidth of the illumination beam of the inflatable Cassegrain type antenna can be modified in orbit by changing the shape of the main and secondary reflectors, wherein independent pressure control of first and second the cavities are used to control the shapes of the main and secondary cavities to modify the antenna characteristics.

Assignees

• Embraer Sa

Inventors

• Neto João Roberto Moreira
• Kono Janio

Classifications

• H01Q1/081

  Inflatable antennas · CPC title

• H01Q1/288

  Satellite antennas · CPC title

• G01S13/90 Primary

  using synthetic aperture techniques {, e.g. synthetic aperture radar [SAR] techniques} · CPC title

• G01S7/03

  Details of HF subsystems specially adapted therefor, e.g. common to transmitter and receiver · CPC title

• G01S2013/0263

  Passive array antenna · CPC title