Aircraft or spacecraft based synthetic aperture radar

• US 6,388,606 B1
• Filed: 08/16/2000
• Issued: 05/14/2002
• Est. Priority Date: 08/18/1999
• Status: Expired due to Fees

• Current Assignee: Deutsches Zentrum Fã¼R Luft- Und Raumfahrt E.V.
• Original Assignee: Deutsches Zentrum Fã¼R Luft- Und Raumfahrt E.V.
• Inventors: Schröder, Reinhard, Suss, Helmut, Zeller, Karl-Heinz, Keydel, Wolfgang
• Primary Examiner(s): Gregory, Bernarr E.
• Application Number:
  US09/639,329
• Time in Patent Office: 636 Days
• Field of Search: 342/25, 342/59, 342/159, 342/160-164, 342/190-197
• US Class Current: 342/25.00R
• CPC Class Codes: G01S 13/904 SAR modes
• CPC Class Codes: G01S 2013/0263 Passive array antenna
• CPC Class Codes: G01S 7/03 Details of HF subsystems specially adapted therefor, e.g. common to transmitter and receiver
• CPC Class Codes: H01Q 1/28 Adaptation for use in or on aircraft, missiles, satellites, or balloons

Abstract

In the inventive aircraft based or spacecraft based radar system with synthetic antenna aperture (SAR=Synthetic Aperture Radar) a transmit antenna and a receive antenna are provided according to a bistatic radar, which are arranged above the earth'"'"'s surface, physically separate and on different platforms of which at least one is moving, so that a relative movement results between the transmit antenna and the receive antenna. Either the transmit antenna, the receive antenna, or both antennas are designed for ambiguity suppression. The radar system according to the invention is useful particularly for the systematic imaging of the earth'"'"'s surface.

Claims

1. An aircraft or spacecraft based radar system with synthetic antenna aperture for imaging the earth'"'"'s surface in such a way that a side-lobe suppression and an ambiguity suppression are produced by an antenna directionality such that the width of a resulting ground swath illumination does not generate ambiguity areas caused by radar transmit signal periodicity, said system comprising:

an antenna divided, according to a bistatic radar, into a transmit antenna and a receive antenna, the transmit antenna and the receive antenna being respectively located above a surface of the earth to be imaged on respectively different platforms of which at least one is moving so that a relative movement results between the transmit antenna and the receive antenna, and wherein at least one of the antennas is designed for ambiguity suppression.

2. A radar system according to claim 1, wherein a transmitter platform that carries the transmit antenna also carries associated transmitting units, and a receiver platform that carries the receive antenna also carries associated receiving units.

3. A radar system according to claim 2, wherein the transmit antenna that is arranged on the transmitter platform is designed to be narrow-beam and that through the transmit antenna, the ambiguity suppression is generated both in azimuth as well as in elevation, and that the receive antenna that is arranged on the receiver platform has antenna characteristics such that the receive antenna illuminates at least approximately an entire given access area to be imaged.

4. A radar system according to claim 3, wherein to cover an access area, a plurality of narrow-beam antennas covering swaths that are ambiguity-free are provided, with the antennas oriented so that, in an entirety thereof, by combining a plurality of such swaths that are free of ambiguities the antennas cover the entire access area.

5. A radar system according to claim 3, wherein to cover an access area, a narrow-beam electronically phased antenna array is provided that covers swaths, which are free of ambiguities, through steering of the main lobe.

6. A radar system according to claim 5, wherein the antenna array is divided into a plurality of lines in the elevation, each of which has a time delay shifter so that a signal time delay of each antenna line can be adjusted separately before signals of the individual lines are added up to an antenna sum signal, and that amplitude adjusters are added up to phase or time delay shifters for an adjustment of the antenna main lobe width and pointing.

7. A radar system according to claim 6, wherein the electronically phased antenna array is arranged as a receive antenna on a receiver platform, that, in the assigned receiver unit following a phased antenna array, a low-noise amplifier (22), a filter (23) for suppression of ambiguities in the frequency range, as well as a fast analog/digital converter (24) are provided for each antenna line (Z1 . . . ZN), and that the antenna sum signal is formed only subsequently in a computer (25).

8. A radar system according to claim 2, wherein the receive antenna that is arranged on the receiver platform is designed to be narrow-beam and that through the receive antenna, the ambiguity suppression is generated both in azimuth as well as in elevation, and that the transmit antenna that is arranged on the transmitter platform has antenna characteristics such that it illuminates at least approximately an entire given access area to be imaged.

9. A radar system according to claim 2, wherein to generate an ambiguity suppression in azimuth, the transmit antenna that is arranged on the transmitter platform is designed to be narrow-beam in azimuth, according to resolution requirements, whereas it is considerably less narrow-beam for an elevation level so that the transmit antenna illuminates an entire access area or at least a large portion of the access area in the elevation, that, to generate an ambiguity suppression in the elevation, the receive antenna that is arranged on the receiver platform is designed to be narrow-beam in the elevation according to required resolution, whereas the receive antenna is designed comparatively significantly less narrow-beam for the azimuth level, so that it illuminates the entire access area or at least a large portion of the access area in the azimuth, and that minimum directionality required for the ambiguity suppression is defined by a resulting interface of footprints of both the transmit antenna and receive antenna.

10. A radar system according to claim 2, wherein the transmit antenna with an associated transmitter is arranged on a geostationary (GEO) satellite platform and that one or more receive antennas are arranged with associated receiving units on one or more satellite platforms that move in a near earth orbit (LEO) or on aircraft-mounted platforms, which receive backward scatter from radar waves.

11. A radar system according to claim 2, wherein the transmit antenna with an associated transmitter is arranged on a geostationary (GEO) satellite platform and that one or more receive antennas with associated receiver units are arranged on one or more satellite platforms that move in a near earth orbit (LEO) or on aircraft-mounted platforms, which receive a forward scatter from radar waves.

12. A radar system according to claim 2, wherein, the transmit antenna with an associated transmitter is mounted on a satellite platform that moves in a near earth orbit (LEO), and that one or more receive antennas with their associated receiver units are arranged on satellite platforms, which move on an identical orbit, but time-shifted.

13. A radar system according to claim 2, wherein the transmit antenna with an associated transmitter is mounted on a satellite platform that moves in a near earth orbit (LEO) and that one or more receive antennas with their associated receiver units are arranged on satellite platforms, which move on different orbits.

14. A radar system according to claim 2, the transmit antenna with an associated transmitter is mounted on a satellite platform that moves in a near earth orbit (LEO) and that one or more receive antennas with their associated receiver units are arranged on aircraft based platforms.

15. A radar system according to claim 2, wherein the transmit antenna with an associated transmitter is mounted on a platform located on a mountain top (BG) and that one or more receive antennas with the associated receiver units are arranged on satellite platforms, which move on a near earth orbit (LEO).

16. A radar system according to claim 2, wherein the transmit antenna with an associated transmitter is mounted on a platform located on a mountain top (BG) and that one or more receive antennas with the associated receiving units are arranged on aircraft based platforms.

17. A radar system according to claim 1, further comprising a digital chirp generator for generating a transmit signal constituted by a periodic FMCW signal, said generator being connected for supplying the transmit signal to the transmit antenna.