Saab Ab

Other

Telefonaktiebolaget Lm Ericsson (publ)

Totalforsvarets Forskningsinstitut

Totalf&ouml;rsvarets Forskningsinstitut

Hans Hellsten

Lars Ulander

Patrik Dammert

Torbjörn Elfström

Nils Dagås

Lars-Gunnar Andersson

Mats Peterson

A method for detecting a horizontally buried linear object is provided, the horizontally buried linear object having a longitudinal extension. The method comprises moving, with a flying platform comprising a radar for synthetic aperture radar, SAR, vertical imaging, along a trajectory corresponding to a synthetic aperture. The method further comprises transmitting and receiving radar signals while moving along the trajectory corresponding to the synthetic aperture. The method also comprises forming a SAR image based on collected data representing radar signal reflections received from the ground. The method additionally comprises detecting one or more features in the formed SAR image relating to the horizontally buried linear object. Said trajectory is oriented in a direction substantially perpendicular to an expected orientation of the longitudinal extension of the horizontally buried object and traversing the horizontally buried object.

Methods, computer programs, radar systems, antenna systems, and flying platforms for detecting a horizontally buried linear object

The present invention relates to a method for determining a synthetic aperture of a synthetic aperture radar, SAR, system using information from a global navigation satellite system, GNSS, which includes a plurality of satellites each transmitting a radio frequency signal comprising a unique pseudo random number, PRN. The method comprises: receiving the radio frequency signal from a group of satellites in the GNSS, determining a first maximum correlation peak of the PRN of the received radio frequency signal from each satellite in the group of satellites, determining the phase shift between the first determined maximum correlation peak and a second determined maximum correlation peak of a received PRN from the same satellite at a later time, for each satellite in the group of satellites, determining a line-of-sight, LOS, movement of the SAR system relative each of the satellites in the group of satellites by means of the determined phase shift for each satellite in the group of satellites, and determining a synthetic aperture using the LOS movement relative each satellite in the group of satellites.

Method for determining a synthetic aperture of a SAR using GNSS

The present invention relates to a method for a continuous arbitrary waveform radar configured for transmitting and receiving signals over a selected communication band. The method comprises: generating the radar transmit signal with a waveform having a non-monotonic frequency change, modifying the waveform to obtain at least one spectral notch and isolating reception and transmission by cancellation. Each spectral notch at a selectable frequency with a selectable bandwidth, and the waveform is modified to maintain the spectral density of the transmit radar signal.

Short range radar cohabitation

A method and a device for detecting at least one target in an image, wherein the image comprises a set of pixels with a magnitude assigned to each pixel is provided. The method comprises an iterative process until the K+1th target does not show a probability increase above a predetermined threshold value. The method is performed by creating a candidate free image, calculating, for the candidate free image, the probability of there being a target at each pixel, by using Bayes theorem, determining a location of the candidate target K+1 in the image, determining the probability that there is a target at the determined location, by determining the calculated probability of there being a target at the determined location. By performing the above, the most probable locations for targets in the image are located together with the probability that the location holds a true target.

Detecting objects in images

A method and system for obtaining SAR images with reduced or eliminated surface clutter to detect subsurface targets, the method comprising the following steps:&#x2014;selecting a first frequency and an incidence angle for the radar signal such that the ratio of surface backscattering to subsurface target backscattering is significantly larger for vertical polarization than for horizontal&#x2014;obtaining vertically and horizontally polarized SAR images based on the same SAR path exploiting the selected first frequency and viewing angle&#x2014;weighting and differencing the vertically and horizontally polarized SAR images so that the surface backscattering completely cancels between the two images and only the combination of the target backscattering components remains.

Subsurface imaging radar

An antenna system () comprising a single antenna element having first () and second () antenna ports arranged to pass a respective first and second antenna signal. The first and second antenna signals being derived from a first common antenna signal (J) and arranged to be essentially equal in envelope. An antenna pattern of the system being arranged to be selectable between a first antenna pattern having a first polarization and a second antenna pattern having a second polarization substantially orthogonal to the first polarization. The first antenna pattern being selected by setting the first and second antenna signal to have the same polarity on first () and second () antenna ports, the second antenna pattern being selected by setting the first and second antenna signal to have substantially opposite polarities on first () and second () antenna ports.

Antenna system for polarization diversity

A method and system for obtaining SAR images with reduced or eliminated surface clutter to detect subsurface targets, the method comprising the following steps: &#x2014;selecting a first frequency and an incidence angle for the radar signal such that the ratio of surface backscattering to subsurface target backscattering is significantly larger for vertical polarization than for horizontal&#x2014;obtaining vertically and horizontally polarized SAR images based on the same SAR path exploiting the selected first frequency and viewing angle&#x2014;weighting and differencing the vertically and horizontally polarized SAR images so that the surface backscattering completely cancels between the two images and only the combination of the target backscattering components remains.

A transmitter/receiver arrangement comprises a digital arbitrary waveform generator AWG connected to a transmitter. Said waveform generator is configured to generate an arbitrary waveform within a given bandwidth. Said transmitter/receiver arrangement further comprises an antenna arrangement configured to emit a transmitter signal, and to receive an incident signal, a receiver configured to receive a receiver signal, and an analog isolator connected to said antenna arrangement, said transmitter, and said receiver. Said analog isolator is adapted to route said transmitter signal from said transmitter to said antenna arrangement, and said incident signal from said antenna arrangement to said receiver, and to isolate said transmitter signal from said receiver signal. Said receiver is adapted to cancel any residual transmitter signal in said receiver signal by means of at least one digital model of at least said isolator, said antenna arrangement, and said transmitter.

Wideband transmitter/receiver arrangement for multifunctional radar and communication

A radar system for a synthetic aperture radar including an arrangement of at least one transmitter, two receivers, two antennas and signal processing means located on a platform. The platform is arranged to move over ground and arranged to transmit a known signal shape and receive signals reflected from the ground. The received signals are used to produce a synthetic aperture radar image of the ground. The synthetic aperture radar image includes a number of resolution cells. The radar system is further arranged to operate in a frequency band with a center frequency and with a wide bandwidth of at least one octave. A first antenna and a second antenna have a length of less than half the wavelength of the center frequency. The radar system is further arranged for: a radar system transfer function to be flat over the frequency band and one-sided beam forming with wideband antenna gain. Also a corresponding method.

Radar system and method for a synthetic aperture radar

A method for detecting targets including moving and stationary targets with a radar system equipped with Synthetic Aperture Radar (SAR) onboard a SAR platform including navigation equipment for accurate determination of the position of the SAR platform. The SAR platform is transversing a stationary ground region and targets in the ground region, in which the SAR platform obtains radar data utilizing at least one antenna. A SAR processor records the radar data and the position of the antenna or antennas for each transmitted radar pulse. Radar data within synthetic sub-apertures, are successively merged in N iteration steps into SAR images of increasing resolution of the surveyed region and wherein each iteration step includes forming a new SAR image at a new iteration level by a linear combination of neighboring SAR images in the previous iteration step. A radar system and a SAR processor used for calculating the detection and positioning of targets including moving and stationary targets.

SAR radar system

A filter scheme for broadcast interference cancellation that is computationally efficient and numerically robust Airborne Low Frequency Synthetic Aperture Radar (SAR) operating in the VHF and UHF bands has been shown. At least interference Doppler filtering or interference cancellation is utilized. The interference cancellation involves prediction of the interference for each particular reception interval of mixed interference and radar ground response. This prediction is then coherently subtracted from the incoming signal.

RFI suppression in SAR

A radar system comprising a platform movable along a path in relation to a ground surface portion and carrying a positioning device, a timing device and a radar equipment. It is adapted to implement synthetic aperture radar (SAR) for imaging the ground portion. It includes recording means for collecting radar raw data comprising radar echo amplitudes annotated with distance and the moment of time of collection and being intertwined with platform position measurement data annotated with the respective moment of time of collection thereof.

Radar system and a method relating thereto

A method of for processing signals in a radar system is shown comprising an antenna system having at least two antenna elements, a beam forming arrangement (ABF_RX, ABF_TX) for selectively steering the directivity of the antenna system in a given selected direction, the directivity of the antenna system having a main lobe in the selected direction and a back lobe (BL) in another direction and of a lower magnitude than the main lobe. By utilizing various scale and subtract processing both noise levels and ghost signals can be considerably reduced. A SAR radar apparatus has moreover been shown.

Antenna back-lobe rejection

A radar device () comprising transmit and receive parts, and a control unit (CU). The transmit part includes means (WG) for generating a signal within a certain band, and the receive part comprises a filter (AAF), an AD-converter (ADC) and a Fourier transform unit (FFT). The transmit part generates a group of signals, each having a first bandwidth between a first and a second frequency, in such a way that a larger bandwidth (B-B) is covered by the group. The receive part is open over said larger bandwidth (B-B) during reception of each signal in said group, and the transmit part comprises means (PAD, FFT) for creating FFT-copies of the received signals and means (CONJ) for creating conjugates of said copies. The receive and transmit parts comprise means (EXTR) for extracting data from the FFT from the first bandwidth covered by a received signal, and the radar device comprises means (DIFF) for correlating said extracted FFT-data.

Stepped frequency radar device

The present invention can be summarized by use of a diffraction limited SAR giving large integration angle and a short depth of field which gives that energy from underground targets is focused independently at different depths to enabled imaging. The radar device according to the invention should be implemented by considering the following parameters: Choice of the appropriate illumination geometry, i.e. elevation angle &#x3b8;, and the appropriate use of low frequency diffraction limited SAR processing to obtainD imaging, and the choice of an appropriately low radar frequency.

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Linköping, Sweden

Hans Hellsten