News Column

Patent Issued for Active Radar System and Method

August 20, 2014



By a News Reporter-Staff News Editor at Journal of Engineering -- From Alexandria, Virginia, VerticalNews journalists report that a patent by the inventors Stirling-Gallacher, Richard (Stuttgart, DE); Wang, Qi (Esslingen, DE), filed on November 23, 2011, was published online on August 5, 2014.

The patent's assignee for patent number 8797208 is Sony Corporation (Tokyo, JP).

News editors obtained the following quote from the background information supplied by the inventors: "Active radar systems, in particular for use as active imaging systems, are becoming increasingly popular at ultrasonic, microwave, millimeter and terahertz frequencies for a number of applications including medical and security applications. Security active imaging systems for example enable suspicious items hidden under clothes or in bags to be visualised and to be easily identified. Medical active imaging systems on the other hand enable the visualisation of a huge variety of biological items.

"There are various active radar systems and methods known using various means for separating the different transmitted signals, in particular for a MIMO (Multiple Input Multiple Output) Radar or MIMO Imaging system.

"J. H. G. Ender, J. Klare, 'System Architectures and Algorithms for Radar Imaging by MIMO-SAR', IEEE Radar Conference 2009 proposes two different methods. The first method time multiplexes the different transmitted signals to the different antennas, i.e. only one transmit antenna transmits a signal at one time. The second method transmits on all the transmitters at the same time, but each one transmits on a different band (which is a fraction of the overall system bandwidth). The mapping of bands to transmitter antennas may change from one time slot (or pulse duration) to the next.

"J. Klare, O Saalmann, H. Wilden, 'First Experimental Results with the imaging MIMO Radar MIRA-CLE X', EUSAR Conference 2010 proposes to multiplex the different transmitted signals to the different antennas, i.e. only one transmit antenna transmits a signal at one time.

"J. Klare, 'Digital Beamforming for a 3-D MIMO SAR--Improvements Through Frequency and Waveform Diversity', IEEE Geoscience and Remote Sensing Symposium (IGARSS 2008) proposes two different methods. The first method transmits on all of the transmitters at the same time, but each one uses a different band. The mapping of bands to transmit antennas changes from one time slot (pulse duration) to the next. The second method transmits on all of the transmit antennas at the same time but with Doppler tolerant orthogonal coded waveforms.

"B. J. Donnet, I. D. Lonstraff, 'MIMO Radar--Waveforms and applications'. 4th EMRS DTC Technical Conference--Edinburgh 2007 describes a MIMO Radar system using OFDM (Orthogonal Frequency Division Multiplex) which uses Doppler tolerant Costas codes (and Golay codes) for determining the frequency hopping patterns of OFDM different transmitted waveforms.

"B. J. Donnert et al, 'MIMO Radar, Techniques and Opportunities', 3rd European Radar Conference proposes a MIMO system which uses OFDM and changes the frequencies on the different transmitted antennas in discrete steps. Different transmitters always send on different discrete frequencies.

"J. H. Kim et al, 'Investigation of MIMO SAR for Interferometry', Proceedings of 4th European Radar Conference proposes a MIMO system in which the different transmit signals are separated by using a space time block code (STBC).

"G. Brooker, 'Understanding Millimeter Wave FMCW Radars', 1st International Conference on Sensing Technology, Nov. 21-23, 2005, Palmerston North, New Zealand explains frequency modulated continuous wave (FMCW) radar systems. Such radars operate using the homodyne principle, i.e. a CW radar in which an oscillator serves as both the transmitter and local oscillator.

"The above mentioned known systems have the drawbacks that they require much time since all transmit signal are to be transmitted subsequently one by one, require the use of special (complex, possibly non-optimal) codes, do no use the available bandwidth efficiently, are complex to implement, and/or require special (complex, expensive) hardware."

As a supplement to the background information on this patent, VerticalNews correspondents also obtained the inventors' summary information for this patent: "It is an object of the present invention to provide an active radar system and a corresponding active radar method which overcome the above mentioned drawbacks, in particular require less time for signal transmission, reception and analysis, do not require the use of special codes or hardware for signal transmission and reception and can be easily implemented.

"According to an aspect of the present invention there is provided an active radar system comprising

"at least two transmit antennas that each transmits radiation to a scene as a transmit signal, said transmit signal comprising a series of frequency modulated pulses,

"at least one receive antenna that receives radiation from said scene as a receive signal,

"a controller that controls said at least two transmit antennas such that the transmissions of the transmit signals of the various transmit antennas are subsequently initiated with time offsets, which time offset between two subsequently initiated transmissions of transmit signals is controlled to be larger than the time delay between transmission of a first transmit signal of said two transmit signals and reception of radiation of said first transmit signal by said at least one receive antenna and to be smaller than the time duration of a complete frequency modulated pulse of said first transmit signal, and

"a signal analyser that analyses said receive signal.

"According to a further aspect of the present invention there is provided a corresponding active radar method comprising the steps of

"transmitting radiation to a scene as at least two transmit signals, each transmit signal comprising a series of frequency modulated pulses,

"receiving radiation from said scene as a receive signal,

"controlling the transmission of said at least two transmit signals such that the transmissions of the various transmit signals are subsequently initiated with time offsets, which time offset between two subsequently initiated transmissions of transmit signals is controlled to be larger than the time delay between transmission of a first transmit signal of said two transmit signals and reception of radiation of said first transmit signal and to be smaller than the time duration of a complete frequency modulated pulse of said first transmit signal, and

"analysing said receive signal.

"Preferred embodiments of the invention are defined in the dependent claims. It shall be understood that the claimed active radar method has similar and/or identical preferred embodiments as the claimed active radar system and as defined in the dependent claims.

"The present invention is based on the idea to transmit the transmit signals with a small time offset from each other, i.e. the transmit signal overlap in time. To ensure that the different transmit signal maintain their orthogonality, the time offset between two subsequently initiated transmissions of transmit signals is a) larger than the time delay between transmission of a first transmit signal of said two transmit signals and reception of radiation of said first transmit signal and b) smaller than the time duration of a complete frequency modulated pulse of said first transmit signal. Preferably, the time offset corresponds to a frequency offset which is set to be much greater than the total anticipated frequency difference between the transmit and receive signals due to distance (beat frequency) and movement (Doppler frequency).

"By the proposed active radar system and method various advantages are achieved compared to the known systems and methods.

"Known systems in which the transmit signals are time multiplexed require N pulse durations (where N is the number of transmit antennas) to send all of the transmit signals one at a time. The proposed active radar system requires a much shorter period of time to send all of the transmit signals since the transmit signals are sent with an overlap in time. This resulting speed increase means that objects can be scanned much more quickly with the proposed active radar system.

"Known systems in which codes are used to distinguish the transmit signals need to find a suitable set of codes for the required number of transmit signals. Furthermore, MIMO systems using codes to distinguish the transmit signals do not have perfect orthogonally which leads to performance degradation. The proposed active radar system can, however, yield perfect orthogonally which provides an improved performance.

"Known systems that use different bands to distinguish the transmit signals have a limited amount of bandwidth for each chirp duration (i.e. duration for a single transmit signal). Such systems have to use different multiple signal generators (also called chirp generators) to cover the different bands, which leads disadvantageously to higher complexity. The proposed active radar system does not have these disadvantages.

"Known systems which use OFDM with stepped frequency continuous waves require a wideband IFFT (Inverse Fast Fourier Transform) to be implemented. Typically, MIMO radar systems would have transmission bandwidths of several GHz, and to implement this with OFDM (using IFFT) is very difficult. The proposed active radar system does not have these disadvantages.

"Known systems which use STBC (Space Time Block Codes) to separate the transmit signals are only available for certain numbers of transmit antennas (i.e. 2, 4, 8 etc.) which can restrict the design of a MIMO radar (imaging) system, since only certain numbers of transmit antennas can be used. The proposed active radar system does not have these disadvantages.

"The proposed active radar system and method can, for instance, advantageously be used for a MIMO radar system or MIMO imaging system, in particular using FMCW, whereby the (preferably all) transmit signals are orthogonal to each other (hence yielding optimum performance) and which does not require a transmission time consisting of multiple pulse durations. Furthermore, the proposed active radar system and method do not require the use of special codes. The proposed active radar system and method are especially (but not exclusively) applicable for short distance (and/or indoor applications) where the distance between the transmit antennas and the objects to be viewed (or imaged) is relatively short, for instance below 10 m.

"It should be noted that in practice an active radar system will comprise two or more transmit antennas and two or more receive antennas. While it is general sufficient that the time offset between two subsequently initiated transmissions of transmit signals is larger than the time delay between transmission of a first transmit signal of the two or more transmit signals and reception of radiation of said first transmit signal by at least one receive antenna, it is preferred that the time offset between two subsequently initiated transmissions of transmit signals is larger than the time delay between transmission of a first transmit signal of the two or more transmit signals and reception of radiation of said first transmit signal by all receive antennas. This ensures that the transmitted signals are received generally at the same time at all receive antennas.

"In an aspect of the present invention an active radar system is presented comprising:

"at least two transmission means for each transmitting radiation to a scene as a transmit signal, said transmit signal comprising a series of frequency modulated pulses,

"at least one receiving means for receiving radiation from said scene as a receive signal,

"a control means for controlling said at least two transmission means such that the transmissions of the transmit signals of the various transmission means are subsequently initiated with time offsets, which time offset between two subsequently initiated transmissions of transmit signals is controlled to be larger than the time delay between transmission of a first transmit signal of said two transmit signals and reception of radiation of said first transmit signal by said at least one receiving means and to be smaller than the time duration of a complete frequency modulated pulse of said first transmit signal, and

"a signal analysis means for analysing said receive signal."

For additional information on this patent, see: Stirling-Gallacher, Richard; Wang, Qi. Active Radar System and Method. U.S. Patent Number 8797208, filed November 23, 2011, and published online on August 5, 2014. Patent URL: http://patft.uspto.gov/netacgi/nph-Parser?Sect1=PTO1&Sect2=HITOFF&d=PALL&p=1&u=%2Fnetahtml%2FPTO%2Fsrchnum.htm&r=1&f=G&l=50&s1=8797208.PN.&OS=PN/8797208RS=PN/8797208

Keywords for this news article include: Sony Corporation.

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Source: Journal of Engineering


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