Multi-Channel Beam Steering SAR And GMTIm With High Resolution

As an active sensor, SAR is able to work day and night under all weatherconditions, which improve the capability of radar in information acquisition. SAR iswidely used in civil application, such as monitoring of urban areas, marine andterrestrial surveillance, sea ice monitoring and deforming observing, and also in militaryapplication, such as battlefield reconnaissance and monitoring of military motion. Withthe development of SAR technology and SAR application, the beam steering, highresolution and wide range swath become more and more important for SAR observing.To obtain the flexibility, the technique of beam steering (BS) is incorporated inSAR (BS-SAR). The BS corrpesonds to different SAR modes, such as sidelook SAR,squinted SAR, spotlight SAR, sliding spotlight SAR, Scan SAR, TOPS SAR and so on.To obtain high resolution and wide range swath, the muti-channel and BS-SAR arecombined. The muti-channel BS-SAR can improve the imaging ability of traditionalSAR. If the freedom degree of muti-channel is enough big, the muti-channel BS-SARcan also be used for moving target imaging (GMTIm).With the improvement of imaging resolution, the available threshold of traditionalmodel proposed by J. C. Curlander will not hold any more. In this case, the imagingmodel should be reknown. The BS-SAR corresponds to different SAR modes, such ashighly squinted SAR, sliding spotlight and TOPS SAR. The imaging algorithm shouldbe studied. Different SAR modes with or without muti-channle configure need relateddata processor. To simplify the processor development of different SAR modes with orwithout muti-channle configure and low the cost, we need to study a serial of generalprocess algorithm. In addition, to indicate and image moving target by multi-channelBS-SAR, we need to study suitable moving target imaging algorithm.To satisfy the tread requirement of observing with high resolution and wide rangeswath, and to solve the key problems in BS-SAR imaging, we expand the work fromsignal model, BS-SAR imaging, muti-channel BS-SAR imaging and moving targetimaging. The relevant work is supported by the National Science Foundation of China(No.60890072), the "973" Program (No.2010CB731903) and the Doctoral Foundation(No.200807010002). The main content of this dissertation is summarized as follows.1. A new signal model for a wideband synthetic aperture imaging sensor wasproposed. The model is more accurate than the traditional one based on “go-stop-go”assumpation. Due to the requirement of imaging with high resolution, the bandwidth becomes wider and pulse duration becomes longer. In this case, the “go-stop-go”assumpation doses not hold any more because two kinds of motion have been ignored inthis assumpation: the sensor motion during the signal receiving and transmitting, thesensor motion between the signal receiving and signal transmitting. With this newmodel, we obtain the signal model and then the2D spectrum expression. Then, theboundary where the traditional model holds is deduced.2. Two imaging algorithms are proposed for squinted SAR. According to the signalproperty of the2D spectrum, we divided the imaging algorithms into two categories:methods based on skew spectrum and on orthogonal spectrum. For the first category,the range-variant higher order terms are analyzed. Then, an extended NCS algorithm isproposed to deal with the range-variant of third and higher order terms. In this method,the range-variant can be weakened. For the second category, we proposed a “squintminimized” method. With the sheared orthogonal spectrum, we proposed an modifiedCS algorithm based on the azimuth NCS. This method is suitable for the case of highsquint angle and may be usefull for the spaceborne SAR with orbital trajectory.3. For the newly emergying SAR mode, such as sliding spotlight SAR and TOPSSAR, two focusing methods are proposed. The first method is based on the idea of“Two-Step” approach in spotlight SAR imaging. Traditional algorithm is utilized tocorrect RCM. And a scaling deramping method is proposed to focus azimuth signal.The second method is a general PFA based on azimuth scaling. The azimuth derampingfunction is modified in the sliding spotlight SAR and TOPS SAR to avoid azimuthaliasing. Then, the well-known2D interpolation is performed and signal is well rangecompressed. In the azimuth focusing module, a scaling operation is introduced.4. For the commonly studied SAR modes, such as strip SAR, spotlight SAR,sliding spotlight SAR and TOPS SAR, a unified analysis is performed by introducingthe rotation center range. Then, we proposed the conception, beam steering SAR ingeneral, and these four SAR modes are specific form of BS-SAR. By using the unifiedanalysis, a unified focusing algorithm is proposed. The algorithm flow and parametersselection are analyzed. The relationship between classical imaging algorithms and UFAis detailed.5. A full-aperture pre-processing method is preposed to resolve azimuth aliasingfor multi-channel BS-SAR (MC-BS-SAR) and then a unified imaging flow is obtainedfor multi-channel BS-SAR. In the MC-BS-SAR, two kinds of aliasing exist. The firstone is that the azimuth bandwidth is greater than equvilent PRF. The second one is thatthe instantaneous bandwidth of one channel is greater than PRF. These two aliasings is leaded for two different reasons. To introduce new method, we introduced theconception of “four planes”. Then, to change the distribution of signal in these planes,the beam and bandwidth compressions method is proposed to weaken the signal aliasingand multi-channel signals is utilized to resolve the azimuth aliasing.6. Multi-channel could also be utilized to detect and image moving target. For thetarget with spectrum not entirely in a PRF band and unknown motion parameters, anazimuth deramping Keystone processing based instantaneous range-Doppler algorithmis proposed to deal with resulting spectrum folding and large RCM. The method candecrease the azimuth bandwidth by azimuth deramping operation but does not changethe signal distribution in angle-Doppler plane. After clutter suppression, the target couldbe focused and its SNR could be improved.