A Simulation for Synthetic Aperture Radar with Digital Beam-Forming in Elevation

In this paper, we present the experimental results of a Digital Beam Forming (DBF) Synthetic Aperture Radar (SAR) performance on the purpose of the High-Resolution Wide-Swath (HRWS) SAR concept. A ground-based SAR system successfully demonstrated the DBF SAR operation. The demonstrator acquired SAR raw data with very dense spatial sampling rate in order to obtain various sampling rates. We evaluate DBF performance with respect to the image quality factor with two different types of the beam former, a fixed-beam former and an adaptive beam former. The results show that an adaptive DBF algorithm offers a wide range of the selection of the pulse repetition frequency (PRF). In addition we evaluate the noise performance compared to a reference mono-static SAR system on the same condition on single target experiment.

Moving targets are usually smeared and imaged at incorrect positions in synthetic aperture radar (SAR) images due to the target motions during the illumination time. Moreover, a moving target will cause multiple artifacts in the reconstructed image since pulse repetition frequency (PRF) operated in high-resolution wide-swath (HRWS) SAR is very low. In order to reliably indicate moving targets, a robust cancellation algorithm is derived in this paper for clutter suppression in multichannel HRWS SAR, which is free by velocity searching and covariance matrix estimation of clutter plus noise. The proposed multilayer channel-cancellation combined with the deramp processing is designed to sequentially suppress the seriously aliased clutter in HRWS SAR. Experimental results show that the proposed algorithm is efficient and robust in tough situations, and have a superior detection ability in weak targets and low-velocity targets. In addition, the radial velocity estimation algorithm combined with the channel cancellation is exploited to relocate moving targets. The effectiveness of the proposed algorithms is validated by actual spaceborne SAR data acquired by a coordination experiment with two controllable vehicles.

Synthetic aperture radar (SAR) system has inherent constraints between high azimuth resolution and wide swath width. Achieving more phase center samples is one of the key solutions to resolve this limitation. By multiple N transmitting and N receiving channel concept, an increased resolution or a widened swath width could be obtained. In this paper, comprehensive analysis for shifting multiple-input multiple-output (MIMO) SAR system is presented. System resolution enhancement has been demonstrated based on the distributed target simulation by a factor of N compared to conventional displaced phase center antenna (DPCA) system.

The next generation of spaceborne synthetic aperture radar (SAR) remote sensing systems will emphasize on high-resolution and wide-coverage imaging. For these design goals, digital beamforming (DBF) in elevation is a promising candidate. DBF-SAR can provide global monitoring capacity for the continuous observation of a highly dynamic and rapidly changing world with high spatial resolution and short repeat intervals. A spaceborne experiment regarding a real complex scene and real spaceborne wave propagation channel effects remains a necessary step to complete the experimental verification of this advanced technique. Fortunately, the spaceborne-stationary bistatic configuration offers a potential chance to validate the advanced technique. The aforementioned experiment can be considered as a test bed for the development and implementation of DBF radar techniques applicable to Earth observation science and planetary measurements. The DBF experiment based on spaceborne-stationary bistatic configuration with TerraSAR-X as an illuminator has been successfully conducted in June 2013 by the Department of Space Microwave Remote Sensing System, Institute of Electronics, Chinese Academy of Sciences.

Near-space, defined as the region between 20 km and 100 km, offers many new capabilities that are not accessible to low earth orbit (LEO) satellites and airplanes, because it is above storm and not constrained by either the orbital mechanics of satellites or the high fuel consumption of airplanes. By placing radar transmitter/receiver in near-space platforms, many functions that are currently performed with satellites or airplanes could be performed in a cheaper way. Inspired by these advantages, this paper introduces several near-space vehicle-based radar configurations, such as near-space passive bistatic radar and high-resolution wide-swath (HRWS) synthetic aperture radar (SAR). Their potential applications, technical challenges and possible solutions are investigated. It is shown that near-space is a satisfactory solution to some specific remote sensing applications. Firstly, near-space passive bistatic radar using opportunistic illuminators offers a solution to persistent regional remote sensing, which is particularly interest for protecting homeland security or monitoring regional environment. Secondly, near-space provides an optimal solution to relative HRWS SAR imaging. Moreover, as motion compensation is a common technical challenge for the described radars, an active transponder-based motion compensation is also described.

For a synthetic aperture radar (SAR) system, the platform attitude drift will affect the image qualities. During SAR system design computer simulation can be used to determine the attitude stability which can satisfy the users' demands. In the computer simulation, the first step is to create the mathematic model. General models of platform attitude drift are usually created in the time domain, such as the sinusoid one, and the model presented is done in the frequency domain. For each attitude angle (roll, yaw, pitch), the amplitude and phase values are first generated in the frequency domain. Because the attitude parameters are sampled with PRF (pulse repetition frequency) in SAR system, the maximum frequency is set to PRF/2. The amplitude may be changed with the frequency (for example, inversely proportional to the square of frequency), while the phase may be uniformly distributed between 0 to 2/spl pi/. Then the inverse Fourier transformation converts this data into the time domain. Because the phase center of the SAR's antenna is usually offset from the platform center, the attitude drift will change the slant range between the antenna's phase center and the target on the ground. These changes will affect the Doppler history in azimuth direction for the SAR. After these changes are simulated, the SAR raw data of a point target can be generated. With the general SAR procession, the simulated image is obtained. Using the analysis software, the authors can get the effects on the image qualities of the attitude drift. At last, the simulation steps and an example are also presented.

High-resolution wide-swath (HRWS) imaging has emerged as a focal point in synthetic aperture radar (SAR) research. However, conventional SAR systems face challenges in achieving both high azimuth resolution and wide swath simultaneously due to the minimum antenna area constraint. In this paper, we propose a HRWS imaging method based on multifrequency pulse diversity (MFPD) and azimuth multichannel (AMC) technique, capable of resolving range and Doppler ambiguities concurrently. In MFPD mode, range ambiguous echoes can be separated by matched filters in the range frequency domain, as multifrequency pulses are transmitted by a single channel in the transmitter. To further enhance the ambiguity resolution ability of the system and address azimuth incoherence, a novel scheme applying the MFPD to AMC system is proposed, categorized into two distinct scenarios. 1) Uniform Sampling: This scenario satisfies the displaced phase centre antenna condition. Under this condition, high range resolution imaging can be achieved through spectrum splicing in range frequency domain, simultaneously resolving Doppler ambiguity. 2) Non-uniform Sampling: In this scenario, the ambiguous echoes are processed by spatial digital beamforming and spectrum splicing in two-dimensional frequency domain. Finally, the HRWS imaging can be obtained by performing the traditional SAR algorithm. Furthermore, the proposed method can synthesize a wideband signal from multifrequency signals, thereby enhancing the feasibility of super-high-resolution imaging. Simulation results demonstrate the effectiveness of the proposed method.

The Synthetic Aperture Radar (SAR) system is a kind of modern high-resolution microwave imaging radar used in all-weather and all day long to provide remote sensing means and generate high resolution images of the land under illumination of radar beam. Unlike optical sensors, SAR algorithm needs a post-processing process on the data acquired to form the final image. In this article, we use the General Purpose Graphic Processing Units (GPGPU) to accelerate two of SAR algorithms, PGA (Phase Gradient Autofocus) and PDE (Partial Differential Equations), which are two computational intensive algorithms in the post-processing process for the system. Our work shows that the GPU architecture has different acceleration effects on the two algorithms. PGA can achieve an acceleration of 21.7% and PDE can get a speed up of 2.58\(\times \) on GPGPU. We analyse the reasons for the results and conclude that GPU is a promising platform to accelerate the SAR system.

Multi-channel synthetic aperture radar (SAR) systems enable high-resolution wide-swath imagery thus overcoming the inherent limitation of conventional SAR. A possible realization based on the combination of multi-aperture SAR signal reconstruction in azimuth with digital beamforming on receive in elevation is given in [1]. The present paper turns focus to advanced concepts for the imaging of even wider swaths while still providing high azimuth resolution [2]. In this regard, the operation of multi-channel SAR systems in burst modes like ScanSAR or TOPS is introduced and aspects of applying the multi-aperture reconstruction algorithm to burst mode data are analyzed. The influence of the digital processing network on performance parameters as signal-to-noise-ratio and azimuth ambiguity-to-signal-ratio in multi-channel burst mode systems is considered and embedded in the design example of a ScanSAR system that allows for the imaging of a 400 km wide swath with a geometric resolution of 5 m. Finally, first results for a multi-channel TOPS system are presented and an optimized TOPS processing approach is introduced.

A polarimetric SAR (synthetic aperture radar) system was designed in The Netherlands. The project is carried out in two steps. In this work, the first step, consisting of the preparatory studies including a SAR testbed, is described in detail. This SAR system will have limited capabilities, but will serve the purpose of acquiring experience with aircraft SAR and its technology. The system is built with state-of-the-art technology. Remarkable features are the fixed antenna and the low peak power, generated by solid-state devices. The use of monolithic microwave integrated circuits (MMICs) in the PHARUS was investigated in a preparatory study on antenna technology. Application of MMICs would further reduce the dimensions of the radar system. >

This chapter presents a completely new type of Synthetic Aperture Radar (SAR) system that radiates short carrierless pulses, namely the Impulse SAR (ImpSAR). A SAR system radiates chirped pulses from different equispaced positions along the azimuth, which is usually a straight line; a linear array is thus synthesized. Higher range resolution of ImpSAR requires shorter radiated pulses, implying lower average radiated power, while radiated pulse amplitude is dictated by the currently available hardware technology. In order to implement the polychromatic SAR imaging system, the bandwidth of the scattered pulse must be broken down into subbands, which are processed independently. Raw polychromatic SAR data is processed, yielding a number of microwave images, which are coincident to those obtainable with conventional SAR systems. Polychromatic SAR has the useful capability of generating multiple images simultaneously, which is of particular importance to the target detection and identification process.

This paper presents a digital beamforming (DBF) synthetic aperture radar (SAR) for future spaceborne earth observation systems. The objective of the DBF-SAR system is to achieve a low cost, light weight, low power consumption, dualband (X/Ka) dual-polarized module for next-generation spaceborne SAR system in Europe. The architectures and modules of the proposed DBF-SAR system are designed according to a realistic mission scenario, which is compatible with future small/micro satellites platforms. This system fills an important gap in the conception of future DBF-SAR, facilitating a high level of integration and complexity reduction. The proposed system is considered to be not only the first demonstrator of a receive-only spaceborne DBF system but also the first X/Ka-band dual-polarized SAR system with sharedaperture. This paper presents a description of the proposed instrument hardware and first experimental validations. The concept and design of the DBF multi-static SAR system are discussed and presented first, followed by the design of Subsystems such as digital beamforming networks (DBFN), MMIC and antennas. Simulated and measured results of the sub-Systems are presented, demonstrating that the proposed SAR Instrument architecture is well-suited for the future SAR applications.

Advanced Antennas that can operate in several bands and with multiple polarizations are required for the development of modern synthetic aperture radar (SAR) systems. SAR systems already have their working modes expanded by using dual-band dual-polarized (DBDP) antennas. The shared-aperture design has been used in many configurations to reduce the size of these antennas. This work presents an innovative Dual-band Dual-Polarized Aperture Antenna (DBDP), which operates on a single layer circuit board at X- and Ku-bands. The operating frequency of X band is 9.3 GHz and operating frequency of Ku band is 13.265 GHz. To utilize the common aperture, 5-elements (4-groups) planar array with square microstrip patches are utilized for both Xband and for Ku-band 5-elements (1-group) microstrip patch antenna is used. The proposed design is to enhance the gain and isolation by using series-fed center-fed network. The interelement spacing between two patches is considered <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$0.7\lambda$</tex> for the ±25° scan range requirements. The impedance matching bandwidth is 147/266 MHz (X/Ku), Return loss is −19/− 22.24 dB (X/Ku) and high isolation is 66.9 dB. The size of the antenna is <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$160\ \text{mm}\times 160\ \text{mm} \times 0.8\ \text{mm}$</tex> using RT/Duriod 5880 substrate with permittivity 2.2 and the height is 0.8 mm (31 mil). The Simulations has been done in CST Microwave Studio. This research shows that using a dual-frequency dual-polarization SAR antenna in a single aperture to suit user needs in future SAR aircraft is a viable option.

In this paper, an effective high-resolution imaging approach of moving targets is proposed for the space-borne multi-channel in azimuth high-resolution and wide-swath (HRWS) synthetic aperture radar (SAR) system, which is based on the multi-target tracking technique. Firstly, the echo of multi-channel in the azimuth multi-channel SAR system is utilized to deduce the sub-aperture focusing image of moving targets, where the sub-aperture division and imaging technology is involved. Then, the tracks of the moving targets in the sub-aperture focusing image can be obtained by using the multi-target tracking technology. After that, extract the corresponding data of each moving target in the sub-aperture focusing image, and stitch the data according to the tracks to obtain the secondary focus image of the moving target. Finally, some simulation experiments are implemented to validate the theoretical investigations and the proposed approach in this paper.

This paper analyzes the synchronization of a bistatic synthetic aperture radar (SAR) system based upon a geostationary transmitter and small receive-only SAR systems mounted on airplanes or unmanned aerial vehicles (UAVs), namely GEO Spaceborne-Airborne Bistatic SAR. This paper will analyze and present our solution of the space synchronization, time synchronization, frequency synchronization and phase synchronization for the GEO Spaceborne-Airborne bistatic SAR respectively. It will first introduce the GEO Spaceborne-Airborne bistatic SAR system and geometry model briefly. Then possible solutions of the system synchronization will be discussed. It will introduce the synchronization scheme based on the direct path between the transmitter and receiver. It uses synchronization modules to realize the time and frequency synchronization. A mathematical model considering the time and frequency synchronization error is given and a phase error analysis is performed. Range and azimuth compressions of a single target are implemented by simulations.