In this letter, we present a new waveform technique for the use of multiple transmitters in synthetic aperture radar (SAR) data acquisition. This approach is based on the principle of the orthogonal-frequency-division-multiplexing technique. Unlike multiple subband approaches, the proposed scheme allows the generation of multiple orthogonal waveforms on common spectral support and thereby enables to exploit the full bandwidth for each waveform. This letter introduces the modulation and the demodulation processing in regard to typical spaceborne SAR receive signals. The proposed processing techniques are verified by a simulation for the case of pointlike targets. Index Terms-Digital beamforming (DBF), multiple-input multiple-output (MIMO) synthetic aperture radar (SAR), orthogonal frequency division multiplexing (OFDM), orthogonal waveform, SAR.

Over the past years, the use of multiple antenna apertures combined with digital beamforming (DBF) has been spotlighted as a promising solution for the fundamental restriction for high-resolution and wide-swath spaceborne synthetic aperture radar (SAR) imaging. In this paper, we present the first spaceborne experiment of a DBF technique on receive, using the TerraSAR-X dual receive antenna mode. For this experiment, we implemented a DBF module, which includes the reconstruction filter as a digital beam former and associated signal processing for calibration and channel balancing. The experimental results exhibit the successful ambiguity suppression capability of the DBF and validate the high potential of the DBF both for advanced future and current SAR systems.

In this paper, we introduce a novel multiple-input multiple-output (MIMO) synthetic aperture radar (SAR) concept for multimodal operation. The proposed system employs waveforms based on the orthogonal frequency division multiplexing (OFDM) technique and digital beamforming (DBF) on receive. Thereby, it becomes feasible to maximize spatial degrees of freedom, which are necessary for the multimodal operation. The proposed MIMO SAR system produces multiple high-resolution wide-swath SAR imageries that are used for coherent postprocessing. Through this paper, we aim to open up a new perspective of using MIMO concept for a wide-swath SAR imaging with high resolution in interferometric and polarimetric modes, based on OFDM and DBF techniques. Therefore, this paper encompasses broad theoretical backgrounds and general system design issues as well as specific signal processing techniques and aspects.Index Terms-Digital beamforming (DBF), high-resolution wide swath (HRWS), multichannel synthetic aperture radar (SAR) processing, multiple-input multiple-output (MIMO), orthogonal frequency division multiplexing (OFDM) waveform, reconfigurable SAR system, SAR.

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In this paper, we present the experimental results of a Digital Beam Forming (DBF) Synthetic Aperture Radar (SAR) performance on the purpose of the HighResolution 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.