Felipe Queiroz de Almeida

Airborne Demonstration of Multichannel SAR Imaging

Multichannel synthetic aperture radar (SAR) makes it possible to obtain high-resolution wide-swath imagery, thus overcoming an inherent limitation of conventional SAR. To cope with a nonuniformly sampled data array in azimuth caused by variations of the pulse repetition frequency, these systems require appropriate coherent processing such as the multichannel reconstruction algorithm. This letter presents the applicability of this algorithm to airborne measured multichannel X-band data. In this context, impact and performance of different channel-balancing methods are investigated. Furthermore, the analytic prediction of residual azimuth ambiguities is verified in the measured data by means of a point target analysis.

MirrorSAR: A fractionated space radar for bistatic, multistatic and high-resolution wide-swath SAR imaging

This paper introduces the concept of a fractionated MirrorSAR which is based on a set of mutually separated transmitter and receiver satellites. As opposed to previously published bi- and multistatic SAR systems, the receiver satellites are considerably simplified, as their main functionality is reduced to a kind of microwave mirror (or space transponder) which routes the radar echoes towards the transmitter. The forwarded radar signals are then coherently demodulated within the transmitter by using the same oscillator that had been used for radar pulse generation. This avoids the necessity of a bidirectional phase synchronization link as currently employed in TanDEM-X. Since the needs for fully equipped radar receivers, on-board memory and downlink are also overcome, the weight and costs of the receiver satellites can be significantly reduced. This allows for a scaling of their number without cost explosion, thereby paving the way for novel applications like multi-baseline SAR interferometry and single-pass tomography. Several additional opportunities make the MirrorSAR concept even more attractive. First, the separation of the transmitter and receiver front-ends reduces not only RF losses by avoiding switches and circulators, but it may also lower the peak power in the transmitter satellite by employing a frequency-modulated continuous wave (FMCW) illumination. This simplifies the design of the high-power amplifier and increases its efficiency. Second, the opportunity for continuous radar data collection enables new modes for the imaging of ultra-wide swaths with very high resolution, thereby overcoming an inherent limitation of conventional monostatic SAR systems. Third, the joint availability of all receiver signals in a centralized node offers new opportunities for efficient data compression, as the multistatic radar signals from close satellite formations are characterized by a high degree of mutual redundancy. Fourth, the use of a sufficiently separated transmitter satellite can avoid the risk for mutual illumination, which challenges the design and operation of fully-active multistatic SAR systems. Further advantages arise from the scalability and reconfigurability, which support new redundancy concepts and pave at the same time the way to new modes like MIMO-SAR tomography.

Digital beamforming techniques for multi-channel synthetic aperture radar

SAR instruments with multiple transmit/receive channels allow for a variety of operation modes. The trade-space includes the instrument and antenna parameters designed to enable various operation modes. These are utilized to achieve a required SAR performance derived from the mission and user requirements. Finding a solution in this multi-dimensional trade space is not trivial and often involves the compromise of parameters. This paper addresses the topic of SAR instrument design tailored to a set of operation modes. It explains and compares the SAR techniques and gives the performance.

Multichannel staggered SAR with reflector antennas: Discussion and proof of concept

Synthetic Aperture Radar (SAR) spaceborne imaging with High Resolution Wide Swath (HRWS) capabilities has been the subject of increasing interest and active research, driven by applications posing requirements of high spatial resolution and short revisit times which cannot be directly fulfilled with conventional system architectures. In this context, the paper examines a combination of two promising HRWS techniques, namely staggered SAR - a pulse repetition interval variation allowing wide continuous swaths - and a multiple receiver architecture in azimuth - a proven alternative for fine azimuth resolution - with the objective of combining the strengths of both methods. The paper explains the novel multichannel staggered SAR architecture and provides a first proof of concept using data acquired with an experimental ground-based multichannel feed reflector antenna system.