A Novel Real-Time Echo Separation Processing Architecture for Space–Time Waveform-Encoding SAR Based on Elevation Digital Beamforming
, Zhimin Zhang 1, Zhen Chen 2, Shuo Han 2, Wei Wang 1,*, Yuhao Wen 2, Xiangrui Meng 2 and Huaitao Fan 1Round 1
Reviewer 1 Report
General description:
An original real-time echo separation processing architecture for space-time waveform encoding -SAR system based on elevation digital beamforming is proposed in the present study.
Digital beamforming with space-time waveform encoding technique in elevation is a technique that enables a space-borne synthetic aperture radar to achieve high-resolution wide swath imaging based on received echoes from multiple sub-swaths simultaneously with a single receive window. In order to separate the echoes from different directions, adaptive single-null steering technique for digital receive beam pattern is proposed.
A multi-null constrained echo separation scheme is also proposed to effectively adjust the width of the notch to track the time-varying pulse extension angle. The hardware implementation details of the corresponding real-time processing architecture are also discussed.
Four significant problems in the suppression of interfering energy in a space borne SAR are pointed out, pulse extension loss, the effect of undulating terrain on the DBF receive performance, to the spatial distribution of echo, and antenna array steering.
The process of digital beamforming is modeled by vector equations in respect of the vector of observation and vector of thermal noise, vector of DBF weights, array manifold vector.
The proposed theory, methods and algorithms are verified by two-dimensional simulation data and raw data of an X-band channels DBF-SAR airborne system.
Remarks:
The article contains of convincing mathematical derivations and models, simulation numerical results and graphs, tables with simulation system parameters and calculation data, and illustrations of results obtained by application of the developed approach to real measurements.
It is recommended the authors to extend conclusion remarks with emphasis on the mathematical derivations, models and algorithms.
Author Response
Please see the attachment.
Responses to the comments from Reviewer 1 are listed from Page 2 to Page 3.
Author Response File: 
Author Response.pdf
Reviewer 2 Report
In this paper, the adaptive single-null steering technique for digital receive beam pattern is proposed to separate the echoes from different directions. In general, the method in this paper is well described. However, some further improvements should be enhanced before acceptance.
- Section 5 lack of performance comparison with other methods. The authors should present some comparison results. With this operation, the authors’ method would be much more convincing.
- The authors refer the ‘real-time’ in the paper title. However, the authors’ discussion in section 3.3 is not sufficient. On the one hand, the authors should conduct the comparison of computational load between their method and traditional method. On the other hand, the processing time in section 4 and section 5 should be further presented.
Author Response
Please see the attachment.
Responses to the comments from Reviewer 2 are listed from Page 4 to Page 6.
Author Response File: Author Response.pdf
Reviewer 3 Report
There should be no acronyms in the title, so remove all acronyms.
The Abstract should be redone, You start with a description of the State of the Art, which should not be done. You need to explain well the problem that your method proposes to solve.
Then describe briefly (in two lines) what it is, and then conclude the abstract by explaining the results you obtained (saying if you used real and/or simulated data).
In Fig. 1, the procedural diagram of how the multi-channel strategy is approached is not clear. You need to siege it better. In particular how many independent transmitters and receivers you are using, then you have to explain in a more exact way the echoes separation strategy and, very well, with all the problems you are facing, the separation ratio between a burst and the other, belonging to previous swaths.
The previous remark is clear in Figure 2, where you say that you suppress the previous echoes, (how does this happen)?
Explain better the strategy of the chirp you want to transmit, including an explanation of how you perform the frequency allocation. Then you have to explain better how you handle the possible non-orthogonality of signals belonging to different non-adjacent swaths, what you receive in the various time delays.
Good work
Author Response
Please see the attachment.
Responses to the comments from Reviewer 3 are listed from Page 7 to Page 10.
Author Response File: Author Response.pdf
Round 2
Reviewer 3 Report
Accepted
