Is it possible to observe more area in azimuth than physically traveled in stripmap SAR? I have been examining stripmap SAR algorithms, mainly Range Migration Algorithm. When I check the textbook examples so far I always saw the data trajectory is larger than scene that is observed. An example from Melvin, Scheer et. al page 309.


As you can see, the platform trajectory roughly travels -20 to 20 and scene is half of it. Similarly, if you check this RMA implementation, this RMA Matlab implementation from the book "Spotlight SAR" by Carrara et. al., you can see the along-track axis of the reconstructed image is actually some subset of trajectory points. Just like the case above.

My question is, what happens in the opposite scenario? For instance in image above, we travel a small distance [-5 to 5] and try to produce, maybe not so precise, the image of the scene [-10 10]. If our antenna does not have high directivity, we should also able to get reflections from targets that are not directly in front of the antenna, but how we should map the frequencies in RMA? 

I know that in Stolt mapping of RMA, we shift and strech each azimuth column, but in that case I should retrieve more azimuth columns than I have.. I don't know, if there is a such imaging type in SAR literature, please refer me to correct terminology, I am new to that area so I might be missing correct nomenclature.
It's so that the cross-range (along-track) resolution is consistent for all targets in the scene. There is no reason why you could not use the flight path between [-5,5] to form the same size image. However, in that case, the targets on the edge of the scene will have been illuminated for a smaller angle than the targets in the middle of the scene, which will given them a smaller region of support in the frequency domain and, hence, a coarser resolution.

When choosing the first and last sensor locations that are used to form the image, it's common to select the first point to be that where the beam first enters the imaged scene and the last point to be when it leaves it. Picture the footprint of the beam on the ground as the sensor flies by; it's usually an oval or cone or something like that. At -20 is where the edge of the oval (or whatever shape it is) begins to intersect the imaged scene. At +20 is where it stops intersecting it.

I should add that, in general, the size of the imaged scene is limited only by the PRF of the sensor.