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Hi,



I have a quasi-optical system where the source and detector are co-located. This is basically because I want to simulate a sub-THz system, or better a quasi-optical system, where the source\detector is a horn antenna, which radiates a gaussian beam.



The system is made of the source, a lens, and a target. Ideally, the antenna illuminates the lens, which directs the beam on a reflective target. The lens also collects back (part of) the reflected beams and focuses them back on the detector. 



What would be a good way of evaluating the directivity of the detected radiation? The non-sequential mode has a polar detector available, but it seems to work mainly to detect the directivity of rays coming out of a source. In other words, I would like to estimate the directivity of a source, whose rays are the same that the ones reaching my detector, but with opposite direction.



Even better, it would be to be able to estimate a coupling efficiency between the source and the detector: is it sensible to do so in ray-tracing? What would be an effective way to do it?



Best,



Mariangela



  



 



 

Hi Mariangela,



Ray tracing is a good method for determining coupling and other parameters so long as as diffraction effects are unimportant. Generally this means that feature sizes are large with respect to wavelength and that self-diffraction in a coherent beam is also unimportant.



For such systems there are a number of ways of evaluating beam characteristics. A Detector Polar can be used, and not just with sources. It should be positioned with its origin at the apparent source, and for an extended source its radial size should be made much greater than the size of the source. A Detector Rectangle can also be used. It can be set to display in either position or angle space. In optimization, the NSDD operand can also measure in angle space as well as position space. For example, it can be set to report the centroid locations as well as the RMS sizes in angle space.



Having said this, I am concerned about your design being quasi-optical sub-THz, and using a horn antenna. In my meager experience, such implementations often do not meet the requirement that feature sizes are much greater than a wavelength. OpticStudio does have capabilities for working with such systems using physical optics propagation. But this capability, like the rest of OpticStudio, is really designed to handle traditional optics simulation. I know of no way to simulate in OpticStudio a horn antenna being modeled as an expanding waveguide.



Kind regards,



David

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