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Hello Michael Jernigan

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Considering your application, there is an excellent chance that the problem of interest to you is what is called "electrically large," i.e., it involves geometries and distances that span many, many wavelengths. If so, there may be only a limited role for finite-element based numerical solutions. (Finite elements is the primary numerical method employed in Comsol Multiphysics.) If you are interested in the design/modeling of small antennas relevant to your radar, or even of scattering from structures of small to moderate size (probably not as electrically large as a car, however, at 77 GHz!), then Comsol Multphysics may contribute to your problem solution. There is also a ray-tracing capability in the code, and far-fields can be extracted from near-field solutions, as well. But this is not "really" an optics code... You could create your own "physical optics" models via leveraging far-field antenna solutions, I suppose. But if you really want to model the EM response of something like an automobile to illumination at 77 GHz, then you probably want to employ alternative approximate EM techniques, such as GTD/UTD, or various moment-based or multipole-expansion based methods, which are not directly implemented in Comsol Multiphysics (at least, not as of the last time I looked). Good luck! And if you have a specific Comsol model that you want others to comment on, I encourage you to post it here, for a more detailed response.