Doing some experiments we could recognize that the sonar sensor included in USARSim does not create a cone as it is supposed to do.
That's why we modified the existing model. It supports different resolutions and scan intervals.
You can download the UnrealScript source of the modified sensor at our website.
I think that it is great that you are creating new code for USARSim. However, USARSim resides on sourceforge and we would like to keep all of its code there. Can you please check-in your code? If you are not already a developer, I invite you to join!