ok this might serve your purpose.
Create a poly torus and make it with quite few sub divisions (something like 30 - 40 ), then scale it's section radius to something like 0.01 so it more or less looks like a curve circle .With it selected go to dynamics and create a particle emitter (emit from object)and have it set to omni.In the emitter particle shape node set the lifspan mode to Constant and its lifespan to something like 0.5 depending on the size of particle ring you want, you might also have to play with the particle rate but i manged it with a setting of 20 per second.
Now you should have a ring of particles, with the particle selcted go up to fields and create a radial field.Move the radial field about 30 grid units away (depending on the size of your particle circle) but far enough for the length of your radio signal.Now in the radial field attributes play with the magnitude slider until the particle come toward the radial field and end when they meet, set the attenuation in your filed attributes to 0.1 and you should now have a cone of intermittant particle when you play your simulation.
If you want it animated you may have to render it out seperpartely and reverse animation since the the particles are traveling from the large cone down to a point but i think it will work out.

hope it is useful for your purpose .