A third way is by diffraction- any beam, including a laser, will spread out as it travels. You get less spread with short wavelengths and large transmitters, bu

A third way is by diffraction- any beam, including a laser, will spread out as it travels. You get less spread with short wavelengths and large transmitters, but both of those imply expense. If you use long wavelengths and small transmitters, you need huge receivers to get all the beam energy back.