IMPROVED ANTENNA DESIGN THROUGH USE OF A FLIP
Original Publication Date: 1997-Mar-01
Included in the Prior Art Database: 2002-May-15
The standard omnidirectional antenna used in land mobile radio applications has the problem that part of the energy radiated by the antenna is neces- sarily directed towards the user of the radio. That energy is largely absorbed by the user in the form of heat and is, therefore, not available for communica- tions purposes. The degree to which the energy is absorbed is dependent on a number of factors, including the shape of the absorbing structure, its composition, and the separation between the absorbing structure and the antenna. Therefore, we would expect much mote absorption from a radio worn on the belt, with the antenna pressed against the user's side or back, than we would expect from a radio held in the interconnect position. The effect that is at work here is not simply the user subtend- ing part of the solid angle into which the antenna is radiating energy. When the user is close to the antenna, effects due to the near electromagnetic fields dominate. These effects drop off rapidly with distance (d-S according to Andersen'), and, as Jensen and Rahmat Samii2 note, peak SAR (specific absorption rate) decreases in a nearly exponential fashion with handset-body separation. But, because this is not a simple geometrical problem, we have seen in simulations that a radiating antenna placed close to a dielectric half plane can have more than 80% of its energy absorbed by the plane.