Current issues have arisen in areas of cost savings and complexity of systems developed for the US Army. One of these systems is an identification system for ground vehicles. The issue for this system is whether the system should utilize circular polarized or linear polarized antennas. The identification system will be operating in the millimeter wave spectrum. The system is a question and answer system, therefore, the signal transmitted only needs to reach the receiver, where a reply is sent from the interrogated vehicle. One of the proposed reasons for using circular polarized antennas is to combat the effects of multipath on the signal. Multipath occurs, when the main beam of an antenna is pointed at a low incidence angle toward a target or receiver such that part of the beam intersects the ground. The transmitted signal can follow several different two-way paths. In this systems case, since we are dealing with forward scatter only, the receiver will see direct path and indirect path. These variations and simultaneous paths can result in interference effects at the receiving antenna, which acts as an electromagnetic (EM) vector-summing device. This EM vector summation is called multipath interference.

The antennas that comprise the identification system are a directional antenna, which is used for the interrogation, and an omni-directional antenna, which is used to receive the interrogation. The cost savings to outfit a single vehicle with either circular or linear polarized antennas does not seem to be a major issue. However, when the Army is proposing to outfit thousands of vehicles with a system, the cost savings could be tremendous. These antennas are made to be throw away items also, which means if they are damaged at all, they will be replaced with a new one, instead of trying to fix the damaged antenna. Using raw test antenna data that was recorded in 1995, a comparision of similar antennas to the proposed systems can be made. The testing was performed on a flat asphalt surface. The testing performed included circular and linear polarized horns and omni-directional antennas operating in the millimeter wave spectrum. Because of the primary mission of the platforms this system will be integrated on, the operation of this system will be mostly on non-reflective surfaces. With the theory that the propagation loss of a signal will show less variations over an absorbing surface than a smooth reflective surface and the utilization of a mathematical model to calculate predictable results, a comparison of using linear polarized antennas instead of circular polarized antennas will be performed.