Predicted and measured patterns of vehicle-mounted whip and loop antennas for near vertical incidence skywave (NVIS) propagation

We have combined the relatively mature numerical technique of the moment method computer modelling with a powerful, though less well-known, method of antenna synthesis which is based on the procedure of characteristic modes (CM), to both analyse and then to design optimum antenna systems for vehicular NVIS applications. Regardless of the maturity of an analytical technique however, the acid test of its accuracy can only be determined by means of a series of careful measurements of the performance of the candidate antennas when mounted on their appropriate host vehicle. This paper presents both analytical and experimental results for the existing whip antenna, at various angles of inclination, as well as for the vertically orientated loop, which has been proposed as a more appropriate antenna for this application. In addition, a loop configuration with an unconventional feed system is analysed and shown to provide improved performance