Validation of NEC-3 (Numerical Electromagnetics Code) with Applications to MF and HF Antenna Technology

The family of electromagnetic modeling computer programs known as NEC (Numerical Electromagnetics Code - Method of Moments) is widely used throughout government and industry. This work describes the first major effort to validate NEC-3, which is capable of modeling antennas which intersect and/or penetrate the air-earth interface. Several large high-frequency antennas are constructed in the field, and their important electrical parameters are measured; the results are then compared with values generated from NEC-3. A scale model of one antenna is built and tested in an anechoic chamber, and this data is also compared with NEC-3 predictions. NEC-3 modeling suggests that an elevated vertical monopole antenna with a sparse-radial elevated ground system is competitive with a conventional ground-mounted antenna utilizing 120 buried radials. Field tests at a variety of locations appear to confirm this hypothesis, and several commercial broadcast stations are planning to construct these antennas. A novel method of feeding power to phased arrays of vertical monopoles (or other types of antennas) is developed and successfully tested. The analysis, which relies upon matching two or more voltage vectors, is extended from the ideal (loss-free) case to include lossy transmission lines as well. Advisors/Committee Members: Radcliff, Roger.