Application of characteristic mode analysis to HF low profile vehicular antennas

Low-profile vehicular antennas are electrically small in the near-vertical incidence skywave (NVIS) frequency range (2 - 10 MHz), which makes them inefficient and narrowband. Considering a vehicle to be the largest part of radiating system, the characteristic mode analysis shows that the widest bandwidth is achieved when the horizontal electric dipole current distribution is excited on the vehicle. By applying an edge port excitation it is demonstrated that bandwidth of 24 kHz can be achieved above most realistic grounds at the expense of very low gain at 2 MHz.