Abstract :
The design is studied of the mechanical element implementing the wanted height, once the optimum electrical height of an antenna for medium-wave transmission is determined. The problem of how to determine the velocity factor is complex and not yet completely solved in mathematical terms, particularly as regards nonresonant antennas and having a height near to the half wave. The mean factor of velocity is obtained, taking into account both the termination effect caused by top charges on the terminal section of the antenna and the mean phase velocity for a distribution different from the sinusoidal one, but of the real current. The mean factor of velocity, calculated in this way, has a value that not only depends on the height-to-radius-ratio of the tower, but also varies when the antenna height or the frequency varies, namely as a decrease toward resonance. Thus, for a fixed electrical height, the tower should be shortened proportionately to how low this ratio is and the nearer to the resonance the height of the antenna is
Keywords :
antenna theory; dipole antennas; MW; electrical height; mean phase velocity; mechanical dimensions; medium-wave antenna; monopoles; termination effect; tower; velocity factor; Antenna radiation patterns; Conductivity; Directional antennas; Directive antennas; Frequency; Poles and towers; Power supplies; Resonance; Shape; Surface waves;
