Can anyone help me? The overall context of this question is the extraction efficiency of a dipole representing a generic mechanical structure from the point of view of rf fields (> 30 MHz) and ignition of explosive and flammable atmospheres. A British standard I have been looking at assumes that the structure has the rf energy extraction efficiency of a half wave dipole (I am ignoring here the extra gain also assumed due to the potential for the structure to behave as an antenna with extra gain).
The basic question is to do with the extraction efficiency of a dipole versus frequency, since, if the rf frequency is known and the structure is known then it need not be assumed that the structure will act as a half wave dipole (the frequency and structure dimensions may not be compatible) My specific questions are these: Assuming that what I am actually taking about is dipole gain (I am a bit of an ignoramus I'm afraid) Can anyone give me a basic approximate formula for the variation of gain with frequency for frequencies that are up to a factor of (say) 10 away (above and below) from the resonant frequency of a half wave dipole. Is the maximum gain cyclic (e.g is there a resonance at, say, a dipole length of 1.5, 2.5 etc wavelengths or does the gain just "disappear" when the frequency moves away from a half wave dipole condition?). If the gain is cyclic what would be an approximate formula for the gain at, and around, these cyclic frequencies?(Note that I am not interested in polar diagram directions, merely gain) I am not entirely sure that I have made these questions very clear - but I hope so. Has anyone got any formulae or does anyone know where I can get some? In hope Dave Palmer, UK
