On the effect of substrate thickness and permittivity on printed circuit dipole properties

The effect of substrate thickness and relative permittivity on the radiation properties of printed circuit dipoles (PCD's) is investigated. A trade-off between substrate thickness and resonant input resistance, bandwidth, and radiation efficiency is presented for a polytetrafluorethylene (PTFE) glass random fiber substrate. It is found that for a fixed substrate thicknessh, the resonant length and directivity decrease with increasing relative dielectric constant\epsilon_{r}. TheE- andH-plane normalized power pattern is also examined as a function of\epsilon_{r}andh. It is shown that even for thin substrates, multiple-beam radiation can result for certain values of\epsilon_{r}by the excitation of surface waves. Multiple-beam patterns can also be obtained with increasinghfor a given\epsilon_{r}. In fact ashincreases it is determined that the resonant length, bandwidth, and resonant resistance approach the apparent value of a PCD on a dielectric halfspace.