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 PTFE glass random fiber substrate. It is found that for a fixed substrate thickness
B
, the resonant length and directivity decrease with increasing relative dielectric constant
\varepsilon_{r}
. The
\bar{E}
-plane normalized power pattern is also examined as a function of
\varepsilon_{r}
and
B
. It is shown that even for very thin substrates, multiple beam radiation can result for certain values of
\varepsilon_{r}
by the excitation of surface waves. Multiple beam patterns can also be obtained with increasing
B
for a given
\varepsilon_{r}
In fact, as
B
increases it is determined that the resonant length, bandwidth and resonant resistance approach the apparent value of a PCD on a dielectric half space.