Design of Antennas for Handheld DVB-H ... - Lunds tekniska högskola

4.5 Folded-Patch
With the PIFA-antenna the most critical measure is the height above the ground
plane. Therefore the antenna element was flipped up and placed at the same height
as the ground plane (see figure 4.7). After a lot of testing the antenna fulfilled the
demand to have at least a 6 dB return loss in the frequency range 470-702 MHz,
the return loss graph is shown in figure 4.8.
The ground plane for this antenna measures 62*51mm. The antenna element is
folded around a 1mm plastic substrate and measures 36*51mm.
The critical measure in this antenna is the distance between the antenna and the
ground plane, which in this case is 19mm. This distance is critical because the
antenna is a ground free antenna and the antenna element cannot be placed closer
than 19 mm to the ground plane. The antenna bandwidth is increased with the
distance. Another important measure is the width of the antenna, which is 51mm.
If the width is decreased the resonance frequency is increased. A lot of different
antenna patterns were tried, the one in the picture gave the best result.
The location of the feeding point is another important factor for the characteristic
of the antenna. To get the wished performance of the antenna it has to be fed on a
strip line as the picture shows.
Figure 4.7a. Folded-patch, front side.
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