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

4.6 Loop antenna
Figure 4.10. Return loss graph of the folded-patch 2.
When the work with the wideband folded-patch antenna was finished we read
Perlos patent application SE0403110-0 about a loop antenna. This loop antenna is
a narrowband antenna that is tunable over the whole DVB-H frequency band. The
work with the loop antennas in section 4.6 is based on this patent.
The concept consists of a loop antenna that is tuned by two variable capacitance
diodes (see figure 4.11). An analogue voltage controls the diodes, for simplicity
the same voltage that controls the tuner in the DVB-H receiver. The inductance
between the two diodes prevents the signal from leaking into the control circuit. If
there in some way leaks signal through the inductance the capacitance will ground
this signal.
To be able to feed at the same point as the ground point, which is preferable to get
a balanced antenna, the length of the feeding loop can be changed to get the
desired performance.
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