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

using an H-field antenna together with an E-field antenna). Another advantage
with this solution is the narrow bandwidth that gives a function like a filter, which
also lowers the risk for interference.
Disadvantages with this antenna are the complexity with the control signal and
that it cannot be placed over a ground plane in a cell phone. This means that the
loop antenna must be placed on an external flap to have good performance.
Another disadvantage is that the control signal must be very precise to tune in
exactly right frequency, because the bandwidth is not much wider than the
channel.
4.7 Switched Monopole
Today nobody wants an external antenna on a mobile phone. Therefore this
embedded prototype antenna was designed. With today’s small mobile phones it
is hard to achieve required bandwidth for DVB-H with an embedded antenna. The
solution to this problem is a switched monopole antenna along one of the sides of
a mobile handset. The idea to this solution came from Perlos patent SE525069.
The antenna is controlled by two switches/multiplexers so different matching
circuits can be connected, a model with three matching circuits is presented in
figure 4.18.
Figure 4.18. Model of switched monopole concept.
The idea of this antenna type is that some different matching circuits together can
cover the whole DVB-H frequency band as shown in figure 4.19 The number of
matching circuits needed depends on the antenna requirements, but to be sure that
the requirements will be fulfilled four matching circuits have been used for all
switched monopoles in this chapter.
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