Digital Signal Processing Reference
In-Depth Information
Fig. 10.10
5.2 GHz load impedance transformation caused by the embedding network. Target
load impedance also shown
The target load impedance is also depicted in the figure. With a 1.8 pF capacitor
in shunt with the 50
microstrip between points
3
and
4
, the load impedance gets
close to the target value as shown in Fig.
10.11
.
Operation at 5.2 GHz requires special attention to the apparent capacitance that
the discrete capacitors present at this frequency. The S parameters provided by the
manufacturer [
22
] show that, at 5.2 GHz, a 1 pF chip capacitor has the apparent
capacitance the closest to 1.8 pF among the available components (other options
were 1.5 pF, 1.8 pF, and 2.2 pF). This chip capacitor was chosen for the output
matching network.
10.3.5.2 Matching the Input
At the input, the departing point is also 50
and the objective is to transform it in
the desired source impedance given in Table
10.2
:
Z
MS
=
8-i47
.
4 at 5.2 GHz. Using
again the Smith Chart tool, the departing point is depicted as point
1
in Fig.
10.12
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