Page 140 - Complete Wireless Design

Amplifier Design

Amplifier Design 139

Figure 3.40 Designing a T network for use between a resistive source and load.

9. The circuit is shown completed in Fig. 3.41. Other possible circuit configu-
rations can be used as required (Fig. 3.42). Figure 3.42a, b, and c are com-
bined as in step 8 above, but the signs must be maintained for b and c
because of the opposite reactance employed ( for inductors and for
capacitors).

Wideband matching. Sometimes it may be necessary to design a low-Q, very
wideband matching network. This can be done as follows, by using Fig. 3.43a
for a pure resistive load that is smaller than the pure resistive source or by
employing Fig. 3.43b for a pure resistive load that is larger than the pure
resistive source. X and X can be considered as a separate L network from
S1 P1
X and X , so each L may be oriented any way that is convenient. For
S2 P2
instance, X may be an inductor, so X must then be a capacitor; however, X
S1 P1 S2
may be the capacitor, with X being the inductor:
P2
1. Solve for “R”:
"R" R R 8.7 ohms
S L
2. Solve for loaded Q:

"R"
Q 1 2.2
R
SMALLER
3. Complete for Fig. 3.43a:

"R" "R"

1 3.97 ohms (Q 2.19)
X |Q and
P2 Q 2 R 2
2 L
X Q R 3.28 ohms
S2 2 L
R R
S
S

1 22.9 ohms (Q 2.18)
X |Q and
P1 Q 1 "R" 1
1
X Q "R" 18.96 ohms
S1 1
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