4.3 Matching two unequal resistive impedances
183
4.3.3 Three elements Matching
An evident disadvantage of two-elements, L-section matching is that, once the source
resistance R
SOURCE
and the load resistance R
LP
are determined (Figure 4.3-2), the Q of the network is
fixed (eq. (4.3-2)). This means that, if an L-section is employed, the designer does not have a choice
of the circuit Q. Three element networks overcome this issue since they allow the designer to design
for a specific Q. Their potential disadvantage is a narrower bandwidth however, in some
applications, this may also be an advantage!
There are two main types of 3-element matching:
1) The Pi Network. This is effectively the combination of two back-to-back L-networks and is
shown in Figure 4.3-16.
Figure 4.3-16 Three-element matching, pi-network
2) The T-Network. Its topology is shown in Figure 4.3-17.
Figure 4.3-17 Three-element matching, T-network
We will not be looking at the algebraic calculations to determine these networks since there is a
much easier way to design them which makes use of Smith charts and will be illustrated in section
4.4.
X
1
V
SOURCE
R
SOURCE
R
LOAD
X
2
X
3
X
2
V
SOURCE
R
SOURCE
R
LOAD
X
1
X
3
Conquer Radio Frequency
183 www.cadence.com/go/awr
