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198 Impedance Matching
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Figure 6.23. SWR/reflection limitations versus decrement of a lowpass or bandpass matching
network of degree n.
A graph that plots SWR (and equivalent reflection magnitude) versus
decrement (6.49) for.various network degrees (n) is a useful design tooL This is
easily obtained from Programs B6-2 and A6-3 (see Figure 6.23). Recall that an
n= I network is the load itself (Figure 6.18); n=2 represents a single matching
element in a lowpass network, and clearly this is the greatest single improvement
possible. The data in Example 6.10 and Figure 6.23 show the rapidly
diminishing return for increasing the total network degree to greater than n = 5
or 8.
6.3.4. Summary of Fano's Broadbund·Mutching Limitations. Fano (1950)
published a complete analysis of ideal, lumped-element matching networks
that were terminated by load subnetworks of similar structure and ended in a
resistance. The usual theoretical extensions of his results have been for
lowpass networks, but the common application has been for bandpass cases.
There is a simple correspondence between lowpass and bandpass networks
that is useful to have in mind during development of the subject; it was
introduced here, but its details will be described in Section 6.5. Fano's
approach does not deal with the task of load classification, the process of