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342 Other Direct Filter Design Methods
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Figure 9.6. Calculated and measured results for N =3, K = I. [From Hindin, H. J., and Tauh, J.
J. IEEE Trans. Microwave Theory Tech., Vol. MIT-IS, No.9, pp. 526-527, September 1967. ©
1967 IEEE.1
Example 9.2. Design, analyze, and test a filter having three 50-ohm stubs in
a 50-ohm system by using a center frequency of 4700 MHz. Hindin and Taub
(1967) constructed this filter. The calculated and measured results are shown
in Figure 9.6. The midband loss is L o =0.2 dB.
9.1.3. Variations for Printed-Circuit Filters. The spaced-stub implementation
shown in Figure 9.lc probably is not the main application of this filter
design method. Because of several important network equivalence relations,
the same response may be obtained in filters that are conveniently implemented
in stripline or microstrip configurations. Consider the network in
Figure 9.7, which is dual to that in Figure 9.lc. Changing admittance K to
impedance Z in (9.9) adapts the entire development to open-circuited stubs,
instead of the original short-circuited stubs. Thus selectivity function (9.18)
and the selectivity graphs in Figures 9.4 and 9.5 apply when K is replaced
z"
z"
Figure 9.7.
Quarter-wave open-circuited stubs with quarter-wave spacing.