Page 291 - Complete Wireless Design

Filter Design

290 Chapter Six

and
1
CP
50 (525 MHz 475 MHz)
63.6 pF
2

Transfer these values to Fig. 6.34, the bandpass filter’s half-section. Begin
adding and combining half-sections (Fig. 6.35). Continue combining half-sec-
tions until the 6-pole filter of Fig. 6.36 is obtained.

6.2 Distributed Filters

6.2.1 Introduction
Most distributed filters are constructed as microstrip structures. The actual
materials to build them are low in cost, consisting of copper and a substrate.
However, they can—depending on the passband frequency and the dielectric
constant of the board material—take up much more space than lumped LC fil-
ters. Distributed filters are, nonetheless, usually the only economical and
practical choice over 1.5 GHz for many applications. Unfortunately, distrib-

Figure 6.32 A BPF half-section.

Figure 6.33 Combining two BPF half-sections when placed (a) tank-to-tank and (b) series-to-series.

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