Page 172 - DSP Integrated Circuits
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4.18 Lattice Wave Digital Filters 157
The reflectance is an allpass function:
where
and
In some cases it may be advantageous to use a series resonance circuit since
the multiplication by -1 in the wave-flow graph shown in Figure 4.46 is avoided.
Higher-order reflectances can be obtained by connecting circulators loaded
with reactances as shown in Figure 4.47. The reflectance corresponding to the
open-ended unit element in Figure 4.47 is
where
Figure 4.47 Higher-order circulator structure
Circulators can be implemented in the microwave range where they are used
to, for example, direct signals from the transmitter to the antenna and from the