Using (G.54) to convert to normalized waves
, the
Kelly-Lochbaum junction (G.60) becomes
It is interesting to define
, always
possible for passive junctions since
, and note that
the normalized scattering junction is equivalent to a 2D rotation:
While it appears that scattering of normalized waves at a two-port junction requires four multiplies and two additions, it is possible to convert this to three multiplies and three additions using a two-multiply ``transformer'' to power-normalize an ordinary one-multiply junction [408].
The transformer is a lossless two-port defined by [127]
Figure G.20 illustrates the three-multiply
normalized scattering junction [408]. The one-multiply
junction of Fig. G.18 is normalized by the transformer on its
left. Since the impedance discontinuity is created locally by
the transformer, all wave variables in the delay elements to the left
and right of the overall junction are at the same wave impedance.
Thus, using transformers, all waveguides can be normalized to the same
impedance, e.g.,
.
It is important to notice that and
may have a large dynamic
range in practice. For example, if
, the
transformer coefficients may become as large as
. If
is the ``machine epsilon,'' i.e.,
for typical
-bit two's complement arithmetic normalized to lie in
, then the
dynamic range of the transformer coefficients is bounded by
. Thus, while transformer-normalized
junctions trade a multiply for an add, they require up to
% more bits
of dynamic range within the junction adders.