The reactive divider input power is
limited only by the transmission lines;
the output power split can be unequal.
Its input match is limited only by the
input transformer, but that has an impedance transformation twice that of
the PRD. Its output VSWR is almost
twice the number of outputs. Also, a
failure at one of the output loads can
short out all the outputs.
The Wilkinson input match has the
same impedance transformation as
the reactive divider. The input power
can be large, but will be limited if the
output loads are not perfect. The output powers can be unequal. The output match and isolation can be very
good. Wide bandwidth with multiple
outputs or unequal output powers
is very difficult in an individual unit.
Cascading units to obtain multiple
outputs adds to path losses and match
problems.
resistive, Prd aNd reactive
divider desigN aNd
PerformaNce
The values in Table 1 assume perfect transformers and resistors. The
taBLe i
N-way divider Parameters
Type
Path Loss (dB)
Isolation (dB)
Resistive
-20Log(N)
-20Log(N)
PRD
-10Log(2N-1)
-20Log(2N-1)
Reactive
-10Log(N)
-20Log(N)
Output VSWR
Transformer Z ratio
Series R (ohm)
1.0
1.0
Zo(N-1)/(N+1)
1.0
N2/(2N-1)
Zo(N-1)/N
2N-1
N
None
input and output impedances are as-
sumed to be equal (Zo). The values
obtained from Table 1 can be used to
design a PRD for any number of out-
puts. Figure 2 shows the path losses
and isolation for the three different
power dividers. A narrow band and a
wide band application are described
below.
Narrow BaNd 22-way L-BaNd
Prd
This unit was prototyped for possible use in Iridium communications
0
REACTIVE PATH LOSS
PRD PATH LOSS
RESIS TIVE PATH LOSS and ISOLATION
REACTIVE ISOLATION PRD ISOLATION
5
PATH LOSS (dB)
10
15
20
25
Square Peg,Round Hole?
30
35
2 4 6 8 10 12 14 16 18 20
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s Fig. 2 Path loss and isolation values for
different power dividers.
s Fig. 3 Photograph of a 22-way PRD.
satellites. The path loss ( 27 dB) of a
resistive divider would be excessive.
The high output VSWR (43:1) of a
reactive divider ruled it out. (Adding
circulators to a reactive divider would
add complexity and weight.) A cascaded Wilkinson divider would be much
more complex. A single-stage, 22-way
