<s>
A	O
rat-race	B-Algorithm
coupler	I-Algorithm
,	O
also	O
known	O
as	O
a	O
hybrid	B-Algorithm
ring	I-Algorithm
coupler	I-Algorithm
,	O
is	O
a	O
type	O
of	O
coupler	O
used	O
in	O
RF	O
and	O
microwave	O
systems	O
.	O
</s>
<s>
In	O
its	O
simplest	O
form	O
,	O
it	O
is	O
a	O
3	O
dB	O
coupler	O
and	O
is	O
thus	O
an	O
alternative	O
to	O
a	O
magic	B-Algorithm
tee	I-Algorithm
.	O
</s>
<s>
Compared	O
to	O
the	O
magic	B-Algorithm
tee	I-Algorithm
,	O
it	O
has	O
the	O
advantage	O
of	O
being	O
easy	O
to	O
realize	O
in	O
planar	O
technologies	O
such	O
as	O
microstrip	O
and	O
stripline	O
,	O
although	O
waveguide	O
rat	O
races	O
are	O
also	O
practical	O
.	O
</s>
<s>
Unlike	O
magic	B-Algorithm
tees	I-Algorithm
,	O
a	O
rat-race	O
needs	O
no	O
matching	O
structure	O
to	O
achieve	O
correct	O
operation	O
.	O
</s>
<s>
The	O
rat-race	B-Algorithm
coupler	I-Algorithm
has	O
four	O
ports	O
,	O
each	O
placed	O
one-quarter	O
wavelength	O
away	O
from	O
each	O
other	O
around	O
the	O
top	O
half	O
of	O
the	O
ring	O
.	O
</s>
<s>
Rat-race	B-Algorithm
couplers	I-Algorithm
are	O
used	O
to	O
sum	O
two	O
in-phase	O
combined	O
signals	O
with	O
essentially	O
no	O
loss	O
or	O
to	O
equally	O
split	O
an	O
input	O
signal	O
with	O
no	O
resultant	O
phase	O
difference	O
between	O
its	O
outputs	O
.	O
</s>
