<s>
A	O
slot	B-Algorithm
antenna	I-Algorithm
consists	O
of	O
a	O
metal	O
surface	O
,	O
usually	O
a	O
flat	O
plate	O
,	O
with	O
one	O
or	O
more	O
holes	O
or	O
slots	O
cut	O
out	O
.	O
</s>
<s>
The	O
shape	O
and	O
size	O
of	O
the	O
slot	O
,	O
as	O
well	O
as	O
the	O
driving	O
frequency	O
,	O
determine	O
the	O
radiation	B-Device
pattern	I-Device
.	O
</s>
<s>
Slot	B-Algorithm
antennas	I-Algorithm
are	O
usually	O
used	O
at	O
UHF	O
and	O
microwave	O
frequencies	O
at	O
which	O
wavelengths	O
are	O
small	O
enough	O
that	O
the	O
plate	O
and	O
slot	O
are	O
conveniently	O
small	O
.	O
</s>
<s>
At	O
these	O
frequencies	O
,	O
the	O
radio	O
waves	O
are	O
often	O
conducted	O
by	O
a	O
waveguide	O
,	O
and	O
the	O
antenna	O
consists	O
of	O
slots	O
in	O
the	O
waveguide	O
;	O
this	O
is	O
called	O
a	O
slotted	B-Algorithm
waveguide	I-Algorithm
antenna	I-Algorithm
.	O
</s>
<s>
Multiple	O
slots	O
act	O
as	O
a	O
directive	O
array	B-Algorithm
antenna	I-Algorithm
and	O
can	O
emit	O
a	O
narrow	O
fan-shaped	O
beam	O
of	O
microwaves	O
.	O
</s>
<s>
They	O
are	O
used	O
in	O
standard	O
laboratory	O
microwave	O
sources	O
used	O
for	O
research	O
,	O
UHF	O
television	O
transmitting	O
antennas	O
,	O
antennas	O
on	O
missiles	O
and	O
aircraft	O
,	O
sector	O
antennas	O
for	O
cellular	O
base	O
stations	O
,	O
and	O
particularly	O
marine	B-Algorithm
radar	I-Algorithm
antennas	O
.	O
</s>
<s>
A	O
slot	B-Algorithm
antenna	I-Algorithm
's	O
main	O
advantages	O
are	O
its	O
size	O
,	O
design	O
simplicity	O
,	O
and	O
convenient	O
adaptation	O
to	O
mass	O
production	O
using	O
either	O
waveguide	O
or	O
PC	O
board	O
technology	O
.	O
</s>
<s>
As	O
shown	O
by	O
H	O
.	O
G	O
.	O
Booker	O
in	O
1946	O
,	O
from	O
Babinet	O
's	O
principle	O
in	O
optics	O
a	O
slot	O
in	O
a	O
metal	O
plate	O
or	O
waveguide	O
has	O
the	O
same	O
radiation	B-Device
pattern	I-Device
as	O
a	O
driven	O
rod	O
antenna	O
whose	O
rod	O
is	O
the	O
same	O
shape	O
as	O
the	O
slot	O
,	O
with	O
the	O
exception	O
that	O
the	O
electric	O
field	O
and	O
magnetic	O
field	O
directions	O
are	O
interchanged	O
;	O
the	O
antenna	O
is	O
a	O
magnetic	O
dipole	O
instead	O
of	O
an	O
electric	O
dipole	O
;	O
the	O
magnetic	O
field	O
is	O
parallel	O
to	O
the	O
long	O
axis	O
of	O
the	O
slot	O
and	O
the	O
electric	O
field	O
is	O
perpendicular	O
.	O
</s>
<s>
Thus	O
the	O
radiation	B-Device
pattern	I-Device
of	O
a	O
slot	O
can	O
be	O
calculated	O
by	O
the	O
same	O
well-known	O
equations	O
used	O
for	O
rod	O
element	O
antennas	O
like	O
the	O
dipole	O
.	O
</s>
<s>
Antennas	O
consisting	O
of	O
multiple	O
parallel	O
slots	O
in	O
a	O
waveguide	O
are	O
widely	O
used	O
array	B-Algorithm
antennas	I-Algorithm
.	O
</s>
<s>
They	O
have	O
a	O
radiation	B-Device
pattern	I-Device
similar	O
to	O
a	O
corresponding	O
linear	O
array	O
of	O
dipole	O
antennas	O
,	O
with	O
the	O
exception	O
that	O
the	O
slot	O
can	O
only	O
radiate	O
into	O
the	O
space	O
on	O
one	O
side	O
of	O
the	O
waveguide	O
surface	O
,	O
180°	O
of	O
the	O
surrounding	O
space	O
.	O
</s>
<s>
Longitudinal	O
slotted	B-Algorithm
waveguide	I-Algorithm
antenna	I-Algorithm
The	O
slots	O
 '	O
axis	O
is	O
parallel	O
to	O
the	O
axis	O
of	O
the	O
waveguide	O
.	O
</s>
<s>
This	O
has	O
a	O
radiation	B-Device
pattern	I-Device
similar	O
to	O
a	O
collinear	O
dipole	O
antenna	O
,	O
and	O
is	O
usually	O
mounted	O
vertically	O
.	O
</s>
<s>
The	O
radiation	B-Device
pattern	I-Device
is	O
almost	O
omnidirectional	O
in	O
the	O
horizontal	O
plane	O
perpendicular	O
to	O
the	O
antenna	O
over	O
the	O
180°	O
azimuth	O
in	O
front	O
of	O
the	O
slot	O
,	O
but	O
narrow	O
in	O
the	O
vertical	O
plane	O
,	O
with	O
the	O
vertical	O
gain	O
increasing	O
approximately	O
3dB	O
with	O
each	O
doubling	O
of	O
the	O
number	O
of	O
slots	O
.	O
</s>
<s>
For	O
broadcasting	O
,	O
a	O
cylindrical	O
or	O
semicircular	O
waveguide	O
is	O
sometimes	O
used	O
with	O
several	O
columns	O
of	O
slots	O
cut	O
in	O
different	O
sides	O
to	O
give	O
an	O
omnidirectional	O
360°	O
radiation	B-Device
pattern	I-Device
.	O
</s>
<s>
Transverse	O
slotted	B-Algorithm
waveguide	I-Algorithm
antenna	I-Algorithm
The	O
slots	O
are	O
almost	O
perpendicular	O
to	O
the	O
axis	O
of	O
the	O
waveguide	O
but	O
skewed	O
at	O
a	O
small	O
angle	O
,	O
with	O
alternate	O
slots	O
skewed	O
at	O
opposite	O
angles	O
.	O
</s>
<s>
Its	O
largest	O
use	O
is	O
for	O
microwave	O
marine	B-Algorithm
radar	I-Algorithm
antennas	O
.	O
</s>
<s>
The	O
slot	B-Algorithm
antenna	I-Algorithm
was	O
invented	O
in	O
1938	O
by	O
Alan	O
Blumlein	O
,	O
while	O
working	O
for	O
EMI	O
.	O
</s>
<s>
He	O
invented	O
it	O
in	O
order	O
to	O
produce	O
a	O
practical	O
type	O
of	O
antenna	O
for	O
VHF	O
television	O
broadcasting	O
that	O
would	O
have	O
horizontal	O
polarization	O
,	O
an	O
omnidirectional	O
horizontal	O
radiation	B-Device
pattern	I-Device
and	O
a	O
narrow	O
vertical	O
radiation	B-Device
pattern	I-Device
.	O
</s>
<s>
Prior	O
to	O
its	O
use	O
in	O
surface	O
search	O
radar	O
,	O
such	O
systems	O
used	O
a	O
parabolic	O
segment	O
reflector	O
,	O
or	O
"	O
cheese	B-Algorithm
antenna	I-Algorithm
"	O
.	O
</s>
<s>
The	O
slotted	B-Algorithm
waveguide	I-Algorithm
antenna	I-Algorithm
was	O
the	O
result	O
of	O
collaborative	O
radar	O
research	O
carried	O
on	O
by	O
McGill	O
University	O
and	O
the	O
National	O
Research	O
Council	O
of	O
Canada	O
during	O
World	O
War	O
II	O
.	O
</s>
