NEO-5
-
Hardware
Integration
Manual
Preliminary
Product
Testing
GPS.G5-MS5-08003-A2
u-blox
proprietary
Page 40
Figure 25: Typical Radiation Pattern of a Patch Antenna, MuRata, Inc.
For
the
specific
example
shown
in
one
can
easily
see
that
the
so-called
axial
ratio,
the
relation
of
major
to
minor
axis
of
the
elliptical
polarization
has
a
minimum
at
the
50
mm
2
square
ground
plane.
At
this
point,
the
polarization
of
the
antenna
is
closest
to
an
ideal
circular
polarization
(axial
ratio
=
0
dB).
At
a
100
mm
2
square
ground
plane
size
this
particular
patch
shows
an
axial
ratio
in
the
order
of
10
dB,
which
is
closer
to
linear
polarization
than
to
circular
and
will
result
in
respective
losses.
This
effect
can
also
be
seen
in
the
left
graph
of
the
figure,
where
gain
no
longer
increases
with
increasing
ground
plane
size.
In
conclusion,
the
correct
dimensions
for
the
size
of
the
ground
plane
can
serve
as
a
useful
compromise
between
maximum
gain
and
reasonable
polarization
loss.
Figure 26: Typical Gain and Axial Ratio of a Patch antenna with respect to ground plane size, MuRata, Inc.
A
good
allowance
for
ground
plane
size
is
typically
in
the
area
of
50
to
70
mm
2
.
This
number
is
largely
independent
of
the
size
of
the
patch
itself
(when
considering
ceramic
patches).
Patch
antennas
with
small
ground
planes
will
also
have
a
certain
back-lobe
in
their
radiation
pattern,
making
them
susceptible
to
radiation
coming
from
the
backside
of
the
antenna,
e.g.
multi-path
signals
reflected
off
the
ground.
The
larger
the
size
of
the
ground
plane,
the
less
severe
this
effect
becomes.
Smaller
sized
patches
will
usually
reach
their
maximum
gain
with
a
slightly
smaller
ground
plane
compared
to
a
larger
size
patch.
However,
the
maximum
gain
of
a
small
sized
patch
with
optimum
ground
plane
may
still
be
much
lower
than
the
gain
of
a
large
size
patch
on
a
less
than
optimal
ground
plane.
