NEO-5
-
Hardware
Integration
Manual
Preliminary
Product
Testing
GPS.G5-MS5-08003-A2
u-blox
proprietary
Page 41
It
is
not
only
gain
and
axial
ratio
of
the
patch
antenna
that
is
affected
by
the
size
of
the
ground
plane
but
also
the
matching
of
the
antenna
to
the
50
Ohms
impedance
of
the
receiver.
See
Appendix B.6
for
more
information
on
matching.
B.4 Helix Antennas
Helix
antennas
can
be
designed
for
use
with
or
without
ground
plane.
For
example,
the
radiating
elements
on
board
the
GPS
and
GALILEO
satellites
have
a
ground
plane.
Using
an
array
of
helix
antennas,
the
GPS
and
GALILEO
satellites
can
control
the
direction
of
the
emitted
beam.
If
a
helix
antenna
is
designed
without
ground
plane
it
can
be
tuned
such
to
show
a
more
omni
directional
radiation
pattern
as
shown
in
Figure 27: Radiation pattern of helix antenna without ground plane, Sarantel, Ltd.
Although
we
can
determine
an
axial
ratio
close
to
9
dB
between
zero
degree
and
90
degrees
elevation,
which
compares
to
the
patch
antenna,
the
back
lobe
of
the
helix
generally
degrades
much
smoother
and
does
not
show
any
sensitivity
at
the
–180
degree
direction.
In
contrast,
the
back
lobe
of
a
patch
antenna
depends
very
much
on
size
and
shape
of
the
ground
plane.
As
with
patch
antennas,
filling
the
antenna
with
a
material
with
a
high
dielectric
constant
can
reduce
the
size
of
helix
antennas.
Sizes
in
the
order
of
18
mm
length
and
10
mm
diameter
are
being
offered
on
the
market.
Again,
antenna
gain
will
decrease
with
decreased
size.
B.5 Helix or Patch, which selection is best?
For
practical
applications
the
possibilities
of
integrating
a
certain
style
of
antenna
into
the
actual
device
is
of
primary
concern.
Some
designs
naturally
prefer
the
patch
type
of
antenna,
e.g.
for
rooftop
applications.
Others
prefer
the
pole
like
style
of
the
helix
antenna,
which
is
quite
similar
to
the
style
of
antennas
used
in
mobile
phones.
Furthermore,
it
is
important
that
the
antenna’s
main
lobe
points
to
the
sky
in
order
to
receive
as
many
satellites
as
possible
with
maximum
gain.
If
the
application
is
a
hand
held
device,
the
antenna
should
be
designed
in
such
a
way
that
natural
user
operation
results
in
optimum
antenna
orientation.
The
helix
antenna
seems
to
be
more
appropriate
in
this
respect.
However,
one
has
to
keep
in
mind
that
comparable
antenna
gain
requires
comparable
size
of
the
antenna
aperture,
which
will
lead
to
a
larger
volume
filled
by
a
helix
antenna
in
comparison
to
a
patch
antenna.
Helix
antennas
with
a
“reasonable”
size
will
therefore
typically
show
a
lower
sensitivity
compared
to
a
“reasonably”
sized
patch
antenna.
