TIM-5H
-
Hardware
Integration
Manual
Appendix
GPS.G5-MS5-07015-A-1
u-blox
proprietary
Page 43
your position is our focus
Another
area
of
optimization
is
accurate
determination
of
the
phase
center
of
the
antenna.
For
precision
GPS/GALILEO
applications
with
position
resolution
in
the
millimeter
range
it
is
important
that
signals
from
satellites
at
all
elevations
virtually
meet
at
exactly
the
same
point
inside
the
antenna.
For
these
types
of
applications
receivers
with
multiple
antenna
inputs
are
often
required.
At
the
low
end
of
the
spectrum
of
possible
antenna
solutions
-
if
the
user
is
willing
to
accept
significant
signal
losses
-
a
simple
linear
polarized
whip
or
strip
antenna
will
work.
Compared
to
a
circular
polarized
antenna,
a
minimum
of
3
dB
of
signal
to
noise
ratio
will
be
lost.
B.2 Active and Passive Antennas
Passive
antennas
contain
only
the
radiating
element,
e.g.
the
ceramic
patch
or
the
helix
structure.
Sometimes
they
also
contain
a
passive
matching
network
to
match
the
electrical
connection
to
50
Ohms
impedance.
Active
antennas
have
an
integrated
low-noise
amplifier.
This
is
beneficial
in
two
respects.
Firstly,
the
losses
of
the
cable
no
longer
affect
the
overall
noise
figure
of
the
GPS/GALILEO
receiver
system.
Secondly,
the
receiver
noise
figure
can
be
much
higher
without
sacrificing
performance.
Therefore,
some
receivers
will
only
work
with
active
antennas.
Active
antennas
require
a
power
supply
that
contributes
to
total
GPS/GALILEO
system
power
consumption,
typically
in
the
region
of
5
to
20
mA.
Usually,
the
supply
voltage
is
fed
to
the
antenna
through
the
coaxial
RF
cable.
Inside
the
antenna,
the
DC
component
on
the
inner
conductor
will
be
separated
from
the
RF
signal
and
routed
to
the
supply
pin
of
the
LNA.
The
use
of
an
active
antenna
is
always
advisable
if
the
RF-cable
length
between
receiver
and
antenna
exceeds
approximately
10
cm.
Care
should
be
taken
that
the
gain
of
the
LNA
inside
the
antenna
does
not
lead
to
an
overload
condition
at
the
receiver.
For
receivers
that
also
work
with
passive
antennas,
an
antenna
LNA
gain
of
15
dB
is
usually
sufficient,
even
for
cable
lengths
up
to
5
m.
There’s
no
need
for
the
antenna
LNA
gain
to
exceed
26
dB
for
use
with
u-blox
receivers.
With
shorter
cables
and
a
gain
above
25
dB,
an
overload
condition
might
occur
on
some
receivers.
When
comparing
gain
measures
of
active
and
passive
antennas
one
has
to
keep
in
mind
that
the
gain
of
an
active
antenna
is
composed
of
two
components,
the
antenna
gain
of
the
passive
radiator,
given
in
dBic,
and
the
LNA
power
gain
given
in
dB.
A
low
antenna
gain
cannot
be
compensated
by
high
LNA
gain.
If
a
manufacturer
provides
one
total
gain
figure,
this
is
not
sufficient
to
judge
the
quality
of
the
antenna.
One
would
need
information
on
antenna
gain
(in
dBic),
amplifier
gain,
and
amplifier
noise
figure.
B.3 Patch Antennas
Patch
antennas
are
ideal
for
an
application
where
the
antenna
sits
on
a
flat
surface,
e.g.
the
roof
of
a
car.
Patch
antennas
can
demonstrate
a
very
high
gain,
especially
if
they
are
mounted
on
top
of
a
large
ground
plane.
Ceramic
patch
antennas
are
very
popular
because
of
their
small
size,
typically
measuring
25
x
25
mm
2
down
to
12
x
12
mm
2
.
Very
cheap
construction
techniques
might
use
ordinary
circuit
board
material
like
FR-4
or
even
air
as
a
dielectric,
but
this
will
result
in
a
much
larger
size,
typically
in
the
order
of
10
x
10
cm
2
.
shows
a
typical
example
of
the
radiation
pattern
of
a
16
x
16
mm
2
ceramic
patch
antenna.
This
measurement
only
shows
the
upper
sphere
of
the
radiation
pattern.
Depending
on
ground
plane
size
there
will
also
be
a
prominent
back
lobe
present.
